Neutron Scattering

this way even at a comparatively low average neutron flux very high pulsed fluxes may be
obtained . In the thermal range for example, the Rutherford source is able to surpass the ILL
with respect to the peak flux significantly . Such pulsed sources can be used in particularly
well for time of flight experiments which will be discussed later in the school .
2 .4 Neutron detection
Generally the detection of neutrons is performed indirectly through particular nuelear
reactions which produce charged particles . A number of possible reactions are listed in
Table 2 .2 .
Proportionality counters operate wich a gas volume of 3He or BF 3 (enriched with' °B) . Such
counters deliver sensitivities to nearly 100% . Scintillation counters absorb neutrons within a
polymer or glass layer which is enriched by 6 Li and ZnS . Neutron absorption then leads to
fluorescence radiation which is registered via a photo multiplayer or directly wich a
photographie film. Finally, fission chambers use the n + 235U reaction and have generally only
a low counting probability . They are mainly used in order to control the beam stability and are
applied as monitors.
Table 2 .2 :
Nuclear reactions used for neutron detection .
The cross sections are given in barns (lb =10 -28 m 2 ).
Reaction Cross Section for Particles Energy Total Energy
25meV neutrons generated [MeV] [MeV]
P 0.57 0 .77
n + 3He 5333 b 3 T 0 .2
6 n + Li
941 b
3T 2 .74 4 .79
4He 2 .05
4He 1.47 2 .30
n +' °B 3838 b 7 Li 0 .83
y 0.48(93%)
n + 235U 681 b fission 1-2
2-8