The difference between a uranium bomb and a hydrogen bomb

At first glance, the kablooey aspects of the two bombs look pretty much the same. My question is mainly about the fallout- uranium bombs scatter radioactive fallout far and wide, while hydrogen bombs… what? There will still obviously be a lot of fallout, but it can’t be quite the same. What is the difference?

Are there any other differences between the effects of these two kinds of bombs I ought to know about?

You’re talking about fission vs fusion bombs, or uranium bombs vs non-uranium? Both fission and fusion (hydrogen) bombs can be made with or without uranium.

A Hydrogen bomb is ignited by a Uranium or Plutonium bomb.
They both create tremendous amounts of fallout. Generally a Fusion bomb will create more fallout, simply because it’s bigger, and gets a lot of it’s power from the fast fusion of the casing, which is generally U-238.

Fission devices, both uranium and plutonium, are set off by chemical explosives. Fusion devices are set off by a fission device and are generally more powerful than a fission device.

Fission vs. fusion is a better way to put it. There are plutonium fission bombs, and thorium ones too I suppose. Looks like I posted too hastily.

There’s never been a Thorium bomb.
Although there are several fissionable isotopes that could potentially be used to make a bomb, only U-235 and PU-239 have ever been used.

More fission products mean more fallout, but it should be noted that a surface burst is going to result in a huge amount of severe local fallout, versus the same bomb detonated high in the atmosphere.

A thermonuclear weapon using a uranium tamper could produce a huge amount of fission products; conversely, a pure fusion weapon could theoretically produce a massive neutron burst but less radioactive fallout.

The OP may be conflating “H-bombs” with the “Neutron” bomb. It was hyped to kill people without destroying buildings, although that wasn’t really accurate. Some called it the “Capitalist” bomb, as it destroyed people, but not property. Its proponents felt this made it morally superior to fusion bombs.

Basically it was a hydrogen bomb without the Uranium 238, chaos, heat, and especially the force of the blast aspect were reduced. No Uranium meant no fallout (“long-term” radiation). The neutrons, however were initially lethal, (“short-term” radiation) and so would kill any troops in the vicinity. This is the real reason it was morally superior - it could be aimed, and the destruction kept to a much smaller area, with no drift.

The idea was that it could be used as a Tactical weapon, and aimed at actual soldiers, instead of taking out entire civilian populations.

A neutron bomb will still destroy buildings close to ground zero. A nuke is a nuke, after all. Its radius of building-destruction is smaller than for a more typical H-bomb design, but that wasn’t actually a design feature. The main purpose for a neutron bomb is to disable a lot of tanks very quickly, which goal it accomplishes by killing the tank crews.

A pure fission device (the technical nomenclature specifically avoids use of the term ‘bomb’ except in final, operation configuration such as the B-61 ‘gravity bomb’) creates a yield of energetic radiation, along with a small but unavoidable amount of wasted neutrons and radionuclides (residual daughter products from the nuclear material and activated components which themselves undergo a chain of radioactive decay) by causing a prompt fission reaction in [SUP]235[/SUP]U or [SUP]239[/SUP]Pu, which is contained and enhanced by a tamper.

A thermonuclear fusion device uses a fission ‘Primary’ to trigger the conditions for a fusion reaction (and often uses neutron yields from the Primary to breed tritium from [SUP]6[/SUP]Li as tritium is very expensive and has a short half-life of 12.3 years) to create a significant yield of energy from fusion which is primarily X-rays. This is also described as a “multistage” weapon because it could be built with additional stages of fission and fusion, but all deployed weapons are a fission Primary and fusion Secondary, with the yield of the Secondary sometimes used to significantly enhance the yield of the Primary by compressing a tamper made of [SUP]238[/SUP]U (or potentially other fertile materials; [SUP]232[/SUP]Th could be used for this, but in practice is not since there is plenty of [SUP]238[/SUP]U left over from uranium enrichment). While the energetic yield of pure fission weapons tops out at a few megatons of TNT equivalent, there is no theoretical limit to the yield of a nuclear fusion device. The US built and fielded a 25 MT device, while the Soviets tested the ‘Tsar Bomba’ which had an estimated yield of 52 MT but was incomplete in configuration, and had a projected yield in excesss of 100 MT in full configuration.

A boosted fission device injects a small amount of tritium into a fission reaction in order to get a small amount of “incomplete” fusion in order to further compress the fission Primary and get a large yield. It is essentially a less complex version of a fusion device with most of the yield coming from fission that is “boosted” by fusion.

A “neutron” device is basically a boosted fission device which is optimized to produce a large shower of neutrons instead of maximizing the electromagnetic radiation. It still produces radiation and blast effects, but of much smaller magnitude. (The thermal pulse and blast overpressure effects, as well as the characteristic mushroom cloud formed by the vacuum of superheated air rapidly rising are all due to the atmosphere absorbing X-rays from the device, and dictate the energetic yield in tons of TNT equivalency.). The effects of a neutron device are much more localized because of the modest blast effects and because neutrons don’t interact much with the atmosphere; instead, they penetrate deeply into solid materials and are absorbed, converting normally stable elements into highly radioactive isotopes.

As Chronos notes, one of the purported uses of neutron weapons is to turn the dense armor and ammunition used on modern tanks (made of depleted uranium, which is just [SUP]238[/SUP] left over from enrichment) into highly radioactive species, rendering them useless for protection. However, despite the reputation as being a tactical or urban weapon, the main use for neutron devices is actually in an anti-ballistic missile application where exposing opposing nuclear weapons to a high surge of penetrating neutrons, causing them to prematurely fission, poisoning the intended detonation schedule.

There are also in theory pure fusion weapons, in which the fusion weapon is initiated by some highly energetic non-fission reaction (e.g. an X-ray laser creating fusion-level temperatures and confinement, proton generators, or so-called ballotechnic explosives) but as far as the public is aware, none have every been developed or tested, much less fielded, and the energies necessary to initiate fusion without a fission primary have required massive capacitor banks or large arrays of the world’s most powerful lasers, so it seems unlikely that pure fusion weapons exist or will every be practical without some kind of major innovation in materials and energy technology.

While massive multi-megaton weapons are possible, they are energetically inefficient as beyond a certain size they simply result in pushing more atmosphere “up”. The atmosphere is opaque to X-rays over long distances and will limit the range over which atmospheric heating can occur. Early weapons, such as those on the LGM-25C, were massively overpowered to compensate for the low precision of the guidance system, but most operational weapons are in the <1 MT range, which is more than sufficient for hardened surface and unprotected urban targets, especially since such targets are typically assigned multiple weapons. There are also variable yield (‘Dial-A-Yield’) devices with a configurable yield option by varying the amount of boosting material injected, allowing use as a tactical-scale weapon with controllable range of effect. (The division of nuclear weapons into battlefield ‘tactical’ and international ‘strategic’ weapons is somewhere between a joke and a deception; any use of nuclear weapons between players with large nuclear arsenals is likely to become a strategic exchange just because there is no way to protect conventional forces from attack other than scattering them to reduce losses.)

‘Fallout’, by the way, is primarily due to material from the ground being sucked up into the mushroom cloud, activated by neutrons, and then dispersed by wind over a broad area. There is some of the device material and unconsumed nuclear material as well, but it is a modest amount compared to the many tons of debris which may be drawn up by the rising atmosphere. Fallout can be avoided by using higher altitude (>5 kft) detonation. Alternatively, fallout can be enhanced by near ground level bursts combined with a jacket of fertile material which the neutron output can convert to aggressive radionuclides, ‘salting’ the downwind real estate and making it uninhabitable and unpassible without protection for dozens or even hundreds of years.


Virtually never. The US 1955 teapot met test was a plutonium and u233 composite.

India’s 1998 shakti V was low yield u233

U 233 is derived from thorium

almost correct-fast fission. :slight_smile:
I am sure that was just a typo.

This is really the punchline for the OP right here.

Fallout is almost entirely *not *parts of the bomb. It’s not created directly by the bomb itself. It’s radioactivated dust formed from ordinary dirt, rocks, trees, buildings, people, etc.

The bigger the detonation and the closer to the ground it occurs, the more ordinary junk gets pulverized, irradiated, sucked upwards, and eventually distributed downwind.

The specific atomic/nuclear technology of the device is *mostly *immaterial except as that’s connected to total yield.

Even then the burst height is by far the major determinant of fallout volume; even a ginormous device can be exploded high enough to produce minimal fallout. it just depends on which weapons effects are most desired: cratering and fallout, or a wider spread of firestorms and prompt radiation. Or to maximize EMP.

Along these lines I just posted a query ( a real one, as SDGQ goes) on the energy in carbonated water vs plain water, and I reference it here, and ask the present company to consider it–because I forgot to put fusion energy as a bizarre possibility in the subject header.

[I honestly didn’t think of this till now, but the Seltzer Thermonuclear Bomb might be thought of by some as the ultimate Jewish evil weapon dreamed up by a Learned Elder of Zion.]

A nice response to my question, thanks everybody. I did not realize that radioactive fallout is mainly the result of neutron bombardment, or that ‘fusion’ bombs are really hybrids. I guess if you really want a ‘green’ WMD, you’ll have to be satisfied with something like the MOAB…?

As stated above, you could attack with fire and EMP from about 5k feet, and produce very little long term radiation.

The joke answer, of course, is that since Hydrogen bombs are fusion based, and fused hydrogen turns into helium, that the difference between the two, is that survivors of the uranium blast will speak normally, and survivors of the hydrogen blast will have high squeaky cartoon like voices.

Let’s clarify this …

Fission products from Uranium/Plutonium bombs include Strontium-90, Caesium-137 and Iodine-131. Fusion weapons with a Uranium-238 tamper produce large amounts of these fission products plus unfissioned material.
Neutron-activation produces lighter elements like Carbon-13/14, Hydrogen-2/3, Oxygen-19 etc as well as Plutonium from the tamper.

Neutron production (and thus neutron activation) occurs in the first 50 microseconds of a nuclear blast, maybe a bit longer in a fusion blast. That isn’t long to produce activation products apart from the bomb casing itself.

My question is how much more actual radioactive material is produced in a ground burst, as opposed to more physical material being contaminated by fission and activation products for dispersal, and faster dropout due to more incorporated mass and larger particulate sizes.

A fusion bomb with U-238 tamper will produce vastly more fission products and unfissioned material than a small efficient fission bomb, whether ground or air burst.
The ground burst will just mix all that radioactive material with dust and water and make it fall back down much closer to the bomb site. Lots more fallout, but not many more Curies.