Nuclear reaction - where do we get the first neutron to initiate fision?

Question

Every book explains us about the nuclear reaction and chain reaction but no one tells us where do we get the first neutron to start the reaction. Is there any special instrument to give neutrons? where do we get the first neutron? Please explain in detail

Answer 1

The natural decay creates a certain number of neutrons.

The rate at which reactions occur depend on the number of "slow" neutrons available for reaction - and the density of the nuclear fuel.

You can provide more "slow" neutrons by placing the nuclear reactor in so-called "heavy" water - which has a higher than normal concentration of H2O molecules that include extra neutrons. Collisions between the fast neutrons from most of the natural decay reactions and the heavy water slow down the neutrons so that the number of slow neutrons increases.

At the same time, you surround the reactor with neutron reflectors - to keep the neutrons from leaving the reactor and not taking part in the reactions.

When there is enough fuel, and enough slow neutrons - the number of neutrons created by the reactions caused by the slow neutrons approaches and can surpass 1:1 ratio. If the ration is exactly 1:1 - the reaction is called "critical" - namely that the reaction produces all of the neutrons that it needs. If the ratio exceeds 1:1 - the reaction is super-critical. This can happen when starting up a nuclear reactor - or in an atomic fission bomb where the number of reactions increases geometrically - more neutrons causing reactions are created than reactions taking place - so in each generation there are more and more reactions.

In a reactor, you can control the increase in neutrons - to prevent the reactor from exploding - by placing neutron absorbing rods in the reactor - and placing the rods at just the right place to hold the reaction critical without going super-critical.

When a reactor has an emergency caused by a super-critical transient - you can stop the reaction all-together with a fail-safe spring/gravity loaded lead rods that will go into the reactor and absorb alot of neutrons to slow down and stop the reactions from getting out of control.

Answer 2

I believe the fissionable materials (U235 and Plutonium239) are naturally unstable and fission naturally. When you get enough the the material close enough together these neutrons impact other atoms to create more neutrons in a chain reaction that the energy release increases exponentially.

For weapons (from Wikipedia),

Neutron trigger or initiator:

One of the key elements in the proper operation of a nuclear weapon is initiation of the fission chain reaction at the proper time. To obtain a significant nuclear yield, sufficient neutrons must be present within the supercritical core at just the right time. If the chain reaction starts too soon, the result will be only a 'fizzle yield', well below the design specification; if it occurs too late, there may be no yield whatsoever.

Several ways to produce neutrons at the appropriate moment have been developed. Early neutron triggers consisted of a highly radioactive isotope of polonium (Po-210), which is a strong alpha emitter, combined with beryllium, which will absorb alphas and emit neutrons. This isotope of polonium has a half life of 138 days. Therefore, a neutron initiator using this material needs to have the polonium replaced frequently. The polonium is produced in a nuclear reactor. To supply the initiation pulse of neutrons at the right time, the polonium and the beryllium need to be kept apart until the appropriate moment and then thoroughly and rapidly mixed by the implosion of the weapon. This method of neutron initiation is sufficient for weapons utilizing the slower gun combination method, but the timing is not precise enough for an implosion-weapon design.

Answer 3

From a neutron source. Duh.

It can be an amount of instable material that emits neutrons in the decay proces. Colliding heavy isotopes of light particles also produce neutrons, so shooting hydrogen nuclei at such a material will produce a neutron beam.

Answer 4

definite, they do desire neutron ingredients to start up a swifter-than-commonplace breakdown. fortunately, nonetheless, the fissile textile is definitely one of those source, as some atoms will spontaneously fission and spit out some neutrons. the main concern in fission reactors isn't commencing the reaction, that is controlling it and battling it if needed.

Answer 5

From my limited understanding, to create a nuclear blast you must first have fissionable material that is encircled by high explosives in order to get a compression wave to release the energy to begin the nuclear process. To create any reaction would require some similar process, but with other means to initiate the requisite energy level. (Power plants do not use explosives to initiate the chain reaction.)

Handling these materials are dangerous for your health, and there are serious legal issues handling this sort of material as well. Leave it to professionals please!

Answer 6

A neutron from a particle accelerator or a radioactive substance.

Answer 7

you dont have to.

Fission can be accomplished by a numerous amount of ways. I believe bombarding it with gamma waves... (or it may be x-rays )

and it violently shakes it apart releasing neutrons which chain reaction other molecules.