The Monte-Carlo simulation on a scintillator neutron detector

A simulation of the properties of the shifting scintillator neutron detector using 6LiF/ZnS(Ag) scintillation screens is performed.The simulation results show that the light attenuation length of standard BC704 scintillator is about 0.65 mm.Its thermal neutron detection efficiency,gamma sensitivity and intrinsic spatial resolution can achieve around 50.0%,10 5and 0.18 mm(along X-axis) respectively.For the detector,air coupling position resolution is better than the silicone oil coupling.Some of the simulation results are compared with experimental results.They are in agreement.This work will be helpful for constructing neutron detector for high intensity powder diffractometer at Chinese spallation neutron source.     

Neutron fluence spectrometry using disk activation

A simple and robust detector for spectrometry of environmental neutrons has been developed. The technique is based on neutron activation of a series of different metal disks followed by low-level gamma-ray spectrometry of the activated disks and subsequent neutron spectrum unfolding. The technique is similar to foil activation but here the applied neutron fluence rates are much lower than usually in the case of foil activation. The detector has been tested in quasi mono-energetic neutron fields with fluence rates in the order of 1000–10000 cm⁻² s⁻¹, where the obtained spectra showed good agreement with spectra measured using a Bonner sphere spectrometer. The detector has also been tested using an AmBe source and at a neutron fluence rate of about 40 cm⁻² s⁻¹, again, a good agreement with the assumed spectrum was achieved.     

Developments of a 2D position sensitiveneutron detector

China Spallation Neutron Source (CSNS), one project of the 12^th Five-Year-Plan scheme of China, is under construction in Guangdong province. Three neutron spectrometers will be installed during the first phase of the project, and two-dimensional position sensitive thermal neutron detectors are required. Before the construction of the neutron detectors, a prototype of a two-dimensional 200 mm×200 mm Multi-wire Proportional Chamber (MWPC) with Ar/CO₂ (90/10) flowing gas has been constructed. In 2009, the prototype was tested with the ⁵⁵Fe X-ray using part of the electronics, and performed well.
Following the test in 2009, the neutron detector was constructed with the complete electronics and filled with the 6 atm. ³He+2.5 atm. C₃H₈ gas mixture in 2010. The neutron detector has been primarily tested with an Am-Be source. In this paper, new developments of the neutron detector including the design of the high pressure chamber, the optimization of the gas purifying system and the gas filling process will be reported. The results and discussion are also presented in this paper.     

Two-dimensional thermal neutron detector

A two-dimensional thermal neutron detector for neutron diffraction experiments has been developed and designed at the St. Petersburg Nuclear Physics Institute, Russian Academy of Sciences. The detector is based on a multiwire proportional chamber with cathode-strip delay line readout. The detector aperture is 170 × 300 mm² and the anode wire spacing is 4 mm. The chamber is filled with a 1.5 atm ³He + 2 atm CF₄ gas mixture. To conserve high purity of the gas mixture, all electrodes are made of quartz glass. The spatial resolution of the detector is 2.5 mm and the detection efficiency is 60% for 9 Å neutrons.     

散裂中子源高气压二维位置灵敏3He探测器的实验研究

为满足中国散裂中子源多功能反射谱仪中子探测器的基本物理要求:有效面积达到200 mm×200 mm、探测效率大于50%（2Å）、位置分辨好于2 mm等,中国科学院高能物理研究所研制了3He高气压二维多丝正比室位置灵敏中子探测器。该探测器采用二维多丝室结构,腔体内充3He/C₃H₈（6 atm/2.5 atm）的组合气体。本文首先利用Am/Be中子源完成对探测器全面积均匀性测试,均匀性指标达到了95.1%;探测器在中国散裂中子源的20号束流线站安装后,对其进行了在束测量,通过飞行时间选取波长2.8Å的慢中子,测量了探测器二维位置分辨和二维成像性能。在X方向（垂直于阳极丝的方向）的位置分辨为0.99 mm,Y方向（平行于阳极丝的方向）的位置分辨为1.36 mm,探测器具有很好的二维位置分辨和二维成像能力。测量结果表明探测器满足反射谱仪的研制要求。     

Study of the57Fe low-energy states

The low energy states of⁵⁷Fe has been studied by means of thermal neutron radiative capture. The gamma-ray spectrum below 3 MeV was measured using a Ge(Li) detector of an intrinsic volume 5.4 cm³. On making use of other experiments beside the good resolution of the Ge(Li) detector it was possible to suggest a decay scheme and to get some valuable informations. The transitions from the levels 366.7keV to the ground- and first-excited states seem to be pureM1 transitions. An evidence for the existence of a transition from the level 1725.5 keV to the 1018.6 keV with an absolute intensity 2.4% is shown.     

Determination of the neutron binding energy of the delayed neutron emitter137Xe

The neutron binding energy of¹³⁷Xe has been deduced to be 4025.2±0.6 keV from a study of the¹³⁶Xe(n, γ)¹³⁷Xe reaction. The importance of a precise value for this quantity is due to the fact that an accurate determination of binding energies of delayed neutron emitters is possible only for⁸⁷Kr and¹³⁷Xe, neighbouring stable isotopes. Nuclear reaction.¹³⁶Xe(n,γ), enriched target; measurede89-01, deduced neutron binding energy, Ge(Li) detector.     

A capture-gated fast neutron detection method

To address the problem of the shortage of neutron detectors used in radiation portal monitors(RPMs),caused by the ~3He supply crisis, research on a cadmium-based capture-gated fast neutron detector is presented in this paper. The detector is composed of many 1 cm × 1 cm × 20 cm plastic scintillator cuboids covered by 0.1 mm thick film of cadmium. The detector uses cadmium to absorb thermal neutrons and produce capture γ-rays to indicate the detection of neutrons, and uses plastic scintillator to moderate neutrons and register γ-rays. This design removes the volume competing relationship in traditional ~3He counter-based fast neutron detectors, which hinders enhancement of the neutron detection efficiency. Detection efficiency of 21.66% ± 1.22% has been achieved with a 40.4 cm × 40.4cm × 20 cm overall detector volume. This detector can measure both neutrons and γ-rays simultaneously. A small detector(20.2 cm × 20.2 cm × 20 cm) demonstrated a 3.3 % false alarm rate for a ~(252)Cf source with a neutron yield of 1841 n/s from 50 cm away within 15 s measurement time. It also demonstrated a very low(0.06%) false alarm rate for a 3.21 × 10~5 Bq ~(137)Cs source. This detector offers a potential single-detector replacement for both neutron and the γ-ray detectors in RPM systems.     

DViN-2 stationary inspection complex

A DViN-2 stationary inspection complex has been designed and manufactured for identifying hidden explosives and drugs. The identification of hidden substances is based on the method of tagged neutrons. The source of the tagged neutron beam, which has an energy of 14.1 MeV produced in the reaction d + t → α + n, is a portable neutron generator with a built-in 9-channel silicon α detector. The DViN-2 makes it possible to identify hidden explosives and drugs with a mass of from 100 g to 50 kg in objects with dimensions from 50 to 400 mm in all three directions. The results of 76 experiments testify to the high efficiency of the DViN-2 in regards to identifying hidden explosives and drugs and it has a rather low probability of false actuations: the probability of identifying explosives and drugs is 94%, and that of false alarms rate is 3%. The time it takes to identify hidden substances, depending on their mass and the thickness of the shielding material layer, is 3–7 min for an average neutron beam intensity into a solid angle of 4π of 2 × 10⁷s^?1.     

A study of the50Cr(d,n)51Mn and54Fe(d,n)55Co reactions

The⁵⁰Cr(d, n)⁵¹Mn and⁵⁴Fe(d, n)⁵⁵Co reactions have been studied at an incident deuteron energy of 5.5 MeV. Angular distributions of neutron groups to a number of low-lying levels in the residual nuclei have been recorded. Time-of-flight techniques have been used to record neutron spectra. A liquid scintillator with pulse-shape discrimination property has been used as neutron detector. DWBA calculations have been performed and relative spectroscopic strengths determined for transitions with variousl _p values. The ratios between spectroscopic strengths forl _p =3 andl _p =1 transitions were found to be considerably larger than corresponding ratios obtained from the (³He,d) reactions. Two-step stripping processes competing with the direct stripping process are suggested as explanation of the discrepancy between the (d, n) and the (³He,d) results.     

The (p,nγ) reaction on Al and Si

The reactions ²⁷Al(p, n γ) ²⁷Si and ²⁸Si(p, n γ)²⁸P have been studied at E_p = 16 and 23 MeV, respectively, with a Ge(Li) detector in coincidence with a neutron detector. In ²⁷Si, two new γ-tran- sitions were detected and accurate excitation energies were determined. In ²⁸P, the γ-decay scheme was studied for the first time and new levels were located at 879 and 1602 keV excitation energy. For both nuclei the γ-ray spectra were supplemented by neutron time-of-flight spectra. The excitation energies are compared with those of the analogue nuclei and with the predictions from Coulomb displacement calculations.     

Unfolding the fast neutron spectra of a BC501A liquid scintillation detector using GRAVEL method

Accurate knowledge of the neutron energy spectra is useful in basic research and applications. The overall procedure of measuring and unfolding the fast neutron energy spectra with BC501A liquid scintillation detector is described. The recoil proton spectrum of 241Am-Be neutrons was obtained experimentally. With the NRESP7 code, the response matrix of detector was simulated. Combining the recoil proton spectrum and response matrix, the unfolding of neutron spectra was performed by GRAVEL iterative algorithm. A MatLab program based on the GRAVEL method was developed. The continuous neutron spectrum of ²⁴¹Am-Be source and monoenergetic neutron spectrum of D-T source have been unfolded successfully and are in good agreement with their standard reference spectra. The unfolded ²⁴¹Am-Be spectrum are more accurate than the spectra unfolded by artificial neural networks in recent years.     

First observation of low lying states in the doubly odd nucleus132Pr from beta decay of132Nd

Excited states of ¹⁰⁸ Te were populated in the ⁵⁴ Fe + ⁵⁸ Ni (270 MeV) reaction using the NORDBALL detector array equipped with charged-particle and neutron detector systems for reaction channel separation. Gamma rays belonging to the neutron deficient nucleus ¹⁰⁸ Te were identified for the first time. On the basis of γγ-coincidence and angular correlation relations a level scheme was constructed with tentative spin and parity assignments. The structure of the nucleus is discussed in the framework of systematics of heavier Te nuclei.     

A rotational band in82Zr

The neutron deficient nucleus⁸²Zr has been studied through the reaction⁵⁸Ni(²⁸Si, 2p 2n)⁸²Zr with a calculated cross section of 0.3% of the total fusion cross section atE(²⁸Si)=128 MeV. Gamma rays from excited states of⁸²Zr were measured and identified using the NORDBALL escape-suppression array at the Niels Bohr Institute. Reaction channel selection was performed by use of neutron and charged particle detector arrays in conjunction with the germanium detectors. A rotational band in⁸²Zr has been identified with spins up to 20 ? by analysis of reaction channel selectedγ-γ coincidence matrices. Band crossings were identified at frequencies 0.57 and 0.69 MeV.     

Measurement of the beta spectrum of the 0− (120 keV) state of16N

We have measured the beta spectrum of the 0^?(120 keV,t _1/2=5.25 μs) state of¹⁶N. The response function of our detector has been measured, parameterized and then fitted to known spectral shapes taken under conditions close to those in the actual experiment. Using this response function and subtracting a 56 μs half-life background due to neutron capture in the detector, the measured 0^? spectrum compares well with the allowed shape for the 0^?→0⁺ spectrum plus a small contribution from the allowed 0^?→1^? transition.     

Precise determination of neutron binding energy of <Superscript>64</Superscript>Cu

The neutron binding energy in ⁶⁴Cu has been accurately measured in thermal neutron capture. A composite target of natural Cu and NaCl was used on a high flux neutron beam using a large measuring time. The γ-ray spectrum emitted in the (n, γ) reaction was measured with a HPGe detector in large statistics (up to 10⁶ events per channel). Intrinsic limitations of HPGe detectors, which restrict the accuracy of energy calibration, were determined. The value B _n of ⁶⁴Cu was determined as 7915.867(24) keV.     

The study of short-lived nuclei in the regionZ=59–68

β ⁺ -ray endpoint energies for mass-separated samples of neutron deficient Rare-Earth isotopes have been measured using an intrinsic germanium detector. Q_EC values have been obtained and new isomeric states have been identified for the first time.     

An apparatus of the NBC type and the physics results obtained

A nonbubble chamber (NBC) setup, especially designed to perform a series of experiments, is described. The setup consists of a neutron missing-mass spectrometer coupled with a system of large electromagnetic shower detectors. In spite of its large dimensions (the sensitive surface and volume are 2.16 × 10⁴ cm² and 7.8 × 10⁵ cm³, respectively), the neutron spectrometer has a time resolution of ±0.70 nsec FWHM, with ∼25% detection efficiency in the range (70–390 MeV) neutron kinetic energy. The time equalization between the various components of the neutron spectrometer has been established to within ±0.1 nsec. At present this is the most powerful and the most accurate high-energy neutron detector. The electromagnetic shower detector is based on the principle of simultaneous measurements of the spatial development of the electromagnetic cascade and of its energy release. This is obtained with nine elements of lead foil — spark chamber — plastic scintillator, all sandwiched together. The sensitive surface and volume of the electromagnetic shower detector are 1.45 × 10⁴ cm² and 7.2 × 10⁵ cm³, respectively.     

A study of high spin states in the transitional nucleus90Mo

The reaction⁵⁸Ni(³⁶Ar, 4p)⁹⁰Mo has been studied at a beam energy of 149 MeV. A detector array consisting of the OSIRIS spectrometer (12 Compton-suppressed Ge detectors), four charged-particleδE detectors and seven NE-213 neutron detectors at the VICKSI accelerator in Berlin has been used to measure the gamma radiation inγγ- and particle-γγ-coincidence mode. An additional Ge detector was placed at 162? to the beam direction to provide information on DCO ratios. The level scheme of⁹⁰Mo has been extended up to an excitation energy of about 12 MeV and probable spin 23?. Some 70 transitions and 40 levels have been newly identified. Spin assignments have been proposed on the basis of measured DCO ratios. Shell model calculations in a model space consisting of the proton 1f _5/2, 2p _3/2, 2p _1/2, and 1g _9/2 orbits and the neutron 2p _1/2, 1g _9/2, 1g _7/2, 2d _5/2, 2d _3/2, and 3s _1/2 orbits with some truncation were made for states above 9? and the predicted structure of these states is discussed.     

Prototype of a large neutron detector based on MWPC

A prototype of large-area position sensitive neutron detector was designed and constructed according to the requirements of the Small-Angle Scattering spectrometer of China Spallation Neutron Source(CSNS).The detector was based on the 3He neutron convertor and MWPC with an effective area of 650 mm×650 mm.A prototype was completed and tested with 55Fe X-ray.The high-pressure vessel was designed and constructed with high-strength aluminum alloy.A position resolution of about 4.6mm×2.3 mm(FWHM)and efficiency65%for neutrons with wavelength of 1.8?was determined after the operational gas filled.