Direction Of Incident Neutrons Research Articles

Model-based design evaluation of a compact, high-efficiency neutron scatter camera

This paper presents the model-based design and evaluation of an instrument that estimates incident neutron direction using the kinematics of neutron scattering by hydrogen-1 nuclei in an organic scintillator. The instrument design uses a single, nearly contiguous volume of organic scintillator that is internally subdivided only as necessary to create optically isolated pillars, i.e., long, narrow parallelepipeds of organic scintillator. Scintillation light emitted in a given pillar is confined to that pillar by a combination of total internal reflection and a specular reflector applied to the four sides of the pillar transverse to its long axis. The scintillation light is collected at each end of the pillar using a photodetector, e.g., a microchannel plate photomultiplier (MCP-PM) or a silicon photomultiplier (SiPM). In this optically segmented design, the (x,y) position of scintillation light emission (where the x and y coordinates are transverse to the long axis of the pillars) is estimated as the pillar’s (x,y) position in the scintillator “block”, and the z-position (the position along the pillar’s long axis) is estimated from the amplitude and relative timing of the signals produced by the photodetectors at each end of the pillar. The neutron’s incident direction and energy is estimated from the (x,y,z)-positions of two sequential neutron–proton scattering interactions in the scintillator block using elastic scatter kinematics. For proton recoils greater than 1 MeV, we show that the (x,y,z)-position of neutron–proton scattering can be estimated with < 1 cm root-mean-squared [RMS] error and the proton recoil energy can be estimated with < 50 keV RMS error by fitting the photodetectors’ response time history to models of optical photon transport within the scintillator pillars. Finally, we evaluate several alternative designs of this proposed single-volume scatter camera made of pillars of plastic scintillator (SVSC-PiPS), studying the effect of pillar dimensions, scintillator material (EJ-204, EJ-232Q and stilbene), and photodetector (MCP-PM vs. SiPM) response vs. time. We demonstrate that the most precise estimates of incident neutron direction and energy can be obtained using a combination of scintillator material with high luminosity and a photodetector with a narrow impulse response. Specifically, we conclude that an SVSC-PiPS constructed using EJ-204 (a high luminosity plastic scintillator) and an MCP-PM will produce the most precise estimates of incident neutron direction and energy.

Fission Reaction Event Yield Algorithm FREYA 2.0.2

FREYA (Fission Reaction Event Yield Algorithm) is a fission event generator which models complete fission events. As such, it automatically includes fluctuations as well as correlations between observables, resulting from conservation of energy and momentum. The purpose of this paper is to present the main differences between FREYA versions 1.0 and 2.0.2 : additional fissionable isotopes, angular momentum conservation, Giant Dipole Resonance form factor for the statistical emission of photons, improved treatment of fission photon emission using RIPL database, and dependence on the incident neutron direction. FREYA 2.0.2 has been integrated into the LLNL Fission Library 2.0.2, which has itself been integrated into MCNP6.2, TRIPOLI-4.10, and can be called from Geant4.10. New version program summaryProgram title:FREYA 2.0.2Program Files doi: ” http://dx.doi.org/10.17632/2mssy7r3gt.1”Licensing provisions: BSD 3-clauseProgramming language: Fortran 90, C++Journal Reference of previous version: J. M Verbeke, J. Randrup, R. Vogt, “Fission Reaction Yield Algorithm FREYA for Event-by-Event Simulation of Fission,” Comp. Phys. Comm. 191, pp. 178–202; doi:10.1016/j.cpc.2015.02.002 (2015).Does the new version supersede the previous version? Yes.Reasons for the new version: New physics and more fissionable isotopes.Summary of revisions: Additional fissionable isotopes, angular momentum conservation, Giant Dipole Resonance form factor for the statistical emission of photons, improved treatment of fission photon emission using RIPL database, and dependence on the incident neutron direction.Nature of problem: Modeling of fission events.Solution method: Simulation of complete fission events, production of secondary fission fragments, fission neutrons and photons.Restrictions: Restricted to spontaneous fission of 238U, 238Pu, 240Pu, 242Pu, 244Cm, 252Cf; neutron-induced fission of 233U, 235U, 238U, 239Pu, 241Pu, for incident neutron energies less than 20 MeV.

What Is the Real PFNS of 235U at Thermal Point?

The traditional assumption of prompt fission neutron spectra (PFNS) integrated over emission angle applies for any calculation of the neutron interaction inside fissile material. Only these evaluated data are included in any neutron data library. But this is not correct. Prompt fission neutrons have very strong angular energy distribution relative to fission fragment (FF) direction. The FFs have anisotropy relative to direction of incident neutrons. What is the influence of this assumption or simplification? Results of Monte Carlo simulation are submitted in this paper. The incorporation of “real” angular energy distribution changes the yield of 238U fission, and this difference may be compensated by changing the average energy of PFNS in the traditional approach. This effect is connected with correlations between different characteristics of interacted neutrons inside the environment. An additional type of correlation between multiplicity and energy of fission neutrons, named ν-E correlation, is also discussed.

Reduced efficiency variation in perforated neutron detectors with sinusoidal trench design

The design of an idealized perforated (microstructured) planar diode neutron detector is presented that has little variation in efficiency as a function of the incident neutron's direction. The reduced angular variation is obtained by using sinusoidal-trench perforations rather than previous hole or straight-trench perforations. The resulting efficiency variation from changing the azimuthal angle of neutron incidence exhibits a variation of only 3% about the mean azimuthal efficiency. The efficiency variation resulting from changes in the polar angle of neutron incidence is limited to 10% of the normal-incidence efficiency over the polar range of 0–60°. 10B, 6LiF, and 6Li-metal filled perforations are considered.

The ratio R dp of the quasielastic nd → p(nn) to the elastic np → pn charge-exchange-process yields at the proton emitting angle θ p,lab = 0° over 0.55–2.0 GeV neutron beam energy region. Experimental results

New experimental results on ratio R dp of the quasielastic charge-exchange yield at the outgoing proton angle θ p,lab = 0° for the nd → p(nn) reaction to the elastic np → pn charge-exchange yield, are presented. The measurements were carried out at the Nuclotron of the Veksler and Baldin Laboratory of High Energies of the JINR (Dubna) at the neutron-beam kinetic energies of 0.55, 0.8, 1.0, 1.2, 1.4, 1.8, and 2.0 GeV. The intense neutron beam with small momentum spread was produced by breakup of deuterons which were accelerated and extracted to the experimental hall. In both reactions mentioned above the outgoing protons with the momenta p p approximately equal to the neutron-beam momentum p n,beam were detected in the directions close to the direction of incident neutrons, i.e., in the vicinity of the scattering angle θ p,lab = 0°. Measured in the same data-taking runs, the angular distributions of the charge-exchange-reaction products were corrected for the well-known instrumental effects and averaged in the vicinity of the incident-neutron-beam direction. These corrected angular distributions for every of nd → p(nn) and np → pn charge-exchange processes were proportional to the differential cross sections of the corresponding reactions. The data were accumulated by Delta-Sigma setup magnetic spectrometer with two sets of multiwire proportional chambers located upstream and downstream of the momentum analyzing magnet. Inelastic processes were considerably reduced by the additional detectors surrounding the hydrogen and deuterium targets. The time-of-flight system was applied to identify the detected particles. The accumulated data treatment and analysis, as well as possible sources of the systematic errors are discussed.

Measurements of the ratio Rdp of the quasi-elastic nd $ \rightarrow$ p(nn) to the elastic np $ \rightarrow$ pn charge-exchange process yields at zero proton emission angle over the 0.55-2.0 GeV neutron beam energy region

New experimental results on the ratio Rdp of the quasi-elastic charge-exchange yield at the outgoing proton angle $ \theta_{{p,{\rm Lab}}}^{}$ = 0° for the nd $ \rightarrow$ p(nn) reaction to the elastic np $ \rightarrow$ pn charge-exchange yield are presented. The measurements were carried out at the Nuclotron of the Veksler and Baldin Laboratory of High Energies of the JINR (Dubna) at the neutron beam kinetic energies of 0.55, 0.8, 1.0, 1.2, 1.4, 1.8 and 2.0GeV. The intense neutron beam with small momentum spread was produced by break-up of deuterons which were accelerated and extracted to the experimental hall. In both reactions mentioned above the outgoing protons with the momenta p p approximately equal to the neutron beam momentum p n, beam were detected in the directions close to the direction of incident neutrons, i.e. in the vicinity of the scattering angle $ \theta_{{p,{\rm Lab}}}^{}$ = 0° . Measured in the same data taking runs, the angular distributions of the charge-exchange reaction products were corrected for the well-known instrumental effects and averaged in the vicinity of the incident neutron beam direction. These corrected angular distributions for every of nd $ \rightarrow$ p(nn) and np $ \rightarrow$ pn charge-exchange processes were proportional to the differential cross-sections of the corresponding reactions. The data were accumulated by the Delta-Sigma set-up magnetic spectrometer with two sets of multiwire proportional chambers located upstream and downstream of the momentum analyzing magnet. Inelastic processes were considerably reduced by the additional detectors surrounding the hydrogen and deuterium targets. The time-of-flight system was applied to identify the detected particles. The new Rdp data are compared with the existing ones, which were obtained below 1GeV, and with the calculations which were made using the phenomenological NN amplitude sets.

スピンカイラリティの電場制御と中性子による検出

A polarized-neutron-diffraction study has been performed on a single crystal sample of TbMnO3, where the ferroelectricity and spiral magnetic order coexist. The spin helicity, detected as the change in intensities of magnetic satellites with the spin direction of incident neutrons, can be controlled by the poling electric field alone. The temperature dependence of the change well agrees with that of the electric polarization. These results establish that an inverse effect of the Dzyaloshinskii-Moriya interaction is the origin of spontaneous electric polarization in the spiral ordered phase of TbMnO3.

SONTRAC: An imaging spectrometer for MeV neutrons

An instrument capable of unambiguously determining the energy and direction of incident neutrons has important applications in solar physics, environmental monitoring, and medical/radiological sciences. The SOlar Neutron TRACking (SONTRAC) instrument is designed to operate in the neutron energy range of 20–250MeV. It is based on non-relativistic double scatter of neutrons off ambient protons within a block of scintillating fibers. Using this double-scatter mode it is possible to uniquely determine neutron energy and direction on an event-by-event basis. A fully operational science model of such an instrument has been built and its performance (energy resolution, angular resolution) calibrated at MeV energies. The science model consists of a 5×5×5cm3 cube of orthogonal plastic scintillating fiber layers. Two orthogonal imaging chains allow full 3D reconstruction of scattered proton particle tracks. We report the results of the instrument development and calibration efforts, and discuss ongoing developmental efforts to improve performance.

A Neutron Source Imaging Detector for Nuclear Arms Treaty Verification

In this paper a detector design that is capable of finding the image of neutron sources within a nuclear missile is discussed. The method involves the double scatter of a neutron in an array of organic scintillator elements and the partial reconstruction of the incident neutron direction vector from the information the array provides. The Monte Carlo simulation results for a basic design and several modifications are presented. The results of an experimental demonstration of the technique using a crude prototype detector are given. Problems expected in a real application are discussed.

Recoil energy effects and defect processes in neutron irradiated metals

Subdivision of primary recoil energy into sub-cascades in 14 MeV neutron irradiated fcc metals is analyzed in reference to the primary recoil energy spectrum, 10–20 keV per sub-cascade depending on the kind of metals. Shape and size of sub-cascade groups are also related to the recoil energy, including the anisotropy with reference to the incident neutron direction. The extent of the overlapping of sub-cascades to produce vacancy clustered defects are classified from the spacing between sub-cascades, significant overlapping for narrow spacing less than 5 nm in Ag and Au, and no overlapping for wide separation more than 10 nm in Ni and Cu. The amount of point defects annihilated within the cascade zone is estimated and the roles of interstitial atoms released from the zone are categorized to propose a simplified kinetics modeling of the microstructure development. A discussion is made on the irradiation rate dependence from the defect cluster formation mechanism and from the degree of cascade-overlap. Analysis and diagnosis of the neutron-temperature history in fission reactor irradiation leads to a proposal of an essential improvement of the reactor irradiation.

Realization of a high sensitivity neutron rem counter

Abstract Two types of high sensitivity rem counters were realized by using large volume and high pressure 3He spherical counters: one filled with 10 atm 3He having a diameter of 5.08 cm, and one filled with 5 atm 3He having a diameter of 12.7 cm. The responses to neutron energy from thermal to 15 MeV were experimentally determined by using the national neutron standard field at the Electrotechnical Laboratory. It was confirmed that these two rem counters have about 10 and 70 times higher sensitivities, respectively, than the commercial rem counter Studsvik 2202D, and their neutron responses are well fitted to the ICRP-21 rem response and are almost isotropic to the incident neutron direction.

Method for locating and characterizing neutron sources

Counting neutron-induced tracks in plastics as a function of the orientation relative to the arrival direction of incident neutrons makes possible a rugged method of measuring the direction, fluence, and average energy of a directional flux of fast neutrons and the distance and strength of the source.

A scintillation counter array for detection of high energy neutrons

An array of 32 liquid scintillation counters used to detect neutrons in the energy range 20 to 340 MeV is described. Each unit consisted of a cylinder 45 cm long and 7 cm diameter, with the axis of the cylinder parallel to the incident neutron direction. The array was calibrated in the above energy range by use of neutron-proton elastic scattering. The average efficiency was 0.45. Some secondary properties of the array have been studied and are described.

The 14N(n, xγ) Reaction for 5.8 ≤ En ≤ 8.6 MeV

We have obtained gamma-ray spectra for the reactions 14N(n, n′γ)14N, 14N(n,þγ)14C, and 14N(n, αγ)11B for incident mean neutron energies En = 5.8, 6.4, 6.8, 7.4, 8.0, and 8.6 MeV. The gamma rays were detected using a coaxial Ge(Li) detector of 30 cm3 active volume. The detector was placed at 55 and 90° with respect to the incident neutron direction, and was 77 cm from the sample; time-of-flight was used with the gamma-ray detector to discriminate against pulses due to neutrons and background gamma radiation. The sample was 100 g of Be3N2 in the form of a right circular cylinder. Data were also obtained using a 75-g Be sample to provide an estimate of the background. The incident neutron beam was produced by bombarding a deuterium-filled gas cell with the pulsed deuteron beam of appropriate energy from the ORNL 6-MV Van de Graaff. The resulting neutron beam was monitored using a scintillation counter; a time-of-flight spectrum from this detector was recorded simultaneously with the gamma-ray data. These data have been studied to obtain absolute cross sections for production of gamma rays from 14N for the incident neutron energies quoted above. The cross sections have been compared, where possible, with previously measured values with good agreement. However, there are several important differences with previous data and these are discussed. In particular, summing the partial cross sections yields a value for the total nonelastic cross section that is approximately half of the total nonelastic cross section obtained from the difference between the total cross section and the total elastic cross section.