A method of monitoring gas saturation in carbon dioxide injection heavy oil reservoirs by pulsed neutron logging technology

A method is proposed to characterize the fast neutron scattering cross-section ( s f) quantitatively by the combina-tion of inelastic gamma rays and captured gamma rays, so as to realize the gas saturation evaluation of CO_(2)-injected heavy oilreservoirs based on the three-de tector pulsed neutron logging technology. Factors influencing of the evaluation effect of thismethod are analyzed and the effectiveness of this method is verified by a simulation example. By using the Monte Carlo simu-lation method and the physical model of bulk-volume rock, the relationship between s f and CO_(2) saturation is studied, and thesaturation interpretation model is established. The influences of formation temperature and pressure, heavy oil density, bore-hole fluid and reservoir methane content on the evaluation results of CO_(2) saturation are analyzed. The results show that thecharacterization of s f by the combination of secondary gamma information can eliminate the influence of formation lithology,borehole fluid and methane content are the main factors affecting the quantitative monitoring of CO_(2) saturation, and the ef-fects of formation temperature and pressure and heavy oil density are negligible. The simulation example verified the feasibilityof the method for evaluating the CO_(2) saturation of CO_(2)-injected heavy oil reservoirs.

Measurement and simulation of the leakage neutron spectra from Fe spheres bombarded with 14 MeV neutrons

Iron is commonly used as a structural and shielding material in nuclear devices. The accuracy of its nuclear data is critical for the design of nuclear devices. The evaluation data of ^(56)Fe isotopes in the latest version of the CENDL-3.2 library from China was significantly updated. This new data must be tested before it can be used. To test the reliability of this data and assess the shielding effect, a shielding benchmark experiment was conducted with natural Fe spherical samples using a pulsed deuterium–tritium neutron source at the China Institute of Atomic Energy(CIAE). The leakage neutron spectra from the natural spherical iron samples with different thicknesses(4.5, 7.5, and 12 cm) were measured between 0.8 and 16 MeV after interacting with 14 MeV neutrons using the time-of-flight method. The simulation results were obtained by Monte Carlo simulations by employing the Fe data from the CENDL-3.2, ENDF/B-VIII.0, and JEDNL-5.0 libraries. The measured and simulated leakage neutron spectra and penetration rates were compared, demonstrating that the CENDL-3.2 library performs sufficiently overall. The simulation results of the other two libraries were underestimated for scattering at the continuum energy level.

The Neutron-Gamma Pulse Shape Discrimination Method for Neutron Flux Detection in the ITER

The neutron flux monitor （NFM）, as a significant diagnostic system in the International Thermonuclear Experimental Reactor （ITER）, will play an important role in the readings of a series of key parameters in the fusion reaction process. As the core of the main electronic system of the NFM, the neutron-gamma pulse shape discrimination （n-γ PSD） can distinguish the neutron pulse from the gamma pulse and other disturbing pulses according to the thresholds of the rising time and the amplitude pre-installed on the board, the double timing point CFD method is used to get the rising time of the pulse. The n-γ PSD can provide an accurate neutron count.

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.

Application of a BC501A Liquid Scintillation Detector with a Gain Stabilization System on the EAST Tokamak

A 2＂×2＂BC501A liquid scintillation detector with a gain stabilization system is developed and applied to neutron andγ-ray measurement on the EAST tokamak.Energy calibration of a liquid scintillator using a fast coincidence method is presented and compared with the Monte Carlo simulation.Determination of the proton light output function of the BC501A is presented.Results from dedicated experiments with an Am-Be neutron source,γsource and quasi-monoenergetic neutron beams,and from measurements on EAST tokamak are presented and discussed.

China Spallation Neutron Source-an overview of application prospects

The China Spallation Neutron Source （CSNS） is an accelerator-based multidisciplinary user facility to be constructed in Dongguan, Guangdong, China. The CSNS complex consists of an H- linear accelerator, a rapid cycling synchrotron accelerating the beam to 1.6 GeV, a solid-tungsten target station, and instruments for spallation neutron applications. The facility operates at 25 Hz repetition rate with an initial design beam power of 120 kW and is upgradeable to 500 kW. Construction of the CSNS project will lay the foundation of a leading national research center based on advanced proton-accelerator technology, pulsed neutron-scattering technology, and related programs including muon, fast neutron, and proton applications as well as medical therapy and accelerator-driven subcritical reactor （ADS） applications to serve China＇s strategic needs in scientific research and technological innovation for the next 30 plus years.

Proposal for muon and white neutron sources at CSNS

The China Spallation Neutron Source （CSNS） is a large scientific facility with the main purpose of serving multidisciplinary research on material characterization using neutron scattering techniques. The accelerator system is to provide a proton beam of 120 kW with a repetition rate of 25 Hz initially （CSNSⅠ）, progressively upgradeable to 240 kW （CSNS-Ⅱ） and 500 kW （CSNS-Ⅱ＇）. In addition to serving as a driving source for the spallation target, the proton beam can be exploited for serving additional functions both in fundamental and applied research. The expanded scientific application based on pulsed muons and fast neutrons is especially attractive in the overall consideration of CSNS upgrade options. A second target station that houses a muon-generating target and a fast-neutron-generating target in tandem, intercepting and removing a small part of the proton beam for the spallation target, is proposed. The muon and white neutron sources are operated principally in parasitic mode, leaving the main part of the beam directed to the spallation target. However, it is also possible to deliver the proton beam to the second target station in a dedicated mode for some special applications. Within the dual target configuration, the thin muon target placed upstream of the fast-neutron target will consume only about 5% of the beam traversed; the majority of the beam is used for fast-neutron production. A proton beam with a beam power of about 60 kW, an energy of 1.6 GeV and a repetition rate of 12.5 Hz will make the muon source and the white neutron source very attractive to multidisciplinary researchers.