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Gas detectors
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  • The main problem with measuring neutrons is that they are uncharged and do not directly excite ionization in the matter through which they are travelling.
  • They are detected by nuclear reactions which produce charged particles. These particles are collected and processed.
  • The concern here, using gas detectors, is with slow neutrons, i.e. those with energies below the cadmium cut off (~ 0.5 eV)

Commonly used detectors are:

The BF3 (boron trifluoride) detector
Boron lined detectors
3He detectors
Fission counters

Nuclear reactions used in neutron detection
Target reaction Product Q(MeV) Thermal sn
3He n,p 3H 0.764 5330
6Li n,a 3H 4.780 940
10B n,a 7Li 2.792 6% of 3840
10B n,a 7Li 2.310 94% of 3840
235U n,f f.f. ~200 582
238U n,f f.f. ~200 (En > 1 MeV)
 

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