Thermal-radiation detector reactors

You should be aware that cadmium has a high cross-section for the absorption of thermal neutrons. During this absorption, or thermal neutron capture reaction, gamma radiation is emitted, the most noticeable of which is at an energy of 558 keV. If a detector system is to be used in a neutron field, then cadmium in the graded shield should be avoided. Fortunately, tin has a much lower thermal neutron cross-section and can be used instead. Difficulties due to neutron capture might be expected, and indeed have been observed, when operating a detector close to a nuclear reactor but the problem can also occur in environmental measurements (see Chapter 13, Section 13.3.4.2.)... 

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