Crystal lattice effects in the Sm(n, α)Nd reaction induced by thermal neutrons

The thermal neutron induced reaction, ¹⁴⁹Sm(n, α)¹⁴⁶Nd, is influenced by the chemical form and temperature of the target material. The detection of this dependence is due to the rather unique features of the thermal neutron capture of ¹⁴⁹Sm which make it particularly sensitive to the effective neutron energy spectrum.     

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.     

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.     

Design of the thermal neutron detection system for CJPL-Ⅱ

A low background thermal neutron flux detection system has been designed to measure the ambient thermal neutron flux of the second phase of the China Jinping Underground Laboratory(CJPL-Ⅱ),right after completion of the rock bolting work.A ~3He proportional counter tube combined with an identical ~4He proportional counter tube was employed as the thermal neutron detector,which has been optimised in energy resolution,wall effect and radioactivity of construction materials for low background performance.The readout electronics were specially designed for long-term stable operation and easy maintenance in an underground laboratory under construction.The system was installed in Lab Hall No.3 of CJPL-Ⅱ and accumulated data for about 80 days.The ambient thermal neutron flux was determined under the assumption that the neutron field is fully thermalized,uniform and isotropic at the measurement position.     

Environmental neutron measurements with solid state track recorders

Abstract

The suitability of using ¹⁰B and ⁵LiF in contact with cellulose acetate butyrate (CAB) for the measurement of slow neutron densities has been investigated. The upper energy threshold of clear Diacel cellulose nitrate (CN) and of the CAB have also been measured. The CAB in good contact with thick ¹⁰B or ⁵LiF sources offers good promise for the detection of slow neutrons. For the actual CAB samples used, the CAB-¹⁰B combination had an efficiency of ～1.3 × 10^?2 tracks per thermal neutron incident in a 2π solid angle. The corresponding number for the CAB⁶-Li combination is ～5.6 × 10^?3 tracks per thermal neutron.     

The (nth, α) reaction on 147Sm, 151, 153Eu and Yb isotopes

The (n, α) reaction has been studied using the highly pure thermal neutron beam from the 87m curved neutron guide at the Grenoble high flux reactor. The ¹⁴⁷Sm(n, α)¹⁴⁴Nd reaction showed up five lines corresponding to the ground and the first four excited states of the final nucleus. It is shown that ≈53 % of the 581 μb (n, α) cross section comes from the neutron capture by a bound level of the ¹⁴⁸Sm compound nucleus. The 8.7 ± 3 μb cross section of ¹⁵¹Eu(n, α)¹⁴⁸Pm seems to consist principally of at least two lines corresponding to the ground and the second excited states of ¹⁴⁸Pm. The ¹⁵³Eu(n, α)¹⁴⁹Pm cross section for thermal neutrons is ≦ 1 μb. The lower limits of (n, α) thermal neutron cross section values on ytterbium isotopes are ≈ 20 to 40 times lower than the published data.     

Monte Carlo simulation of thermal neutron flux of americium–beryllium source used in neutron activation analysis

The neutron activation analysis is a method of exclusively elemental analysis. Its implementation of irradiates the sample which can be analyzed by a high neutron flux, this method is widely used in developed countries with nuclear reactors or accelerators of particle. The purpose of this study is to develop a prototype to increase the neutron flux such as americium–beryllium and have the opportunity to produce radioisotopes. Americium–beryllium is a mobile source of neutron activity of 20 curie, and gives a thermal neutron flux of (1.8 ± 0.0007) × 10⁶ n/cm² s when using water as moderator, when using the paraffin, the thermal neutron flux increases to (2.2 ± 0.0008) × 10⁶ n/cm² s, in the case of adding two solid beryllium barriers, the distance between them is 24 cm, parallel and symmetrical about the source, the thermal flux is increased to (2.5 ± 0.0008) × 10⁶ n/cm² s and in the case of multi-source (6 sources), with-out barriers, increases to (1.17 ± 0.0008) × 10⁷ n/cm² s with a rate of increase equal to 4.3 and with the both barriers flux increased to (1.37 ± 0.0008) × 10⁷ n/cm² s.     

Enhancement of antibacterial effect of quaternary ammonium with inorganic nanosheets against <Emphasis Type="Italic">Enterobacter cloacae</Emphasis>

To suppress nosocomial infections, numerous studies of quaternary ammonium cations (R₄N⁺) to improve the antibiotic properties have been investigated. However, most of them reported developments of novel organic or polymeric materials with R₄N⁺. To pioneer antibacterial inorganic materials hybridized with R₄N⁺, a colloidal solution of metal oxide nanosheets, which have a small particle size (typically less than 10 nm), is considered to be a suitable option because oxide nanosheets with a negative surface charge strongly interact R₄N⁺. Herein, we demonstrate for the first time that the high antibacterial/bactericidal effects of titanate nanosheets (TNS) adsorbing tetramethylammonium (TMA-TNS) or tetrabultylammonium ions (TBA-TNS). Their antibacterial effects against Enterobacter cloacae were evaluated using a colony forming unit (CFU) counting method. The results showed that the synthesized TNS composites had superior antibacterial and bactericidal effects to those of free R₄N⁺ and TBA-TNS exhibited the strongest effect (69% CFU reduction compared with that of free TBA⁺ and 98% CFU reduction compared with the control) among the samples examined. Dark incubation was employed to ensure that photocatalytic reaction of semiconducting TNS did not contribute to the process. Compared with TiO₂ spherical particles, such high bactericidal effect would be induced by a synergistic function of TBA⁺ and TNS, which physically damages bacteria due to long hydrophobic alkyl chains and an anisotropic nanocrystalline structure with sharp edges, respectively.     

Determination of Moisture Content in Coke with <Superscript>239</Superscript>Pu–Be Neutron Source and BGO Scintillation Gamma Detector

A series of experiments has been conducted at the Frank Laboratory of Neutron Physics (FLNP) of the Joint Institute for Nuclear Research (JINR) in order to study the possibility of determining the moisture content of coke using a standard neutron source. The proposed method is based on a measurement of the spectrum of prompt γ rays emitted when samples are irradiated by fast and/or thermal neutrons. The moisture content is determined from the area of the peaks of characteristic γ rays produced in the radiative capture of thermal neutrons by the proton (E_γ = 2.223 MeV) and inelastic scattering of fast neutrons by ¹⁶O (E_γ = 6.109 MeV). The ²³⁹Pu–Be neutron source (〈E _n 〉 ~ 4.5 MeV) with an intensity of ~5 × 10⁶ n/s was used to irradiate the samples under study. A scintillation detector based on a BGO crystal was used to register the characteristic γ radiation from the inelastic fast neutron scattering and slow (thermal) neutron capture. This paper presents the results of humidity measurement in the range of 2–50% [1, 2].     

Assessment of fast and thermal neutron ambient dose equivalents around the KFUPM neutron source storage area using nuclear track detectors

A set of five ²⁴¹Am–Be neutron sources are utilized in research and teaching at King Fahd University of Petroleum and Minerals (KFUPM). Three of these sources have an activity of 16 Ci each and the other two are of 5 Ci each. A well-shielded storage area was designed for these sources. The aim of the study is to check the effectiveness of shielding of the KFUPM neutron source storage area. Poly allyl diglycol carbonate (PADC) Nuclear track detectors (NTDs) based fast and thermal neutron area passive dosimeters have been utilized side by side for 33 days to assess accumulated low ambient dose equivalents of fast and thermal neutrons at 30 different locations around the source storage area and adjacent rooms. Fast neutron measurements have been carried out using bare NTDs, which register fast neutrons through recoils of protons, in the detector material. NTDs were mounted with lithium tetra borate (Li₂B₄O₇) converters on their surfaces for thermal neutron detection via and nuclear reactions. The calibration factors of NTD both for fast and thermal neutron area passive dosimeters were determined using thermoluminescent dosimeters (TLD) with and without a polyethylene moderator. The calibration factors for fast and thermal neutron area passive dosimeters were found to be 1.33 proton tracks and 31.5 alpha tracks , respectively. The results show variations of accumulated dose with the locations around the storage area. The fast neutron dose equivalents rates varied from as low as up to whereas those for thermal neutron ranged from as low as up to . The study indicates that the area passive neutron dosimeter was able to detect dose rates as low as 7 and from accumulated dose for thermal and fast neutrons, respectively, which were not possible to detect with the available active neutron dosimeters.     

Thermal neutron flux detection near the Earth’s surface

The thermal neutron flux near the Earth’s surface has been measured using large unshielded neutron scintillator detectors of a new type, based on ZnS(Ag) and lithium fluoride, enriched with ⁶Li to 90%. The existence of a gradient of the thermal neutron concentration near the Earth’s surface is shown.     

Thermal neutron flux monitoring using new-type detectors

The applicability of new-type unshielded detectors based on zinc sulfide ZnS(Ag) and lithium fluoride enriched with ⁶Li isotope to 90% to thermal neutron measurements is demonstrated. The results of measurements of the thermal neutron counting rate and flux near the Earth’s surface are presented. The existence of the concentration gradient of thermal neutrons near the Earth’s surface at placing the counter at the various levels (from −4 to 10.5 m) in an experimental building is shown. The effect of meteoparameters on the counting rate of thermal neutrons for a long time is shown.     

In the wonderland of ultra-parallel neutron beams

Bragg reflections from single crystals yield angular widths of a few arcsec for thermal neutron beams. The Bonse-Hart proposal to attain a sharp, nearly rectangular profile by Bragg reflecting neutrons multiply from a channel-cut single crystal, was realized in its totality three and a half decades later by achieving the corresponding Darwin reflection curves for 5.23 Å neutrons. This facilitated SUSANS (Super USANS) measurements in the Q ～ 10^?5 Å^?1 range. The polarized neutron option was introduced into the SUSANS set-up by separating the up- and down-spin neutron beams by ～10 arcsec with a magnetic (air) prism. The neutron angular width has recently been reduced further by an order of magnitude to ～0.6 arcsec by diffracting 5.3 Å neutrons from a judiciously optimized Bragg prism. This constitutes the most parallel monochromatic neutron beam produced to date. I present the first SUSANS spectra probing the Q ～ 10^?6 Å^?1 domain, recorded with this beam.     

The thermal neutron induced fission cross section of 232Th

The thermal neutron induced fission cross section of ²³²Th was measured using the highly pure thermal neutron beam from the 87 m curved neutron guide at the High Flux Reactor of the ILL (Grenoble). An upper limit of 4 μb was obtained for the fission cross section, which is an order of magnitude smaller than previous results. This result is discussed in terms of the double-humped fission barrier theory.     

Microdosimetry for the characterization of the THOR epithermal neutron beam

The epithermal neutron beam of the Tsing Hua Open-pool Reactor (THOR) was constructed for the study of boron neutron capture therapy (BNCT). The THOR epithermal neutron beam was mainly composed of thermal neutrons, fast neutrons, and photons. For fast neutrons and photons, the absorbed dose and the relative biological effectiveness (RBE) were used to characterize radiation dose and radiation quality. The short-ranged alpha particles and lithium ions produced from ¹⁰B(n,α)⁷Li reactions in the BNCT required cellular- and micro-dosimetry characterizations. Due to the non-uniform microdistribution of boron in cells, these characterizations should depend on the source–target geometry. In this case, the geometry-dependent specific cellular dose and lineal energy could be used to describe radiation dose and radiation quality. In the present work, cellular- and micro-dosimetry were studied for the THOR epithermal neutron beam. The specific cellular dose and lineal energy were calculated for thermal neutron-induced α-particles and ⁷Li-ions with different source–target geometry and various cell sizes. Applying the linear energy dependent-biological weighting function, the geometry-dependent RBE of thermal neutron-induced heavy particles was determined. Finally, the effective RBE of the THOR epithermal neutron beam was estimated for tumors and normal tissues of specified ¹⁰B concentrations. This effective RBE should be multiplied by the total absorbed dose to determine the corresponding biological dose required in the treatment planning.     

Neutron detection with LiCaAlF6 scintillator doped with 3d-transition metal ions

Capability of thermal neutron detection was examined for LiCaAlF₆ (LiCAF) scintillators doped with 3d-transition metal ions. Their radioluminescence spectra were measured with an 241-Am source to simulate ⁶Li(n, α)³H reaction. The sufficiently intense radioluminescence was observed for the Mn, Co and Cu dopants, while only a weak one was observed for Ti, V, Fe and Ni. A Mn doped LiCAF crystal, which showed the highest radioluminescence intensity, was coupled with a Si avalanche photodiode for the examination of its neutron response. It was confirmed that the average current of the photodiode clearly increased under excitation with 13.5 meV neutron flux.     

ZnS(Ag)/<Superscript>6</Superscript>LiF and LiI(Eu) scintillators and silicon photomultipliers for thermal neutron detectors with high space and time resolution

ZnS(Ag)/⁶LiF and LiI(Eu) scintillators for thermal neutron detectors have been investigated and neutron detectors based on these scintillators and photomultipliers have been tested. The efficiencies of these detectors are 5 and 66%, respectively. The possibility of developing position-sensitive detectors of thermal neutrons with high space and time resolution is discussed.     

A possible mechanism for magnetar soft X-ray/γ-ray emission

Once the energies of electrons near the Fermi surface obviously exceed the threshold energy of the inverse β decay,electron capture(EC) dominates inside the magnetar.Since the maximal binding energy of the 3 P 2 neutron Cooper pair is only about 0.048 MeV,the outgoing high-energy neutrons(E k(n) > 60 MeV) created by the EC can easily destroy the 3 P 2 neutron Cooper pairs through the interaction of nuclear force.In the anisotropic neutron superfluid,each 3 P 2 neutron Cooper pair has magnetic energy 2μ n B in the applied magnetic field B,where μ n = 0.966 × 10 23 erg.G 1 is the absolute value of the neutron abnormal magnetic moment.While being destroyed by the high-energy EC neutrons,the magnetic moments of the 3 P 2 Cooper pairs are no longer arranged in the paramagnetic direction,and the magnetic energy is released.This released energy can be transformed into thermal energy.Only a small fraction of the generated thermal energy is transported from the interior to the surface by conduction,and then it is radiated in the form of thermal photons from the surface.After highly efficient modulation within the star’s magnetosphere,the thermal surface emission is shaped into a spectrum of soft X-rays/γ-rays with the observed characteristics of magnetars.By introducing related parameters,we calculate the theoretical luminosities of magnetars.The calculation results agree well with the observed parameters of magnetars.     

The real part of the nucleon-nucleus optical potential

The nucleus²⁴Na has been investigated by studying the gamma-rays emitted following thermal neutron capture in²³Na, with curved crystal and Ge(Li) spectrometers. Of the 277 transitions assigned to²⁴Na, 216 were placed in the²⁴Na level scheme containing 45 levels, of which six (1,961, 1,977, 3,866, 5,810, 5,918, and 6,222 keV) are reported for the first time. An average gamma-ray multiplicity of 3.3 gammas per neutron capture was observed. The neutron binding energy was determined to be 6,959.73 (14) keV. The resulting level scheme is compared to shell and rotational model predictions.     

The level structure of 114Cd from (n, γ) and (d,p) studies

Gamma rays and conversion electrons have been measured following thermal neutron capture in ¹¹³Cd using the crystal spectrometers GAMS and the β-spectrometer BILL at the High Flux Reactor of the ILL at Grenoble. Primary γ-rays following thermal and average resonance neutron capture at E_n = 2 keV and 24 keV were recorded at the High Flux Beam Reactor at the Brookhaven National Laboratory. The ¹¹³Cd(d, p)¹¹⁴Cd reaction was studied with the Q3D spectrograph at the Munich tandem accelerator. Combining all these experimental results an almost complete level scheme of ¹¹⁴Cd was constructed up to 3.3 MeV including 48 excited levels with spin and parity information. The level scheme is discussed in terms of particle-hole excitations across the Z = 50 closed shell coupled to collective states, as well as in an interacting boson configuration mixing scheme.