[Corvettaholic]

Ah yes, I get the two of them mixed up quite a bit.

About the gun-design nuke, I think the main wad of uranium also has beryllium or something like that in it. Right smack in the middle. When the pellet is shot out of the gun, it hits the main ball, and somehow lets the beryllium (or whatever) do its thing and emit neutrons. Gives the reaction a good kick in the pants, and since you now have a critical mass... let the fireworks begin.

[jdurg]

Ah yes, I get the two of them mixed up quite a bit.

About the gun-design nuke, I think the main wad of uranium also has beryllium or something like that in it. Right smack in the middle. When the pellet is shot out of the gun, it hits the main ball, and somehow lets the beryllium (or whatever) do its thing and emit neutrons. Gives the reaction a good kick in the pants, and since you now have a critical mass... let the fireworks begin.

I'm fairly certain that is incorrect, because when a mass goes critical, it's instantaneous.  It's not like a reaction which slowly gets going and then goes "BOOM."  As soon as criticality is achieve, the fission takes place so fast that there is no time for anything to absorb a neutron and convert into neptunium, then decay into plutonium, then fission.  Generally speaking, the area around where the "fuel" combines is composed of U-238 shielding since U-238 is a VERY good neutron/radiation blocker.  If a neutron escapes the fuel, it will be bounced right back in there.  Some of the U-238 will indeed turn into plutonium, but the metal will have been vaporized so quickly that it's really inconsequential.  Another reason why I think the Be core of the bomb is false is because in order for criticality to be achieved, all of the mass has to be in one confined area.  By putting in a Be core, you're lessing the chance that the subcritical masses will form a critical mass, and increasing the chance that you'll have a very expensive dud.  

[Corvettaholic]

well that sounds logical, but I remember reading something about a core in some book on nuclear weapons. not that books always tell the truth. now isn't it with a nuclear weapon, once you have a critical mass you want as much fission to go on before the explosion blows whats left of the fuel all over the place? I think the first nuclear weapon only had something like 5% of fuel that went through fission... could be wrong though.

[Scratch-]

http://people.howstuffworks.com/nuclear-bomb5.htm

Both gun-triggered fission bombs and implosion-triggered fission bombs use a neutron generator such as a beryllium/polonium generator to start a chain reaction. Just because something is a supercritical mass doesn’t mean it just blows up, it means it can sustain a chain reaction.

[budullewraagh]

apparently thorium is about 2-5% or something in thoriated tungsten welding electrodes

actually you'd be better off  using lantern mantles.  just torch them all and reduce with an alkali metal or alkaline earth metal.

as for your neptunium problem, i'm here to help with my handy chart of the nuclides published by a handful of professional nuclear chemists/physicists to whom i know

alpha bombardment of Pu 239 would be certainly sketchy considering you'd get curium 243 which has a half-life of 29.1 years.  the Np isotope you are looking for is 237 as its half-life is 2.14*10^6 years and it releases a bit less gamma than say 234 which is just insane.  fortunately, you can get to Np237 from Am241 although it'll take you a great deal of time.  alpha bombaerdment of Pa235 wouldn't work because its half-life is 24.4 minutes...  there is (somewhat) good news.  you could do what david hahn did and bombard thorium 232 with neutrons, have the 233 decay to protactinium 233 and instead of letting it decay to fissionable uranium 233 just alpha bombard it to Np 237.  depending on how well thorium 233 and protactinium 233 accept alpha particles, this may even work.  best of luck

[jdurg]

The thing is, you can't just sit an alpha particle emitter by a target source and expect the alpha particles to be absorbed.  The positive charge on the alpha particles and the positive charge of the nucleus means that the alpha particles need to be accelerated to massive speeds in order to overcome the nuclear repulsion.  With neutrons, since they are neutral particles there doesn't need to be any "nuclear force" to be overcome.  That's why you can just sit a nuetron emitter by a target source and have the target absorb neutrons.  With alpha particles, you really need to figure out a way to increase their energy if you are going to get any appreciable nuclear reactions.  

[Limpet Chicken]

Could a cyclotron be used to accelerate alpha or beta radiation  instead of electrons by substituting a radiation source instead of an electron beam in the center?

[jdurg]

Could a cyclotron be used to accelerate alpha or beta radiation  instead of electrons by substituting a radiation source instead of an electron beam in the center?

I belive that's what they use at Los Alamos National Laboratories in their nuclear research.  I think their particle accelerator is about 6 km in circumference.  Definitely not something you can setup in your basement lab.  

[Limpet Chicken]

One of the first cyclotrons was only an inch in diameter, I just read this today, not powerfull admittedly, but a cyclotron up to about 40 m wouldn't be impossible where I live (or at least near by).

Besides, say if SWIM was to attempt building one, and doing experiments with elements with obscene half lives, would the power, within limits and so long as the new nuclides were forming, actually matter, the cyclotron could merely be left on for XXX amount of time while SWIM patiently waited for results