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After reading "Project Orion", the 1950's plan to launch a large mass spaceship using small nuclear devices, (and also from common sense), I realise that a lot of nuclear research is classified.

The output of a typical nuclear device can roughly be split into

  • Blast Effects (50%)
  • Thermal Radiation (40/30%)
  • Fallout (20/10%.)

I have read through Nuclear Weapon Design and, although it goes into pretty exhaustive (and, to me, depressing) detail about how good a bomb we can make, I cannot see any spectrum of the radiation output.

My question is: if we wanted to create a bomb for something like a future Project Orion, or any other specific peaceful purpose, could we, in theory, "salt" the explosive mixture with elements to produce, for example, more infrared, rather than soft X rays, (which are the main component of present day bombs.)

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  • $\begingroup$ The wasted a lot of money on "nuclear plowshare" kind of devices: en.wikipedia.org/wiki/Operation_Plowshare, but it really didn't amount to anything. Even things like project Orion are based on wishful thinking rather than solid physics. If you want a nuclear spacecraft drive, then spend the money that it will take to design a controllable fission or fusion device. Thermal fission rockets have been developed to actual usefulness, with up to roughly 800s of ISP. With fission and ion drives one could easily reach 10,000s+ of ISP, which would open up the entire solar system. $\endgroup$
    – CuriousOne
    Jun 4, 2016 at 21:17
  • $\begingroup$ @CuriousOne In the book, the author , George Dyson, says Feynman was approached to get involved, but, possibly due to his war work, he told the Orion team he wanted nothing to do with "that pie in the sky". I wonder how many RPF stories are actually true :). $\endgroup$
    – user108787
    Jun 4, 2016 at 22:20
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    $\begingroup$ Feynman must have known better and was a realist. Any kind of neutron device is inherently dirty. If one could find a gamma-only reaction (not even fusion offers that), then one could dream about reasonably "clean" nuclear devices, but given what nature offers... that's probably not on the menu. The problem with fusion, even for space propulsion, is the tritium supply, anyway... there is just not enough of it. $\endgroup$
    – CuriousOne
    Jun 5, 2016 at 1:59

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The spectrum of emitted rays is defined by the energy output of the reactions happening in the device and its surroundings. Basically, after an exothermic nuclear reaction, the produced particles smash into surrounding material and bounce for some time until their energy is dispersed. This energy heats up the medium which begins to emit black-body radiation spectrum with high temperature.

I believe this black-body spectrum is what you refer to as "soft X rays" as typical photons created directly in a nuclear reaction will be far more energetic, in the gamma ray part of spectrum, no matter what.

Black-body spectrum is just the thermal radiation emitted by any heated body. It has continuous distribution with the peak at the energy $\sim 3 kT$. So, basically, if you want to reduce the energy of the produced radiation, you will have to reduce the temperature of plasma and hence the energy of explosion.

Anyhow, this black-body spectrum will be present only in the atmosphere and it is anyhow a pretty bad idea to detonate near the surface.

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  • $\begingroup$ Thanks very much for the answer, I agree that the spectrum can't be altered no matter what you throw into the mix, it was just a thought. $\endgroup$
    – user108787
    Jun 5, 2016 at 12:00

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