Neutron Spectroscopy System Research Articles

A fully-automated, liquid-moderated neutron spectrometer system

A novel, water-based, neutron spectroscopy system has been designed, simulated, and tested at the National Research Council of Canada. The active part of the detection system is a small proportional counter sensitive to thermal neutrons. The proportional counter is suspended along the symmetry axis of a large, rectangular water bath, and can be positioned remotely anywhere along this axis down to the bottom face. Measured count rates as a function of depth of the counter for both an americium–beryllium and a californium-252 neutron source demonstrate the ability of the system to discriminate between sources with different energy spectra. An MCNP6 simulation of an AmBe source agrees with the data within uncertainties at the 2%-level and is used to construct the response functions of the spectrometer system. Unfolded energy spectra are determined using an analysis of the singular value decomposition of the response matrix. Finally, a Monte Carlo study of the system indicates an ability to measure the fluence rate of the radionuclide sources.

Fast neutron spectroscopy with a volumetrically-sensitive, moderating-type neutron spectrometer in a high-radiation environment

Non-fission nuclear reactions were investigated by NASA as part of efforts to develop long-lasting electric power systems for space applications where solar energy is weak or unavailable. Key to investigation of nuclear reactions is spectroscopy of the neutron energies produced in such reactions. In addition to employing a standard scintillating-type neutron spectrometry system, the NASA team investigated the application of a moderating-type neutron spectrometer in a high-radiation environment as a parallel approach. The unfolded log-scale and linear-scale spectra of well-known calibration neutron sources are presented along with the ISO standard spectra for comparison. This new technology shows promise as a compact instrument capable of neutron spectroscopy in laboratory settings, and in particular, space applications where small size, low data rate and no onboard computation are advantages.

Spectrometry of leakage photoneutrons of 18 MV medical accelerator head by Sohrabi passive multi-directional spherical neutron spectrometry system

PurposeSpectrometry of leakage photoneutrons (PN) of a Siemens ONCOR medical linear accelerator head by applying recently invented Sohrabi passive multi-directional multi-detector neutron spherical spectrometry system; measurements of scientific interest and of importance for meeting the regulatory and safety standards. MethodsThe neutron spectrometry system applied consists of 6 polycarbonate/10B detectors mounted on 6 sides of a polyethylene cube used as bare and also embedded at center of 8 PE spheres of different diameters. Multi-directional and mean PN spectra at isocenter as well as at the left and right sides of head at 100 cm distance from the X-ray target on its plane of 10x10 cm2 18-MV X-ray beams were determined applying Multisphere Neutron Spectrometry Unfolding Code (MNSU + ). ResultsThe well-resolved unfolded directional leakage PN spectra obtained at the 3 positions showed a thermal PN peak of lower intensityfollowed by a tail of epithermal PNs before reaching a fast PN higher peak.“ The mean PN energy are 0.47 ± 0.03 MeV and 0.48 ± 0.02 MeV respectively for the left and right sides of the head and 0.48 ± 0.02 MeV at the isocenter. ConclusionsDue to importance of leakage PN spectra of an accelerator head being of scientific interest and for meeting regulatory and safety standards, well-resolved leakage PN spectra of 3 locations of the medical accelerator head were determined using Sohrabi passive multi-directional neutron spectrometry system. It is a novel learning that the mean PN spectra and mean PN energy of the 3 locations are quite similar within statistical variations.

Development and experimental validation of a fast neutron spectrometry system based on Superheated Drop Detectors (SDDs) operating under different external pressures

In this paper, the spectrum of 241Am-Be neutron source was measured by developing and using a neutron spectrometer system based on Superheated Drop Detectors (SDDs) operating under various external pressures. The system consisted of a set of SDDs fabricated by in situ polymerization method. The external pressures were controlled by the amount of Freon-12 added onto the surface of detectors. Also, this system includes a Geant4 simulation application capable of calculating the response of SDDs made from various materials at various temperatures and pressures. Ultimately, the system contained a customized program to design and train the Adaptive Network-based Fuzzy Inference System (ANFIS) for fast neutron spectrum unfolding. This program has the capability of designing the ANFIS with different rule structures and various parameters of the fuzzy inference system.In the present study, the simulation application was used to calculate the response matrix of five SDDs under external pressures of 0.86, 1.93, 2.72, 3.48, and 3.85 atm in 20 energy bins from 0.5 MeV to 514 MeV at 28 °C. Furthermore, the customized program was utilized to design a FIS structure using the FCM method with six membership functions for each input.Neutron spectra published in the IAEA technical reports series no. 403 and 318 were utilized as the Target data. The response matrix was used to obtain the input data of ANFIS by multiplying the target data by the response matrix. 99% of data (373 out of 377) was considered as the train data and the rest as the test data.After fabrication of SDDs, they were exposed to an 241Am-Be neutron source. The average numbers of the formed bubbles in SDDs with different external pressures were introduced to the trained ANFIS, and finally, the unfolded spectrum was the output of the ANFIS. The RMSE for the measured neutron spectrum was the acceptable value of 0.016. The reasonable agreement between the unfolded and reference 241Am-Be neutron spectra shows that the developed neutron spectrometry system can be a suitable candidate for fast neutron spectrometry.

Photoneutron spectrometry by novel multi-directional spherical neutron spectrometry system

Neutron spectrometry in science and technology applications in general and accurate exotic photoneutron (PN) dosimetry of cancer patients undergoing high-dose high-energy X-rays therapy in medical accelerators in particular is of vital need. In this study, a novel passive multi-directional multi-detector neutron spectrometry system was developed and home-made using 6 polycarbonate/10B detectors on 6 sides of polyethylene (PE) cubes used bare and also embedded at center of PE spheres of 8 different diameters. The system provided well-resolved unfolded directional PN spectra showing thermal and fast PN peaks of 6 sides and mean spectrum in 5 field sizes at isocenter and other locations in 18 MV Siemens ONCOR medical linear accelerator bunker. The neutron spectrometry system developed has unique characteristics such as being simple, efficient, low cost, practical, and insensitive to low-LET radiation with well-resolved directional and mean spectra easily applicable in medicine, health, environment, science and technology in developing and developed laboratories.

Design of a multi-shell portable neutron spectrometry system based on indium foil detectors

A portable neutron spectrometry system was designed based on thermal neutron detectors embedded in concentric polyethylene spherical shells. The system is flexible and can accommodate the use of either active or passive neutron detectors in different configurations. In this work, the response matrix of the system with In-115 foil detectors was calculated with MCNP5 v.1.6. Activation foils were chosen as an ideal detector for the planned use of the system in medical accelerator environments. Calculations were performed using ENDF/B VII.0 and ENDF/B VIII.0 data libraries. The response functions calculated with the two libraries differ by as much as 11.6% in the thermal energy region for the largest moderator. A sensitivity analysis was also performed to evaluate the effect of main design parameters on the response matrix.

Shielding designing of 241Am-Be neutron source housing experiment and Monte Carlo simulation

Shielding of a neutron source housing for 1 Ci 241Am-Be source has been designed and fabricated based on the simulation carried out using Monte Carlo code FLUKA. Neutron and photon dose equivalent rates at the surface and at 1 m distance from the surface of the housing were calculated using FLUKA simulation and measured using gamma and neutron dose rate meters. The calculated and measured gamma and neutron dose equivalent rates agree well. Neutron spectra outside the source housing were generated using FLUKA simulation and measured with the ROSPEC + simple scintillation spectrometer neutron spectrometry system and also agree reasonably well. Gamma spectra outside the source housing and residual activity due to activation products in stainless steel and lead of the housing were also generated through simulation.

Neutron spectroscopy & H*10 dosimetry with tensioned metastable fluid detectors

This article discusses outcome of research for a novel, fast-to-thermal, continuous and pulsed neutron-spectroscopy enabled H*10 dosimetry capable (gamma-beta blind), high intrinsic efficiency sensor system utilizing the tensioned metastable fluid detector (TMFD) architecture. In our past studies the response matrix was developed in single-atom-spectroscopy mode due to which TMFD sensing fluids were limited to one with molecules for which only one atom was considered as causing detection for fast energy neutrons (>0.1 MeV). In this paper, we describe how these limitations were overcome using a new approach for determination of the response matrix — resulting in a generalized development of a neutron spectroscopy system for any arbitrary fluid, and for spectrometric detection of thermal and fast energy neutrons. Unlike for gamma-beta radiation where the dose weight-factor is invariant with energy, for neutrons it is highly non-linear with the induced dose per unit neutron flux increasing ∼100 times with neutron energy from eV to MeV; this must be accounted for to avoid significant conservatisms inherent in non-spectroscopic general purpose neutron detectors. The neutron spectrometry enablement for TMFDs was utilized to develop H*10-TMFD rapid, high efficiency neutron dosimetry for ultra-low (∼5 μRem/h) to high (potentially >10 Rem/h) environments, while remaining 100% gamma-beta blind. Comparisons were performed against the mainstay standard Bonner Sphere Spectrometer (BSS) in which, for 252Cf and Pu-Be/Am-Be isotope source neutron spectra the two systems offered results within +∕−10% of each other in >100 μRem/h fields. Notably, when under ultra-low (∼10 μRem/h) fields the BSS and other traditional detectors proved impractical (effectively dysfunctional); whereas, the H*TMFD system measured hard and soft neutron spectra to within +∕−5% of those from MCNP predictions of the same experiments. Comparisons were also made for monoenergetic D-D (2.45 MeV) neutron based radiation fields (∼20–30 mRem/h) for which the H*TMFD system successfully predicted both the H*-10 dose and spectrum nuance characteristics (including for the effect of tritium contamination caused 14 MeV component) whereas, the BSS system was unable to do so appropriately.

Development of an high resolution neutron spectroscopy system using a diamond detector and a remote digital acquisition methodology

The need of performing high resolution fast neutron spectroscopy in a very harsh environment like that of the Radial Neutron Camera (RNC) of ITER, requires to develop new detectors and methodologies. Diamond detectors have been proved to be excellent candidates but the electronics needs a substantial improvement. Because of the high radiation level and the temperatures expected near the detector positions in the RNC, the electronics must be placed several meters away. A novel Fast Charge Amplifier (FCA) was developed that, connected to a diamond detector using several tens of meters of low capacitance coaxial cable, is able to produce fast output signals suitable to be processed by digital electronics. These fast output signals allow to operate at high count rates avoiding pile-up problems. This novel amplifier connected to a digitizer is here tested in the neutron energy range from 5 to 20.5MeV using the mono-energetic neutrons produced by the Van de Graaff (VdG) accelerator of the EC-JRC-IRMM and by the PTB cyclotron. From the measurements the experimental response functions of the diamond detector at different neutron energies were obtained. The shape of the response functions have been compared with that predicted with a routine which was implemented for the Monte Carlo code MCNPX with the scope to validate the calculations versus the experimental data. The goal is to develop a tool which allows to calculate the diamond detector response functions also in term of absolute efficiency. This methodology along with the ability to measure at high reaction rates and the insensitivity to radiation damage launches the system described in this paper as a promising method for neutron spectrometry in the RNC of ITER.

Response matrix of a neutron spectroscopy system comprised of successive BF3and H2O arrays

The response matrix of a neutron spectroscopy system is studied. The system is comprised of successive rectangular parallel layers of BF 3 followed sequentially by water layers. In total, ten BF 3 (96% 10 B) layers and nine H 2 O ones are configured in periodic order. Two different geometries are investigated; system A and system B. MCNP-4C is used to estimate the response functions of both systems. The response matrix of system A shows higher magnitude than those obtained from system B. In addition, the response matrix of system A shows more distinctive behavior than that obtained from system B.

A Canadian high-energy neutron spectrometry system for measurements in space

Bubble Technology Industries Inc. (BTI), with the support of the Canadian Space Agency, has finished the construction of the Canadian High-Energy Neutron Spectrometry System (CHENSS). This spectrometer is intended to measure the high-energy neutron spectrum ( ∼ 1 – 100 MeV ) encountered in spacecraft in low earth orbit. CHENSS is designed to fly aboard a US space shuttle and its scientific results should facilitate the prediction of neutron dose to astronauts in space from readings of different types of radiation dosimeters that are being used in various missions.

Monte Carlo calculations and neutron spectrometry in quantitative prompt gamma neutron activation analysis (PGNAA) of bulk samples using an isotopic neutron source

An activation analysis facility based on an isotopic neutron source (185 GBq 241Am/Be) which can perform both prompt and cyclic activation analysis on bulk samples, has been used for more than 20 years in many applications including 'in vivo' activation analysis and the determination of the composition of bio-environmental samples, such as, landfill waste and coal. Although the comparator method is often employed, because of the variety in shape, size and elemental composition of these bulk samples, it is often difficult and time consuming to construct appropriate comparator samples for reference. One of the obvious problems is the distribution and energy of the neutron flux in these bulk and comparator samples. In recent years, we have attempted to adopt the absolute method based on a monostandard and to make calculations using a Monte Carlo code (MCNP4C2) to explore this further. In particular, a model of the irradiation facility has been made using the MCNP4C2 code in order to investigate the factors contributing to the quantitative determination of the elemental concentrations through prompt gamma neutron activation analysis (PGNAA) and most importantly, to estimate how the neutron energy spectrum and neutron dose vary with penetration depth into the sample. This simulation is compared against the scattered and transmitted neutron energy spectra that are experimentally and empirically determined using a portable neutron spectrometry system.

Design, calibration and testing of the NRCAM fast neutron spectrometry system

This paper describes the design, calibration and testing of all aspects of an NE-213 detection system which was built for measuring neutron spectra from 1 to 30 MeV . To cover the whole energy range two detectors are required. A smaller detector is usually used for the lower energy range, but for the upper energy limit, in which we are interested, a larger detector is needed. Particular attention has been paid to cell construction and reflective paint covering. Decisions on the length of light guide which leads to optimum resolution have been made on the basis of experiment and Monte Carlo simulation of the photon transport within the cell and light guide, previously reported. Response matrix information for the detector has been prepared with the codes 05S (A Monte-Carlo code for calculating the pulse-height distributions due to monoenergetic neutrons on organic scintillators. Oak Ridge National Laboratory ORNL-4160) and SCINFUL (SCINFUL: a Monte Carlo based computer program to determine a scintillator full energy response to neutron detection for En between 0.1 and 80 MeV : program development and comparisons of program predictions with experimental data. Oak Ridge National Laboratory ORNL-6463), with validation at a few energy points against quasi-monoenergetic neutron sources available at the cyclotron of NRCAM. The unfolded spectra obtained by the detector when exposed to Americium–Beryllium, 15.2 and 28.2 MeV neutron fluences are shown as overall validation of the performance of the detector.

TFTR natural diamond detectors based D–T neutron spectrometry system

Three natural diamond detectors (NDD) based spectrometry systems have been developed and used on TFTR to perform D–T neutron spectrum and flux measurements. DT neutrons interact with the NDD through the 12C(n, alpha)9Be reaction to produce a narrow peak in the pulse height distribution which has 2%–3% energy resolution and is well isolated from other reactions by ∼2 MeV in energy. The NDD detector is also highly radiation resistant (5×1014 n/cm2) and compact in size (diameter ∼4 mm, thickness ∼0.2 mm). Three detectors have been installed near TFTR. One, installed in a central sight line of the neutron collimator views perpendicularly from below. Two other detectors placed inside radiation shields in the TFTR test cell have tangential and perpendicular cones of view. These three spectrometers provide spectrometry of D–T neutrons escaping the tokamak with angles with respect to plasma current in the ranges close to 90°, 110°–180°, and 60°–120° correspondingly. The fastest standard electronics have been used to reduce the influence of pulse pileup during spectrometry measurements at count rates up to 3×105 counts/s. Results of the first D–T neutron spectra and flux dynamics measurements made with the three NDD based spectrometers during TFTR high power neutral beam injection are presented.

A 2.5 MeV neutron spectrometry system with a tangential line of sight for the D-D phase at the JET tokamak

The neutron spectrometry system described in this report is in routine use at the Joint European Torus (JET). Designed for the D-D phase of operations it consists of a complementary set of compact neutron spectrometers housed in a shielding block in the torus hall. The collimation system, which has an adjustable aperture, defines a horizontal line of sight with a significant directional component tangential to the plasma axis. The shielding, the spectrometers, and the auxiliary sensors and systems are described. The operating limits of the spectrometers, and the methods of data analysis, are discussed. Examples of analysed data are given.

Comparison of Response Function Calculations for Multispheres

An intercomparison of computer calculations to determine the response function of a multisphere neutron spectrometry system has been undertaken by EURADOS-CENDOS Working Committee IV. For this purpose, a standard multisphere spectrometer was adopted. This consisted of four polyethylene spheres, radii 38.1, 63.5, 101.6 and 152.4 mm with a central 3He detector, diameter 32 mm, having an atomic density of 4.25 × 1019 atoms.cm-3 (pressure, 172 kPa). The calculations were made for two polyethylene densities (0.92 and 0.95 g.cm-3). The Monte Carlo computer codes MCNP and BOKU (developed at PTB specifically for these calculations) and the discrete ordinates code ANISN were used to calculate the response of the detector for a variety of monoenergetic incident neutrons. Preliminary results for the 38.1 and 63.5 mm radii spheres are presented to compare these codes and their application at different laboratories. Discrepancies are discussed. In addition, further calculations were undertaken to compare the effects of various factors on the response functions, including: the effect of using cross sections without taking into account the binding of the carbon and hydrogen in the polyethylene; the effect of the steel walls of the 3He detector; and the effect of the stem of the counter.

Neutron Spectrometry System for Radiation Protection: Measurements at Work Places and in Calibration Fields

Neutron Spectrometry System for Radiation Protection: Measurements at Work Places and in Calibration Fields

Neutron Spectrometry System for Radiation Protection: Measurements at Work Places and in Calibration Fields

Neutron Spectrometry System for Radiation Protection: Measurements at Work Places and in Calibration Fields

LANSA: A large neutron scintillator array for neutron spectroscopy at Nova (abstract)

A neutron spectroscopy system for use at Nova is currently under construction. It consists of 960 channels of neutron sensitive liquid scintillator detectors coupled to photomultiplier tubes. Each channel also has a discriminator, ADC, and TDC to allow measurement of neutron arrival time and pulse size. This facility will primarily be used to measure time-of-flight spectra for secondary and tertiary neutrons. Details of the detector design will be presented as well as a brief overview of the proposed use. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.

Measurement of the Neutron Spectrum inside the Containment of a PWR

Abstract Neutron spectra inside the containment building of a PWR at Gosgen, Switzerland have been measured using a high resolution, transportable, neutron spectrometry system based on proportional counters. Small spherical proportional counters, filled with hydrogen to pressures of 100, 300 and 1000 kPa, were used to cover the energy range from 50 keV to 1.5 MeV. A larger cylindrical counter, filled with 600 kPa of 4He plus 400 kPa Ar was used to extend the measurement range up to 16 MeV. Compact electronics provided simultaneous data acquisition for up to four counters allowing spectrum measurements to be performed in dose equivalent rates down to ~50 µSv.h-1. Supporting measurements were made with a multisphere spectrometer to determine the fraction of neutrons below 50 keV. The neutron spectra measured at two positions show a steady rise in the neutron fluence as the neutron energy decreases, with very few neutrons having energies above 700 keV.