Jeffrey LewisBibi’s Bomb: Guide for the Perplexed

UN Photo, Credit: J. Carrier
UN Photo/J Carrier

Note from Jeffrey: I’m still on blog sabbatical in baby-land. Here’s another anonymous guest post.

Let’s be fair. It’s hard to simplify what’s not so simple. And it’s harder still to get your point across if few make the effort to understand. The Acme-brand bomb diagram brandished by Israeli Prime Minister Binyamin (Bibi) Netanyahu before the UN General Assembly on Thursday has left the multitudes scratching their heads, but it didn’t have to be that way. The media have done an altogether poor job of interpreting the message. For the most part, they haven’t even tried, reporting instead on the ensuing confusion. Or the smirk-inducing graphic-design choice. You know what? That’s shoddy work.

Now, with just a bit of background information, it’s not hard to gather what Bibi was saying about Iran and The Bomb. Which isn’t to say that it’s wise, in wider perspective, to “draw a red line” where the Israeli PM literally has done. It isn’t.

Let’s see if we can’t break this down.

What the cartoon bomb meant

Let’s start with the numbers. Here’s what Bibi said:

This is a bomb; this is a fuse. In the case of Iran’s nuclear plans to build a bomb, this bomb has to be filled with enough enriched uranium. And Iran has to go through three stages. The first stage: they have to enrich enough of low enriched uranium. The second stage: they have to enrich enough medium enriched uranium. And the third stage and final stage: they have to enrich enough high enriched uranium for the first bomb. Where’s Iran? Iran’s completed the first stage. It took them many years, but they completed it and they’re 70% of the way there. Now they are well into the second stage. By next spring, at most by next summer at current enrichment rates, they will have finished the medium enrichment and move on to the final stage. From there, it’s only a few months, possibly a few weeks before they get enough enriched uranium for the first bomb.

The Prime Minister then cited the reports of the International Atomic Energy Agency as the source of this information, and proceeded to draw a red line — yes, a literal red line — at the 90% mark.

A careful reader would tell you that the 70% and 90% figures in the cartoon don’t appear in the IAEA reports. Bibi isn’t wrong on this point, though; the information is indeed present, but framed differently. The IAEA measures Iran’s enriched uranium stockpile in terms of the amounts (mass) of material at different levels of enrichment — not how close the stockpile comes to “enough high enriched uranium for the first bomb.” Unlike the Prime Minister of Israel, the IAEA doesn’t presume that Iran’s nuclear program is military in character. The reports are instead phrased in terms of Tehran’s failure thus far “to establish international confidence in the exclusively peaceful nature of Iran’s nuclear programme.” It’s left to others to judge the relevance of the enriched uranium stockpile to the “possible military dimensions” of the Iranian program.

The latest IAEA report gives cumulative figures through August 2012 for how much uranium hexafluoride (UF6) Iran has produced at two levels of enrichment: up to 5% and up to 20%. Weapons-grade uranium is about 90% enriched (or 93%). That sounds like a big step up, but it isn’t really. In terms of separative work — the amount of processing needed to reach a particular level of enrichment — 5% enriched is about 70% of the way to weapons-grade, and 20% enriched is about 90% of the way there.

70% and 90%. If those numbers seem unfamiliar, consult the photo at the top of this post.

“Enrichment” is really “separation”

Jeffrey discussed why enrichment works this way a couple of years ago and again in the comments more recently [with a slight correction]:

 …20 percent is something like 9/10ths of the way to 90 percent.

To understand why, recall that “enrichment” is a misleading term — the method is separation or the removal of unwanted material, nothing is added. The simple example that I like starts with 1000 atoms of uranium. Only seven of them will be the fissile isotope Uranium 235. The rest are useless Uranium 238. (We can ignore the U234 in this example.)

To make typical reactor fuel, Iran or any other country removes 860 of the non-U235 isotopes, leaving a U235:U238 ratio of 7:140 (~5 percent).

To make fuel for the TRR, Iran removes another 105 non-U235 atoms from the 140, leaving a ratio of 7:35 (20 percent).

To make a bomb, Iran need[s] only to remove 27 of the remaining 35 atoms, leading [to] a ratio of 7:8 (~90 percent).

To make a bomb, Iran needs only to remove 34 of the remaining 35 U-328 atoms, leading to a ratio of 7:1 (~90 percent).

Which takes less work? Moving 965 atoms or 27 atoms 34 atoms? This simplification does omit the important concept of tails and some other details at very high levels of enrichment (say 95 percent and beyond). But those details aren’t enough to alter the nice smooth curve by Drell et al (on page 59) that shows cumulative separative work units to various levels of enrichment. Notice the sharp “knee bend” around 20 percent.

There is a reason that Iran’s enrichment to 20 percent is provoking a real crisis.

The Washington Post devised a graphic illustrating enrichment-as-separation back in February 2010. But for good measure, here’s Fig. 3.2 from Drell et al. (“Verification of Dismantlement of Nuclear Warheads and Controls on Nuclear Materials,” JASON Report JSR-92-331, Jan. 1993). Notice the “knee bends,” which really end around 20%:

There. That’s not too hard to grasp, I hope.

The assumptions behind the cartoon

Why draw the red line at the 90%-of-the-way mark — or, based on Netanyahu’s remarks, somewhere just before that mark? Let’s go back to the tape:

By next spring, at most by next summer at current enrichment rates, they will have finished the medium enrichment and move on to the final stage. From there, it’s only a few months, possibly a few weeks before they get enough enriched uranium for the first bomb.

Going by this statement, it appears that Bibi has taken a single “significant quantity,” or SQ, as the basis of his timetable. That’s a reference measure used in the context of IAEA safeguards. According to Ron Ben Yishai of Yediot Aharonot, 

For Netanyahu, the term “too late” refers to a situation whereby Iran will have sufficient weapons-grade material (or uranium enriched to 93% purity level) to produce one atomic bomb. Currently the Iranians do not have even one ounce of weapons-grade material, but they have already amassed about 200 kilograms (about 440 pounds) of 20% material.

As soon as Iran will have stockpiled some 260 kilograms (573 pounds) of uranium refined to 20% purity level they will be able to immediately move on to the final stage (enriching the same amount to 93%). With 260 kilos of 20% material it would take Iran a few weeks to two months to produce 26-28 kilos (57-62 pounds) of uranium enriched to 93%, which can be used to build one nuclear warhead.

That 26-28 kg of weapons-grade material translates to about 25 kg of U-235 content, or 1 SQ. For the reasons discussed here, 1 SQ is off-base; Iran is probably already beyond the point of having enough U-235 in its up-to-20%-enriched stockpile for a realistic first weapon. Furthermore, it’s not clear where Bibi gets his growth projection for UF6 enriched up to 20%; as Greg Thielmann has pointed out, Iran’s stockpile of this material actually diminished slightly between May and August 2012. Even as Iran produced more, much of it was being made into uranium oxide suitable for reactor fuel.

But these cavils are probably beside the point. The Prime Minister’s remarks betray a conviction that just as Iran produced a large amount of UF6 enriched up to 5% before starting to use some of it to make UF6 enriched up to 20%, it will in due course start producing UF6 enriched up to 90%. Bibi’s goal comes down to not to getting salami-sliced to weapons-grade uranium, as Joshua would put it. For that purpose, a line simply needs to be drawn at some distinct and recognizable point.

The liabilities of the Netanyahu theory

So what’s the problem? The short version is that committing to use force prior to an Iranian attempt to make weapons-grade uranium is a very dangerous idea. There’s basically no chance that bombing will stop the Iranian nuclear program. But it might spur Iran to take its bomb program off the back burner, speeding up the weapons timetable. As Joshua put it a couple of years back:

It’s often asserted, with an air of worldy maturity and sobriety, that a resort to arms will only provide a few years’ breathing room…. The truth is closer to the opposite.

Here’s how Jeffrey put it recently:

The benefit of a strike is an induced pause in the program — more or less what we have now[,] though imposed through force.  The question is whether an airstrike creates more delay than the current indecision of the Supreme Leader.  So far, I think, the best answer has been no…

It’s gratifying to see, in Sunday’s New York Times, that this message is finally starting to creep into broader awareness, a mere five years since the 2007 NIE.

With Jeffrey’s indulgence, I’ll return to this theme again before long.


  1. anon2 (History)

    I agree with your assessment: “For the reasons discussed here, 1 SQ is off-base; Iran is probably already beyond the point of having enough U-235 in its up-to-20%-enriched stockpile for a realistic first weapon.”

    However, I think that Netanyahu’s decision to draw the red line at the “90%” level and to state that that level will not be achieved until Spring or Summer is meant to be conciliatory with the U.S. policy, i.e. to give one final shot at negotiations over the next three to six months. This accommodation to the U.S. and thus towards negotiation with the counter-party (Iran) is being overlooked.

    In short, I believe that Natanyahu gave everything he reasonably could towards achieving a peaceful solution. It is time for the Iranian side to come to the table and work out a solution.

    Natanyahu was also clear that with continued enrichment to or beyond the red line, an attack will occur. As has been discussed elsewhere, removing this ambiguity may act to remove the possible assessment by the Iranian leadership that neither Israel nor the United States are serious to the point of military action about preventing Iran from obtaining nuclear weapons. This makes the potential cost to Iran of proceeding with weaponization both risky and expensive.

    Unfortunately the only response we have seen from Ahmedinejad, is that negotiations will not resume for two more months until after the U.S. election. Thus, Iran’s negotiating behavior remains consistent with stalling for time while the centrifuges run, perhaps in preparation for a sprint to finish line.

    • Mohammad (History)

      Iran has already worked out a solution: the West accepts Iran’s right to a full-scale civilian nuclear program, and Iran cooperates (perhaps by halting 20% enrichment and converting all of its 20% uranium to fuel plates). The ultimate solution would be the removal of sanctions by the West in return for ratifying the Additional Protocol by Iran.
      Iran’s negotiating behavior is consistent with making the West realize that Iran will not back down from its rights to civilian nuclear program, even under sanctions and threats (otherwise it would legitimize such measures and encourage their use in other disputes). Iran’s behavior during 2003-2006, particularly suspending fuel cycle activities and implementing the AP, was not consistent with stalling for time. If the IAEA board had not reported Iran to the UNSC, Iran would still be implementing the AP.

  2. Dan (History)

    Why on earth would Iran take seriously negotiations in October when it does not know who it will be negotiating with in November, Romney may be spouting nonsense for electoral purposes but he is surrounded by people who really believe the solution is start bombing Tehran tomorrow.

    Bibi is right that once sufficient amount of 20% is available, moving on to make sufficient 90% would not take that long, but Tehran also has a legitimate need for 20% for the Tehran Research Reactor and it is as it said it would converting the first production of 20% into fuel for that reactor. It does not need much for that small reactor how much is enough?

    Beyond the TRR the issue of 20% becomes national pride and ego, they are doing it because we are telling them not to, now at some point that is not a good enough reason, or it is for a bomb.

    Now to get a halt to 20% production what are we offering them, a temporary removal of some sanctions, sometime maybe. Most of the real sanctions are mandated by a US congress which is simply not going to remove them.

  3. kme (History)

    Note that the figures in Jeffrey’s explanation of separative work are a little off – for example a 7:8 ratio of U235 to U238 is an enrichment level of 47% rather than 90%.

    • The author (History)

      Hey, you’re right. Pretty clearly, he meant “7 out of 8,” not a 7:8 ratio. So let’s correct Jeffrey’s example to read like so:

      “To make a bomb, Iran needs only to remove 34 of the remaining 35 U-328 atoms, leading to a ratio of 7:1 (~90 percent).

      “Which takes less work? Moving 965 atoms or 34 atoms?”

      It’s by accident, but it actually illustrates the intended point that a difference of a mere 7/1000ths doubles the enrichment level at this extreme.

  4. blowback (History)

    Netanyahu was responsible for that pathetic cartoon bomb. If he didn’t think of it directly, it was one of the arrogant toads who works for him,so he “owns” it. Why should the media take up the effort of correcting his stupidity and arrogance after all they do little to correct their own errors such as the “wiping Israel off the map” or the more recent “eliminate Israel” garbage.

    As for the “negotiations” with Iran, I do feel a bit sorry for Netanyahu as his main concern (Iran not getting the bomb) is at odds with Washington’s (regime change). However, if he had really wanted to stop Iran progressing beyond 5% enrichment, he could have done so by making sure that Iran had adequate fuel for the TRR, which suggests to me that deep down he also wants regime change in Tehran. Perhaps Washington and Tel Aviv will now regret not taking up the deal negotiated by Brazil and Turkey to do this, although they are too stupid and arrogant to realize it.

    • anon2 (History)

      I disagree about Iran’s need for 20% uranium for the TRR. This was just a negotiating tactic by Iran to create a “reason” for continued enrichment beyond the 3.5 to 5% level for nuclear power, i.e. “medical isotopes” for the poor cancer patients. (Who cannot have sympathy for cancer patients?)

      What Iran needed was an unimpeded and inexpensive supply of the medical isotopes (Mo-99/Te-99m for example) to support its patient population. That could have been arranged by the West gratis, and that fact that the West was too foolish to formally and publicly offer this tells you something about the people negotiating for the West. Point award to Iran for effectively beating the West here.

      The next canard is Iran’s new “requirement” for 90% enriched Uranium for naval vessel propulsion.

      While Iran is at it, how about a need for nuclear explosives for mining research??

      Or while we are going there, spherical explosion research for nanodiamond industrial production?

    • Derick Schilling (History)

      Washington and Jerusalem, not Washington and Tel Aviv.

    • blowback (History)

      anon2 – Iran really did need the isotopes, the west was not prepared to supply them or the means to produce them, so the west and only the west has itself to blame for this fiasco.

      Derick Schilling – please tell me which countries, other than Israel and perhaps Micronesia, recognize Jerusalem as Israel’s capital.

    • anon2 (History)


      My point exactly: the West’s negotiators erred by not formally and publicly offering to supply all the medical isotopes that Iran reasonably required. Brain-dead obvious.

    • hass (History)

      Iran would not have accepted any offer of isotopes since these offers hinge on Iran giving up a sovereign right to enrich its own uranium. Futhermore, as noted on this very blog by Geoff Forden, Iran has a legitimate case for making its own isotopes (which incidentally are in short supply worldwide)

    • anonymous (History)

      I guess if all the wests negotiators are going to offer iran is aeroplane parts instead of serious talk on sanctions removal then its not too surprising that iran might just decide that nuclear propulsion both naval and civilian is the way of the future I mean it does seem silly to have oil tankers burning up huge amounts of fuel just to deliver huge amounts of fuel when they could be burning up tiny amounts of nuclear fuel or that low yield civilian pne`s might have real applications in the field of hydrocarbon recovery and iran does have a lot of hydrocarbons.What?! that sounds silly I hear you say,well no more silly than offering iran aeroplane parts in return for limiting or even halting their enrichment program

    • anon2 (History)


      I agree with you that the West should have made an offer that would have allowed Iran to continue to enrich.

      However, I believe that the deal should have been made to minimize the breakout risk, by having Iran agree to enrich only to the <5% level for conventional nuclear power generation.

      With regard to the medical isotopes, I don't really know what short supply means, Chalk River plant issues not withstanding. I believe that every patient on earth that needs a Te-99m study can get their Te-99m one way or the other, if the West decides to put the necessary investment into a non-proliferative plant somewhere in Canada, France, or the United States. The is clearly a better option than having every potential nuclear weapons sovereign state manufacture their own medical isotopes. To not take the issue off the table with a clear and public offer — to do whatever it takes to supply the isotopes to Iran, was a clear error.

      Finally, I do not dispute sovereign "right" of any country to do whatever they want to do internally as long as they are not harming others or their own people. Its not a question of moral "rights" or legal "rights", its a question of how to reduce the risks of Iran manufacturing a nuclear weapon. This is realpolitik.

    • blowback (History)

      anon2 – “fact that the West was too foolish to formally and publicly offer this ”

      This implies that the west informally and/or privately made such an offer. I have yet to see any evidence for this; if you have any please provide a link.

      Even if such an offer had been made, it would have been meaningless unless the west, and very specifically Washington, had completely renounced its intentions for “regime change” in Tehran. Washington has a very long history of ignoring its treaty obligations when it suits it, so who is to say that at sometime Washington wouldn’t have cut of the supply of medical isotopes.

    • anon2 (History)


      I did not imply any offer to supply medical isotopes. I believe this was overlooked in error.

      Regeme change: The Carter Admin renounced this to end the hostage crisis. But I think your general point is why should there be any negotiations between two distrusful nations at all? I think there should be diplomacy to prevent war.

    • Derick Schilling (History)

      blowback: The reality is that Jerusalem is the capital of Israel, whether foreign governments choose to recognize this fact or not. The cabinet meets in Jerusalem, as does the Knesset, as does the Supreme Court, etc. This will not change, even if Israel signs a final agreement with the Palestinians.

  5. Ohioguy (History)

    My take is a little more grim. Ignoring the 20% converted to fuel plates for a moment, at the last IAEA report Iran had 91.4 kg on hand. They were producing at appx 14kg per month using Fordow and the Pilot Fuel Enrichment plant as of the last report. If you were to assume that all of the installed but not yet enriching centrifuges at Fordow are brought on line in Sept with the same efficiency as the existing cascades at Fordow, you might have as much as 173kg on hand by the next IAEA report period in Nov, and the capacity to add another 34kg per month thereafter. (worst case)

    In other words, by the Feb IAEA report, Bibi’s red line would have been passed. If you take him at his word, this means that he would take action BEFORE the red line was hit, after the Nov IAEA report, and after the US elections.

    Iran therefore has a decision to make. Connecting and operating 1400 new centrifuges at Fordow, and utilizing them to enrich to 20% would indicate that they are calling Bibi’s bluff, and are racing ahead. Thus far that has been a good bet.

    To avoid this, they may create more fuel plates and not irradiate them, thus hiding the potential reconsitution in plain site. Bibi’s gambit basically gets past the US election, but by the next IAEA report in late November, it will be easy to project when Iran will pass the red line he has set. That essentially leaves 90 days for a deal to be made I think.

  6. Ron Conte (History)

    ISIS uses 25 kg of uranium metal as enough for one bomb. Bibi seemed to be using their numbers. But if Iran would settle for a 10 kt yield, they could bring that number down below 10 kg per bomb. And if they have an operational covert uranium purification facility, well, the situation is much worse than anyone realizes.

  7. Nick (History)

    What surprises me is that why the folks around PM did not bother fully explain what 90% meant. His confusing remarks implies that Iran is already and 90% for 235 enrichment level (HEU).

    Of course, for the not sophisticated US voters, the message is clear for scaring them to death, but the main stream media and well informed NYT reporters, such as Bill Broad and others did not bother explaining it better. The simple explanation is that the cartoonish bomb refers to the amount of work needed to purify uranium, that is all.

  8. Dean (History)

    Netanyahu seems so serious about preventing an Iranian bomb. My question is, would Iran be so serious about obtaining one if Israel didn’t already have it? If Israel is so serious about it, would it give up its weapons if Iran agreed to give up pursuing it? For me, Israel disarmament needs to be on the table just as much as military action against Iran is on the table. We know if Iran gets it, Saudi will get it. Then Egypt, then who knows. Aren’t we all better off if we can just give up our weapons and disarm?

  9. Rob Goldston (History)

    2 points:
    1) As has been evidenced on this site, the point where Iran will have enough enriched uranium to start a “sprint” to weapons-grade is entirely in the eye of the beholder. Indeed it was argued that Iran already is there. But one can also argue that no one sprints to a single bomb. What we learned at the U.N. is that in Israel’s eyes, it will be at least next spring before the sprint will begin. That is very important.
    2) Whatever Netanyahu said about his diagram, his red line is located at the transition from 20% enrichment to higher values, and consequences come from *crossing* a red line, not just toeing up to it. Thus he is in essence saying that his red line should be considered crossed when Iran’s enrichment exceeds 20% in any significant way. I imagine that expelling inspectors would be viewed as equivalent. IMHO, if you are going to have a red line, >20% enrichment has the advantage that a) there is no credible reason to cross it other than to make a weapon and b) you must cross it to make a weapon.

    • The author (History)

      Here, I’m afraid that I’ve failed you by not quoting the rest of Netanyahu’s words. The diagram failed here, too — it does not communicate what the words communicate.

      He said:

      “So if these are the facts, and they are, where should the red line be drawn?

      “The red line should be drawn right here

      “Before Iran completes the second stage of nuclear enrichment necessary to make a bomb.

      “Before Iran gets to a point where it’s a few months away or a few weeks away from amassing enough enriched uranium to make a nuclear weapon.”

      In other words, before, and not after the production of weapons-grade HEU commences. It’s implicit in his remarks that this final step might well take place at some hidden site, although he did not come out and say so.

    • Rob Goldston (History)

      Yes, of course he said that. Whatever he said, however, he really put the red line at the top of the 20% enriched region. And we all know – including Bibi – that “just below the top” is meaningless. How much you need is ill-defined – for the simplest example, what will the U-235 concentration in the tails be? What is meaningful is enrichment over 20% – literally *crossing* his red line – so I think we should take his graphic as a graphic gesture that he is willing to be negotiated to 20% as the red line that must not be crossed – in trade perhaps for seriousness about enforcing it. He did say that Israel is working with the U.S. on this issue, after all.

      It wouldn’t hurt if Japan and Brazil and Europe, the U.S. and Russia – and so the BOG – would define and accept a formal limit beyond which “peaceful” enrichment does not go, providing Iran with a level playing field. Is that too much to hope for by this spring? Probably.

      BTW, I guess everyone will be glad to add diverting material from Natanz or Fordow (or TRR) to the list of actions that are equivalent to enriching past 20%. As to clandestine enrichment sites, Bibi did argue that weaponization workshops are much harder to find than centrifuges, and we did find Fordow well before it started enriching.

      I’ll admit that I am perhaps desperately looking for some limit that could be put in place, that Iran would respect, so that we could move on to real negotiations rather than threats.

    • kme (History)

      Rob, I do not think that it is realistic to expect a universal, formal limit on the enrichment level that is considered “peaceful” to be negotiated. This is because HEU is used in various non-bomb scenarios already – for example radiation targets for certain types of isotope production and naval propulsion reactors. It also used to be common for scientific research reactors to be HEU fuelled.

    • rwendland (History)

      “>20% enrichment … there is no credible reason to cross it other than to make a weapon”

      Don’t forget that the standard CSA permits a state a bit over 1 kg of HEU (eg at 93%) **exempted from safeguards**, if any state chooses to request that exemption under article 37(a)(ii) of an INFCIRC/153 CSA. In fact the US drafted the formula for this exemption, allowing up to 1 kg of U-235 in the exempted HEU.

      Obviously the drafters of the CSA thought there were perfectly good reasons for any state to have (or make) some >20% HEU, eg “in scientific instruments or small research activities”.

      Also don’t forget Iran already has 5.5kg of HEU, in the form of the spent nuclear fuel from the original US supplied TRR fuel. Still under safeguards in Iran. Also 0.1 kg of Pu in the original TRR neutron source.

      So you will need some careful drafting to match your desire to what is currently on the ground, and a tough sales pitch to get states to accept the change.

    • Rob Goldston (History)

      You make a good point. If we did tighten down on enrichment past 5% for example, there would need to be some complicated issues sorted out, but – like with HEU in research reactors – it might not be a bad thing to have better control in general. The fact that Iran can redefine the activities at Fordow without notice is an example of the problem here. Maybe it would indeed be too hard to make this a legal restriction, but perhaps Brazil et al. could contribute to making it a norm, by some kind of voluntary declaration?

    • kme (History)

      How could Brazil make such a declaration when they plan to enrich unsafeguarded HEU for submarine reactors?

    • Rob Goldston (History)

      Olli Heinonen writes in the CSM that the French are helping the Brazilians with their submarine reactor, and it is believed that it will run on 7.5% enriched U like some French submarine reactors.

    • rwendland (History)

      Although the Brazilians would probably want higher enrichment for submarine reactors in due course, for the same reason as US/UK uses HEU fuel. So the reactor never needs refuelling during the sub’s lifetime. As I understand it, refueling a sub is quite tricky and greatly contributes to the refit duration – as I recall near two years for UK boats.

      In fact no refuelling is a powerful argument for the UK only needing 3 new Trident boats to replace the current 4. The boats needing several long refuelling stoppages takes up much of the 4th boat service time.

  10. Another Halocene Human (History)

    Yes, I am finding your arguments hard to understand. In chemical purification it usually takes more energy to achieve higher and higher purity. For example, one might easily achieve 90%, but 99% will be more difficult and so 99.9%. So why are you arguing that it takes less energy to go from 90% to 93% as it did to go from 5% to 20%? And while I can’t read the units on your perplexing graph, if there is a knee-bend at 20% I would assume that is where *the real costly extraction begins*, which means that, no, weapons grade Uranium is not trivial to achieve. Unless there is some special property of radioactive Uranium that makes it different from every other molecule. Please explain.

    • The author (History)

      The knee-bend in the Drell et al. diagram reflects where much smaller amounts of separative work start producing much larger changes in the percentage of U-235 in the product.

      The label across the top of the figure may be the source of some confusion here. To clarify, the x-axis (fraction U-235) depicts degree of enrichment. The y-axis (SWU per kg) is cumulative separative work.

      The two curves depict two different tails fractions, that is, how much U-235 the operator allows to flow into the tails stream (the waste) rather than the product stream. The knee-bend occurs at the same point in both curves, which are illustrative.

      The basic reason for the sharp bend in the curve, as Jeffrey has explained earlier, is that progressively smaller masses of uranium hexafluoride are subjected to a constant amount of separative work. An enrichment level of just 5% means that the majority of the UF6 has already flowed into the tails stream; it’s all downhill from there.

  11. The author (History)

    He made it pretty clear that accumulation of a certain _amount_ of up to 20% U-235 is his red line, not enrichment beyond that level. If it were as you said, there would be no disagreement between Israel and the U.S.

    This is where the simplicity of the diagram misleads. Enriching more 20% does _not_ inulectably lead to weapons-grade.

    • Rob Goldston (History)

      Yes and no. Bibi knew what he was doing with that diagram, and his red line toes right up to the black one. (Expand one of the high-res pictures on the Web.) He left us an opening, while covering himself amongst hawks at home. Bibi wants a red line, and says he is discussing it with us. We say no red line at all. You say of course the US would consider > 20% enrichment a red line. Seems like there might be a place here for an international agreement.

      Or not.

    • BiBiJon (History)

      You have done a great job at injecting some precision in the PM’s words, and diagram, but he was not out to give a science lecture. It was after all only words and an effort chart tastelessly depicted as a bomb. The poor taste trumped the risk of causing confusion.

      The only thing one can be certain about is that he wanted a red line. Period.

      Given the ‘red line’ goal, he could not draw it too early in the process, nor too late, otherwise either he’d be advocating war as of yesterday, or leaving the gate too wide open.

      While I’m here let me ask another question relating to “the current indecision of the Supreme Leader.”

      Can you or Jeffery tell us what it is the Iranian officialdom have to say, and how often do they have to say it, for it to register as a ‘decision?’ I assume there is no proof that Iran’s actions are completely inconsistent with a country that is satisfying a nation’s legitimate need for developing nuclear technology.

  12. acme products inc (History)
  13. Jonah Speaks (History)

    Between the Bibi cartoon above (too simple and confusing) and the Drell diagram (way too advanced and not intuitive, even for intelligent laymen) there needs to be a simplified graphic that expresses the concepts of concern. A serious problem in the cartoon was confusion caused by referencing 3.5% enrichment as 70% (of SWU) and 20% enrichment as 90% (of SWU). See:

    Netanyahu’s Bomb Diagram During U.N. Speech Stirs Confusion in Israel

    Another thing wrong with the cartoon is the bomb shape (round, not rectangular) so that length and area are not proportional. I suggest dynamite sticks instead. Each bomb’s worth of uranium should be represented by one stick. The lines on each stick can divide the stick in proportion to SWUs, so as to give a good picture of how close Iran may be to weapons-grade enrichment. SWU should be spelled out — Separative Work Unit — for the benefit of intelligent laymen.

    A good graphic needs to explain how many bomb’s worth of uranium have been enriched to which levels. It should also be well-labeled with a view to explaining these concepts clearly along with a visual format that is easily grasped.

    Would anybody here like to create a good graphic?

    • George William Herbert (History)

      The Drell diagram is too hard?

      The labels require certain technical depth, but that’s just labeling…

      If the idea it’s expressing not clear to you from it?

    • Jonah Speaks (History)

      The issue here is not my comprehension, but that of the general public. In my experience, college students frequently need to be taught the basics of how to read a curve on a graph, even one that is clearly labeled.

      The Drell graph is not intuitive for the general public; moreover it is not relevant to Bibi’s issue. What the public needs to understand is how close (or how far) Iran is from developing a bomb or bombs. Both Bibi and the wonks agree that SWU is a good way to portray this. Converting enrichment percents into SWU percents is a technical issue, not directly relevant for public understanding.

      What I have in mind is a bar graph. Each bar represents one bomb’s worth of material. A shaded area within each bar represents the percentage of SWU enrichment accomplished on that material (0% = raw uranium; 100% = bomb-grade uranium). Turning the bars into dynamite sticks is optional, but might improve public understanding.

      Drawing a red line on the graphic is also optional. Incidentally, there are two dimensions along which a red line could be drawn. One dimension is the level of enrichment; the other is the number of bomb’s worth of material.

      So, the question is, can you create a better graphic than the Bibi cartoon? If we might go to war over this issue, maximum public understanding is essential.

    • George William Herbert (History)

      Ok; let me think about that. I have some ideas for diagrams…

    • Jeffrey (History)

      I don’t agree that SWU is a good way to portray the pertinent concerns, especially since I am much more worried about the possibility of covert sites than overt breakout using Natanz. I said as much to Glenn Kessler, explaining “The important question is whether this is a significant measure of capability or an important red line. I don’t think so.”

      Of course, have at it. But I just want to be clear about my views.

    • George William Herbert (History)

      I think SWU are relevant to bound the number of centrifuges in the covert facility, or parameterize the time/size relationship.

      Unfortunately, given how little we know about their centrifuge build rate and lifetime, the facility size they could secretly build without notice is quite likely the limiting factor.

  14. Mark Gubrud (History)

    To point out what should already be clear:

    The level of enrichment by itself is not what matters. If you have 1 mg of 99% U-235 the only thing that is significant about that is the question of how you got it.

    The amount of U enriched to below 80-90% is not what matters. You might have tons of reactor-grade uranium and no means to enrich it to bomb-grade.

    What matters is a combination of the amounts of U on hand in various forms and at various enrichment levels, and the available facilities for its further enrichment and conversion into metallic form and into a weapon.

    In order to reduce that possibly complicated picture to something meaningful, the best single number or two-dimensional trade space diagram for analysts to calculate or estimate is how long it would take Iran to produce one nuclear weapon or n weapons assuming an immediate breakout from IAEA monitoring (if the breakout goal is to produce a few, the first one might take a little longer). Estimates assuming the use of some plausible combination of unknown inventories and facilities may also be of interest.

    As things progress, the breakout timeline grows shorter. Bibi might have looked a little less silly if he’d tried to illustrate that instead of his Acme bomb.

    Beyond producing the HEU metal, weaponization will involve steps whose timeline is harder to predict. At some point, one may judge that the time to weapons production is no longer dominated by the time to produce the HEU metal. When that is the case, all this focus on the amounts and levels of enrichment, even taking into account the numbers and capacity of operating centrifuges, loses relevance.

    • BiBiJon (History)

      Mark Gubrud:

      Hasn’t it already lost relevance? Much of what ‘experts’ predicted to be technical obstacles Iran has overcome, and then some.

      The only path left open to Iran has been to continue her nuclear technology/infrastructure advances within safeguards agreements and with passage of years render the various red lines, as red herrings. Or, capitulate.

      Mr. Netanyahu’s diagram could be just as usefully labeled ‘degrees of irrelevance.’ His 90% of effort line, indicates everything below that line is already irrelevant — we have reached 90% irrelevency; 10% left to negotiate over. All that remains 100% relevant is a measure of Iran’s motivations. Just as one ought not measure eye-sight by poking an eye, probably crippling sanctions and threats of war may not be the best instruments for gauging motivation or intent, as one is liable to alter the very thing one is measuring.

      On the other hand, as seems to be the case in polite company, we must assume omniscience, and a priori ‘know’ what Iran’s intentions are, then, heck, everything becomes irrelevant; 1 gram is as damning as a ton, no?

  15. archjr (History)

    Maybe this is a silly question, but if a sensible red line is needed (which I question) for diplomatic purposes (which I think is what Netanyahu proposed, a good and positive indication of his current thinking nonetheless), why not use conversion to metal at a level of enrichment above 20%? Mark Gubrud I think is leading in this direction. The uses of material in this form are few and far between. I woudn’t advocate this as a starting point for resuming negotiations, of course, but it seems to me this line could be used as a universal standard. Especially since the Agency is unsuited to ascribe a motive as a means for assessment of intent?

  16. archjr (History)

    Another question: if Iran were to convert a required quantity for TRR to plates sufficient for one fueling, shouldn’t that obviate the “need” for more enrichment to that level. And wouldn’t the conversion to metal plates in itself be some kind of technical firebreak to further enrichment?

    • BiBiJon (History)


      Nothing appears to obviate anything. There’s definitely no magical quality to that particular number, 20.

      E.g. Here’s Peter Jenkins a British diplomat negotiating with Iran in the EU-3 format back in 2005:

      “The British objective was to eliminate entirely Iran’s enrichment capability,” Jenkins said. “I remember we couldn’t even allow Iran to have 20 centrifuges for R&D [research and development] purposes, because we ourselves had mastered the technology with even fewer than that.”


    • anonymous (History)

      You don`t give up something of value,irans right to enrich to 20% and also said stockpile,for nothing you give it up in exchange for something of equal or greater value say sanctions relief thats just basic negotiation

  17. JohnLopresti (History)

    A Cartesian plot of an exponential function gives a curve:

    A semilog plot of the same exponential function, retaining one axis in regular Cartesian increments, but rendering the other axis as a log function, yields a straight line plot of the same input data:

    The linked graphs are not exactly the same as Drell’s illustration, being for Sr90; yet they illustrate the Prime Minister’s difficulty in recruiting a graphic chart in the form of a 2-D circle to represent an exponential process, both in terms of work and along a hypothetical time axis.

    The PM ought to have begun with a medieval vase countour for his visual aid; for example,

    However, the image of the museum vase still does not correspond to the Drell curves on p.62 of that 1993 study

    Rather, the neck of the vase would have to be longer.

    Then the PM could put his HEU threshold redline anywhere on the low-volume neck, while the base of the vase shape already was filled, analogously, holding 6/7 of the work in the first 1/5 of the vase’s height. That would have better correspondence to the Drell curves.

  18. George William Herbert (History)

    The Atlantic Wire is reporting ( ) that Iran’s deputy head of their Parliment’s Foreign Policy and National Security Committee, one Mansour Haqiqatpuor, is saying Iran will start enrichment to 60% for subs and ships if the current negotiations fail.

    I’m not familiar with him and his role and connectedness in their decisionmaking process. Credible, off the reservation, bluff, attempt to provoke an attack sooner rather than later, ?

  19. Eve (History)

    Why on the bejesus did he not use the graph? It’s (a) bomb proof.

  20. Rob Goldston (History)

    Wow. Let’s hope this guy is just blowing smoke. But…

    In case anyone on this blog doesn’t know it, for a cascade length that is pretty well optimized to make 3.5% from natural and 20% from 3.5%, the next step is 60% from 20%, and the step after that is 90% from 60%. This assumes the cascade linking the Iranians seem to favor, in which the tails from a cascade are fed back into a cascade just upstream. My arithmetic for this arrangement of ideal cascades puts about 5.6% of the SWUs in the last two steps. And 1.2% in the final step.


    • Denis O'Brien (History)

      Thanks, Rob. This is getting to some enrichment details that seem to me to be confusing Bibi. Certainly got me confused.

      Bibi seems to be acting like Iran begins with a fixed amount of natural U and they enrich all of it to 5%, and when they get it all to 5% then they start enriching to 20%. Once they get the lot to 20% they start enriching to 60%. . . . i.e., a sequential, quantum process.

      Like is the process quantum or continuous? Don’t they start on the 60% to 90% step before they complete the 20% to 60%, etc. so that at some point they have enrichment going on at 2 or 3 or 4 levels simultaneously. Does all of the 60% material going to 90% have to be piled up at the 60% point before the 90% enrichment begins?

      If the process is continuous and not quantum, then the red line is a red herring. But it may have practical implications in view of the so called Entebbe option being discussed by Mark Perry at FP in which US CentCom guys are suggesting Israel’s Sayeret Matakal could go into Fordow and carry out all of the 90% HEU and blow the rest. But if the U is in a continuous stream of being processed, what, physically, would these guys find and carry out if they wanted just the 90% stuff?

    • Rob Goldston (History)

      Quantum or continuous? It is quantum in the sense that you either have a cascade going from 20% to 60% or you don’t. (This is what makes 20% potentially interesting as a red line, either publicly or privately communicated, either international or unilateral.) It is also quantum, but considerably fuzzier, in the sense that you would not start a breakout until you had enough 20% in hand to sprint to your goal – i.e., not having to wait for more – but we don’t really know your goal. (This is a problem with how Bibi described his red line.) It is continuous in the sense that you don’t have enough 20% to use your whole facility on 20% -> 60%, so you might as well use the rest of the facility during the sprint to keep producing 20%. If the sprint takes, say, 2 months, this extra feed makes a modest but useful difference for you.

    • George William Herbert (History)

      Denis –

      We know some things. The IAEA is still inspecting Fordow and Natanz. They’re sampling centrifuge cascade output, and verifying materials that have been enriched. They know what’s in the various process inputs and outputs, and how much materials are involved.

      We don’t know if they have additional feedstock they didn’t declare, or additional centrifuge facilities they didn’t declare and we don’t know about (at least publicly).

      What we do know is that they have a large (almost 7 ton) inventory of the 5% enriched stuff, and smaller of the 20% enriched (a few fuel plate loads’ worth for their medical reactor; more than they need right now, but not so much more that it can’t be explained by “we’re going to do 20-30 years worth of fuel elements all now”). About half the 20% was fabricated into medical reactor fuel elements.

      That 5% and 20% material has been verified as sitting stably at those levels and inventories. So it’s not continuously being pushed into a more widespread 20% program, a 60% program, a 90% program.

      Again, we don’t know about possible other facilities operating in secret or inventories whose feedstock was never declared. My sense of the consensus is that they probably haven’t got a huge undeclared feedstock, but we can’t prove that. It’s highly possible that there’s a 3rd or 3rd and 4th site. The probability of an undetected 3rd or 4th site would seem to depend on size and how long it’s been there. Another Natanz seems unlikely. Another Fordow, still unlikely. A smaller, few-cascades facility seems more easy to have gotten away with hiding.

      A bigger facility could do bomb materials in reasonable time (years) from scratch. A smaller one would require input of already enriched materials (i.e., diversion from Natanz / Fordow). Which we (or, the IAEA) has been monitoring and watching for, and seems reasonably sure has not happened.

  21. Luca (History)

    Look guys – I hope you know how much your discussions on this website help the rest of us political analysts who didn’t really assimilate an awful lot of Physics in school – so forgive me for probably asking the proverbial idiotic question that sooner or later everyone of us in their respective professional subject matters is forced to hear – here it goes: if it’s plausible to assume by now that, given the obstinate attitude of the regime in the nuke dispute, they might not just want to prove a point of principle (inalienable right to enrichment at what cost? regime change inspiring economic collapse??); Wouldn’t it also make sense to have all the other weaponisation stages and components of a bomb ready BEFORE taking the 20% to 90%? In other words does it make sense to first get the fissile material and only AFTER going through the motions of weaponisation? And I don’t mean conversion of UF6 to metal, I’m talking bomb design that fits inside a shahab 3 (or better a Sejjil) nosecone, manufacture of explosive lenses, all the computer modelling…the whole 9 yds stopping short of atmospheric testing basically. Wouldn’t having all that in place already, while waiting the weeks necessary to get the bomb grade uranium, significantly shorten the amount of time they would spend with enough weapons grade stuff but no device and no missile?
    Last thing and then I shall shut up forever – is a neutron initiator the same thing as the R265 generator allegedly passed by Danilenko to the iranians?

    • George William Herbert (History)

      As it happens, there is significant evidence that the R265 is not an initiator, but that Shahab-compatible bomb design, already tested in 2003 and 2004 with inert cores.

    • Rob Goldston (History)

      There are three reasons I can imagine that Iran stopped its organized weaponization program: 1) Fear associated with US invasion of Iraq and discovery of Natanz, 2) Relief associated with downfall of Saddam, and 3) They had finished the job and all they needed was the HEU. What is known in the open literature that would clarify this?

    • George William Herbert (History)

      Rob wrote:
      There are three reasons I can imagine that Iran stopped its organized weaponization program: 1) Fear associated with US invasion of Iraq and discovery of Natanz, 2) Relief associated with downfall of Saddam, and 3) They had finished the job and all they needed was the HEU. What is known in the open literature that would clarify this?

      They also might never have affirmatively decided to cross the line, though they fairly clearly intend to be a credible threshold power at least.

      The technical side has been very leaky; their political side less so.

      Regarding 3); I believe and am writing – slowly and painfully, proliferation concerns are real – an open article substantiating how a R265 bomb works and arguing point three. That said, they could be undecided or against crossing the line and consider a bomb design or a built bomb on a shelf with no core to be threshold activities not active weaponization. I think it hints but want to make it clear that that’s only an opinion, not a technically derived statement or well supported deduction.

    • Rob Goldston (History)

      ISIS says that IAEA documents are clear that Iran did not finish the job, and even Israeli sources say the same publicly. But… I am looking forward to George’s analysis.

  22. Ara Barsamian (History)

    All of you need to revise some numbers:

    1)Little Boy used 80% and 89% HEU in a WC tamper; yield about 12kT

    2) UKAEA Handbook of Experimental Criticality Data AHSB(S) Handbook 5 states the following:

    80.5% and 22.73 kg delayed critical and reflector of nat U
    67.6% and 30.73 kg delayed critical and reflector of nat U
    47.3% and 57.23 kg delayed critical and reflector of nat U

    The lower the enrichment, the higher the critical mass and longer neutron generation time, which lowers the yield (assuming no boosting)

    Assuming R265 imploder exists and it is not a sophisticated deception, should be able to get a minimum compression of 2, potentially more (depends whether it uses a thin HEU shell or more conservative thicker shell)

    So please get off the 90% or 93.6% enrichment mindset.

    I am sure Bibi doesn’t care whether he gets threatened with 5kT or 12kT..

    • George William Herbert (History)

      I am backing through more primitive R265 models that I can publish without leaking too much, but…

      I seriously doubt R265 can double the density of a 57 kg U core. That’s M/C of somewhere between 0.8 and 1.15; Simplifying this like a symmetrical flat plate / flyer (as I am in no way going to type the spherical implosion Gurney equation on an iPhone…) (no, this is not a safe accurate simplification, but it overstates imploder energy); the equation is :

      V/sqrt(2e) = 1 / sqrt(2 M/C + 1/3). Sqrt(2e) for the relevant explosives is 2.8 to 2.9 km/s. for M/C 0.8, the inner term sums to 1.93, sqrt is about 1.4, inverse is about 0.7. So roughly 2 km/s. 2 Mj/kg of velocity energy; even assuming 1:1 efficiency into shock compression…

      Compression about 1.8, again with every systemic edge overstating more accurately modeled detail results. Without doing modeling I can’t publish, I thing the real energy transfer is about 0.5-0.6 of that and compression would be more like 1.5.

      Keep in mind that the compression effect on criticality goes as density squared; so 2.0 is 4x criticality, 1.5 is 2.25x. Big difference.

      I get max critical masses for the 50% enriched core less than 1.0 for realistic numbers.

      Again, limited by security concerns and typing in an iPhone. Not going to stop other work to do a detailed spherical imploding Gurney, much less shockwaves model or do a computer sim implosion of that system. Envelope suggests not worth those efforts….

  23. Ara Barsamian (History)


    I did a Hirsch simulation of R265 (assuming ISIS got it right), and the rough numbers are:

    80% enrichment: P=6.78 Mbar, Compression=1.96, Yield: at least 20kT with a neutron tube initiator

    67% enrichment: P=5.17 Mbar, Compression=1.78, Yield: at least 10kT with a neutron tube initiator

    47% enrichment: P=1.49 Mbar, Compression=1.25, Yield: at least 20-100 tons (a la Davy Crockett)

    Bibi will not be happy with any of the alternatives; even at 100 tons, you have lethal prompt radiation to a couple of hundred meters…Have you ever been in Tel Aviv at lunch time?

    So 67% enrichment based R265 is good enough to both mount on an existing rocket and in terms of radiation lethality. This also reduces the SWU required and the time to achieve it significantly (by half?)

    So 47% enrichment based R265 is good enough to mount on an existing rocket but not in terms of yield/damage. Nevertheless, even though 100 ton yield is unacceptable, this also reduces the SWU required and the time to achieve it significantly (by three quarters?)

    So the enrichment duration numbers from 5% or 20% to 47, 67, or 80% need to be re-visited.

    • George William Herbert (History)

      Ara, again doing this while mobile, but… Still confused.

      What I have online is Mc of 50% HEU is 170 kilograms. So 57 kg for your “47% enriched” core is about a third of a critical mass.

      If you get compression of 1.25, that’s a criticality increase of 1.56, still short of a critical mass…

      I don’t have the more detailed tools with me on the trip, so I could be working off references that are wrong, but can you please document a bit more? I worked off Carey Sublette’s FAQ, Table for the critical masses, and Fig for the compression energy. Again, these aren’t the full tools by any means. I’m on the road at a conference at the moment.

  24. Jeannick (History)

    A single bomb would be near useless ,
    a dozen , or more ,deployed weapons would be the reqired number to get some serious respect as a credible disuation
    the size hardly matter if reliable
    might as well make them with less material
    since it would hypotheticaly be rocket borne
    the lesser weight also would be desirable

    This is highly hypothetical ,
    one thing is certain ,the U.S. has consistently sabotaged any attempt by the Iranians to negotiate a solution
    the U.S. has pushed Iran on the road to 20%
    selling them the plates would have been easy ,legal,
    and in the spirit of the NPT

    the ghost of Iran nuclear bomb is the prime reason given for developing and deploying the missile shield program.

    No Iranian bomb scare not much reason for deployment
    Israel is full aware of the non existence of any threat from the Iranian program but is very keen on getting
    a full missile shield for free as pay back for playing ball

    • George William Herbert (History)

      A single bomb would be near useless ,
      a dozen , or more ,deployed weapons would be the reqired number to get some serious respect as a credible disuation

      A single fission bomb could kill more than 5% of Israel’s population. While not the end of their nation or race, it would be a catastrophic loss for their country.

      That’s the point with nuclear weapons. If their use against civilian targets is on the table (and for deterrence or terror / destruction purposes, they are) then catastrophic losses can result. Even a single use is a global catastrophe by any measure.

    • Jeffrey (History)

      One wouldn’t be useless, but it would have a very limited value compared to, say, two. I’d put the knee in the curve of diminishing value somewhere between 10 and 100. You?

    • George William Herbert (History)

      Jeffrey writes:
      One wouldn’t be useless, but it would have a very limited value compared to, say, two. I’d put the knee in the curve of diminishing value somewhere between 10 and 100. You?

      I’m at a computer science conference, and slept badly, but as a first response.

      It depends on what they (Iran, in this case) would want to do with the weapons.

      If they intend to fight a nuclear war with them, then “enough to vaporize Israel and its nukes preemptively” plus “enough to deter everyone else from vaporizing Tehran” would seem to be the number, which could be very large compared to their current weapons program we see. Towards 100, but the problem with this is that a mental state or policy conclusion necessary to support this being a reasonable course would imply thinking that’s counter to our “rational shared consensus” used in most of these analyses, and if that’s a precondition for this case then pretty much any modeling we’re trying to do is operating from different assumptions than they are. While I am not sure about their conventional rationality, I see no sign that their leadership is that far out. Any sign that they were looking towards 100 weapons would either imply strategic insanity, or thinking towards battlefield weapons (which would open up a very nasty analytical / policy challenge).

      If they intend to hold Israel at risk in a MAD deterrence sense, and potentially US bases and SA bases and the like, then … I don’t know. 10? Enough to deter cohersion (and deter ongoing economic blockade, possibly), or so they’d hope.

      If they intend to establish a minimum credible deterrent, 1 or 2 would be that. Enough to deter direct invasion for regime change, or so they’d hope, and the west and Israel might agree.

    • Jeffrey (History)

      The problem with relying on one to deter an invasion is two-fold. First, there is no hold-back so the decision to use is really only credible as a last, last resort. Any chance that the regime might survive to preside over a denuded body politic ends after the one and only is used. (On the other hand, the threat of two allows a relatively early use for unspecified losses of territory.)

      Second, there is the small numbers problem relating to reliability and control. Missile success rates are only about one in ten, and that’s without a very committed air campaign to find the warhead and delivery vehicle or defenses. A very determined adversary may conclude that there are inherent survivability problems below some arbitrary number like 10.

      I realize that political leaders are likely to be much more cautious and less rational than this little outline, but it seems to me that an aggressive leader might find many more excuses to attack a state with one bomb, rather than two, to say nothing of two rather than ten.

    • Ohio (History)

      So, a Nuclear Weapon destroys Tel Aviv, AND Israel is surrounded by hostile Arab Countries that out number them 1000 to one. Presuming that Israeli leadership survives the attack, are the Israelis going to nuke Gaza, Lebanon, Egypt, Syria AND Iran when tanks come pouring into the country to take back Jerusalem and Palestinian land?

      One weapon can create all the military advantage that is needed to push the Israelis into the sea. All that has to be done is to tip the balance of power for a few days and Israel is gone. The allied Arab armies have only tried this three times sans one nuke. They want the land back intact, they are Holy lands, not a steaming pile of glass.

      Never mind, holding the Strait of Hormuz hostage and issuing demands. A nuke at the throat of the Gulf would crash the world economy.

      You guys make great engineers, but crappy asymmetric warfare tacticians. This is not the Russians V2.0. One Black Swan event with a nuke could rewrite all of the rules of warfare. The Iranians have had 30 years or so to ponder this.

      If I shoved you all in a room and told you that you had one nuke, and your goal was to become as powerful as possible, regardless of the consequences, I bet you could come up with some really interesting ideas. That’s why the red line was set, and containment is unacceptable.

    • George William Herbert (History)

      Just as an aside, I think this requires deeper longer thinking, so I’m giving my quick response with the disclaimer that a longer thought is required soon. Sitting at a computer science conference is not entirely conducive to deep nonproliferation thinking.

      Jeffrey wrote:
      The problem with relying on one to deter an invasion is two-fold. First, there is no hold-back so the decision to use is really only credible as a last, last resort. Any chance that the regime might survive to preside over a denuded body politic ends after the one and only is used. (On the other hand, the threat of two allows a relatively early use for unspecified losses of territory.)

      I think 2 is better than 1, and 3 is better than 2 (and 4 better than 3; among other things, with 3-4 you can “test” one as a warning, without actually nuking people). The question is at which point deterrence starts to be useful, and I think that’s one. Nobody’s going to take a claim of a HEU R265 based weapon and assume it’s not credible. If numbers indicate that N is almost certainly 1 then you can’t test-fire one as an invasion deterrent. If it might be 2, then uncertainty kicks in…

      Second, there is the small numbers problem relating to reliability and control. Missile success rates are only about one in ten, and that’s without a very committed air campaign to find the warhead and delivery vehicle or defenses. A very determined adversary may conclude that there are inherent survivability problems below some arbitrary number like 10.

      The success rate is really a combination of weapons deterred/destroyed prior to launch, launch/flight failure, targeting error (miss target by a little, or a lot), warhead fires or doesn’t.

      The deter/destroy prior to launch, launch/fight failure, miss target by a lot, and warhead fails to fire problems will still affect a nuclear IRBM/SRBM. But the “miss by a little” will not matter for a nuclear weapon (with mile-wide destruction zone) targeted on a multiple mile wide urban target area. Without giving GPS coordinates, there appear to be Israeli city target areas where a 5 km angular error and 10 km short or long range error would still place the effects zone of a 20 kt weapon entirely on what appear to be high-density city area. Going 100 km long or short would be a different situation of course.

      I’d actually invert the equation a bit; they could put one warhead on any of probably 30 missiles they’ve built (at first guess) which are mostly in silos or deep TEL bunkers. As a potential attacker, you have to think about 30 potential targets to eliminate before you’re sure you got the one that has the warhead. Sure, if they actually mounted the warhead and you kill 16 of them, you probably got it, but how sure are you? How many drones do you fly through debris clouds with air sensors/ dust collectors, looking for HEU (or Pu) in the air?

      What if the don’t mount the live warhead? Then you have to kill or interdict all 30, or find the 1 warhead in a bunker or down in a mine shaft with commandos on the ground or a really lucky LGB hit if it’s not deep enough. And being sure you got it, again very difficult. The weapon is inherently compact and easy to conceal or protect, much more so than the missile, which is much more so than the enrichment facility.

      If you miss 1 missile, and the warhead, and they are able to hook them up on a road outside Tehran after the war starts, they’re ready to go. How sure are you that the number of missiles is 30 and not 32 or 34? ….

      What if they mount a pit-less R265 in each of 30 missiles, and a 25 kg pit is all you’re hiding / shuffling around…

      I realize that political leaders are likely to be much more cautious and less rational than this little outline, but it seems to me that an aggressive leader might find many more excuses to attack a state with one bomb, rather than two, to say nothing of two rather than ten.

      I think a lot of this focuses down on operational intelligence.

      If you know – for sure – N=1 and where the singular warhead / pit is, then you can accept the costs to go get it (even if that’s a nearly suicide run commando mission in the middle of a hostile country in wartime). N=2 is still doable. The statistical combinatorial risk of failure to intercept / capture / destroy at least one of them starts to approach unity as N increases. For 90% reliable attacks the overall total success goes as 90%-81%-73%-66%-59%-53% (0.9^N). For 75% reliable attacks the overall total success goes as 75%-56%-42%-32%…

      And overall success is a combination of intelligence success and attack success; if intel fails and attack succeeds, it was still a failure.

      What I am seeing from our and the IAEA engagement with Iran seems* to lack operational intelligence success. We’re getting strategic leaks at a significant rate (existence of Fordow, R265 details, etc) but that’s over years.

      * by seems, I would like to indicate that I am not working for or with US intelligence agencies, and am working in this instance off entirely public information. What they know and what’s been made public or leaked public could well be two very different things; I don’t want to imply any certainty either way about the actual state of intelligence, only what I see…

      Short summary – I think that even one weapon introduces significant difficulties in interdiction, for various reasons, and that it gets exponentially worse as N goes up in single digits.

    • Rob Goldston (History)

      Another problem with one bomb: If Iran threatened to use a bomb on Israel, and this was credible to the population of Israel – who have seen a lot of suicide bombers – there could be a great deal of emigration. Iran could win without actually doing anything.

  25. archjr (History)

    With apologies to Pink Floyd: “There is no red line, really. As a matter of fact, it’s all red.”

  26. jeannick (History)

    Nuclear weapons are useful only as last resort life insurance ,
    A strike on Israel is pure fantasy ,
    but just across the water there is plenty of juicy targets ripe for some rewarding threats
    the oil instalation of Koweit , Saudi Arabia , the gas liquefaction plants of Quatar plant and should it get really personnal ,the US central command assets in Bahrain and last but not least the shiping lanes of the Ormuz straits ,
    a good dozen should be credible , twenty or so better still
    some would fail , some would be intercepted

    Al those are within easy reach , China , Japan Korea , Europe and pretty much the whole world would wet their pants at any deliberate intent to take the Gulf down with them
    Israel , honestly , beside much anguish amongst some and rejoicing amongst others , it would affect stock market that much , crude oil exports on the other hand would see hundred of millions of unemployed

    That’s leverage , big time

  27. rwendland (History)

    Reuters is suggesting today Iran thinks a swap deal might still be possible:

    “If a guarantee is provided to supply the 20 percent (enriched) fuel for the Tehran Research Reactor, our officials are ready to enter talks about 20 percent enrichment,” Foreign Ministry spokesman Ramin Mehmanparast said at a Eurasian media forum in Kazakhstan on Friday, according to Iran’s Press TV.

    Foreign Minister Ali Akbar Salehi told the German newsmagazine Der Spiegel earlier in the week: “If our right to enrichment is recognised, we are prepared to offer an exchange. We would voluntarily limit the extent of our enrichment program, but in return we would need a guaranteed supply of the relevant fuels from abroad.”

  28. Rob Goldston (History)

    Well, enough of Bibi. How about Joe?

    I find myself concerned that Tehran could read Joe’s statements at the Vice Presidential debate as indicative that their firing up centrifuge cascades to enrich from 20% to 60% would have little risk of bring about military consequences. I hope there is a clearly different message being passed to Iran privately.

    The October 8 ISIS report ( ) outlines breakout scenarios, and suggests – along with Bibi – that military intervention after WGU is produced would be much more difficult than before. IMHO, the breakout scenarios to WGU are shorter than the time it takes to form an international consensus on military action, so – again – I hope that there are messages being passed privately on this topic as well.

    What do the wiser heads on this blog think?