About this site
 |
Neutron Production If nuclei contain too many neutrons in relation to protons to be stable they usually decay by emitting a beta (minus) particle. This transforms a neutron within the nucleus into a proton (and an antineutrino is also given out - A level standard knowledge!).
But there are some very short lived delayed neutron emitting nuclei found among fission products. When fission occurs there are two fission fragments and some lone neutrons produced. Occasionally on of the lone neutrons stays associated with a fragment for a while before it breaks free.
. |
Follow me...
|
Commercial
sources of neutrons can be produced by creating neutron rich nuclei, for
example by mixing an alpha emitting radioisotope with a material such
as beryllium. If beryllium 9Be is bombarded with alpha particles emitted
by 241Am(americium) neutrons can be released. The alpha particles emitted
by the 241Am have an energy greater than 3.7 MeV. This is big enough to
overcome the coulomb repulsion between the alpha particle and the nucleus
(Beryllium is suitable because of its low Coulomb force) and to allow
it to 'get into' the beryllium nucleus.
An
alpha particle consists of two neutrons and two protons- it interacts
with a Be (Beryllium) nucleus, increasing its nucleon number by three
and the proton number by two and it freeing 1 neutron. Since the alpha
particles slow down by different amounts before striking the Beryllium
target, neutrons produced by this interaction have a spectrum of energies,
but most are slow neutrons - however, ones that will increase the probability
of a successful fission being instigated need then to be slowed even further
to thermal energy. See table below for the names of different energy range
neutrons.
Cyberphysics - a web-based teaching aid - for students of physics, their teachers and parents....
