Proton Recoil Proportional Counter Research Articles

Neutron spectrometry with proton-recoil proportional counters in the energy region up to 10 MeV

Large cylindrical proportional counters have been used in parallel neutron beams for spectrum measurements in the energy region up to 10 MeV. Measurements with monoenergetic neutrons and a series of comparisons with other techniques showed that results with similar accuracies, as are claimed in the low energy region (2 MeV), can be obtained. Problems specially related to the high energy region are discussed.

Response functions for proton-recoil proportional counter spectrometer

The accurate determination of neutron spectra with proton-recoil proportional counters requires that corrections be made for non-ideal electric-field effects and for wall-and-end effects. The use of field tubes to define a sensitive volume leads to a distortion of the internal field lines near the ends of the sensitive region and produces a counter whose multiplication is a function of position of the event along the anode. Wall-and-end effects are present when some proton-recoil tracks deposit only part of their energy in the sensitive region of the counter. Correction schemes have been obtained for electric-field distortion based on the solution of the electric field everywhere in the counter together with measured multiplication versus voltage data and for wall-and-end distortion based on analytically determined track length probability functions and measured stopping-power and range-energy data. The investigation of electric-field effects indicated that by using an unconventional counter design in which the diameter of the cathode over the field tube is reduced, it is possible to reduce the influence of electric-field distortion and produce a counter better suited for spectroscopy and absolute counting applications. Calculated pulse-height distributions have been compared with experimentally determined distributions. The extent of corrections for these effects has been assessed for a representative fast-reactor spectrum.

Measured Neutron Spectra in a Number of Uranium- and Plutonium-Fueled Reactor Assemblies

Central neutron spectra were measured with proton-recoil proportional counters in a number of uranium- and plutonium-fueled fast reactor assemblies. The energy range of the measurements is from 1 keV to 2 MeV. Short descriptions are included of the experimental technique and of the correction schemes necessary to remove inherent systematic errors in this method of spectroscopy.The measured neutron spectra are compared with homogeneous fundamental-mode calculated spectra. ENDF/B Version I data were used. In general, the agreement between the measured and calculated spectra is good. The comparisons have revealed some systematic discrepancies which are believed to be outside of experimental error near neutron scattering resonances and at low and high energies. These differences are beyond those associated with heterogeneity effects introduced by the plate loadings of the cores.

Fast neutron spectrum measurements in the MTR scandium and iron filtered beams

The energy response of proton-recoil proportional counters was studied by making fast neutron spectrum measurements in the MTR scandium and iron filtered beams over the energy range of 200 eV to 1 MeV. Results of the measurements were compared with time-of-flight data. It was found that the calibration technique suggested by Bennett is adequate for accurate measurements if the hydrogen counter data is corrected for calibration pulse height losses due to shaping time constants in the linear amplifier. Further evidence of the energy loss per ion pair for hydrogen ( W) being constant with energy down to 2 keV was found. Cutoff models suggested for the hydrogen W, which account for an energy variation near 2 keV, can cause errors in the measured neutron spectrum. The results also showed that W for methane is energy dependent in the region around 100 keV.

Mesure de l'efficacité d'un scintillateur de verre Au 6Li par une méthode de particule associée pour des neutrons de 100 keV à 500 keV

The purpose of this experiment is to calibrate accurately some scintillators used to measure neutron fluxes in cross section determinations. 3He particles from T(p,n) 3He reaction are detected at 10 o from the proton beam. The backing of the titanium-tritium target is thin enough to let the beam through. The glass scintillator is placed in such a way as to intercept all neutrons associated with the detected 3He particles. Coincidences between detected neutrons and 3He particles are registred, and the total number of 3He particles as well. The detector efficiency is in principle equal to the ratio of these two numbers. An analyser combining electrical and magnetic fields is used to separate 3He particles from the tremendous rate of protons scattered from the target. A few minor corrections are needed to account for multiple scattering of 3He particles in the target, and for multiple scattering of neutrons in the glass scintilator. An overall accuracy of 2.5 to 3% is achieved. The same neutron flux has been measured with this calibrated device, and with a proton recoil proportional counter. Both results agree within experimental errors.

Investigation of the specific energy loss of protons in hydrogen above 1 keV with regard to neutron spectrometry

The variation of ionization, created in hydrogen filled proton-recoil proportional counters by protons with energies between 1 and 20 keV was measured, using quasi-monoenergetic neutrons from a slowing-down time spectrometer. The measured variation can be described by E = I−0.15+ exp(− I 1.76 ) , where E means the neutron energy (in keV) and I the ionization (in keV). The results are in satisfactory agreement with results of work described in literature and should contribute to improve the accuracy and reliability of proton-recoil neutron spectrometry in the low energy range.

Error estimates for iterative unfolding

Some approximate formulas are developed for errors arising from the application of iterative unfolding to experimental measurements. For the practical case of a dominantly diagonal response matrix of large order, it is shown that the relative error of the unfolded solution is approximately that of the original measurement. To demonstrate this behavior, actual experimental results from a proton-recoil proportional counter detection system have been included.

Effects of finite size in 4 π-recoil proportional counters

An analysis of finite size effects in 4 π proton-recoil proportional counters is given from the viewpoint of an unfolding problem. The response function is determined empirically. Experimental and analytical methods used to obtain proportional counter response functions are described. Iterative unfolding is employed to obtain distortion-free proton-recoil spectra from about 0.5 MeV upwards; an energy region subject to increasingly severe wall-and-end effect corrections.

The flux and spectrum of cosmic-ray produced neutrons as a function of altitude.

A series of measurements of neutron flux as a function of altitude has been made with the following neutron detectors: bismuth fission ionization chamber, proton-recoil proportional counter, and moderated and bare BF3 proportional counters. In addition, data were also taken with a Simpson pile. Altitudes ranged from sea-level to 40,000 ft and latitudes from 28° to 49°N. Appropriate treatment of the data can be made to yield information about the neutron spectrum and the average neutron energy, and, consequently about the dose rate.