Recoil Proton Method Research Articles

Development of experimental technique for measurement of (n,xn) double-differential cross sections above 20 MeV

The experimental technique for measurement of (n,xn) double differential cross sections above 20 MeV has been developed with continuous-energy neutrons up to 400 MeV. Neutrons were produced in the spallation reaction by the 800-MeV proton beam, which was incident on a thick, heavily shielded tungsten target at the WNR facility at Los Alamos National Laboratory. The energies of incident neutrons were determined by the time-of-flight method. Emitted neutrons were detected by the recoil proton method at 15°, 30° and 90°. A phoswich detector consisting of NaI(Tl) and NE102A plastic scintillators was used for detecting recoil protons. We obtained the neutron energy spectra by use of the unfolding code, FERDO. The response functions of the NaI(Tl) scintillator for protons were calculated by the calculation code of Particle and Heavy Ion Trasnport code System (PHITS). We compared the experimental cross section data with the calculations by the PHITS and QMD codes.

Mixed Neutron and Gamma Spectra Measurements and Calculations in Pure Iron Benchmark Assembly with Cf-252 Neutron Source

The neutron and gamma leakage spectra measurements have been made for a benchmark spherical iron assembly with diameter of 50 cm. The Cf-252 neutron sources with different emissions were placed into the centre of the iron sphere. Independent laboratories took part in the leakage spectra measurements. The proton recoil method was used with stillbene crystals and hydrogen proportional counters for neutron spectra measurement. Spectrometers using stilbene, germanium and silicon detectors were used for gamma spectra measurement. The working range of spectrometers is for neutrons in the energy range from 0.02 to 16 MeV, and for gamma from 0.40 to 12 MeV. Some adequate calculations based on different data libraries have been done and compared with measurements. The authors propose to analyse carefully the leakage mixed neutron and gamma spectrum from an iron sphere of 50 cm diameter and than adopt that field as a standard. Analogous measurements and calculations performed on pure iron spheres of diameters 20, 30 and 100 cm are briefly discussed in the report.

A charge-collection method for measurements of pulsed fast-neutron flux

A charge-collection method for measuring the flux of pulsed fast neutrons in current mode has been developed, which is based on the well-known recoil-proton method combined with ion-induced secondary electron emission from solid surfaces. The detection unit consists of four elements: an n–p converter, an absorber, a collector, and a rear insulator. The assembly does not require vacuum for operation. Recoil protons from the n–p converter and the secondary electrons induced by the passing protons on the interface of the absorber and the collector contribute to the detector output signal. By properly choosing the materials and the combination of the absorber and the collector, the fraction of secondary electrons in the output signal can be determined experimentally. This detection concept allows one to design a medium type of fast-neutron detector for measurements of extremely intense pulsed neutron flux with a number of advantages over the existing systems.

Neutron and gamma spectra measurements and calculations in benchmark spherical iron assemblies with 252Cf neutron source in the centre

The neutron and gamma spectra measurements have been made for benchmark iron spherical assemblies with the diameter of 30, 50 and 100 cm. The 252Cf neutron sources with different emissions were placed into the centre of iron spheres. In the first stage of the project, independent laboratories took part in the leakage spectra measurements. The proton recoil method was used with stilbene crystals and hydrogen proportional counters. The working range of spectrometers for neutrons is in energy range from 0.01 to 16 MeV, and for gamma from 0.40 to 12 MeV. Some adequate calculations have been carried out. The authors propose to carefully analyse the leakage mixed neutron and gamma spectrum from iron sphere of diameter 50 cm and then adopt that field as standard.

00/01620 Hydrogen determination in coal samples by the recoil proton method

00/01620 Hydrogen determination in coal samples by the recoil proton method

Hydrogen determination in coal samples by the recoil proton method

A procedure has been developed to use the recoiled protons produced in neutron-proton scattering process for fast, nondestructive determination of the hydrogen contents of coal samples. Samples from Hungary, Poland and Russia have been bombarded with 2.85 MeV neutrons from a small home-made neutron generator and the recoiled protons detected by a simple surface barrier detector. To convert proton counts into hydrogen content, a calibration procedure was established for the method using prepared standards of known hydrogen content and range for 2.85 MeV protons. Exploratory results obtained by this method compare favourably with those obtained by the neutron reflection method.

Deuterated plastic scintillator for proton detection in a neutron background

Abstract Deuterated scintillators are proposed as detectors in neutron spectrometers based on the proton recoil method as a means to reduce the interference from background. Specifically, the use of a deuterated scintillator hodoscope in the focal plane of a magnetic proton recoil spectrometer is considered. The response of the hodoscope to signal protons and background neutrons is determined with Monte Carlo simulations and measurements with a 239 PuBe source. The results are discussed relative to the use of regular hydrogen based scintillators with an assessment of the expected gain in a focal plane detector for fusion neutron applications.

The unfolding of neutron spectra based on the singular value decomposition of the response matrix

Abstract The unfolding procedure utilizing singular value decomposition of the detector response matrix is described. The paper also concerns the problems caused by the transformation of the detector response function to the matrix form and suggests how to take into account the influence of this matrix on the uncertainty of the resulting neutron spectrum measured by the proton recoil method.

A new approach to neutron spectrum unfolding by differentiation

A review of previous results in unfolding continuous neutron spectra measured by the recoil-proton method and registered with organic scintillators is presented. Mathematical and numerical aspects of the approach proposed are then discussed. A central element of the method developed is the use of numerically built orthonormal polynomials which account for the optimum condition of matrices involved. Moreover, specific properties of such polynomials lead to a natural and numerically stable way of differentiating both the spectra processes and the auxiliary functions needed, e.g. the light-output function for protons. To further improve the quality of fit, suitable functional transforms are applied. Special attention is also paid to the representation of the spectrometer transfer function and to its energy calibration. Both model and real spectra unfolded are discussed and a comparison with the output of existing programs is carried out. Spectra dealt with include quasi-monoenergetic neutrons, ramp-up, ramp-down, T(d, n) 4He and Pu-Be sources.

An accurate photo-neutron standard

Abstract An easily reproducible, RdTh-D2O, photo-neutron standard has been built. Its calibration is based on the associated charged particle method. We have determined its photoneutron yield to an accuracy of 1.1%. After calibration, the ionisation current of the RdTh source was compared to the ionisation current of a standard radium source, on a Curie chamber. The yield of any substandard can be determined, apart from small geometrical corrections, by a simple comparison of the RdTh source to the radium standard on the Curie chamber. Background neutrons from (α-n) reactions in the RdTh source contribute to 3% of the total yield. The number of neutrons emitted by the source used has been determined by the recoil proton method, using an ionisation chamber and by chemical integration in a manganese nitrate solution. The total yield of the standard is known to an accuracy of 1.25%.

Absolute Flux Measurement of Anisotropic Neutron Spectra with Proton Recoil Tracks in Nuclear Emulsions

A technique for the measurement of neutron spectra which is independent of neutron direction has been studied. The technique consists of measuring all proton tracks in a known volume of type C2 Ilford emulsion, in which shrinkage has been reduced by treating the plates with rosin. By a suitable differentiation of the proton spectrum the absolute flux of neutrons as a function of energy is determined. Rotated plates were exposed to 0.8 and 1.3 Mev neutrons. 4000 tracks were measured, and two peaks with a width ∼150 kev at half-maximum were obtained. The statistical accuracy of the neutron flux in the two peaks is about ten percent. The flux determination was checked by a fixed C2 plate in which the conventional proton recoil method was used. Good agreement was obtained.