Neutron Scattering

Appendix
Neutron Sources - an overview [4]
1 .A.1 Spontaneous nuclear reactions
Although every heavy nucleus is unstable against spontaneous fission, this reaction is generally
suppressed by a-decays beforehand .
hand, an exotic isotope, 252Cf,
With the advent of nuclear reactors, on the other
became available in suffcient amount from reprocessing spent
nuclear fuel, where 3% of the decays are by spontaneous fission. The rest is a-decay . The
data of a 252Cf-source are :
- yield: 3 .75 neutrons / fission
resp . 2.34 x 1012 neutrons / (gram s)
- half life : 2 .65 y (including a-decay)
- average neutron energy : 2.14 MeV (fission spectrum)
1 .A.2 Forced nuclear reactions
In this case we can distinguish between reactions initiated by both charged and neutral particles
. In this context y-quanta are regarded as neutral "particles".
1 .A .2 .1 Reactions with charged particles
Although we will restrict the discussion to light ions such as protons, deuterons and a-particles,
a wide field is covered from the historically important radium-beryllium-source to the
latest sources like plasma focus or spallation sources .
(a,n)-Reactions
Reaction partners with these sources are either natural (Radium, Polonium) or artificial
(Americium, Curium) radioactive isotopes and a light element such as Beryllium as target
material .
Using a radium-beryllium-source Bothe and Becker discovered in 1930 a new
particle, which they failed to identify it as the neutron . Two years later Chadwick accomplished
this earning him the Nobel prize for this feat. Modern sources employ artificial isotopes
alloyed with Beryllium . Yields are between 10 -4 and 10-3 neutrons per particle . The
technical parameters of a modern 241 Am/Be- source are :
- yield: 0 .9 x 10 7 neutrons / s per gram
- half life : 433 y
- neutron energy : a few MeV (complex line spectrum)
241
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