Detecting neutrons by forward recoil protons at the Energy & Transmutation facility: Detector development and calibration with 14.1-MeV neutrons

As part of the Energy & Transmutation project, we are developing a detector for neutrons with energies in the 10–100 MeV range emitted from the target irradiated by a charged-particle beam. The neutron is detected by measuring the time-of-flight and total kinetic energy of the forward-going recoil proton [1] knocked out at a small angle from a thin layer of plastic scintillator, which has to be selected against an intense background created by γ quanta, scattered neutrons, and charged particles. On the other hand, neutron energy has to be measured over the full range with no extra tuning of the detector operation regime. Initial measurements with a source of 14.1-MeV neutrons are reported.     

中国散裂中子源反角白光中子束流参数的初步测量

中国散裂中子源(CSNS)已于2018年5月建设完工,随后进行了试运行.其中的反角白光中子束线(Back-n)可用于中子核数据测量、中子物理研究和核技术应用等多方面的实验.本文报道对该中子束的品质参数测量实验过程以及最终实验结果.实验主要采用中子飞行时间法,利用~(235)U,~(238)U裂变室和~6Li-Si探测器测量了中子能谱和中子注量率,又利用闪烁体-互补金属氧化物半导体探测系统测量了中子束斑的剖面,得到了该束线的初步实验测量结果.其中白光中子的全能谱测量范围eV—100 MeV,给出了不确定度分析;给出了中子注量率两个实验厅位置的满功率值;给出了白光中子在直径60 mm情况下的全能区束斑.通过与模拟结果的比较探讨了以上结果的合理性,并提出了改进计划.这些实验结果为以后该束线的核数据测量和探测器标定实验奠定了基础.     

Investigation of neutron emission in the interaction of relativistic protons and deuterons with lead targets

Measurements of neutron double-differential cross sections and yields in time-of-flight experiments with various lead targets and beams of protons and deuterons with an energy of about 2 GeV are discussed. Space and energy distribution of neutrons in an extended lead target is studied by threshold detectors in the proton energy range of 1–3.7 GeV. The average multiplicity of neutrons, neutron energy, and neutron multiplication in lead as functions of target dimension, type, and energy of the beam particle are analyzed.     

Photoproduction of high-energy neutrons in thick targets by electrons in the energy range 150 to 270 MeV

Photoneutron spectra with energies greater than 12 MeV produced by electrons incident on a thick lead target have been measured for primary electron energies between 150 and 266 MeV and at a fixed angle of 90 ° to the beam axis. Measurements of the neutron yield have furthermore been performed at a primary energy of 234 MeV as a function of target depth for the same lead target and as a function of the mass number for C, Al, Cu, Cd and Pb targets. The results were obtained with three independent neutron detectors: two proton recoil counters and one time-of-flight set-up. The high-energy regions of the spectra are compared with the predictions of the phenomenological quasi-deuteron model and a satisfactory agreement in shape and scale of the spectra is found. Additional high-energy neutrons from pion reabsorption processes were observed at electron energies of 234 and 266 MeV.     

Gamma ray and π0 production from hydrogen and complex nuclei by 270–375 MeV gamma rays

Measurements are reported on the differential cross section for secondary gamma ray production on hydrogen and nuclear targets at 90° in the laboratory through the interactions of primary gamma rays in the energy range 270–375 MeV. A difference method using bremsstrahlung beams at different end point energies was employed. The gamma ray detector was a high resolution Nal(Tl) spectrometer and time of flight discrimination was used to reject neutrons. For incident gamma rays in the range 270–375 MeV the first pion nucleon resonance is strongly excited and the observed gamma ray yields are consistent with those expected due to an admixture of coherent and incoherent π⁰ photoproduction in the resonance region. The experiment marks the first successful use of a large Nal(Tl) crystals as a gamma ray spectrometer at a high energy electron linear accelerator, despite the low duty cycle and its accompanying difficulties for such detectors.     

Nuclear Reactions under Irradiation of Deuterated Structures by X Rays

Measurements of emission from nuclear reaction products (neutrons and protons) have been carried out appearing in the deuterated structures of textured CVD diamond, palladium, titanium, and zirconium under irradiation with a beam of X rays using independent methods (neutron detector based on He-3 counters, Si surface-barrier semiconductor detectors and CR-39 track detector). The possibility of enhancement of both DD reaction and multi-particle deuterium fusion by the beam of X rays with energy ranging 20–30 keV in solid deuterated targets has been established. Analysis of X-ray fluorescence spectra of the target bombarded by beams of ions has revealed “additional” peaks, the occurrence of which cannot be related to any of the known elements, and requires separate study.

     

The 10,000,000,000-Volt question: What is the best choice of proton energy to drive a pulsed spallation neutron source?

In pulsed spallation neutron sources, higher proton beam current or higher proton energy brings higher proton beam power, and from greater beam power come more neutrons. Consequently, accelerator scientists and target systems designers conceive systems to produce ever-higher intensities of neutrons, and the question arises: What is the best choice of proton energy to drive a pulsed spallation neutron source? Meanwhile target engineering, radiation shielding, and neutronic coupling to moderators must be accomplished effectively. This paper addresses the title question from the target side, assessing the neutron yield, the distribution of leakage neutrons, and the power density distribution as functions of proton energy.     

Deeply virtual Compton scattering on a virtual pion target

We study deeply virtual Compton scattering on a virtual pion that is emitted by a proton. Using a range of models for the generalized parton distributions of the pion, we evaluate the cross section, as well as the beam spin and beam charge asymmetries in the leading-twist approximation. Studying Compton scattering on the pion in suitable kinematics puts high demands on both beam energy and luminosity, and we find that the corresponding requirements will first be met after the energy upgrade at Jefferson Laboratory. As a by-product of our study, we construct a parameterization of pion generalized parton distributions that has a non-trivial interplay between the x and t dependence and is in good agreement with form factor data and lattice calculations.     

Latest results from GRAAL collaboration

The GRAAL experimental set-up consists of a polarized and tagged photon beam that covers an energy range from a minimum of 600 MeV up to a maximum of 1500 MeV, of a liquid Hydrogen or Deuterium target and of the 4π Lagrange detector optimized for photon detection. It allows the study of pseudo-scalar and vector meson photoproduction on the nucleon in the energy range corresponding to the second and the third resonance regions. In the following, the Σ beam asymmetries in η and π~0 photoproduction on quasi-free nucleon are shown. Also single and double polarization observables in K~+A photoproduction on free proton are shown; they are important to confirm the role of new or poorly known resonances in the 1900 MeV mass region.     

Experimental neutron flux measurements with a diamond detector at the QUINTA setup

The operational capability of a diamond detector used to measure the neutron spectrum by the response function on the QUINTA setup [1] installed at the proton beam of the phasotron [2] (Laboratory of Nuclear Problems, Joint Institute for Nuclear Research) was demonstrated in the energy interval of 2.1–20 MeV. The neutron-flux count rate was measured. The energy of neutrons was estimated at 7.4–25.7 MeV based on the diamond-detector response spectrum. The dependence of the diamond-detector response spectra on the angle between the proton beam and the line going through the detector and the center of the QUINTA setup was investigated. The angular anisotropy of the neutron flux was demonstrated. Measurements at different distances from the detector to the QUINTA setup were performed.     

Response of a Si-diode-based device to fast neutrons

Semiconductor devices based on a Si-detector are frequently used for charged particle's detection; one application being in the investigation of cosmic radiation fields. From the spectra of energy deposition events in such devices, the total energy deposited by the radiation in silicon can be derived. This contribution presents the results of studies concerning the response of this type of detector to fast neutrons. First, the spectrum of energy deposition was established in fast neutron radiation fields with average energies from 0.5 to 50 MeV. It was found that these spectra vary significantly with the neutron energy. The comparison with the spectra registered in photon beams permitted an estimation of the part of energy deposited that could be attributed to neutrons. It was found that this part increases rapidly with neutron energy. The possibilities to use this type of detector for neutron detection and dosimetry for radiation protection are analysed and discussed.     

Particle production in Pb+Pb collisions at the SPS

Experiment NA49 at the CERN SPS employs a large acceptance detector to study particle spectra, yields and correlations in nucleus-nucleus, nucleon-nucleus and nucleon-nucleon collisions. Preliminary results on pion, kaon, A and ā production in central Pb+Pb collisions at 40, 80 and 158 A·GeV beam energy are shown and compared to measurements at lower and higher energies.     

ICF中子产额测量中统计涨落分析及计算

 塑料闪烁探测器通常用来测量氘氘、氘氚聚变中子产额。中子在闪烁体中产生的质子数的统计涨落及质子在闪烁体中沉积能量的统计涨落为测量结果引入了两项不确定度分量。以氘氚聚变中子为例,分析了这两种统计涨落的概率密度函数的计算方法,该计算方法也适用于其它能量的单能快中子和塑料闪烁体作用的相应计算。     

Simulation study using GEANT4 Monte Carlo code for a Gd-coated resistive plate chamber as a thermal neutron detector

The Resistive Plate Chamber (RPC) has been developed in many application areas ever since its introduction, from high energy physics experiments to positron emission tomography. Such detectors can be coated with a Gd layer that enables them to detect thermal neutrons. Consequently these RPCs can be utilized for industrial and medical purposes. Here, we present the configuration of a resistive plate chamber which is utilized to detect thermal neutrons by employing GEANT4 Monte Carlo code. The response of the RPC was evaluated as a function of neutron energy in the GEANT4 Monte Carlo code. The simulation results are taken for incident neutron energy in the energy range from 25 meV to 100 meV. The detection efficiency was found to be between 10% and 20%, depending on the detector configuration, for incident thermal neutrons of 25 meV energy.     

锂玻璃探测器中子探测效率的刻度

为了精确测量keV能区的中子俘获截面,中国原子能科学研究院正在建造一台4π 全吸收型γ 探测装置---GTAF,锂玻璃探测器将会作为中子束流监视器测量中子能谱。利用5SDH-2 加速器刻度了锂玻璃探测器在两个入射中子单能点(250 和565 keV) 的探测效率,并使用EANT4 和MCNP 程序模拟计算了锂玻璃探测器的相对探测效率。通过归一化实验数据和模拟结果,得到了锂玻璃探测器在10keV~1 MeV 能区的中子探测效率曲线。对于把锂玻璃探测器测量得到的飞行时间谱转化为中子束流能谱,是一项非常重要的工作,同时为探测器效率刻度提供了新方法。In order to accurately measure the neutron capture cross section in the energy range of keVMeV, 4 πgamma-ray total absorption facility (GTAF) is being constructed at China Institute of Atomic Energy (CIAE). The lithium glass detector will be used as a neutron beam monitor for GTAF. The detection efficiency of the lithium glass detector at two incident neutron energy points (250, 565 keV) was calibrated in 5SDH-2 accelerator, and the relative detection efficiency was simulated by GEANT4 and MCNP code. By the normalization of the experimental data and simulation result, the neutron detection efficiency curve of the lithium glass detector between 10 keV and 1 MeV was obtained. This work will be important to convert the Time-of-flight spectrum that be measured by Li-glass detector to the energy spectrum of neutron beam, and provide the new method for calibration of detection efficiency.     

Passage of Fast Neutrons Through the Crystal Structure of Textured CVD Diamond

The passage of fast neutrons through the crystal structure of a textured diamond obtained by chemical vapor deposition (CVD diamond) is studied. Neutrons with an energy of 2.45 MeV from the DD reaction and with an average energy of about 2 MeV from the 252Cf isotope are used as neutron sources. The neutrons are detected by two independent methods: using proportional counters filled with 3Не and a paraterphenyl-based scintillation detector. The measurements show that the neutron-flux incident on the detector depends on the orientation of the target. In the case of isotropic samples containing diamond and carbon, such effects are not observed. A possible explanation for the effect is the channeling of deuterium ions and neutrons in channels of textured CVD diamond.     

Dosimetry and fast neutron energies characterization of photoneutrons produced in some medical linear accelerators

This work focusses on the estimation of induced photoneutrons energy, fluence, and strength using nuclear track detector (NTD) (CR-39). Photoneutron energy was estimated for three different linear accelerators, LINACs as an example for the commonly used accelerators. For high-energy linear accelerators, neutrons are produced as a consequence of photonuclear reactions in the target nuclei, accelerator head, field-flattening filters and beam collimators, and other irradiated objects. NTD (CR-39) is used to evaluate energy and fluence of the fast neutron. Track length is used to estimate fast photoneutrons energy for linear accelerators (Elekta 10 MV, Elekta 15 MV, and Varian 15 MV). Results show that the estimated neutron energies for the three chosen examples of LINACs reveals neutron energies in the range of 1–2 MeV for 10 and 15 MV X-ray beams. The fluence of neutrons at the isocenter (Φ_total) is found to be (4×10⁶ n cm² Gy^?1) for Elekta machine 10 MV. The neutron source strengths Q are calculated. It was found to be 0.2×10¹² n Gy^?1 X-ray at the isocenter. This work represents simple, low cost, and accurate methods of measuring fast neutrons dose and energies.     

Neutral pion production in the threshold region Conclusive Symposium of the Collaborative Research Centre 443

We give an overview of the physics motivation and evolution of the neutral pion photoproduction measurements in the threshold region conducted in the A2 collaboration at MAMI. The latest two experiments have been performed with the almost 4π Crystal Ball detector. The first was with a linearly polarized photon beam and unpolarized liquid-hydrogen target. The data analysis is now complete and the linearly polarized beam asymmetry along with differential cross sections provide the most stringent test to date of the predictions of Chiral Perturbation Theory and its energy region of convergence. More recently a measurement was performed using both circularly polarized photons and a transversely polarized butanol frozen-spin target, with the goal of extracting both the target and beam-target asymmetries. From these we intend to extract πN scattering sensitive information for the first time in photo-pion reactions. This will be used to test isospin conservation and further test dynamics of chiral symmetry breaking in QCD as calculated at low energies by Chiral Perturbation Theory.     

Nuclear emissions during self-nucleated acoustic cavitation

A unique, new stand-alone acoustic inertial confinement nuclear fusion test device was successfully tested. Experiments using four different liquid types were conducted in which bubbles were self-nucleated without the use of external neutrons. Four independent detection systems were used (i.e., a neutron track plastic detector to provide unambiguous visible records for fast neutrons, a detector, a NE-113-type liquid scintillation detector, and a NaI gamma ray detector). Statistically significant nuclear emissions were observed for deuterated benzene and acetone mixtures but not for heavy water. The measured neutron energy was 相似文献   

Charged pions from Ni on Ni collisions between 1 and 2 AGeV

Charged pions from Ni + Ni reactions at 1.05, 1.45 and 1.93 AGeV are measured with the FOPI detector. The mean π^± multiplicities per mean number of participants increase with beam energy, in accordance with earlier studies of the Ar + KCl and La + La systems. The pion kinetic energy spectra have concave shape and are fitted by the superposition of two Boltzmann distributions with different temperatures. These apparent temperatures depend only weakly on bombarding energy. The pion angular distributions show a forward/backward enhancement at all energies, but not the Θ = 90⁰ enhancement which was observed in case of the Au + Au system. These features also determine the rapidity distributions which are therefore in disagreement with the hypothesis of one thermal source. The importance of the Coulomb interaction and of the pion rescattering by spectator matter in producing these phenomena is discussed.