Question

Briefly discuss:

(i) The principles of detecting thermal neutrons utilizing a Si detector.
(ii) The physics of fast neutron detection.
(iii) The principle of operation of strip detectors for charged particle detection and
their application.

Answer 1

(i) Neutrons incident on a nucleus can give protons, alpha particles or fission fragments. The distance traveled by reaction products inside the detector has important consequences for detector configuration. The products having certain energy deposition produce electron-hole pair and these electron-hole pairs are then separated.

(ii)Although fast neutrons are moderated to thermal energies before detection but when fast neutrons energies are required, Liquid Scintillators and Plastic detectors can also be used.
The neutron-gamma differentiation is done by Pulse Shaping discrimination.
4-He based MWPC or gas detectors can also act as Pulse shape Discriminator.
NAND detector in IUAC at New Delhi,India uses Saint Gobain Plastic detectors.

(iii) Strip detectors are basically used to know the position and charge of particle produced in the reaction chamber.
A metal wire(really thin wires) grid is capable of detecting type and charge of particles if Pre-amplifier is used of each strip/wire.
This tells us type of particle and the various configuration may tell us,where in space the particle is produced during the reaction.