Development of Prototype Neutron Flux Monitor for ITER

The prototype neutron flux monitor consists of a high purity ^(235)U fission chamber detector and a'blank'detector,which is a fissile material free detector with the same dimension as the fission chamber detector to identify noise issues such as noise coming from gamma rays.The main parameters of the fission chamber assembly that have been measured in the laboratory are confirmed to approach the technological level of the International Thermonuclear Experimental Reactor(ITER)in the near future.This prototype neutron flux monitor will be further developed to become a neutron flux monitor suitable for the operation phase of D-D fusion on the ITER.

Design and construction of the first prototype ionization chamber for CSNS and PA beam loss monitor (BLM) system

Design and construction of the first prototype ionization chamber for CSNS and Proton Accelerator （PA） beam loss monitor （BLM） system is reported. The low leakage current （〈0.1 pA）, good plateau （≈800 V） and linearity range up to 200 Roentgen/h are obtained in the first prototype. All of these give us good experience for further improving the ionization chamber construction.

A measurement system for alpha and beta surface emission rate using MWPC

We have developed a large area multi-wire proportional counter （MWPC） as a standard for the measurement of alpha and beta surface emission rate at the Shanghai Institute of Measurement and Testing Technology （SIMT）. To shorten the preparation time for chamber gas refilling, a self-designed gas control unit was adopted. Various characteristics of the system have been studied. The uncertainties were analysed. Three certified alpha plane sources （Am-241） and six certified beta plane sources （T1-204 and Sr-90/Y-90） were measured by this system, The results show excellent agreement with the surface emission rate reported by the National Institute of Measuring, China （NIM） that En values of all measured sources are within ±1.

A Comparative Analysis of Binary Logistic Regression and Analytical Hierarchy Process for Landslide Susceptibility Assessment in the Dobrovǎt River Basin,Romania

A correct assessment of the landslide susceptibility component is extremely useful for the diminution of associated potential risks to local economic development, particularly in regard to land use planning and soil conservation. The purpose of the present study was to compare the usefulness of two methods, i.e., binary logistic regression(BLR) and analytical hierarchy process(AHP), for the assessment of landslide susceptibility over a 130-km^2 area in the Moldavian Plateau(eastern Romania) region, where landslides affect large areas and render them unsuitable for agriculture. A large scale inventory mapping of all types of landslides(covering 13.7% of the total area) was performed using orthophoto images, topographical maps, and field surveys. A geographic information system database was created, comprising the nine potential factors considered as most relevant for the landsliding process. Five factors(altitude, slope angle, slope aspect, surface lithology, and land use) were further selected for analysis through the application of a tolerance test and the stepwise filtering procedure of BLR. For each predictor, a corresponding raster layer was built and a dense grid of equally spaced points was generated, with an approximately equal number of points inside and outside the landslide area, in order to extract the values of the predictors from raster layers. Approximately half of the total number of points was used for model computation, while the other half was used for validation. Analytical hierarchy process was employed to derive factor weights, with several pair-wise comparison matrices being tested for this purpose. The class weights, on a scale of 0 to 1, were taken as normalized landslide densities. A comparison of results achieved through these two approaches showed that BLR was better suited for mapping landslide susceptibility, with 82.8% of the landslide area falling into the high and very high susceptibility classes. The susceptibility class separation using standard deviation was superior to either the equal interval or the natural break method. Results from the study area suggest that the statistical model achieved by BLR could be successfully extrapolated to the entire area of the Moldavian Plateau.

A boron-lined proportional counter (BLPC) used in a mixed field of reactors

A boron-lined proportional counter （BLPC） with a count rate limit close to the multi-wire proportional counter was manufactured to measure the mixed field around reactors. After measurement with a standard Am-Be neutron source （activity： 100 mCi）, the results show that the operating voltage of the BLPC is 800 V, the plateau length is 100 V and the slope is 13.2%/100 V. The width and rise time of the output pulse of the BLPC are 1.26 μs and 370 ns, respectively. When the BLPC works at a count rate of 1.0 × 10 5 count/s, the pulse pile-up probability of the BLPC is 3.6%. A clear peak can be seen in the pulse height spectrum of the BLPC. and the performances illustrate that a BLPC working in pulse mode can serve as a source range detector of reactors.

Improved design and construction of an ionization chamber for the CSNS beam loss monitor (BLM)

Based on the first ionization chamber （IC） prototype, the structure, working gas component and electrode material of the IC are improved. The test of the improved IC shows that the plateau length is about 2000 V, the plateau slope is less than 0.2%/100 V, the sensitivity is 19.6 pA/rad·h 1, the up-limitation of the linearity can be up to 3.6×105 rad/h, and the applied voltage can be operated to 3500 V. The test results show that the performance of the improved IC meets the requirements of the beam loss monitor.

Development of 3He-filled linear position-sensitive detector for neutron scattering instruments at CSNS

Background Helium-3-filled linear position-sensitive detectors(LPSDs)have been widely applied to neutron scattering instruments in recent decades owing to the high detection efficiency,the excellent neutron/gamma discrimination,and the ability to construct the detector with large area coverage.More than 65%of neutron instruments at the China Spallation Neutron Source(CSNS)require ^(3)He LPSDs for the building of the detector system.The detector of a neutron scattering instrument is normally an array detector composed of a large number of ^(3)He LPSDs.However,no appropriate substitute detector is available for the ^(3)He LPSD for operation over a short period,and its specifications need to be customized to satisfy the requirements of different instruments.This necessitates the development of ^(3)He LPSDs with different specifications for building and upgrading the detectors of neutron scattering instruments at CSNS.Purpose To meet the general requirements specified by the neutron instruments at CSNS,a ^(3)He LPSD was developed and its performances were investigated by using the neutron beam.Methods The neutron beam experiments for this ^(3)He LPSD,including measurements of counting rate plateau curve,position calibration,and position resolution along the tube path,were carried out at the beamline-20 of CSNS.To evaluate its performance in the instrument operation,a detector module made of this ^(3)He LPSD has been installed in the multi-physics instrument(MPI),and the comparison test with the commercial ^(3)He LPSD has been conducted at neutron scattering experiments.Results and conclusion The experimental measurements for this ^(3)He LPSD based on the neutron beam showed that it satisfies the requirements for use in neutron scattering instruments.It reaches a plateau slope of 2.6%/100 V with a plateau range from 1750 to 1950 V and attained a minimal position resolution of 5.3 mm(FWHM),superior to the one achieved by the commercial ^(3)He LPSD.In addition,this ^(3)He LPSD detector module applied to the MPI has been working steadily for half of year and is available for use in experiments.These results provide a sound basis for the subsequent construction and upgradation of the detector of neutron scattering instruments at CSNS.