Detection Of High-energy Neutrons Research Articles

High-fidelity photoneutron detection via neutron activation analysis

To interdict illicit radioactive sources and prevent nuclear terror, governments have deployed portal monitor systems at ports of entry. Such portal monitors rely upon the detection of spontaneously-emitted radiation signatures, however, detection scenarios become more challenging for highly enriched uranium, which emits relatively few spontaneous radiation signatures. Photon active interrogation techniques can augment current cargo inspection scenarios and improve detection capabilities for illicit nuclear material. A high-energy photon interrogation source can induce photofission in nuclear material, producing strong radiation signatures for detection. Prompt fission signals are of specific interest because prompt neutrons are greater than 99% of the fission signal. When using detectors capable of spectroscopy, e.g., pulse shape discrimination-capable organic scintillators, the intense interrogating source often will cause pulse pile-up, degrading particle classification. In this work, we demonstrate photoneutron detection via neutron activation of aluminum and iron. The experiments rely upon nuclear reactions that can only be induced by neutrons, and are robust against pile-up, thereby providing high-confidence neutron rates. In this work, we apply neutron activation analysis for the detection of high-energy neutrons produced by high-energy photon irradiation; the depleted uranium sample was irradiated with a 9-MeV bremsstrahlung beam. We find that the irradiated depleted uranium produced an aluminum activation flux of 1.77 × 105 n cm −2 s−1 and an iron-56 activation flux of 1.05 × 105 n cm −2 s−1. The ability to detect radioactivity induced by neutrons created in (γ, n) and photofission reactions demonstrates a new approach for photon active interrogation to identify nuclear materials.

Study and detection of relativistic Solar Neutrons at ground level with the Spherical Proportional Counter

A novel method of high energy solar neutron detection is proposed with the Spherical Proportional Counter (SPC), taking advantage of the 209Bi(n,f) reaction. This reaction, is considered as a standard for high energy neutron detection, due to large cross section values in the 100 MeV – 1 GeV energy interval, obtained in the n_TOF facility at CERN. A thin spherical shell of Bismuth will be situated in the large volume of the SPC, serving as target for high energy neutrons bombarding the detector, thus resulting in fission fragment emission. Detailed simulation of the 209Bi(n,f) reaction with the INCL++ model, coupled with the ABLA07 de–excitation code is performed (cross section, mass & atomic number distribution, kinetic energy per fragment) in the 100 MeV – 10 GeV energy interval, together with SRIM for the fragments’ projected range in 209Bi. Experimental data from a 252Cf source are obtained, in order to validate the SPC’s efficiency in fission fragment detection. Calculations for the expected reactions in the 209Bi shell have been performed in different atmospheric depths (700 & 1000 g/cm2), and various spherical detector radii.

Optimisation of pulse shape discrimination using EJ299-33 for high energy neutron detection in proton beam therapy

It is widely understood that proton beam therapy has considerable clinical benefits over photon therapy for treating certain types of tumours. Protons deposit most of their energy in a very localised area, the so-called Bragg peak, sparing surrounding healthy tissue and critical organs from radiation. However, secondary neutrons and gamma rays are generated in the beam nozzle and inside the patient. Clinically, it is highly desirable to monitor the neutron dose the patient is exposed to, and this requires a neutron detector sensitive to high energies. EJ299-33 is a solid plastic scintillator capable of discriminating neutrons from gamma rays using pulse shape analysis of scintillation light. EJ299-33 has the potential to detect neutrons with energies up to 100 MeV and does not present leakage and flammability hazards generally associated with liquid scintillators. Experimental measurements with 60Co, 137Cs and 241AmBe sources were performed to calibrate and optimise pulse shape discrimination parameters. We also performed experimental measurements at the Clatterbridge Cancer Centre in a 60 MeV passive scattered beam to detect high energy neutrons.

Nondestructive Inspection System for Special Nuclear Material Using Inertial Electrostatic Confinement Fusion Neutrons and Laser Compton Scattering Gamma-Rays

A Neutron/Gamma-ray combined inspection system for hidden special nuclear materials (SNMs) in cargo containers has been developed under a program of Japan Science and Technology Agency in Japan. This inspection system consists of an active neutron-detection system for fast screening and a laser Compton backscattering gamma-ray source in coupling with nuclear resonance fluorescence (NRF) method for precise inspection. The inertial electrostatic confinement fusion device has been adopted as a neutron source and two neutron-detection methods, delayed neutron noise analysis method and high-energy neutron-detection method, have been developed to realize the fast screening system. The prototype system has been constructed and tested in the Reactor Research Institute, Kyoto University. For the generation of the laser Compton backscattering gamma-ray beam, a race track microtron accelerator has been used to reduce the size of the system. For the NRF measurement, an array of LaBr3(Ce) scintillation detectors has been adopted to realize a low-cost detection system. The prototype of the gamma-ray system has been demonstrated in the Kansai Photon Science Institute, National Institutes for Quantum and Radiological Science and Technology. By using numerical simulations based on the data taken from these prototype systems and the inspection-flow, the system designed by this program can detect 1 kg of highly enriched 235U (HEU) hidden in an empty 20-ft container within several minutes.

X-ray topographic study of growth defects of trans-stilbene crystals grown from solutions

Single crystals of trans-stilbene, C14H12, with properties suitable for high-energy neutron detection were grown from solution in anisole and toluene by the temperature reduction method with growth rates up to 6 mm/day. From these crystals, slices of appropriate orientation and thickness of 2–4mm were cut and studied by X-ray diffraction topography applying the Lang method using CuKα radiation. The topographs exhibit growth defects such as liquid inclusions, dislocations, striations, and faulty growth-sector boundaries. These defects occur in the same typical arrangements and geometries as is observed in all kinds of crystals grown on habit faces from solution. Besides growth dislocations originating from inclusions and propagating with the growth front, many plastic glide dislocations in the shape of loops or half-loops emitted from inclusions by stress relaxation are observed. The glide system underlying this plasticity is discussed.

FLUKA simulations of a moderated reduced weight high energy neutron detection system

Neutron response of the systems containing high density polyethylene (HDPE) spheres coupled with different external metallic converters has been studied using the FLUKA Monte Carlo simulation code. A diameter of 17.8cm (7in.) of the moderating sphere is found to be optimum to obtain the maximum response when used with the neutron converter shells like W, Pb and Zr. Enhancement ratios of the neutron response due to the induced (n, xn) reactions in the outer converters made of W, Pb and Zr are analyzed. It is observed that the enhancement in the response by 1cm thick Zr shell is comparable to that of 1cm thick Pb in the energy region of 10–50MeV. An appreciable enhancement is observed in the case of Zr converter for the higher energy neutrons. Thus, by reducing the dimension of the moderating sphere and using a Zr converter shell, the weight of the system reduces to 10kg which is less compared to the presently available extended high energy neutron rem meters. The normalized energy dependent ambient dose equivalent response of the zirconium based rem counter (ZReC) at high energies is found to be in good agreement with the energy differential H⁎(10) values suggested by the International Commission on Radiological Protection (ICRP). Based on this study, it is proposed that a rem meter made of 17.8cm diameter HDPE sphere with 1cm thick Zr can be used effectively and conveniently for routine monitoring in the accelerator environment.

Pulse Shape Discrimination in Impure and Mixed Single-Crystal Organic Scintillators

Neutron/gamma pulse shape discrimination (PSD) utilized for detection of high-energy neutrons with organic scintillators was investigated using a model system of mixed diphenylacetylene-stilbene single crystals of different compositions. The results of the studies, which include experimental tools of crystal growth and characterization combined with computer simulation, showed that the presence of impurities with lower bandgap energies can be a major factor influencing PSD properties of organic materials. Depending on the concentration, an impurity may suppress or increase the rate of excited triplet state interaction leading, respectively, to a complete disappearance or enhancement of PSD, consistent with a percolation threshold. The results are applied to produce novel materials with controlled decay characteristics. Single crystals with a large fraction of delayed light and enhanced PSD have been grown for high energy neutron detection, while crystals with suppressed delayed light were produced for use as low-afterglow scintillators for energetic neutron detection in time-of-flight experiments.

Online neutron fluence measurement at University Hospital Essen neutron therapy facility using gallium arsenide LEDs

Abstract The detector and sensor group of the West German Proton Therapy Centre (WPE) has developed a novel real-time neutron fluence monitor based on tiny, inexpensive, commercially available GaAs-LEDs. The linear detection range for d(14)+Be neutrons was evaluated to be 5.0 × 108–2.0 × 1011 neutron.cm−2. However, this monitor can be used universally for neutrons of any energy distribution. Using scaling factors, fluence calibration curves for 1 MeV and 14 MeV D+T fusion neutrons have been calculated. The sensitivity of the detector increases with increasing neutron energy. This makes it suitable for the detection of high-energy neutrons, providing an extra advantage for use at a proton therapy facility where there is a high proportion of high-energy neutrons. The detector is practically not sensitive to photons. A prototype of the online GaAs-LED based neutron fluence monitor has been tested successfully at University Hospital Essen neutron therapy facility and will be implemented at WPE in the near future.

Application of solution techniques for rapid growth of organic crystals

Single crystals of a pure hydrocarbon, 1,3,5-triphenylbenzene, with properties suitable for high-energy neutron detection were grown from toluene solutions using slow evaporation and temperature reduction methods with growth rates up to 10 mm/day. Application of the rapid growth technique developed earlier for growth of large water-soluble crystals shows that crystals of aromatic compounds can be successfully grown from solutions in large volumes required for their use as scintillator materials for radiation detection.

Detection of high energy neutrons, protons and He particles by solid state nuclear track detectors

Abstract The career of astronauts is dependent mostly on the lifetime dose received from primary cosmic rays and secondary particles generated within the structuring materials of a space craft. Since the high energy protons and He particles have the highest abundance and the secondary neutrons significantly contribute to the dose, the study of the response of solid state nuclear track detectors (SSNTD) to these particles has a great importance. SSNTDs, having been used for dosimetry on the International Space Station (ISS), were exposed to protons at several accelerators (Loma-Linda, BNL, TSL), to He (HIMAC) and to neutrons (iThemba, TSL). The incident particles cause fragmentation of the constituent elements of the SSNTD composed of C 12 H 18 O 7 . The fragments induce latent tracks inside the detector which can be visualized by chemical processes and investigated by optical microscope. The measurable track parameters and appropriate calibration allow to determine the linear energy transfer (LET) spectrum of the fragments and also the absorbed dose in the nearly tissue equivalent detector material. The LET spectra of different exposures are presented and compared. Additionally, a LET spectrum determined from the MATROSHKA space walk simulation outside the International Space Station (ISS) will be compared to some of those obtained from accelerator experiments.

Direct measurement of the inelastic neutron acceleration by177mLu

The inelastic neutron acceleration (INNA) cross section on the long-lived isomer state of 177m Lu has been measured from a new isomeric target using a direct method. The detection of high energy neutrons has been performed using a specially designed setup and a cold neutron beam at the ORPHEE reactor facility in Saclay.

Active Detection of Shielded SNM With 60-keV Neutrons

Fissile materials, e.g., <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">235</sup> U and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">239</sup> Pu, can be detected non-invasively by active neutron interrogation. A unique characteristic of fissile material exposed to neutrons is the prompt emission of high-energy (E > 1 MeV) fission neutrons. One promising mode of operation subjects the object to a beam of low-energy (E < 1 MeV) neutrons, generated by a proton beam impinging on a Li target. The emergence of high-energy secondary neutrons then clearly indicates the presence of fissile material. Our interrogation system comprises a low-dose 60-keV neutron generator (5 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> /s ), and a 1 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> array of scintillators for high-energy neutron detection. Preliminary experimental results demonstrate the detectability of small quantities (376 g) of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">235</sup> U shielded by steel (200 g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) or plywood (30 g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), with a typical measurement time of 1 min.

Radiation sensitive scintillator/optical fibre system for radiation dosimetry in burning plasma machine

A possibility of applying a compact radiation dosimetry system to burning plasma machines, such as detecting high energy neutrons and gamma-rays with a wide dynamic range at elevated temperatures, has been studied, utilizing radiation resistant optical fibres and radioluminescence (radiation-induced luminescence) materials. Appropriate radioluminescence materials were found for dosimetry of each radiation field, namely, gamma-rays and neutrons. Especially, a high-energy neutron detection system utilizing optical fibres and radioluminescence materials will have several advantages, such as being compact and robust, and can be a strong candidate for diagnostics of fusion neutrons in a burning plasma machine.

Radiator design for detecting high-energy neutrons with a nuclear track detector

Subsequent to the proposal of a two-layer structured radiator for more efficient detection of high-energy neutrons with a plastic nuclear track detector (PNTD), its availability has been investigated both experimentally and theoretically. An inner deuterized hydrocarbon (CD 2) layer adjacent to PNTD should play the role of both a radiator of deuterons recoiled there and a degrader for energetic protons recoiled in the outer layer of a CH 2 material. It was found that the energy dependence of the efficiency was changed sensitively by the thickness of the CD 2 layer. A best combination of CH 2 and CD 2 thickness was estimated under a condition of a constant total thickness. For example, the sensitivity could be flattened within 20% between about 5 and 70 MeV by using 1 g / cm 2 - CD 2 and 2 g / cm 2 - CH 2 .

High-energy neutron detection and spectrometry with superheated emulsions

The response of some superheated emulsions was investigated using quasi-monoenergetic neutron beams in the 46–134MeV energy range at the Université Catholique de Louvain, Louvain la Neuve, Belgium and at The Svedberg Laboratory, Uppsala, Sweden. In order to determine the detector response to the high-energy beams, the spectra of incident neutrons were folded over functions modeled after the cross-sections for the neutron-induced production of heavy ions from the detector elements. The cross-sections for fluorine and chlorine were produced in this work by means of the Monte Carlo high-energy transport code HADRON based on the cascade-exciton model of nuclear interactions.

Production and detection of high energy neutrons and application to shielding-related study

Production and detection of high energy neutrons and application to shielding-related study

Lithium-free scintillation glasses for fast-neutron detection

In this article, we present observed characteristics of new lithium-free scintillation glasses which have been developed to make time-resolved measurements of the 14-MeV neutron flux from deuterium plasmas. These measurements will yield information on the burnup of tritons in today’s deuterium plasmas and are needed to better predict the confinement and slowdown of alpha particles in future D–T burning plasmas. The new glasses were formulated to have good detection efficiency for 14-MeV neutrons, and yet be insensitive to 2.5-MeV and lower-energy neutrons. The glass response to alpha, gamma, and neutron radiation is shown. The intrinsic neutron detection efficiency of the scintillation glass is seen to increase significantly as a function of neutron energy, providing the necessary discrimination against low-energy neutrons. We discuss the reactions which determine the glass neutron response and suggest that this response is dominated at higher neutron energies by gamma rays created by neutrons inelastically scattering from oxygen present in the glass. For high-energy neutron detection in the presence of excessive background gamma radiation, we discuss a new coincidence configuration of lithium-free scintillation glass with NE213 liquid scintillator.

High-energy neutron detection with polymer nuclear track detectors

The response of some polymer nuclear track detectors to high-energy neutrons of E max=680 MeV produced by a proton synchrocyclotron is determined. The studies are carried out with two types of cellulose nitrates and polycarbonates; the detectors are etched by usual chemical etching, one of them electrochemically. The detection efficiencies obtained are of the order of 10 -6-10 -5 tracks per perpendicular-incident neutron.

Particle Counting by Čerenkov Radiation

\ifmmode \check{C}\else \v{C}\fi{}erenkov radiation particle counters of a number of types are in satisfactory use in this laboratory for the counting of high energy mesons, electrons, and protons. The problems associated with \ifmmode \check{C}\else \v{C}\fi{}erenkov counting and some of the uses are discussed together with the design and performance of several types of counters. The uses include high energy electron counting with the exclusion of neutrons and protons, measurement of the velocity of mesons, and the detection of high energy neutrons in the presence of lower energy neutrons by the \ifmmode \check{C}\else \v{C}\fi{}erenkov threshold counting of recoil protons.