MeV Neutron Energy Region Research Articles

Cross section measurement for the 14N(n,α0,1)11B reactions in the 4.5–11.5 MeV neutron energy region

Cross section measurement for the 14N(n,α0,1)11B reactions in the 4.5–11.5 MeV neutron energy region

Research on the application of pulse shape discrimination method in (n, lcp) reaction cross-section measurements

The China Spallation Neutron Source Back-n white neutron source supplies neutrons with a wide energy range for nuclear data measurements and nuclear techniques. In cross-section measurements of neutron induced light charged-particle emission (n, lcp) reactions at Back-n, the identification of charged particles are usually achieved with the ΔE-E method or a two-dimensional spectrum of the signal amplitude of the particles deposited in the detector and the corresponding neutron energies derived from the time of flight, called amplitude-En method. Nevertheless, a deficiency still exists in the measurement range and the identification performance with these methods. The pulse shape discrimination (PSD) method with a silicon detector is supposed to be a supplement to the amplitude-En and ΔE-E methods. With silicon detectors, experiments have been performed to compare the performance of the amplitude-En and the PSD methods. The PSD method shows a good performance in identifying light charged particles in the MeV neutron energy region. Alphas and tritons emitted from 6Li(n, t) reaction can be identified with the low energy threshold around 2.5 MeV. This provides an effective method for the cross-section measurement of (n, lcp) reactions at Back-n.

63Cu(n, α)60Co cross sections in the MeV region

Cross sections of the 63Cu(n, α)60Co reaction in the MeV neutron energy region were measured using both the direct measurement method and the activation method. A twin-gridded ionization chamber was used for the direct measurement while the high-purity germanium detector was used for the activation method. The measured cross sections using the two methods are consistent within measurement uncertainties. The present results support the evaluation data in the ENDF/B-VII.1 library instead of the latest evaluation data in the ENDF/B-VIII.0 library, which is helpful to clarify discrepancies in measurement and evaluation data. TALYS-1.9 code analysis was performed which shows that the measurement cross sections can be well reproduced with minor adjustments of the input parameters. Through the calculation, it is found that the compound mechanism predominates the 63Cu(n, α)60Co reaction with ratios higher than 0.7 for neutron energy less than 20 MeV.

Cross section of the 232Th(n, f) reaction in the MeV neutron energy region

Cross section of the 232Th(n, f) reaction in the MeV neutron energy region

Cross sections for the Cl35(n,α)P32 reaction in the 3.3–5.3 MeV neutron energy region

Cross sections for the $^{35}\mathrm{Cl}(n,\ensuremath{\alpha})\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{P}$ reaction were systematically measured at incident neutron energies in the range of 3.3 to 5.3 MeV. The experiment was carried out on the Van de Graaff accelerator EG-5 at the Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Russia. Fast neutrons were produced in the reaction $^{2}\mathrm{H}(d,n){\phantom{\rule{0.16em}{0ex}}}^{3}\text{He}$. Alpha particles from the ($n,\ensuremath{\alpha}$) reactions were detected using a gridded ionization chamber (GIC) in which various $^{35}\mathrm{Cl}$ samples (NaCl and ${\text{BaCl}}_{2}$, on a tantalum backing) were placed back to back. The relative and absolute neutron fluxes were measured by two samples of $^{238}\mathrm{U}_{3}\mathrm{O}_{8}$ ($99.999%$) inside the GIC. Data obtained in this measurement were compared with other experimental data of the existing library and theoretical calculations by the talys code. Presented data for the $^{35}\mathrm{Cl}(n,\ensuremath{\alpha})\phantom{\rule{0.16em}{0ex}}^{32}\mathrm{P}$ reaction should help to clarify discrepancies in the various published nuclear data.

Cross-section measurements for 58,60,61Ni(n, α)55,57,58Fe reactions in the 4.50 – 5.50 MeV neutron energy region * * Supported by the National Natural Science Foundation of China (11775006) and China Nuclear Data Center and the Science and Technology on Nuclear Data Laboratory

The cross sections at 5 energy points of the 58Ni(n, α)55Fe reaction were measured in the 4.50 MeV ≤ En ≤ 5.50 MeV region while those for the 60Ni(n, α)57Fe and 61Ni(n, α)58Fe reactions were measured at En = 5.00 and 5.50 MeV using the 4.5 MV Van de Graaff accelerator at Peking University. A gridded twin ionization chamber (GIC) was used as the detector, and enriched 58Ni, 60Ni, and 61Ni foil samples were prepared and mounted at the sample changer of the GIC. Three highly enriched 238U3O8 samples inside the GIC were used to determine the relative and absolute neutron fluxes. The neutron energy spectra were obtained through unfolding the pulse height spectra measured by the EJ-309 liquid scintillator. The interference from the low-energy neutrons and impurities in the samples has been corrected. The present data of the 60Ni(n, α)57Fe reaction are the first measurement results below 6.0 MeV, and those of the 61Ni(n, α)58Fe reactions are the first measurement results in the MeV region. The present results have been compared with existing measurements, evaluations, and TALYS-1.9 calculations.

Measurement of the U-238/U-235 fission cross section ratio at CSNS – Back-n WNS

Based on the China Spallation Neutron Source (CSNS) – Back-streaming white neutron source (Back-n WNS), the measurement of the U-238/U-235 fission cross section ratio in 1–20 MeV neutron energy region has been carried out by a multi-cell fast fission ionization chamber using the time-of-flight method. The measured resonance peaks of the 235U(n, f) reaction are in good agreement with those of the ENDF/B-8.0 database. The measured six groups of the U-238/U-235 fission cross section ratios in 1–20 MeV neutron energy region agree with those of the ENDF/B-8.0 database in trend, and the average discrepancies between experiment and database are from 1.9% to 2.6%. The relative experimental uncertainties are 2.3%–3.6% (1.4–20 MeV), and the measured data agree with those of database within experimental uncertainties at most energy points. The measured U-238/U-235 fission cross section ratio could provide information and data support in relevant nuclear data evaluation.

Measurements of neutron-induced light-charged particle emission reactions

In the past two decades cooperating with Frank Laboratory of Neutron Physics (FLNP), Joint Institute for Nuclear Research (JINR) measurements of (n, α) reaction cross sections for 6Li, 10B, 25Mg, 39K, 40Ca, 54,56,57 Fe, 58Ni, 63Cu, 64,67 Zn, 95Mo, 143Nd and 147,149 Sm nuclei were performed in the MeV neutron energy region based on the 4.5 MV Van de Graaff accelerator at Peking University. In recent years, our measurements were extended in three aspects. Firstly, measurements were expanded from two-body reactions to three-body reactions such as 10B (n, t2 α). Secondly, the neutron energy region was extended from below 8 MeV to 8 - 11 MeV by using the HI-13 tandem accelerator of China Institute of Atomic Energy (CIAE), with which cross sections of 54,56 Fe(n, α)53,51Cr reactions were measured. Thirdly, based on the newly-built China Spallation Neutron Source (CSNS) Back-n WNS (White Neutron Source), differential and angle-integrated cross sections for 6Li(n, t) and 10B(n, α) reactions were measured in the neutron energy region from 1 eV to 3 MeV.

Measurements of differential and angle-integrated cross sections for the 10B(n, α)7Li reaction in the neutron energy range from 1.0 eV to 2.5 MeV * * Supported by financially the National Key R&D Program of China (2016YFA0401604) and the National Natural Science Foundation of China (11775006)

Differential and angle-integrated cross sections for the 10B(n, α)7Li, 10B(n, α0) 7Li and 10B(n, α1) 7Li* reactions have been measured at CSNS Back-n white neutron source. Two enriched (90%) 10B samples 5.0 cm in diameter and ~85.0 μg/cm2 in thickness each with an aluminum backing were prepared, and back-to-back mounted at the sample holder. The charged particles were detected using the silicon-detector array of the Light-charged Particle Detector Array (LPDA) system. The neutron energy En was determined by TOF (time-of-flight) method, and the valid α events were extracted from the En-Amplitude two-dimensional spectrum. With 15 silicon detectors, the differential cross sections of α-particles were measured from 19.2° to 160.8°. Fitted with the Legendre polynomial series, the (n, α) cross sections were obtained through integration. The absolute cross sections were normalized using the standard cross sections of the 10B(n, α)7Li reaction in the 0.3 – 0.5 MeV neutron energy region. The measurement neutron energy range for the 10B(n, α)7Li reaction is 1.0 eV≤En < 2.5 MeV (67 energy points), and that for the 10B(n, α0) 7Li and 10B(n, α1) 7Li* reactions is 1.0 eV ≤ En < 1.0 MeV (59 energy points). The present results have been analyzed by the resonance reaction mechanism and the level structure of the 11B compound system, and compared with existing measurements and evaluations.

Investigation of (n,??) Reaction for Rare-earth Elements in the MeV Neutron Energy Region

Cross sections and forward/backward ratios in the laboratory reference system were measured for {sup 143}Nd(n, {alpha}){sup 140}Ce at 4.0, 5.0, and 6.0 MeV, {sup 147}Sm(n, {alpha}){sup 144}Nd at 5.0 and 6.0 MeV, and {sup 149}Sm(n, {alpha}){sup 146}Nd at 6.0 MeV. A twin gridded ionization chamber and large-area back-to-back {sup 143}Nd{sub 2}O{sub 3} and {sup 147,149}Sm{sub 2}O{sub 3} samples were employed. Experiments were performed at the 4.5 MV Van de Graaff of Peking University, China. Fast neutrons were produced through the D(d, n){sup 3}He reaction by using a deuterium gas target. A small {sup 238}U fission chamber was employed for absolute neutron flux determination and a BF{sub 3} long counter was used as neutron flux monitor. Present experimental data are compared with previous measurements, evaluations, and model calculations.

64Zn and 67Zn (n,��) Reactions in the MeV Neutron Energy Region

64Zn and 67Zn (n,��) Reactions in the MeV Neutron Energy Region

Measurement of 10B content in thin-film 10B samples

Two thin-film (10)B samples on tantalum backings were made for measurement of cross sections of the (10)B(n,α)(7)Li reaction in the MeV neutron energy region. The number of (10)B atoms in the samples was determined using the relative comparison method by detecting alpha and triton particles from thermal neutron induced nuclear reactions of (10)B(n(th),α)(7)Li and (6)Li(n(th),t)(4)He with a (6)LiF sample as the reference. A twin gridded ionization chamber was used as the detector of charged particles.

Cross-section measurement for the 67Zn(n, $ \alpha$ )64Ni reaction at 6.0 MeV

Up to now, no experimental cross-section data exist for the 67Zn (n, $ \alpha$ ) 64Ni reaction in the MeV neutron energy region. In the present work, the cross-section of the 67Zn (n, $ \alpha$ ) 64Ni reaction was measured at E n = 6.0 MeV. Experiments were performed at the Van de Graaff accelerator of Peking University, China. Fast neutrons were produced through the D (d, n) 3He reaction using a deuterium gas target. Absolute neutron flux was determined by a small 238U fission chamber and a BF3 long counter was used as a neutron flux monitor. A twin gridded ionization chamber was employed as the $ \alpha$ -particle detector and two back-to-back 67Zn samples were used for $ \alpha$ events measurement. Background was measured and subtracted from foreground. The measured cross-section of the 67Zn (n, $ \alpha$ ) 64Ni reaction was 7.3 (1±15%) mb at 6.0MeV. The present result was compared with existing evaluations and TALYS code calculations.

Measurement of differential and angle-integrated cross sections of the 6Li( n,t) 4He reaction in the MeV neutron energy range

The cross-section of the 6Li( n,t) 4He reaction has been adopted as a standard neutron cross-section from thermal energy to 100 keV. In the MeV neutron energy region, however, there are large discrepancies among the existing data including experimental and evaluated ones. For example, at 1.0 MeV, the cross section of the 6Li( n,t) 4He reaction in JENDL-3 is 18% larger than that in ENDF/B-VI, and at 1.7 MeV the cross section in CENDL-2 is more than 20% larger than that in ENDF/B-VI. Therefore, new measurements are needed. This paper reports the method and the result of the measurement of the differential and angle-integrated cross-sections of the 6Li( n,t) 4He reaction in the MeV neutron energy range. Differential cross-sections were measured by detecting the forward tritons and forward α particles separately. Cross-sections were derived from differential cross-sections in the center of mass reference system. The detection system was a charged-particle spectrometer based on a gridded ionization chamber (GIC). Experiments were performed at the 4.5 MV van de Graaff accelerator of Peking University, China. Nearly mono-energetic neutrons were produced through the T( p,n) 3He reaction and the D( d,n) 3He reaction. The absolute neutron flux was determined by a 238U foil and a calibrated BF 3 long counter. Our results are compared with other author's data.

Differential cross section and polarization for 2.63 MeV neutrons scattered from 12C

The differential cross section and polarization of 2.63 MeV neutrons scattered from 12C have been measured at eight angles between 17° and 118° in the laboratory system. By simultaneously fitting the cross section and polarization data, a set of scattering phase shifts was obtained. The values of the resulting d-wave phase shifts were larger than those of other existing sets of phase shifts in the energy region. A subsequent R-function analysis, reflecting these larger d-wave phase shifts, gave excellent fits to other experimental data below 3 MeV neutron energy region. The influence of narrow states at 7.50 and 7.55 MeV excitation energy in 13C is discussed.