Cross-section measurement for the ~(93)Nb(n,2n)~(92g)Nb reaction at the neutron energy of 14.6 MeV by the AMS method

The cross-section for the~(93)Nb(n,2n)~(92g)Nb reaction has been measured at the neutron energy of 14.6 Me V using neutron activation and accelerator mass spectrometry(AMS)determination of the long-lived product nuclide~(92g)Nb.The neutron energy was generated from the D+T neutron source at the China Institute of Atomic Energy(CIAE).The neutron flux was monitored by measuring the activity of~(92m)Nb produced in the competing reaction channel of~(93)Nb(n,2n)~(92m)Nb.At the neutron energy of 14.6 MeV,the~(93)Nb(n,2n)~(92g)Nb reaction cross-section of(736±220)mb was obtained for the first time.     

Monte Carlo simulations of the production of neutrons at iThemba LABS

FLUKA Monte Carlo radiation transport code has been used to simulate neutron fluence spectrum at iThemba LABS neutron beam facility. Neutron beams with energy up to 200 MeV can be produced using different targets such as ⁷Li, ⁹Be and ¹²C bombarded with monoenergetic protons from the Separated-Sector Cyclotron. Simulated results at 66 MeV were compared with measured data. Different neutron emission angles with respect to the beam axis as well as the neutron background at different positions have been investigated.     

A new simulated neutron workplace field at PIAF

The range of neutron energies encountered at workplaces extends from 10^?2 eV to 10⁷ eV or even higher neutron energies. The monoenergetic neutron calibration fields cover the neutron energy range from 10⁴ eV to 10⁷ eV. Hence calibrations in so-called realistic fields with a broad spectral distribution similar to those at workplaces are still essential for radiation protection equipment.This is the reason why PTB has developed a simulated workplace field. The field is produced using a proton beam on a thick Li or Be target installed in a moderating sphere which produces the intermediate and thermal part of the spectrum. Different target materials and compositions and different constructions of the target were investigated with special focus on the long-term stability of the neutron yield, as well as the stability of the spectral neutron fluence of the primary neutron spectrum. The spectral distribution outside the moderator sphere was measured using the PTB Bonner sphere spectrometer NEMUS and calculated using MCNPX.     

Comparison of nuclear reactions for the production of monoenergetic neutron fields with energies below 100 keV

NPL, PTB, IRMM and IRSN are involved, within a scientific cooperation, in a comprehensive study aimed at developing reference low-energy monoenergetic neutron fields. This paper will explain the importance of such developments, highlighted by the over response of neutron survey meters in the keV energy range, and also describe the main difficulties encountered. The variation of the neutron yield with ion beam energy from the neutron threshold up to about 50 keV has been measured at IRSN AMANDE facility for the ⁴⁵Sc(p,n), ⁶⁵Cu(p,n), ⁵¹V(p,n), ⁵⁷Fe(p,n) and ³⁷Cl(p,n) reactions.     

Neutron production with mixture of deuterium and krypton in Sahand Filippov type plasma focus facility

This Letter reports the order of magnitude enhancement in neutron yield from Sahand plasma focus device with krypton seeded deuterium operation. The highest average neutron yield of 2.2×¹⁰⁹ neutrons per shot was achieved at 1.00 Torr deuterium with 3% krypton which is higher than the best average neutron yield of 3.18×¹⁰⁸ neutrons per shot for pure deuterium operation. Estimation of average neutron energy showed that the maximum and minimum average energies are 2.98±0.6 MeV at 16 kV in 0.25 Torr deuterium with 3% Kr and 2.07±0.2 MeV at 18 kV operation in 0.5 Torr deuterium with 3% Kr, respectively. The anisotropy of neutron emission from Sahand DPF showed that the neutrons are produced mainly by beam-target mechanisms.     

Spin distribution factors for formation of metastable states of 90Y and 91Y through (n,p) reactions over neutron energies 5–15 MeV

The variations in the isomer ratio with the spin distribution factor were studied to obtain the cross-sections for formation of metastable states of ⁹⁰Y and ⁹¹Y nuclei formed respectively through ⁹⁰Zr(n,p)⁹¹Y^m and ⁹¹Zr(n,p)⁹¹Y^m reactions over the neutron energy range 5 to 15 MeV. The theoretical values of the cross-sections could be obtained very close to the respective literature experimental values by varying the spin distribution factor from 1.5 to 2.75. The limiting value of the cross-section was derived from the maximum value of the isomer ratio at that neutron energy, and for this the spin distribution factor was found to vary from 2 to 3.5 over the neutron energies 5 to 15 MeV. Using enriched zirconium targets, cross-sections for formation of ⁹⁰Y^m and ⁹¹Y^m nuclei at 14.8 MeV neutron energy were also measured in the laboratory; the values obtained are 17 ± 2 mb and 22 ± 2 mb respectively for ⁹⁰Y^m and ⁹¹Y^m. Both these values are close to the corresponding limiting cross-sections at 14 MeV neutron energy.     

中子辐照对AlGaN/GaN高电子迁移率晶体管器件电特性的影响

本文采用能量为1 MeV的中子对SiN钝化的AlGaN/GaN HEMT(高电子迁移率晶体管)器件进行了最高注量为1015cm-2的辐照.实验发现:当注量小于1014cm-2时,器件特性退化很小,其中栅电流有轻微变化(正向栅电流IF增加,反向栅电流IR减小),随着中子注量上升,IR迅速降低.而当注量达到1015cm-2时,在膝点电压附近,器件跨导有所下降.此外,中子辐照后,器件欧姆接触的方块电阻退化很小,而肖特基特性退化却相对明显.通过分析发现辐照在SiN钝化层中引入的感生缺陷引起了膝点电压附近漏电流和反向栅泄漏电流的减小.以上结果也表明,SiN钝化可以有效地抑制中子辐照感生表面态电荷,从而屏蔽了绝大部分的中子辐照影响.这也证明SiN钝化的AlGaN/GaN HEMT器件很适合在太空等需要抗位移损伤的环境中应用.     

Computer simulation of an extracted beam for the neutron generator of the Institute for Nuclear Research of the Russian Academy of Sciences

The NG-430 neutron generator at the Institute for Nuclear Research, Russian Academy of Sciences, is being updated. The flux of neutrons produced by the ³H(d,n)⁴He reaction can be as high as 10¹³ s⁻¹. Modernization of the neutron generator involves moving it to a new accelerator hall. The generation of several extracted neutron beams is planned. After they pass through the collimator, the neutron fluxes are calculated by the Monte-Carlo method on the basis of the ABBN [4] neutron constants. The parameters of the biological shielding are estimated.     

The lead nucleus as a miniature surrogate for a neutron star

The nucleus of ²⁰⁸Pb, a system 18 orders of magnitude smaller and 55 orders of magnitude lighter than a neutron star, may be used as a miniature surrogate to establish important correlations between its neutron skin and several neutron-star properties. Indeed, models with a thicker neutron skin in ²⁰⁸Pb generate larger neutron stars that have a lower liquid-to-solid transition density. Further, we illustrate how the correlation between the neutron skin in ²⁰⁸Pb and the radius of a 1.4 solar-mass neutron star may be used to place important constraints on the equation of state of neutron-rich matter and how it may help elucidate the existence of a phase transition at the core of the star.     

Measurement of the neutron beam polarization of BL05/NOP beamline at J-PARC

We measured the neutron beam polarization of the BL05/NOP (Neutron Optics and Physics) beamline at J-PARC with an accuracy of less than 10⁻³ using polarized ³He gas as a neutron spin analyzer. Precise polarimetry of the neutron beam is necessary to understand the beamline optics as well as for the asymmetry measurements of the neutron beta decay, which are planned in this beamline.     

High-spin states in 166Lu

It is shown that the discrepancy between the results obtained for different neutron energy ranges, when neutron polarizability is derived from the neutron scattering data, can be removed if one assumes that at the fast neutron scattering a strong-interaction long-range potential of Van der Waals (～ r ^?6 ) or Casimir-Polder (～ r ^?7 ) is observed. This strong-interaction long-range potential has possibly some experimental confirmation in the elastic p-p scattering.     

Gamma-ray competition with neutron emission in the decay of 137I

Gamma-rays with energies above the neutron binding energy in ¹³⁷Xe have been observed at 3907 and 3994 keV in the decay of ¹³⁷I. Their combined intensity amounts to about 25% of the delayed neutron intensity and demonstrates that γ-ray widths are an important factor in defining the magnitude and energy distribution of the delayed neutron spectrum.     

Dynamic tunnel effect at low-energy nuclear reactions with neutron-rich nuclei

The probability of neutron transfer between nuclei at close low-energy collisions has been investigated as a function of the energy of the neutron separation, the energy in a center-of-mass system E and the collision impact parameter. The energy dependence of the neutron transfer cross section in the ⁶He + ¹⁹⁷Au reaction has been explained.     

Monitoring of the thermal neutron flux in the EDELWEISS II dark matter direct search experiment

The results from measurements of thermal neutron flux in the EDELWEISS II experiment aimed at the direct detection of WIMPs (weakly interacting massive particles) by means of cryogenic germanium bolometers are described. Detailed knowledge of the neutron background is of crucial importance for the experiment, since neutrons with the MeV energy range of scattering seem to be hard to distinguish from the expected WIMP signal within the bolometers. Monitoring of the thermal neutron flux is performed using a mobile detection system with a low background proportional ³He counter. The neutron flux measurements were performed both outside and inside the device’s shielding, in the direct proximity of a cryostat with built-in germanium detectors. The sensitivity of the created thermal neutron detection system is on the level of 10⁻⁹ neutron (cm² s)⁻¹.     

Magnetic Properties of Neutron-Irradiated RPV Steel by Mössbauer Spectroscopy

The neutron irradiated reactor pressure vessel (RPV) steels at various doses of 010¹⁸ n/cm² have been studied with Mössbauer, X-ray diffraction, and VSM. The Mössbauer data show that the value of a magnetic hyperfine field of Fe atom that exists at the martensite is 330 kOe at site 1, and 305 kOe, at site 2. At room temperature, the total absorption area of Mössbauer spectra with respect to irradiation of neutron is constant for the dose of 010¹⁶ n/cm², while over the dose of 10¹⁷ cm² the absorption area decreases rapidly. But the doublet area for the dose of 010¹⁶ n/cm² is constant, while over the dose of 10¹⁷ cm² it increases with an increase in the fluence level of neutron. The value of IS and QS at site 1,2 varied slightly with an increase in the fluence level of neutron. However, at a doublet site existing Fe³⁺ state, over the dose of 10¹⁷ cm², the values of IS and QS increase with an increase in the fluence level of neutron. Note that over the dose of 10¹⁷ n/cm² the neutron irradiated sample loses crystal structure slowly. The coercivity and remanence of the neutron irradiated samples do not change significantly. But the maximum induction decreases by 5% at 10¹⁸ n/cm², us compared with that of the as-received sample.     

Effects of neutron irradiation and subsequent annealing on the optical characteristics of sapphire

In this paper, the effect of neutron irradiation on sapphire single crystal with fast neutron of 1.0×10¹⁸ and 1.0×10¹⁹ neutrons/cm² has been investigated along with the effect of annealing temperature. It is found that the colorless transparent sapphire single crystals were turned yellow after 10 MeV fast neutron irradiation at room temperature. There are peaks at 206, 230, 258, 305, 358 and 452 nm after neutron irradiation. And the intensity of optical absorption bands decrease with wavelength and annealing temperature. A new absorption peak at 452 nm was found after isothermal annealing at 400 °C for 10 min, which was ascribed to F₂⁺ color center. Because of the recombination of interstitial ions and vacancies, color centers were almost removed after annealing at 1000 °C. The TL peaks were found to shift to higher temperature after neutron irradiation. And a higher fluence of the neutron irradiation would result in deep traps revealed as the new TL peaks at 176 and 227 °C.     

Cumulative fission yield measurements with 14.7 MeV neutrons on 238U

The fission yield data in the 14 MeV energy neutron induced fission of ²³⁸U play an important role in decay heat calculations and generation-IV reactor designs. In order to accurately measure fission product yields (FPYs) of ²³⁸U induced by 14 MeV neutrons, the cumulative yields of fission products ranging from ⁹²Sr to ¹⁴⁷Nd in the ²³⁸U(n, f) reaction with a 14.7 MeV neutron were determined using an off-line γ-ray spectrometric technique. The 14.7 MeV quasi-monoenergetic neutron beam was provided by the K-400 D-T neutron generator at China Academy of Engineering Physics (CAEP). Fission products were measured by a low background high purity germanium gamma spectrometer. The neutron flux was obtained from the ⁹³Nb (n, 2n)^92mNb reaction, and the mean neutron energy was calculated using the cross-section ratios for the ⁹⁰Zr(n, 2n)⁸⁹Zr and ⁹³Nb(n, 2n)^92mNb reactions. With a series of corrections, high precision cumulative yields of 20 fission products were obtained. Our FPYs for the ²³⁸U(n, f) reaction at 14.7 MeV were compared with the existing experimental nuclear reaction data and evaluated nuclear data, respectively. The results will be helpful in the design of a generation-IV reactor and the construction of evaluated fission yield databases.     

3PF2 neutron superfluidity in neutron stars and three-body force effect

We investigate the ^3PF2 neutron superfluidity in H-stable neutron star matter and neutron stars by using the BCS theory and the Brueckner-Hartree-Fock approach. We adopt the Argonne V18 potential supplemented with a microscopic three-body force as the realistic nucleon-nucleon interaction. We have concentrated on studying the threebody force effect on the ^3PF2 neutron pairing gap. It is found that the three-body force effect is to enhance remarkably the ^3PF2 neutron superfluidity in neutron star matter and neutron stars.     

Magnetic properties of neutron irradiated RPV steel

The neutron irradiated reactor pressure vessel (RPV) steels at various dose of 0–10¹⁸ n/cm² have been studied with Mössbauer, x-ray diffraction, and VSM. The Mössbauer data shows that the value of magnetic hyperfine field of Fe atom that exist at martensite is 330 kOe at site 1 and 305 kOe at site 2. At room temperature, the total absorption area of Mössbauer spectra with respect to irradiation of neutron is constant for the dose of 0–10¹⁶ n/cm², while over the dose of 0–10¹⁷ n/cm² the absorption area decreases rapidly. But the doublet area for the dose of 0–10¹⁶ n/cm² is constant, while over the dose of 10¹⁷ n/cm² it increases with increasing the fluence level of neutron. The coercivity and remanence of the neutron irradiated samples do not change significantly. But the maximum induction decreases by 5% at 10¹⁸ n/cm², compared with that of the as-received sample.