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.     

Study of dependence of quasi-particle alignment on proton and neutron numbers in A = 80 region through g-factor measurements

Dependence of quasi-particle alignment on proton and neutron numbers has been studied in A?=?80 mass region through g-factor measurements by using TMF-IMPAD. The experimental results show that for the nuclides ⁸⁴Zr, ⁸⁵Zr and ⁸⁶Zr with Z?=?40 the proton alignment is followed by the neutron alignment in ⁸⁴Zr and ⁸⁵Zr, while the neutron alignment is followed by the proton alignment in ⁸⁶Zr, and for the nuclides ⁸²Sr, ⁸³Y, ⁸⁴Zr and ⁸⁵Nb with N?=?44 the proton aligns only in ⁸²Sr, the proton alignment occurs first that is followed by the neutron alignment in ⁸³Y and ⁸⁴Zr and the neutron alignment is followed by the proton alignment in ⁸⁵Nb. Proton and/or neutron alignments lead to different patterns of the g-factor variation with spin.     

Optimised adiabatic fast passage spin flipping for He neutron spin filters

We describe here a method of performing adiabatic fast passage (AFP) spin flipping of polarized ³He used as a neutron spin filter (NSF) to polarize neutron beams. By reversing the spin states of the ³He nuclei the polarization of a neutron beam can be efficiently reversed allowing for the transmission of a neutron beam polarized in either spin state. Using an amplitude modulated frequency sweep lasting 500 ms we can spin flip a polarized ³He neutron spin filter with only 1.8×10⁻⁵ loss in ³He polarization. The small magnetic fields (10-15 G) used to house neutron spin filters mean the ³He resonant frequencies are low enough to be generated using a computer with a digital I/O card. The versatility of this systems allows AFP to be performed on any beamline or in any laboratory using ³He neutron spin filters and polarization losses can be minimised by adjusting sweep parameters.     

Investigation of neutron and proton distributions of He,Li, and Be isotopes using the new Skyrme-Force parameters

The proton and neutron densities, root-mean-square (rms) radii of proton density and neutron density, and neutron skin thickness of ^4–10He, ^6–11Li, and ^7–12Be isotopes are calculated using Skyrme-Hartree-Fock method with SLy4, SLy5, SLy6, and SLy7 force parameters. The evaluated results are compared with experimental data. Also, the results of halo nuclei (^6,8He, ¹¹Li, and ¹¹Be) are compared with the results of other isotopes for selected nuclei having the same neutron configuration.     

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.     

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.     

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.     

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.     

Neutron periphery in light nuclei

A spatial configuration of light nuclei that involves two excess neutrons (⁶He, ¹⁰Be, and ¹²B) is studied by analyzing cross sections for various reactions on these nuclei: ⁶He(α, α)⁶He, ⁹Be(d, p)¹⁰Be, and ¹⁰B(t, p)¹²B. Pole dineutron-transfer mechanisms (dineutron configuration of the neutron periphery) and second-order mechanisms involving sequential neutron transfer (cigar-like configuration of the neutron periphery) are taken into account in the calculations. It is shown that the neutron periphery is drastically different in the nuclei in question: in ⁶He, there is a halo receiving a contribution from both configurations; in ¹⁰Be, there is an only slightly noticeable halo featuring a contribution of practically one neutron from the cigar-like configuration; and, in ¹²B, there is a neutron skin.     

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.     

Application of solid state track recorders for neutron spectra measurements in a reactor irradiation facility

Abstract

In connection with the IAEA-neutron seed irradiation Programme, a standard neutron irradiation facility has been constructed. The application of solid state track recorders for fast neutron spectra measurements inside this facility is discussed. Fissionable targets of ²³⁵U, ²³⁹Pu, ²³⁷Np, ²³⁸W and ²³²Th will be used, an approximative solution for the incident neutron spectrum will be obtained by a five-group method.     

Comparison of unfolding approaches for monoenergetic and continuous fast-neutron energy spectra

Proton-recoil detectors offer the possibility to unfold fast-neutron energy spectra of various sources. However, quantifying the confidence of the unfolding methodology is a complex task. In this paper, we present a comparative analysis of the maximum-likelihood, expectation-maximization (MLEM) method and one-step-late (OSL) method for neutron energy spectra unfolding. The analysis is performed on Monte Carlo simulated data for several monoenergetic neutron sources and continuous-in-energy ²⁵²Cf, ²⁴¹Am–Be and ²⁴¹Am–Li neutron sources. The results obtained for the monoenergetic neutron spectra show that both unfolding methods provide results that are in good agreement with the reference data. Very good agreement between the unfolded and the reference data is achieved for ²⁵²Cf, ²⁴¹Am–Be, and ²⁴¹Am–Li neutron spectra by using the OSL method. In the paper it is demonstrated that the MLEM and OSL methods can be applied to accurately unfold the simulated pulse-height distributions for organic liquid scintillation detectors. Comparative analysis between the two unfolding methods has shown that the OSL method has superior unfolding performance than the MLEM method.     

On the use of averaging stopping power of recoiled nuclei for determining maximum neutron energy of 241Am–Be by superheated drop detectors

The average stopping power of the recoiled nuclei generated by neutron elastic interactions with the Freon-12 drops in a superheated drop detector has been used to determine the maximum neutron energy of the ²⁴¹Am–Be source. In an elastic interaction of neutrons with the Freon-12 liquid, the nuclei of ¹²C, ¹⁹F and ³⁵Cl with different values of stopping power are scattered. The stopping power of these scattered nuclei corresponding to the energy transferred to them through the head-on collision was extracted from the SRIM code. The stopping power values were weighted by considering the neutron–nucleus elastic scattering cross section and the number of each nucleus in the Freon-12 molecule and the average stopping power was calculated from known neutron energy.The maximum energy of the ²⁴¹Am–Be neutron source was estimated as 10.9 ± 3.0 MeV. The consistency between the determined energy and the other reported values confirms the validity of using the average stopping power in the superheated drop detectors. The average stopping power was also used to determine the threshold neutron energy as a function of external applied pressure at different temperatures. Knowing the threshold neutron energy as function of applied pressure, can be used in pressure scanning method for neutron spectrometry by superheated drop detectors.     

Neutron scattering from superfluid 4He at very large momentum transfer

Measurements of inelastic neutron scattering from liquid ⁴He were performed at very large momentum transfer (about 150 Å⁻¹) using an eV spectrometer with a pulsed spallation neutron source. A difference in the scattered neutron spectrum measured at 1.2 and 2.5 K was observed for the first time within this momentum-transfer range.     

Neutron response study of two CR-39 personal dosemeters with air and Nylon converters

A neutron personal dosemeter using CR-39 as a detector and hydrogenated materials as proton converters for fast neutron detection plus an air layer for thermal neutron detection is being developed in our laboratory. To increase the CR-39 response to thermal neutrons, the air converter was substituted with Nylon in some dosemeters. Several dosemeters with these two configurations were mounted on a water-filled phantom and exposed under different incidence angles (0, 30 and 60) to: (i) Three ISO neutron sources (²⁴¹Am–Be, bare ²⁵²Cf and moderated ²⁵²Cf with Cd shielding), and (ii) two realistic neutron sources (SIGMA and moderated ²⁵²Cf) at the IRSN (Cadarache) facilities. The irradiated detectors were electrochemically etched and evaluated in order to determine their dose equivalent response in terms of H_p(10,α). The results obtained are compared to those obtained from Monte Carlo simulations using the MCNPX code.     

Neutron emission in interactions of 1H, 2H, 4He, and 12C nuclei with lead nuclei at 1–2 GeV per nucleon

The double differential cross sections for neutron production that were measured by the time-of-flight method for interactions of 2-GeV p and d, 4-GeV ⁴He, and 24-GeV ¹²C with Pb nuclei are discussed. In the phenomenological model of four moving sources, the neutron energy distribution shape at emission angles above 30° is well reproduced with the temperature parameters for all sources that are almost independent of the type and the energy of incident nuclei. Using the developed model, we estimate the mean neutron multiplicity and the energy removed by neutron emission.     

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.     

Activation detection using indium foils for simultaneous monitoring neutron and photon intensities in a reactor core

In this work, the time-sequential changes in neutron and photon intensities in the core of a research reactor were monitored for 330 days following the time of shutdown. Indium foils, used as activation detectors, were irradiated during different time periods in the core. The activated nuclides ^116m1In and ^115mIn were measured and their activities were used as indices of the changes in neutron and photon intensities during the period of interest. Photon and neutron sources that may have been responsible for the activation reactions with indium foils were identified. The activities of both ^116m1In and ^115mIn rapidly decreased in the first 20 h (Phase I), and subsequently their activity levels were proportionally varied with ¹⁴⁰La activity between 20 and 3000 h (Phases II and III). After 3000 h (Phase IV), neutron fluence rate slowly decreased to levels of less than 10 cm^?2 s^?1. Then, the main neutron sources were identified as the neutron-emitting transuranic nuclides and the most important photon source that activated indium to form ^115mIn was identified as ⁶⁰Co. The activation detectors based on indium foils were found to be effective for simultaneously monitoring the variations of neutron and photon levels in reactor cores under sub-critical conditions.     

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.     

Does the simple statistical model describe delayed neutron emission?: The cases of 85As, 87Br, 135Sb and 137I

Delayed neutron spectra and branching ratios to excited states in final nuclei calculated with the statistical model are compared to experimental data for the decay of ⁸⁷Br, ¹³⁷I, ⁸⁵As and ¹³⁵Sb. For the first two precursors, the calculations support the experimental β-strength functions reported previously. For the latter two, it is shown that the statistical model cannot simultaneously reproduce both spectra and branching ratios for any choice of β-strength function when all levels populated by neutron emission are included in the calculations. The comparisons demonstrate that partial widths for neutron emission are not compatible with optical-model transmission coefficients. We conclude, as pointed out previously, that structure effects in the energy range probed by delayed neutron emission are not averaged out to the extent required by the statistical assumptions.