Page 31 - bukuneutron

cleus can give up a great amount of its energy even
can transfer entire kinetic energy to a proton after one
collision. Imaging, a proton and another proton are
position in one row have identical masses, upon hit-
ting with neutron, first proton moves and hitting another
proton can be made to stop and other proton will start
moving with the same speed. These processes con-
tinue finally resulting in neutron to slow down in the
materials. The neutron with a reduces speed is called
thermal neutron.

In the case of heavy material which contains a heavy
nucleus, the mass of neutron is much less compared
with the mass of heavy atom, such as lead, tungsten
and etc. The neutron will bounce back upon collision
on to heavy nucleus with little changes in speed and
change in scattering direction. Furthermore, neutron
with a slight less energy still can travel in different di-
rection. The slow down or moderation is not happened
significantly in this case.Therefore, lead is quite inef-
fective for stopping neutron and it is not a good mate-
rials for making neutrons shielding.

The ultimate aim of radiation shielding is to elim-
inate all form of radiation to reach and damage the
human and its environment.The slow neutron can still
get through some materials at certain thickness. Ther-
mal neutron can be totally stopped by using high neu-
tron capture cross sections. The materials like boron,
lithium, cadmium, gadolinium and dysprosium have large

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