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Accurate cross section of the 232Th(n, f) reaction are demanded in the design of advanced nuclear systems and in the development of fission theory. However, the existing measurement data are relatively sparse comparing with those of the 238U(n, f) reaction, with big uncertainties and obvious discrepancies. Furthermore, analysis shows that systematic deviations exist between the results measured with mono-energetic neutron sources and white neutron sources, which is the main reason for the differences among different evaluation libraries. This work is dedicated to the clarification of this discrepancy. Based on mono-energetic d-d neutron sources and using back-to-back Th/238U samples, cross section of the 232Th(n, f) reaction were measured at 12 energies in the 4.2–11.5 MeV region. Elaborated measures were taken in the measurement procedure including the exchange of the forward and the backward direction of the samples, as well as in the data processing containing the correction of interference fission counts from low-energy neutrons and the detailed Monte Carlo simulations for the determination of detection efficiencies for fission events. In addition, theoretical analysis was also performed using TALYS-1.9 and UNF codes. The present results agree with existing measurement data using white neutron sources, showing that previous cross section of the 232Th(n, f) reaction measured using mono-energetic neutron sources are systematically overestimated on average. The present results are in accordance with the latest measurement data of Michalopoulou et al., which is helpful in the improvement of nuclear data evaluations of the 232Th(n, f) reaction. [ABSTRACT FROM AUTHOR]

The measurement of the relative differential cross sections of the neutron-deuteron ( n - d) elastic scattering, i.e., the 2 H(n, el) 2 H reaction, for 12 neutron energies from 13.56 MeV to 52.48 MeV has been carried out at the Back-n White Neutron Source of the China Spallation Neutron Source (CSNS). By detection of the recoil deuterons using the light charged particle detector array (LPDA) system, the relative differential cross sections of the neutrons in the center-of-mass frame were obtained and then compared with previous measurements, the theoretical calculations performed using the Nijmegen I nucleon-nucleon potential in the Faddeev formalism, and the evaluated from libraries including the ENDF-B/VIII.0, JEFF-3.3, JENDL-4.0, CENDL-3.2, and FENDL-3.2. The present work was the first measurement relative differential cross sections of the n-d scattering for the 30 MeV < E n ≤ 60 MeV neutron energy range using a white neutron source. [ABSTRACT FROM AUTHOR]

Abstract: Using two 238U samples placed in a gridded ionization chamber and a parallel-plate fission chamber, fluence of monoenergetic fast neutrons was determined. Four runs of measurements were performed. Analysis showed that although the neutron fluences for the two 238U samples differ by 20–33 times in the present work, the fluences at the position of the sample in the gridded ionization chamber determined by the two ways are in agreement within experimental uncertainties. [Copyright &y& Elsevier]

The Multi-purpose Time Projection Chamber (MTPC) is a gas-filled detector designed to measure cross sections of neutron-induced light-charged particle emission and fission reactions at the Back-streaming white neutron facility (Back-n) at the China Spallation Neutron Source. A prototype MTPC has been constructed with a drift volume, a resistive Micromegas charge amplification structure, and a high-density pixelated anode readout plane with 1519 hexagonal pads. Test measurements have been performed using a four-component alpha source. Alpha-particle track reconstruction is performed to obtain the deposited energy and length information of the trajectory. The performance test and characterization of the detector have served as the basis for the optimized design of the MTPC, which is currently undergoing commissioning at Back-n. [ABSTRACT FROM AUTHOR]

Accurate cross sections of neutron induced fission reactions are needed in the development of nuclear science and technology. The time projection chamber (TPC) is viewed as the potential detector to improve the measurement accuracy of the fission cross sections based on its track reconstruction and particle identification capabilities. The TPC developed by the back-streaming white neutron source (Back-n) team of China Spallation Neutron Source (CSNS) was introduced to verify its ability in measuring the cross section of fission reaction. Using our TPC, and based on the mono-energetic neutron source at Peking University and 232Th/238U samples, we have measured the cross section of the 232Th(n , f) reaction at 5.0 MeV. The fission events have been well distinguished from the background alpha events. The present cross section is consistent with the evaluation data from different libraries, which indicates that the fission cross section measurement using our TPC is feasible. By reducing the distance between the two fission samples, the large uncertainty of the present result will be reduced in future experiments. [ABSTRACT FROM AUTHOR]

As the light output function of the EJ309 liquid scintillator is nonlinear with respect to the energy of the recoil proton and it is difficult to be predicted, it need to be measured. In the present work, an EJ309 liquid scintillator, 5.1 cm in diameter and 5.1 cm in length, is calibrated with an AmBe neutron source using the time-of-flight method. A Monte Carlo simulation is performed to improve the accuracy of the measured light output function. The obtained light output function is presented and it is compared with existing measurements. The energy resolution of the EJ309 Liquid scintillator is also illustrated. [ABSTRACT FROM AUTHOR]

A Multi-purpose Time Projection Chamber prototype based on a resistive Micromegas technique has been proposed, designed and fabricated at China Spallation Neutron Source to measure the cross sections of neutron-induced light-charged particle emission reactions and fission reactions at the Back-n white neutron source. For the requirements of working stability with high voltage and high granularity of readout, the prototype is fabricated by applying a resistive Micromegas with high-density pixelated anode plane. In order to fully understand the process of charge spreading and signal induction on the anode plane covered by a resistive layer, a simulation method is developed and the energy correction function is then obtained, which can be used in the further energy correction in the experimental data analysis. Measured with a 55Fe X-ray source, the uniformity of gain and avalanche gap are specially analyzed by combining the simulated gas avalanche parameters with fitting of experimental data in which the parallel plate avalanche model is adopted. [ABSTRACT FROM AUTHOR]

Abstract: A practical method for experimentally determining the fraction of neutrons below 1.5MeV for the Am–Be neutron source is described. The partial neutron spectrum (the n1 group) was measured by time-of-flight accompanied with the 4.438-MeV gamma ray. The fraction of neutrons below 1.5MeV was derived from the 4.438-MeV gamma ray to total neutron ratio and the ratio of the area of the n1 group spectrum to the measured total spectrum above 1.5MeV normalized at the peak near 3.2MeV. The fraction of neutrons with energies below 1.5MeV amounts to (19.1±1.9)% for the Chinese-made Am–Be neutron source. [Copyright &y& Elsevier]

Abstract: An accurate measurement of the 4.438MeV -ray to total neutron ratio, namely , for a Chinese-made Am–Be neutron source is described. The neutron strength of the source relative to a previously standardized source was determined by the manganese bath technique. The -rays spectra of the source were measured using a mm NaI(Tl) detector. The background induced by neutrons and the absolute full energy peak efficiency of the detector were calculated using the MCNP code. The experimental ratio so obtained agrees well with the calculated value. A synthetic evaluated and recommended value of was given. We conclude that the experimental R-value appears an important characteristic for an Am–Be source. [Copyright &y& Elsevier]

The Back-n is a high luminosity white neutron beamline at the China Spallation Neutron Source (CSNS). It started running in 2018 for various nuclear data measurements. A Light charged Particle Detector Array (LPDA) is designed for (n , lcp) reaction experiments, which includes a group of detectors and supporting systems. The Δ E - E telescope, consisting of a Low-Pressure Multi-Wire Proportional Chamber (LPMWPC) and a Si-PIN detector, is the core detector of the LPDA. From the beginning of 2018, several measurements have been performed using the Δ E-E telescopes, and the light charged particles such as 1H, 3H, 4He, and 7Li, were identified successfully. At present, the LPMWPC can identify the protons with energy as low as 0.5 MeV. In the near future, combining with CsI(Tl) crystals, a system consisting of sixteen telescopes with an energy acceptance from 0.5 MeV to 100 MeV (proton) will be constructed for general purpose of (n , lcp) measurements. [ABSTRACT FROM AUTHOR]

The Back-n white neutron source at the China Spallation Neutron Source (CSNS) was put into operation in 2018, providing a good platform for the cross-section measurement of neutron induced light charged particle (l c p) emission (n , l c p) reactions. Currently, in order to detect and identify light charged particles produced in (n , l c p) reactions at Back-n, a silicon detector array has been developed as a part of Light-charged Particle Detector Array. Composed of 15 silicon detectors, the array can detect the emitted particles ranging from 19.2°to 160.8°. The energy resolution of each silicon detector unit is better than 1% for 5.499 MeV α particles. Adopting this silicon detector array, several experimental measurements have been completed. Differential cross sections and angle-integrated cross sections in the neutron energy region ranging from the eV to the MeV range are extracted. Compared with previous measurements and evaluations, new results are obtained in the present measurements. These experiments indicate the feasibility of the silicon detector array in (n , l c p) reaction cross-section measurements. [ABSTRACT FROM AUTHOR]

A white neutron source for nuclear data measurement has been built and put into operation on China Spallation Neutron Source (CSNS). We developeda beam monitor for real-time online monitoring of neutron flux on the white neutron source. The beam monitor work simultaneously with other nuclear data measurement detectors to provide neutron flux for data analysis. To minimize beam disturbance and reduce the background generated by the monitor, a structure in which neutron conversion layer and Si detectors are separated is employed: A 6LiF film with a mass thickness of 360 μ g/cm 2 was deposited on a 10 μ m aluminum foil and placed inside the beam line. Eight Si-detectors with a size of 20 × 20 mm2 were placed around the film outside the beam to maximize the reception of secondary particles from the conversion layer and to avoid neutron beam irradiation. The simulation of the beam monitor (layout, counting rate, neutron disturbance, etc.), construction and online performance are described in the paper. Good online performance of the monitor was achieved during the CSNS white neutron source flux calibration experiment in March, 2018: The counting rate for the beam line operating at Ф30 mm and Ф60 mm beam pattern modes was normalized to 100 kW proton beam power, and the result is consistent with the simulation. The total uncertainty of the normalized counting rate is less than 1%. Moreover, the measurement of neutron flux in low energy region below 10 keV of the white neutron source by the monitor is discussed. [ABSTRACT FROM AUTHOR]