Question

16- how do long counters used in neutron detectors?
17- what are fast neutrons induced reactions?
18- fast neutron scattering
19- what are proton recoil scintillators? How do they work?

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Answer 1

16.

Elastic scattering reactions (also called as proton-recoil) - High energy neutrons generally are detected indirectly through elastic scattering reactions. Neutrons collide with the nuclei of atoms in the detector, then transferring energy to those nuclei and then creation of ions, which are detected by the detector .

17.

In case of fast neutron physicsthe chain reaction in a nuclear reactor at a critical state takes place. Slow neutrons are bombarded to the nuclei of uranium-235, causing the nuclei to fission, or split, and release fast neutrons thereby releasing large amount of energy.

18.

Neutron scattering is generally practiced at research reactors and spallation neutron sources and it provides neutron radiation of varying intensities. Neutron diffraction (also called elastic scattering) techniques are used to analyze structures; where as inelastic neutron scattering is used in studying atomic vibrations and other excitations on the crystalline substances.

19.

The proton recoil technique by plastic scintillators are employed to measure fast-neutron spectra. Associated gamma-ray background are eliminated by using various thicknesses of thin scintillators. The method is based on different ranges of electrons and protons detection of material, and are shown to be useful for measuring neutron spectra over an extended range of energy region.There are four scintillator thicknesses so chosen to cover the entire neutron energy from 1 to 18 MeV, based on practical 100% transmission of Compton-edge electrons.

Working:

The pulse-height spectra of different detectors are well mixed to give a pulse-height spectrum of the combined detector.Unfolding code is developed to unfold the combined pulse-height of spectrum using combination of responses from matrix resulting from the mixing of the calculated responses function for the individual detectors. The neutron spectra of different alpha and neutron sources and of 252Cf spontaneous fission is measured and compared with published experimental data. This technique developed is used only for a neutron energy up to 14 MeV and can be applied in practice to higher energies as well.