Proportional counters filled with hydrogen are used
for neutron spectrometry in the energy range from
10 keV to 3 MeV. The measured energy distribution of the recoil protons can serve as a basis to determine the energy distribution of the neutrons by suitable deconvolution methods. The counters are filled with hydrogen, methane or a hydrogen/argon mixture, a gas pressure of up to 1 MPa being selected. For the used counters with spherical wall, the response is independent of the incident direction of the neutrons. The calculation of the response allows for the fact that part of the recoil protons end in the wall and thus do not lose the whole energy in the gas and that the electric field along the counting wire is not constant due to the spherical shape.
Neutron radiation is always accompanied by photons. These produce electrons in the counter wall, which also deposit energy in the counter. Due to the small stopping power, these electrons may lose up to about 50 keV in the counting volume. Below 50 keV, the pulses produced by the electrons are separated by pulse shape discrimination profiting from the fact that the pulses produced by electrons have a longer rise time than those produced by recoil protons.
Literature:
Knauf, K.; Heimann, C.; Kaldune, N.; Novotny, T.; Wittstock, J.: Spectrometry in a mixed Neutron-Photon Field, Laborbericht PTB-6.42-97-2 (1997)
Knauf, K.; Weyrauch, M.; Simon, F.; Kaldune, N.: SPHERE, A Program Package for Calculating the Neutron Response of Spherical Proton Recoil Proportional Counter, Laborbericht PTB-6.42-98-1 (1998)
Knauf, K. and Wittstock, J.: Neutron Spectrometry with Proton Recoil Proportional Counters - Status of the Technique, PTB-Report-FMRB-114 (1987)
Contact
Dr. Andreas Zimbal
Phone: +49 (0) 531-592-6530
e-mail: Andreas.Zimbal@ptb.de
