核輻射與物質的相互作用

In the previous chapter we have discussed natural radioactivity in which a and B particles and y-rays are emitted from the disintegrating nucleus of an atom. In nuclear fission and fusion reactions neutrons and other particles together with certain radiations are emitted from the nucleus.

Moreover interaction of high energy particles *natural or artificial* with matter produce certain nuclear or atomic reactions with the emission of particles like protons,Deuteronomy,neutrons and ionizing radiations like y-rays from the nucleus and x-rays and ultraviolet rays from the atoms.

These particles and radiations have been studied carefully for their properties and effects which are as follows

 

(1) Alpha Particles.

It shoots out from the nucleus with a high velocity (0.1*10-8m/s)

Thus it possesses very high energy (7.7 MeV) for the most energetic from r ac (i.e: Bismuth-214).

Due to its large size more charge and high energy it can make very large number of collisions with the atoms and i noise them as it passes through them,Before it stops head on collisions are were however it an a particles passes close to an atom the strong electrostatic attraction between it and an electron tears he electron off from the atom and ionizes it an a particles loses about 35 V energy in each collision.Thus a 7.7 MeV a particle from RaV (Bi 214 produces about 0.3 * 10-6 loins before it stops.

The range of a-particles is small (about 7*10-2 m in air and only 4*10-5 m in aluminum for the 7.7 MeV a-particles).

Thus metal sheets form good shields for a particles the number of icons produced by an a particle or its range in air is a measure of its energy.

Alpha particles produce fluorescence on striking certain substance such as zinc sulfide and harlumplatinocynide,

(2) Protons

A protons is also a positively charged particles with properties similar to the a particles.

Its is fourth and charge is one half of that of an a particles it smaller in size and carries less energy at the same velocity.

Obviously it suffers fewer collisions with the atoms of the medium as compared with the a particles and penetrates the medium to a greater distance about (5 至 10 times) before stopping its ionizing power is also much-less about one ah that of the a particle the machine of ionization is however identical….

(3) Beta Particles

A B-particles also ionization the atoms of the medium along its path but this ionization is much less than that produced by an a particle or a proton.

The reason is that due to its very small size the collisions are fewer and far the a part.

Even in a single collisions most of its energy is lost head on collisions bling rare.

It can ionization an atoms by strong electrostatic repulsion when it passes close to its electron the range of B particle in a medium is very large nearly 100 times that of an a particles in a medium the same energy.

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