Helium-3 Filled Proportional Counter for Neutron Spectroscopy

Abstract

The neutron transformation of helium-3 has been applied to neutron spectroscopy in the medium energy range in order to overcome the disadvantages of previous methods which have usually been based on neutron scattering. By observing the pulse-height distribution when a proportional counter filled with helium-3, krypton, and carbon dioxide is irradiated with neutrons, the spectrum can be obtained. Details of the counter construction and vacuum equipment for filling the counter are described. In the range of energy from thermal to 1 Mev the spread (relative standard deviation of a peak) is about 3% and the wall effect agrees with theoretical predictions. The pulse height varies linearly with energy and some evidence suggesting that the mean energy required to produce an ion pair in krypton for helium-3 nuclei is about 6% greater than that for protons is presented. Since the neutron reaction cross section of helium-3, as a function of energy, is required to evaluate neutron spectra from observed distributions, it has been remeasured in the range 120 kev to 1 Mev with greater accuracy than previous measurements made by J. H. Coon [Phys. Rev. 80, 448 (1950)].

/sup 3/H(p,n)/sup 3/He differential cross sections below 5 MeV and the n-/sup 3/He cross sections. [2. 5 and 4. 0 MeV]

“…A new evaluation, including the new data, reduced the scale uncertainties to 3-5%. Besides, it is shown that the use of recent 5% higher total n- 3 He cross sections' resolves the discrepancy between the sum of the partial cross sections of n- 3 He interactions and the total cross section 8 for neutrons below 4 MeV.…”

Measurement Of The Neutron Spectrum Of A DD Electronic Neutron Generator

“…[15,25] Some prior work has found it useful to fit the full-energy neutron peak as the sum of two independent Gaussians. [11,26] Further work is planned to investigate the bestachievable energy resolution from the C-S spectrometer using dPSA techniques, and to study the spectral response of the device, once a higherresolution digitizer is available.…”

ENERGY SPECTRA OF NEUTRONS AND GAMMA RAYS FROM SPONTANEOUS FISSION OF $sup 244$Cm

“…Several spectrometers have been reported that detect neutrons by such exothermic secondary reactions as 3 He(n,p), 6 Li(n,a), 10 B(n,a), and 1 H(n,p). (ao-a 4 l Such spectrometers can be used to measure neutron spectra rapidly and rather simply.…”