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Last week Neil de Grasse Tyson was on Bill Maher's show and the topic of nuclear weapons came up.

Tyson said, "modern nukes don't have the radiation problem.... They're a different kind of weapon than Hiroshima and Nagasaki." When pressed by Maher, he said, no, there is no radiation issue "if it's hydrogen bombs."

With all due respect to Dr. Tyson, does anyone know what in blazes he's talking about?

My understanding is that ALL thermonuclear or "hydrogen" bombs still have a fission primary that uses at least as much fissile material as Fat Man, and therefore even the smallest TN bomb would be at least as irradiative as the original fission bombs, albeit with more "bang for the buck". However, AFAIK most also utilize a shell of additional fissile material which undergoes fission as a result of the huge neutron flux from the fusion, rendering these much dirtier than the original bombs. Wikipedia says specifically that retrofitted W87 warheads use a U235 shell to make the second fission stage even more powerful (and more radioactive).

Is there anything known about "newer" post-cold war weapons designs and/or trends that could justify what he said? My only thought was that he might have been talking about relative "dirtiness" per unit of yield being smaller with modern bombs, but I'm not even sure that much is true when you factor in the fissile shell which seems to be a common feature. Otherwise I'm at a loss to understand why he would say what he said.

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    $\begingroup$ The man is a good science educator who occasionally talks total bullshit. If you are downwind from ANY nuclear explosion, 1970s design or one from 1945 then you better hide for approx. two weeks under 6-8 feet of dirt or the gamma radiation will get you. There are plenty of papers and handbooks by the US government around with all the relevant technical information that you need for the design of efficient bunkers against direct and indirect effects. For the fallout a deep cellar will do but you have to stay in it. $\endgroup$
    – FlatterMann
    Commented Oct 20, 2022 at 21:08
  • $\begingroup$ I was also playing with NUKEMAP and I just came across an interesting fact. If the yield goes above 300kt or so and you select airburst, it says "The initial nuclear radiation equation for 500 rem failed to give a result for the given yield and height settings." So perhaps he meant that under the right combination of altitude and yield the radioactivity would be too spread out to be significant? But who's to say it would be an airburst... $\endgroup$
    – Peter Moore
    Commented Oct 20, 2022 at 22:07
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    $\begingroup$ @PeterMoore The modern military use is typically an airburst. That doesn't help all that much, though, because even in case of an airburst the fallout from the bomb itself spreads lethal radiation doses over hundreds of square miles. That nukes are "clean" is a myth that was probably invented to make people "feel better". $\endgroup$
    – FlatterMann
    Commented Oct 20, 2022 at 22:13
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    $\begingroup$ My understanding is that the some of the highest-yield weapons have the Fission primary (A-bomb), fusion secondary (H-bomb) and a U-238-based third stage that can produce massive amounts of fallout. NOT SAFE! $\endgroup$
    – R. Rankin
    Commented Sep 22, 2023 at 22:18
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    $\begingroup$ Yeah I just rewatched this for the first time in awhile and again while I like Tyson, unless he knows something we don't this is one of the dumbest things he's ever said. He doubled and even tripled down when pressed. Hard to argue it was a slip up or inadvertent mistake. Carl Sagan is rolling in his grave. $\endgroup$
    – Peter Moore
    Commented Sep 23, 2023 at 21:06

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He's not done his homework on this. There are heaps of ("over 300") fissionable and radioactive components created due to the fission initiator of a nuke. Plus gamma rays etc. To say that's not an issue to worry about is wrong. He should apologize it's giving the impression that these things are clean. Reference: https://www.britannica.com/technology/nuclear-weapon/Residual-radiation-and-fallout

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As others have mentioned, hydrogen bombs use a fission trigger.

In addition many used a tamper made of fissile materials. This way the neutrons from the fusion reaction can create an additional fission reaction.

From Wikipedia: "The secondary's relatively massive tamper (which resists outward expansion as the explosion proceeds) also serves as a thermal barrier to keep the fusion fuel filler from becoming too hot, which would spoil the compression. If made of uranium, enriched uranium or plutonium, the tamper captures fast fusion neutrons and undergoes fission itself, increasing the overall explosive yield. Additionally, in most designs the radiation case is also constructed of a fissile material that undergoes fission driven by fast thermonuclear neutrons. Such bombs are classified as two stage weapons, and most current Teller–Ulam designs are such fission-fusion-fission weapons. Fast fission of the tamper and radiation case is the main contribution to the total yield and is the dominant process that produces radioactive fission product fallout."

(Emphasis added by me).

Many hydrogen bomb designs would have a more than 50% fission yield. And since the yield tends to be far greater than the fission only bombs of the Hiroshima and Nagasaki era, potential for radioactive fission by-products can be much worse.

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I would rather say contrary to what Neil de Grasse has said,- Hydrogen nukes is far more dangerous in every aspect, including radioactive one. Due to much bigger blast radius, H-bomb will scatter fission initiator radioactive nuclides in fallout phase across area which approximately is $100 \times$ bigger than in A-bomb case.

Not to mention, that cyclones & air currents will spread radioactivity far more away. Just look at the table how comparatively passive nuclear leak in Chernobyl disaster has increased radioactivity in much more different countries than that one where catastrophe has happened. And in this question we are talking about deliberate spreading of radioactivity, which is far more lethal and has bigger long-term consequences.

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    $\begingroup$ I certainly don't disagree but wasn't the quantity of fissile material involved in Chernobyl far greater than the core of an implosion weapon? $\endgroup$
    – Peter Moore
    Commented Sep 23, 2023 at 20:39
  • $\begingroup$ My point was that in nuclear power plant disaster radioactivity is leaked locally, while in a A/H-bomb explosion it is blasted away in far much greater territories (radioactive nuclides & $\alpha, \beta$ particles). So radioactivity spread mechanism itself is more dangerous in bombs. $\endgroup$
    – Agnius Vasiliauskas
    Commented Sep 24, 2023 at 10:26
  • $\begingroup$ Studies of growth and development of Hiroshima and Nagasaki children have shown significant long-range effects associated with exposure to the atomic bombs. Radiation to the fetus during early pregnancy, even at relatively low doses, may result in reduced growth, smaller head size, and mental retardation.. Just to be sure, how "clean" A/H nukes are. $\endgroup$
    – Agnius Vasiliauskas
    Commented Sep 24, 2023 at 10:48
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    $\begingroup$ Yes but the Tsar Bomba model tested tested - without the fissionable tamper so "2 stage" - was still 50 MT. Yet afterward "[r]adioactive contamination of the experimental field with a radius of 2–3 km (1.2–1.9 mi) in the epicenter area was no more than 1 milliroentgen / hour. The testers appeared at the explosion site 2 hours later; radioactive contamination posed practically no danger to the test participants". en.wikipedia.org/wiki/Tsar_Bomba $\endgroup$
    – Peter Moore
    Commented Sep 29, 2023 at 23:20
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    $\begingroup$ I'm not denying that in some specific cases (like you have mentioned,- pure fusion without U238 tamper + airburst) radioactivity levels per unit area may be somewhat decreased. What I'm saying, is that this argument is not enough to claim that H bombs may be made "safe for radiation", because nobody has done real research (and probably never will) how $10-100 \times$ greater radiation compared to the background level will affect local fauna and flora over the course of $4.5~\text{billion years}$. Say, you gonna punch me and say, I will lower my punch force so this will be ok. No, it's not. $\endgroup$
    – Agnius Vasiliauskas
    Commented Sep 30, 2023 at 21:43

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