Quasi-monoenergetic Neutron Source Research Articles

Compact ultrafast neutron sources via bulk acceleration of deuteron ions in an optical trap

A scheme for a quasi-monoenergetic high-flux neutron source with femtosecond duration and highly anisotropic angular distribution is proposed. This scheme is based on bulk acceleration of deuteron ions in an optical trap or density grating formed by two counter-propagating laser pulses at an intensity of ∼1016W/cm2 in a near-critical-density plasma. The deuterons are first pre-accelerated to an energy of tens of keV in the ambipolar fields formed in the optical trap. Their energy is boosted to the MeV level by another one or two laser pulses at an intensity of ∼1020W/cm2, enabling fusion reactions to be triggered with high efficiency. In contrast to previously proposed pitcher–catcher configurations, our scheme can provide spatially periodic acceleration structures and effective collisions between deuterons inside the whole target volume. Subsequently, neutrons are generated directly inside the optical trap. Our simulations show that neutron pulses with energy 2–8 MeV, yield 1018–1019n/s, and total number 106–107 in a duration ∼400 fs can be obtained with a 25 μm target. Moreover, the neutron pulses exhibit unique angularly dependent energy spectra and flux distributions, predominantly along the axis of the energy-boosting lasers. Such microsize femtosecond neutron pulses may find many applications, such as high-resolution fast neutron imaging and nuclear physics research.

A 30 MeV-cyclotron-based quasi-monoenergetic neutron source

This study developed a quasi-monoenergetic neutron source (QMN) for the semiconductor device's soft error rate test (SER). Quasi-monoenergetic neutrons are generated by Be(p,n)B99 nuclear reaction with a 1 mm beryllium target and 30 MeV protons from a cyclotron. An 8 mm water in the back of the beryllium target is used for avoiding proton penetration. The neutron spectra simulated by MCNP showed that the peak energy was around 26.5 MeV. The heat flow and mechanical properties are numerically analyzed, and the safe operating conditions are therefore determined.

Quenching factor measurements of sodium nuclear recoils in NaI:Tl determined by spectrum fitting

We have performed measurements of sodium nuclear recoils in NaI:Tl crystals, following scattering by neutrons produced in a 7Li(p,n)7Be reaction. Understanding the light output from such recoils, which is reduced relative to electrons of equivalent energy by the quenching factor, is critical to interpret dark matter experiments that search for nuclear scattering interactions. We have developed a spectrum-fitting methodology to extract the quenching factor from our measurements, and report quenching factors for nuclear recoil energies between 36 and 401 keV. Our results agree with other recent quenching factor measurements that use quasi-monoenergetic neutron sources. The new method will be applied in the future to the NaI:Tl crystals used in the SABRE experiment.

Computed tomography with fast-neutron sources

Lawrence Livermore National Laboratory (LLNL) is near-completion of a quasi-monoenergetic neutron source for fastneutron imaging and computed tomography (CT). The source is expected to produce 10-MeV neutrons with an on-axis flux of ~1011 per second per steradian through a collimated aperture with a ~7-degree opening angle. The application for this source is imaging and CT of low-Z materials heavily shielded by high-Z materials. Fast-neutron imaging and CT is a non-destructive technique for very thick objects. We have radiographed a variety of objects using various sources of fast neutrons. We will discuss our CT reconstruction methods and results from these measurements. We will also discuss our results as they relate to our expectations of the near-complete neutron source at LLNL.

INVESTIGATION OF PULSE SHAPE NEUTRON-GAMMA DISCRIMINATION

The role of neutron beam investigation is significant not only for fundamental science but also for various fields of applied science. This work is dedicated to the formation of neutron beams using the external 18-MeV proton beam of IBA cyclotron C18/18 with a beam current of up to 100 µA. The facility is located at the A. Alikhanyan National Science Laboratory (Yerevan Physics Institute). The possibility to obtain thermal or epithermal neutron beams using the external proton beam of the cyclotron is studied using Geant4 simulations. In this case, a quasimonoenergetic neutron source 9Be (p, n)9B reaction is chosen. As a result of the simulations, the optimal thickness of the 9Be beryllium isotope target is determined. The induced neutron beam is accompanied by a gamma ray background. To decrease the number of accompanying gamma rays, the lead absorber is considered. As a method of separating neutrons from gamma rays, the pulse shape discrimination (PSD) technique is developed. This study shows the possibility of neutron-gamma PSD and its applicability using the EJ-299-33A plastic scintillator.

INVESTIGATION OF PULSE SHAPE NEUTRON-GAMMA DISCRIMINATION

The role of neutron beam investigation is significant not only for fundamental science but also for various fields of applied science. This work is dedicated to the formation of neutron beams using the external 18-MeV proton beam of IBA cyclotron C18/18 with a beam current of up to 100 µA. The facility is located at the A. Alikhanyan National Science Laboratory (Yerevan Physics Institute). The possibility to obtain thermal or epithermal neutron beams using the external proton beam of the cyclotron is studied using Geant4 simulations. In this case, a quasimonoenergetic neutron source 9Be (p, n)9B reaction is chosen. As a result of the simulations, the optimal thickness of the 9Be beryllium isotope target is determined. The induced neutron beam is accompanied by a gamma ray background. To decrease the number of accompanying gamma rays, the lead absorber is considered. As a method of separating neutrons from gamma rays, the pulse shape discrimination (PSD) technique is developed. This study shows the possibility of neutron-gamma PSD and its applicability using the EJ-299-33A plastic scintillator.

Characterization Study of Fast Neutron Sources Based on Proton Accelerators at KOMAC

We introduce two neutron sources based on proton accelerators; a quasi monoenergetic neutron source driven by a 1.7 MV tandem accelerator and a pulsed white neutron source based on a 100 MeV linear proton accelerator, which are installed at Korea Multi-purpose Accelerator Complex (KOMAC) of Korea Atomic Energy Research Institute (KAERI). The neutron sources are characterized in terms of Monte Carlo simulations, and experiments based on various type of detectors and activation methods. In the manuscript, specifications of the neutron sources and the partial results of characterization study including energy and flux density measurements of the neutron sources are presented.

Activation Measurements of Cross Sections for Ground and Isomeric States Production in Neutron Threshold Reactions on Y and Au

The paper describes cross-section measurements consisting of neutron activation using a 7Li(p,n) quasi mono-energetic neutron source and gamma-ray spectrometry performed at the Nuclear Physics Institute of the Czech Academy of Sciences in Řež, Czech Republic. The analysis of the excitation functions of neutron-induced threshold reactions for the energy range from 17 up to 34 MeV is presented. The cross sections for the population of both ground and isomeric states were measured in yttrium and gold. A comprehensive comparison of the measured cross sections with earlier experimental data from the EXFOR database, TALYS calculations, and evaluated nuclear data libraries is presented.

Ta181(n,γ) cross section and average resonance parameter measurements in the unresolved resonance region from 24 to 1180 keV using a filtered-beam technique

A new array of four Deuterated Benzene (${\mathrm{C}}_{6}{\mathrm{D}}_{6}$) detectors has been installed at the Gaerttner Linear Accelerator Center at Rensselaer Polytechnic Institute for the purpose of measuring neutron capture cross sections in the keV region. Measurements were performed on samples of $^{181}\mathrm{Ta}$ in the unresolved resonance region (URR) using a filtered-beam technique, by which a 30 cm iron filter was placed in a white-spectrum neutron beam to remove all time-dependent $\ensuremath{\gamma}$-ray background and all neutrons except those transmitted through resonance-potential interference ``windows'' in the iron. The resulting filtered beam was effectively a quasimonoenergetic neutron source, which was used for performing measurements on isotopes with narrow level spacings in the URR. The capture cross-section results obtained for two thicknesses of tantalum are in agreement with those documented in the JEFF-3.2 library, as are the average resonance parameters obtained via a fit to the data using the sammy-fitacs code.

Proposed low-energy absolute calibration of nuclear recoils in a dual-phase noble element TPC using [formula omitted] neutron scattering kinematics

We propose a new technique for the calibration of nuclear recoils in large noble element dual-phase time projection chambers used to search for WIMP dark matter in the local galactic halo. This technique provides an insitu measurement of the low-energy nuclear recoil response of the target media using the measured scattering angle between multiple neutron interactions within the detector volume. The low-energy reach and reduced systematics of this calibration have particular significance for the low-mass WIMP sensitivity of several leading dark matter experiments. Multiple strategies for improving this calibration technique are discussed, including the creation of a new type of quasi-monoenergetic neutron source with a minimum possible peak energy of 272keV. We report results from a time-of-flight-based measurement of the neutron energy spectrum produced by an Adelphi Technology, Inc. DD108 neutron generator, confirming its suitability for the proposed nuclear recoil calibration.

Development of a High-brightness, Quasi-monoenergetic Neutron Source for Neutron Imaging

Lawrence Livermore National Laboratory (LLNL) is developing a high-brightness, quasi-monoenergetic neutron source for fast neutron-based imaging. The intensity of the neutron source is expected to be 1010∼11 n/s/sr with energies set at 7 MeV or 10 MeV with 5% bandwidth at 0-degrees. The neutrons are produced by the D(d,n) reaction using one of two accelerators of consisting of 1 or 2 RFQs (depending on the desired energy) and a DTL. Each accelerator will deliver approximately 100- or 300-uA (depending on the energy) average current deuteron beam onto a pulsed deuterium gas target or a solid target, depending on the application. In this paper, we discuss some of our benchmarking measurements and overall progress in preparation to be online in late 2017. We also discuss our performance expectations and broader set of applications.

The p + 9Be(thin target) reaction as a source of quasi-monoenergetic neutrons

The cyclotron driven fast quasi-monoenergetic neutron source based on the p+ 9 Be (thin target) reaction was studied at the proton energy around 30 MeV Due to higher melting point of Be, the p+ 9 Be(thin), reaction could be considered as an alternative to the most used p+Li(thin) neutron source, providing a similar quasi-monoenergetic neutron spectrum at significantly higher neutron output owing to advance in higher incident proton beam current. The neutron spectrum measured by the time-of-flight method agrees with other experimental data and indicates dominant contribution of ground and first excited states leading to only two peaks, separated by some 2–3 MeV, in the p+thin 9 Be neutron spectrum.

How to Use Benchmark and Cross-section Studies to Improve Data Libraries and Models

Improvements of the Monte Carlo transport codes and cross-section libraries are very important steps towards usage of the accelerator-driven transmutation systems. We have conducted a lot of benchmark experiments with different set-ups consisting of lead, natural uranium and moderator irradiated by relativistic protons and deuterons within framework of the collaboration “Energy and Transmutation of Radioactive Waste”. Unfortunately, the knowledge of the total or partial cross-sections of important reactions is insufficient. Due to this reason we have started extensive studies of different reaction cross-sections. We measure cross-sections of important neutron reactions by means of the quasi-monoenergetic neutron sources based on the cyclotrons at Nuclear Physics Institute in Řež and at The Svedberg Laboratory in Uppsala. Measurements of partial cross-sections of relativistic deuteron reactions were the second direction of our studies. The new results obtained during last years will be shown. Possible use of these data for improvement of libraries, models and benchmark studies will be discussed.

Broad energy range neutron spectroscopy using a liquid scintillator and a proportional counter: Application to a neutron spectrum similar to that from an improvised nuclear device

A novel neutron irradiation facility at the Radiological Research Accelerator Facility (RARAF) has been developed to mimic the neutron radiation from an Improvised Nuclear Device (IND) at relevant distances (e.g. 1.5km) from the epicenter. The neutron spectrum of this IND-like neutron irradiator was designed according to estimations of the Hiroshima neutron spectrum at 1.5km. It is significantly different from a standard reactor fission spectrum, because the spectrum changes as the neutrons are transported through air, and it is dominated by neutron energies from 100keV up to 9MeV. To verify such wide energy range neutron spectrum, detailed here is the development of a combined spectroscopy system. Both a liquid scintillator detector and a gas proportional counter were used for the recoil spectra measurements, with the individual response functions estimated from a series of Monte Carlo simulations. These normalized individual response functions were formed into a single response matrix for the unfolding process. Several accelerator-based quasi-monoenergetic neutron source spectra were measured and unfolded to test this spectroscopy system. These reference neutrons were produced from two reactions: T(p,n)3He and D(d,n)3He, generating neutron energies in the range between 0.2 and 8MeV. The unfolded quasi-monoenergetic neutron spectra indicated that the detection system can provide good neutron spectroscopy results in this energy range. A broad-energy neutron spectrum from the 9Be(d,n) reaction using a 5MeV deuteron beam, measured at 60 degrees to the incident beam was measured and unfolded with the evaluated response matrix. The unfolded broad neutron spectrum is comparable with published time-of-flight results. Finally, the pair of detectors were used to measure the neutron spectrum generated at the RARAF IND-like neutron facility and a comparison is made to the neutron spectrum of Hiroshima.

PHITS Simulation of Quasi-Monoenergetic Neutron Sources from 7Li(p,n) Reactions

Abstract We developed a new method that is a combination of the intranuclear cascade model and the distorted wave Born approximation (DWBA) calculation, and implemented into the particle and heavy ion transport code system (PHITS). The new method was applied to estimate the neutron spectra in reactions induced by protons incident on the 7Li target at incident energies of 150, 246, and 389 MeV. The results obtained by PHITS using the new method reproduced observed sharp peaks in the neutron spectrum as a result of taking into account the transitions to discrete nuclear states by DWBA.

Studies of neutron cross-sections important for spallation experiments using the activation method

A series of experiments devoted to studies of neutron cross-sections by activation method was carried out. The cross-sections of various threshold reactions were studied by means of different quasi-monoenergetic neutron sources with energies from 14 MeV up to 100 MeV. Threshold reactions in various materials are among other used to measure fast neutron fields produced during accelerator driven system studies. For this reason our measurements of neutron cross-sections are crucial. At present, neither experimental nor evaluated data above 30 MeV are available for neutron threshold reactions in Au, I and In published in this proceedings. We studied materials in the form of thin foils and compared our data with the calculations preformed using the deterministic code TALYS 1.4.

Cross-section studies of important neutron and relativistic deuteron reactions

The cross-sections of relativistic deuteron reactions on natural copper were studied by the means of activation method. The deuteron beams produced by JINR Nuclotron (Russia) with energies from 1 GeV up to 8 GeV were used. Lack of such cross-sections prevents the usage of copper foils for beam integral monitoring. The copper monitors will help us to improve the beam integral determination during ADS studies. The yttrium samples are very suitable activation detectors for monitoring of neutron fields not only in the ADS studies. But experimental cross-section data for higher energy threshold neutron reactions are still missing. This situation is the reason why we have started to study neutron reactions on yttrium by the means of quasi mono-energetic neutron source based on NPI Řež cyclotron (Czech Republic).

Design and demonstration of a quasi-monoenergetic neutron source

The design of a neutron source capable of producing 24 and 70keV neutron beams with narrow energy spread is presented. The source exploits near-threshold kinematics of the 7Li (p,n)7Be reaction while taking advantage of the interference ‘notches’ found in the scattering cross-sections of iron. The design was implemented and characterized at the Center for Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory. Alternative filters such as vanadium and manganese are also explored and the possibility of studying the response of different materials to low-energy nuclear recoils using the resultant neutron beams is discussed.

MCNP6 Simulation of Quasi-Monoenergetic 7Li(p,n) Neutron Sources below 150 MeV

The applicability of MCNP6 to simulate quasi-monoenergetic neutron sources from interactions of proton beams with energies below 150 MeV on thick 7Li targets has been studied. Neutron spectra at zero degrees from a 2-mm 7Li layer backed by a 12-mm carbon beam stopper in an Al flange bombarded with protons of 20, 25, 30, 35, and 40 MeV have been calculated with MCNP6 using the recent Los Alamos data library as well as using the Bertini+Dresner and CEM03.03 event generators. A comparison with the experimental neutron spectra shows that the event generators do not provide a good description of such reactions, while MCNP6 using the LANL data library simulates production of neutrons from p + 7Li in good agreement with the measured data.

Analyses of shielding benchmark experiments using FENDL-3 cross-section data starter library for ITER and IFMIF applications

*Recently IAEA has been conducting a coordinated research project to update the FENDL-2.1 nuclear data library to FENDL-3. In the present study, FENDL-3, Starter Library, Release 4 (FENDL-3/SLIB4) has been extensively tested through analysis of many fusion relevant benchmark problems. FENDL-3/SLIB4 gives better results for the FNG ITER shielding benchmark and the tungsten benchmark experiments than the previous FENDL-2.1. As for the shielding benchmark in the neutron energy range above 20 MeV, the TIARA transmission experiments through iron and concrete using p-Li quasi-monoenergetic neutron source have been analyzed. FENDL-3/SLIB4 provides satisfactory results for the TIARA shielding benchmark through iron. For concrete, however, some discrepancy was found. The present analysis suggests importance of 16 O data in