Polycrystalline chemical-vapor-deposited diamond for fast and ultra-fast neutron detection

An intrinsic sensor （diameter 16 ram, thickness 300 μm ） based on chemical vapor deposition derived polycrystailine diamond was developed. Ultra low dark current under 100 pA and high n/γ discrimination of 15.8 were obtained on this device, which enable it to be used for neutron detection in multi-radiation field. Moreover, the neutron sensitivity of this detector was characterized theoretically and experimentally. And for fast and ultra-fast neutron, the detection sensitivity is in the magnitude of 10^-17 to 10^-16 C cm^2/n with good stability and negligible pump effect. All these results indicate that the as-prepared sensor to be ideal for fast and ultra-fast neutron monitoring, and it may pave the way to build neutron detector with low cost and large sensitive area with diamond.

A high-precision multi-channel TAC and QAC module for the neutron detection wall

A single width NIM module that includes eight channels of the time-to-amplitude converter （TAC） and the charge-to-amplitude converter （QAC） is introduced in the paper, which is designed for the large neutron wall detector to measure charge （energy） and time interval simultaneously. The module adopts a high precision gated integration circuit to realize TAC and QAC. ：The input range of TAC is from 30 ns to 1 μs, and the input range of QAC is from 40 pC to 600 pC. The linearity error of TAC is lower than 1.28%, and the time resolution of TAC is less than 0.871%. The linearity error of QAC is lower than 0.81%, and the resolution of QAC is better than 0.936%.

Study of Neutron Cross Talk Rejection Based on Testing Experiment and Simulation

Experimental data analysis and simulation calculations were performed in order to evaluate the cross-talk rejection performance of a typical neutron detection array. For very closely packed scintillation bars, the CT rejection may rely on the position relation between the two signals. The criteria ｜△x｜≤ 15 cm and ｜△y｜≤12 cm are currently proposed for a rejection rate higher than 90%. For signals coming from distanced bars, the energy conservation relationship can be applied to reject the CT events with a similar performance. In both cases the results of simulation agree very well with the experimental data, assuring their applicability to other detection systems and physics problems.

Study on the novel neutron-to-proton convertor for improving the detection efficiency of a triple GEM based fast neutron detector

A high-efficiency fast neutron detector prototype based on a triple Gas Electron Multiplier（GEM） detector, which, coupled with a novel multi-layered high-density polyethylene（HDPE） as a neutron-to-proton converter for improving the neutron detection efficiency, is introduced and tested with the Am-Be neutron source in the Institute of Modern Physics（IMP） at Lanzhou in the present work. First, the developed triple GEM detector is tested by measuring its effective gain and energy resolution with55 Fe X-ray source to ensure that it has a good performance.The effective gain and obtained energy resolution is 5.0×104and around 19.2%, respectively. Secondly, the novel multi-layered HDPE converter is coupled with the cathode of the triple GEM detector making it a high-efficiency fast neutron detector. Its effective neutron response is four times higher than that of the traditional single-layered conversion technique when the converter layer number is 38.

Study on spatial resolution of micromegas as a neutron detector under condition of high neutron flux and γ ray background

In this paper Micromegas has been designed to detect neutrons. The simulation of the spatial resolution of Micromegas as neutron detector is carried out by GEANT4 toolkit. The neutron track reconstruction method based on the time coincidence technology is employed in the present work. The influence of the flux of incident 14 MeV neutron and high gamma background on the spatial resolution is carefully studied. Our results show that the spatial resolution of the detector is sensitive to the neutron flux, but insensitive to the intensity of γ background if the neutron track reconstruction method proposed by our group is used. The γ insensitivity makes it possible for us to use the Micromegas detector under condition which has high γ-rays background.

Design of readout electronics based on peak-holding circuit and multiplexer for a fast neutron spectrometer

Background Fast neutron detection is meaningful in many research fields such as space environment monitoring.A scintillating fiber array model for fast neutron detection was proposed and developed in 1980s.Aerospace applications of the model require electronics in small size.Purpose To design a dedicated electronic system to readout and process the 384-channel signals from scintillating fiber array,and to use the designed system to fabricate a neutron detector for aerospace applications.Methods With the method of nuclear recoil,fast neutron is detected by tracking recoil proton of n–p scatter in scintillating plastic fibers.Using the peak-holding circuits and multiplexers,the system size and power consumption were reduced.Results The detector fabricated with the designed system,had 34 cm×34 cm×27 cm mechanical size,20.4 kg weight,and 30.05W power consumption.Comparing to traditional waveform sampling electronics,the designed electronics was highly integrated and had a small size.The readout electronics also gave a better energy resolution of 39%in neutron detection,while the energy resolution was 43%in previous version.Conclusion In this study,a highly integrated readout electronic system was designed and verified.The detector using the system gave good performance.The designed electronics had potential development in fast neutron detection and other high energy physics detection system.

New organic scintillation fiber detector for the measurement of intense pulsed fission neutron

To measure the pulsed neutron of a pulsed fission source, an organic scintillation fiber （OSF） detector with separation structure has been designed. The proposed detector employs UV optical fibers as the light guide, and the sensitive region of the detector is composed of a linear array of OSFs, which are individually connected to the optical fibers. The other end of the light guide is coupled to a photomultiplier tube. The key properties of the device including the energy response, time response, neutron sensitivity, and radiation effect of the optical fiber were studied. The detector has a relatively high n/γ sensitivity ratio, which increases as the diameter of the OSF decreases, and ratios greater than 10 could be achieved when the diameter of the OSF is less than 0.3 nun. The sensitivity of the detector to neutrons ranges from 10-14 to 10-20 C cm2/n, and has a response time of 3 ns （FWHM）. The proposed detector is also highly flexible. For instance, the probe can be set close to the source, while the PMT can be placed far away from radiation, allowing easy shielding. Due to these characteristics, pulsed fission neutrons in the vicinity of the source can be accurately measured.

Study of a nTHGEM-based thermal neutron detector

With new generation neutron sources, traditional neutron detectors cannot satisfy the demands of the applications, especially under high flux. Furthermore, facing the global crisis in 3He gas supply, research on new types of neutron detector as an alternative to 3He is a research hotspot in the field of particle detection. GEM （Gaseous Electron Multiplier） neutron detectors have high counting rate, good spatial and time resolution, and could be one future direction of the development of neutron detectors. In this paper, the physical process of neutron detection is simulated with Geant4 code, studying the relations between thermal conversion efficiency, boron thickness and number of boron layers. Due to the special characteristics of neutron detection, we have developed a novel type of special ceramic nTHGEM （neutron THick GEM） for neutron detection. The performance of the nTHGEM working in different Ar/CO2 mixtures is presented, including measurements of the gain and the count rate plateau using a copper target X-ray source. A detector with a single nTHGEM has been tested for 2-D imaging using a 252Cf neutron source. The key parameters of the performance of the nTHGEM detector have been obtained, providing necessary experimental data as a reference for further research on this detector.

Study of a position-sensitive scintillator neutron detector

The investigation of a novel thermal neutron detector is developed to fulfill the requirements of the high intensity power diffractometer （HIPD） at the Chinese Spallation Neutron Source （CSNS）. It consists of two layers of 6LiF/ZnS（Ag） scintillators, two layers of crossed WLSF arrays, several multi-anode photo multiplier tubes （MA-PMT）, and the matching readout electronics. The neutron detection efficiency of the scintilltors, the light transportation ability of the WLSF, and the spatial linearity of the readout electronics are measured and discussed in this paper. It shows that the sandwich structure and the compact readout electronics could fulfill the needs of the HIPD. A prototype with a 10 cm×10 cm sensitive area has been constructed to further study the characteristics of the neutron scintillator detector.

Development of novel rare earth doped fluoride and oxide scintillators for two-dimensional imaging

Two topics were focused. The first one was about the gamma-ray scintillator, Pr^3＋：Lu3Al5O12 （LuAG）. The second one was about neutron scintillator, Ce^3＋：^6LiCaAlF6 and Eu^2＋：^6LiCaAlF6 （^6LiCAF）. Those scintillators have been developed very recently for modem imaging applications in the medical and homeland security fields. In both cases, the rare earth ions are playing the crucial role as emission centers. Pr^3＋ in LuAG provided fast 5d→4f transition providing noticeably shorter decay time than that of Ce^3＋. Among several candidate hosts, LuAG showed the best performance. Bulk crystal growth, basic scintillation properties, two-dimensional gamma-ray imaging and positron emission mammography （PEM） application were demonstrated. Due to the international situation, the homeland security was compromized by illicit traffic of explosives, drugs, nuclear materials, etc. and the ways to its improvement became an important R＆D topic. For this purpose the Ce and Eu doped LiCAF appeared competitive candidates. Especially, when substitution of 3He neutron detectors was considered, the discrimination ability of gamma-ray from alpha-ray was important. Bulk crystal growth, basic scintillation properties and two-dimensional neutron imaging were demonstrated.

Experimental study on scintillation efficiency of ZnO:In to proton response

Film ZnO：In crystal is a good candidate for a scintillation recoil proton neutron detection system and the response of ZnO：In to protons is a crucial point. The energy response of ZnO：In to mono-energetic protons in the range of 10 keV–8 MeV was measured. The experiment was carried out in current mode, and Au foil scattering was employed, where the forward scattering protons were used for exciting the sample, and the backward scattering protons were used for monitoring the beam intensity. According to the result, the yield of light non-linearly depends on proton energy, and drops significantly when proton energy is low. The scintillation efficiency as a function of proton energy was obtained, which is very useful for researching the scintillation recoil proton neutron detection system.