Modernized spectrometer for the hydrogen contents analysis in samples

Full text: Determination of the concentration profiles of the hydrogen isotopes in various materials is very actual problem now since hydrogen, if presents, rather strongly affects on physical, chemical, electrical, mechanical and other properties. In the INP AS (Uzbekistan) the specific method of hydrogen isotopes profiling (Neutron-induced Elastic Recoil Detection (NERD) method) has been developed. The energy spectrum of H-ions that are knocked out by fast neutrons gives the information on the depth and concentration of hydrogen in a sample. The method allows obtaining of the concentration profiles for all hydrogen isotopes simultaneously and has the analysable depth up to 1.5 mm for 1H. We have improved the analytical characteristics of the method: By sufficient decreasing the background of the charged particles and reduction of the gamma quanta background in the energy spectra of hydrogen recoils; By reduction of quantity of scattered neutrons along the neutron's trajectory to the analyzed sample; By using the fast output (short pulses) of the detector's preamplifier in the character of spectrometric circuit of electronics before the final 'slow' spectrometric amplifier. We have excluded the background of the charged particles using graphite as a constructional material for the box of the detectors' telescope. The background of gamma - quanta was reduced by removing the metallic elements and materials of the radiation protection as far as possible from a telescope of detectors. We have reduced the quantity of the scattered neutrons worsening the energy resolution by reducing up to a minimum the amount of metal between the neutron source and the sample, and using the materials with small cross sections of elastic scattering of neutrons. We have achieved the precise work of electronics with fast signals due to specially developed electronics: change -sensitive preamplifiers and linear gates. The change-sensitive preamplifiers have small signal duration (not more than 380 ns) and the counting rate ∼4/5x105 counts/s. The linear gate has switching time ∼20 ns and dynamic range not less then 102. Duration of the driving signal can be varied from 300 up to 1000 ns. Due to these improvements we can operate with two-detectors variant of the detecting system instead of the three detectors and simplify essentially the electronics of the spectrometer. Thus we have increased the analyzable depth of a sample. Check of the spectrometer's operation at the neutron flux (En=14 MeV) using the test samples containing hydrogen, deuterium and tritium has shown that the real (full) energy resolution of the spectrometer is equal 400 keV. The energy resolution is determined basically by the geometrical resolution and includes the own resolution of the detectors, energy dispersion of the neutron flux and the effect of scattering of neutrons on small angles before hit on the analyzed sample. This energy resolution results in the following calculated depth resolution:For hydrogen-60 microns. For deuterium-22 microns For tritium- 11 microns. Thus the analyzable depths (for example, in silicon) make: For hydrogen-1200 microns. For deuterium - 500 microns. For tritium - 260 microns. This work was supported by STCU Project no. 3067. (author)