Gamma rays from thermal neutron capture in gold

The thermal column of the 10 kW University of Maryland pool reactor was used as the neutron source for this nuclear spectroscopy study. A 40 cm³ lithium drifted germanium crystal was the gamma (γ) ray detector used to measure the high energy prompt photon emissions from thermal neutron capture. The energy region was from 2.6–7.0 MeV. New capture gamma ray lines were observed.     

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   

Analysis of some Elements in Fuel Oil by using Neutron Capture Gamma Ray Spectroscopy

The analysis of some elements in fuel oil was done by using neutron capture gamma ray spectroscopy. The gamma rays emitted after the reaction of (n, γ) from the fuel oil atoms bombarded with the thermal neutrons emitted from a ²⁵²Cf source were investigated in the energy interval 0 … 10 MeV. The impurity elements in the sample were determined.     

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.     

Thermal neutron calibration method using an intense neutron beam from JRR-3M

We have developed a thermal neutron calibration method using a reactor produced neutron beam in JRR-3M of the Japan Atomic Energy Agency. Neutron-induced prompt gamma ray analysis has usually been performed in this beam line. Neutron energy distributions with negligible contributions from epithermal neutrons were measured by a time-of-flight method with a chopper made of ⁶LiF powder. The thermal neutron flux was determined by a gold foil activation method. We found that the thermal neutron beam in JRR-3M was well suited for calibration, neutron detector development or neutron dosimetry.     

The excitation function of the 13C(α, n)16O reaction and its astrophysical application

Neutron-liberating reactions as well as neutron absorbing processes play important parts in the synthesis of elements in a star and in the different phases of its life sequence. Thus the ¹³C(α, n)¹⁶O reaction is of interest for instance in connection with processes such as hydrostatic and explosive burning, as well as in the synthesis of oxygen and other light elements. A good knowledge of the energy dependence of the cross section of the alpha-carbon reaction is evidently of importance. In the present work the neutron yield from a thick ¹³C target was measured for α-particles in the energy range 0.60 to 1.15 MeV with a sensitive 4π neutron detector. Stellar temperatures between 3.5 and 9.2 × 10⁸ K are involved in this energy region. The observed neutron yield curve was used to determine astrophysical cross section factors S(E) as well as parameters for the 1.056 MeV resonance. Starting from these quantities, an expression for the mean lifetime of ¹³C nuclei interacting with helium was derived.     

探测系统能量分辨在中子能谱数值模拟中的应用

针对中子能谱实验的数值模拟研究中涉及到的探测系统能量分辨问题,基于系统探测伽玛和中子的对应关系以及对伽玛射线的能量分辨率,介绍了一种简便实用的数值模拟方案,利用探测系统对中子、伽玛的光响应对应关系以及其对伽玛的能量分辨率,得到系统对中子的能量分辨率,再进一步把它应用到中子能谱的数值模拟中,并对数值计算结果与相关实验数据进行比较分析。结果表明,该方法可以很好地应用于中子能谱的数值模拟研究。     

STUDY OF ASSOCIATED GAMMA RAY FROM NIOBIUM UNDER 14.9MeV NEUTRON BOMBARDMENTS

The gamma ray spectra from niobium under 14.9MeV neutron bombardments were neasured by means of a pulsed T(d,n)⁴He neutron source,associated particle method,Ge(Li) detector and time-of-flight technique at 7 angles between 30°and 140°.79 gamma lines were determined by a high resolution gamma spectrum analysis program,and reaction types and transition levels of 62 lines were rudely assigned.There were 40 ones of 79 lines,which were first found in reactions induced by neutrons.The differential cross sections of every gamma line at 7 angles were determined.It is shown that associated gamma ray emission from this reaction are basically asotropic.     

溴化镧闪烁体探测器性能及应用研究

LaBr3(Ce)探测器是一种新型闪烁体探测器,具有高光产额,高探测效率,高时间和空间分辨率,高能量分辨率,温度特性良好,抗辐射性能良好,操作简便等优点.从2001年以来,该探测器得到了迅速的研究和应用.LaBr3(Ce)探测器在核共振荧光检测、瞬发γ中子活化分析、爆炸物检测、核医学成像、环境辐射监测、空间辐射探测等方面的应用研究中取得了非常良好的效果.该探测器表现出优于以往用于这些领域的探测器的性能(例如NaI(Tl)探测器、BGO探测器、HPGe探测器等).介绍了LaBr3(Ce)探测器的性能及其应用研究进展,对代表性文献进行了简析和综述,阐明了其良好的应用前景.     

利用252 Cf快裂变室测量BC501A液闪探测器的相对探测效率和响应函数

本文利用²⁵²Cf快裂变室和多参数数据采集系统,逐事例的同时记录了自发裂变中子和瞬发伽马的飞行时间(TOF),脉冲形状甄别(PSD)和反冲能量(RE,裂变中子是通过测量反冲质子;瞬发伽马是通过测量康普顿反冲电子)三维信息.详细介绍了通过离线数据分析完全扣除三维信息中的伽马事例贡献,以获得Φ50.8 mm×50.8 mm的BC501A液闪探测器的相对探测效率和响应函数的方法.在不通过探测器响应函数进行数据转换的条件下,利用中子的能量直接确定了中子的有效测量阈值.得到的中子 关键词： 252Cf快裂变室')" href="#">²⁵²Cf快裂变室 BC501A液闪探测器 相对探测效率 响应函数     

Measurement of cross sections for inelastic cold-neutron scattering in metals and polymers by the method of (<Emphasis Type="Italic">n, γ</Emphasis>) analysis

The results obtained by measuring the cross sections for the inelastic scattering of very cold neutrons for a number of metals and polymers by the method of a neutron-irradiation analysis are presented. The method is based on simultaneously measuring events of inelastic scattering and neutron capture in the sample under investigation via recording gamma radiation with a semiconductor germanium detector. Neutron capture by a nucleus of the sample is accompanied by the prompt radiation of gamma rays having a known spectrum. Upon inelastic scattering, a neutron acquires thermal energy. Upon leaving the sample, this neutron is absorbed in a special converter that contains the isotope ¹⁰B. The capture of the neutron by a ¹⁰B nucleus is followed by the emission of a 477-keV gamma ray. The probabilities of capture and inelastic scattering are proportional to the respective neutron-interaction cross sections, and the ratio of the recorded detector counts corresponding to events of the two types does not depend on the spectrum of the incident flux of very cold neutrons or on the trajectory of neutron motion in the sample. The sought inelastic-scattering cross section at a fixed sample temperature is calculated by using this ratio and the known cross section for neutron capture by the sample isotope having a known gamma-radiation spectrum.     

基于PGNAA的化学武器识别

未知化学武器弹药的定性识别在犀护社会安全方面是十分重要的,可指导化学武器的分类处理。瞬发伽马射线中子活化分析（PGNAA）技术利用分析活化产生的伽马射线能谱可以实现对物质中元素的无损,快速检测,在化学武器识别中具有独特的优势。因此,本研究基于PGNAA技术进行了化学武器弹药类型识别装置的设计,同时使用逻辑树判别方法对化学武器样品进行定性分析。首先,基于高纯锗（HPGe）探测器与Cf-252中子源,使用蒙特卡罗MCNP程序对装置结构进行设计优化,主要包括中子源容器尺寸、伽马屏蔽体厚度以及探测器相对位置等。为了最大化样品活化产生的特征伽马射线,需要提高样品位置处的热中子通量,采用聚乙烯作为慢化体,模拟结果显示聚乙烯厚度达到6 cm,宽度达到12 cm时,样品中热中子通量达到较高水平。为了降低周围材料活化噪声的干扰,选择铅作为屏蔽结构,模拟显示铅屏蔽厚度达到5 cm时,可满足屏蔽要求。同时,探测器与样品之间的距离也会影响对伽马射线的探测,最终模拟确定探测器与样品之间的距离为28 cm时,特征信号计数最高。根据优化结果搭建测量装置,使用分析纯试剂根据真实化学武器元素含量配制化学武器模拟样品,通过对5种化学武器模拟样品的测量获得伽马能谱。对能谱中的特征峰处理过程中,基于特征峰对元素进行分析,针对计数统计性较好的元素（如H,Cl,S）的特征峰,使用高斯及多项式拟合的方式对特征峰处的高能量康普顿平台进行扣除,获得特征伽马射线的全能峰信息。而对统计性较差的元素特征峰（如N元素的10.829 MeV）,采用能量区间加和法,对该能量下的全能峰至单逃逸峰之间的计数求和,进而可确定该元素在样品中的存在情况,最后利用建立的逻辑树判别方法根据元素存在信息对样品类型进行判别。实验结果表明,利用该优化的装置可以获得5种模拟样品的能谱,结合能谱分析方法可以得到化学武器模拟样品中的H,Cl,S和N等元素的存在信息,最后使用逻辑树判别方法可以对化学武器样品种类进行判别。     

D-T中子与平板型聚乙烯材料作用的次级中子角度谱实验研究

基于反冲质子法建立了一种测量D-T中子与平板型宏观样品作用的次级中子角度谱的实验方法.为保证探测器的能量线性并在较低的中子有效测量下阈(0.5 MeV)情况下获得好的中子-伽马射线甄别性能,采用高、低能段分别测量的方法.采用事件记录法,同时记录了次级中子和伴随伽马射线的脉冲形状甄别和脉冲幅度二维信息,利用基于ROOT数据分析平台编写的离线数据分析程序,完成了伴随伽马射线的挑选和扣除,以及高、低两能段反冲质子谱的拼接,并成功的将神经网络技术应用于中子能谱的解谱,获得了D-T中子与9和18 cm厚平板型聚乙烯材料作用的0.5-15 MeV的次级中子角度谱实验结果.实验模型的MC模拟由MCNP5完成,数据库采用ENDF-VI,实验结果和MC计算结果在实验不确定度范围内一致. 关键词： D-T中子 积分中子学 反冲质子法 次级中子能谱     

Neutron moderation in a bulk sample and its effects on PGNAA setup geometry

In a prompt gamma ray neutron activation analysis (PGNAA) setup, the neutron moderation in the bulk sample also plays a key role. This can even dominate the thermalization effects of the external moderator in some cases. In order to study the neutron moderation effect in the bulk sample, moderators with two different sizes of the sample were tested at the King Fahd University of Petroleum & Minerals (KFUPM) PGNAA facility. In these tests, the thermal neutron relative intensity and prompt gamma ray yield from the two moderators were measured using nuclear track detectors (NTDs) and NaI detector, respectively. As predicted by Monte Carlo simulations, the measured intensity of thermal neutron inside the large sample cavity due to the external moderator was smaller than that from the smaller sample cavity. Due to its larger size, additional thermalization of neutrons will take place in the larger sample. In spite of smaller thermal neutron yield from the external moderator at the large sample location, higher yield of the prompt gamma ray was observed as compared to that from the smaller sample. This confirms the significance of neutron moderation effects in the bulk sample and can thereby affect the PGNAA geometry size. This allows larger samples in conjunction with smaller moderators in the PGNAA setup.     

Radon contribution to single particle counts of the ARGO-YBJ detector

The ARGO-YBJ experiment is an air shower detector for gamma ray astronomy and cosmic ray studies with an energy threshold of ∼500 GeV. Working in “single particle mode”, i.e. counting the single particles hitting the detector at fixed time intervals, ARGO-YBJ can monitor cosmic ray and gamma ray transients at energies of a few GeV.The single particle counting rate is modulated by the atmospheric pressure and temperature, and is affected by the local radioactivity from soil and air. Among the radioactive elements, radon gas is of particular importance since its concentration in air can vary significantly, according to environmental conditions. In this paper we evaluate the contribution of the radon daughter gamma ray emitters to the single particle counting rate measured by ARGO-YBJ. According to our analysis, the radon gas contribution is roughly 1–2%, producing a counting rate modulation of the same order of magnitude of the atmospheric effects.     

Measurements of a partial cross section for the reaction 58Ni(n, γ0)59Ni

The partial cross section for radiative neutron capture accompanied by gamma transitions to the ground state of the ⁵⁹Ni nucleus was measured as a function of energy by a new neutron-spectrometry method that employed the shift of a primary gamma transition in response to a change in the energy of the captured neutron. The reaction ⁷Li(p, n)⁷Be was used as source of neutrons for the present measurements. The protons that induced this reaction were accelerated by a Van de Graaff electrostatic generator to energies exceeding the reaction threshold by 60 keV, in which case an appropriate geometry of the experiment permitted irradiation of the sample under study with neutrons whose energy ranged between 10 and 120 keV. The partial widths of some resonances and radiative strength function for hard primary M1 gamma transitions were determined in addition to the above cross sections.     

Evolution of nuclear spectroscopy at Saha Institute of Nuclear Physics

Experimental studies of nuclear excitations have been an important subject from the earliest days when the institute was established. The construction of 4 MeV proton cyclotron was mainly aimed to achieve this goal. Early experiments in nuclear spectroscopy were done with radioactive nuclei with the help of beta and gamma ray spectrometers. Small NaI(Tl) detectors were used for gamma-gamma coincidence, angular correlation and life time measurements. The excited states nuclear magnetic moments were measured in perturbed gamma-gamma angular correlation experiments. A high transmission magnetic beta ray spectrometer was used to measure internal conversion coefficients and beta-gamma coincidence studies. A large number of significant contributions were made during 1950–59 using these facilities. Proton beam in the cyclotron was made available in the late 1950’s and together with 14 MeV neutrons obtained from a C-W generator a large number of short-lived nuclei were investigated during 1960’s and 1970’s. The introduction of high resolution Ge gamma detectors and the improved electronics helped to extend the spectroscopic work which include on-line (p ₇ p′γ) and (p ₇ nγ) reaction studies. Nuclear spectroscopic studies entered a new phase in the 1980’s with the availability of 40–80 MeV alpha beam from the variable energy cyclotron at VECC, Calcutta. A number of experimental groups were formed in the institute to study nuclear level schemes with (α ₇ xnγ) reactions. Initially only two unsuppressed Ge detectors were used for coincidence studies. Later in 1989 five Ge detectors with a large six segmented NaI(Tl) multiplicitysum detector system were successfully used to select various channels in (α ₇ xnγ) reactions. From 1990 to date a variety of medium energy heavy ions were made available from the BARC-TIFR Pelletron and the Nuclear Science Centre Pelletron. The state of the art gamma detector arrays in these centres enabled the Saha Institute groups to undertake more sophisticated experiments. Front line nuclear spectroscopy works are now being done and new informations are obtained for a large number of nuclei over a wide mass range. Currently Saha Institute is building a multi-element gamma heavy ion neutron array detector (MEGHNAD), which will have six high efficiency clover Ge detector together with charged particle ball and other accessories. The system is expected to be usable in 2002 and will be used in experiments using high energy heavy ions from VECC.     

Use of CR-39 films for nuclear radiation shielding efficacy evaluation of lining materials for combat vehicles

All materials provide, to a lesser or greater extent, shielding against nuclear radiations. Armoured fighting vehicles (AFVs) have steel as the structural material, which appears to be a reasonably good gamma and neutron shield material but a shield of pure iron would not be equally effective against whole range of neutron energies as it has a few resonances in electron volt range, and it reduces energy of fast neutrons to lower energy neutrons. These neutrons will be absorbed through radiative capture and emit gamma radiations. Thus it is essential that an effective shield should contain a large amount of moderating material, hydrogen being preferred with low atomic number materials (B, C, Li) and lead (Pb) to ensure that the neutrons do not diffuse at intermediate energies in the shield as well as gamma attenuation will also take place. In order to have a suitable shield material for armoured vehicles which serves as neutron and gamma radiation attenuator, polyethylene polymer with fillers lining materials are preferred. These materials were evaluated against gamma and fast neutrons using radioactive sources for suitability to fitment into combat vehicle as per the requirement of protection factor values. The detector for gamma radiation was used as Nal(Tl) while for neutron, CR-39 film was used.      

Neutron induced reactions in antimony isotopes at 14 MeV

Neutron activation cross-sections in antimony isotopes were measured at an incident neutron energy of 14.2±0.2 MeV. The versatile mixed powder technique and high resolution Ge(Li) detector gamma ray spectroscopy were employed. The measured cross-sections were compared with those reported in literature. The total (n, 2n) cross-sections were compared with the estimates based on statistical theory. The experimental values were found to be smaller than the statistical theory estimates and the resulting diminution was attributed to the precompound effects in (n, 2n) reactions at 14 MeV.     

Highlights of the ARGO-YBJ Experiment at 4,300 m a.s.l.

The ARGO-YBJ experiment in Tibet, China has been operated to survey the northern sky for gamma ray sources, transient or steady, for nearly 6 years. Many astrophysics observational results will be highlighted in this paper, such as the sky survey results, extended source observation, diffuse gamma rays from the galactic plane, and emission mechanism of AGNs and their flares. As the unique detector for EAS with a continuously sensitive area of 5,600 m ², the ARGO-YBJ array catches almost all particles in the central part of showers. The high-quality data set for showers above few TeV has been used for cosmic ray measurements such as the energy spectrum and composition. All those results are summarized here. As one of the next generation ground-based high-altitude air shower detector, LHAASO is briefly introduced as the successor of ARGO-YBJ in the end of the paper.