Pulsed Neutron Beam Research Articles

Fundamental neutron physics beamline at the spallation neutron source at ORNL

We describe the Fundamental Neutron Physics Beamline (FnPB) facility located at the Spallation Neutron Source at Oak Ridge National Laboratory. The FnPB was designed for the conduct of experiments that investigate scientific issues in nuclear physics, particle physics, astrophysics and cosmology using a pulsed slow neutron beam. We present a detailed description of the design philosophy, beamline components, and measured fluxes of the polychromatic and monochromatic beams.

Refractive and diffractive neutron optics with reduced chromatic aberration

Thermal neutron beams are an indispensable tool in physics research. The spatial and the temporal resolution attainable in experiments are dependent on the flux and collimation of the neutron beam which remain relatively poor, even for modern neutron sources. These difficulties may be mitigated by the use of optics for focusing and imaging. Refractive and diffractive optical elements, e.g. compound refractive lenses and Fresnel zone plates, are attractive due to their low cost, and simple alignment. These optical elements, however, suffer from chromatic aberration, which limit their effectiveness to highly monochromatic beams. This paper presents two novel concepts for focusing and imaging non-monochromatic thermal neutron beams with well-known optical elements: (1) a fast mechanical transfocator based on a compound refractive lens, which actively varies the number of individual lenses in the beam path to focus and image a time-of-flight beam, and (2) a passive optical element consisting of a compound refractive lens, and a Fresnel zone plate, which may focus and image both continuous and pulsed neutron beams.

Pulse-width analysis for neutron capture cross-section measurement using an NaI(Tl) detector

A fast data acquisition method based on pulse-width analysis was developed for measuring neutron capture cross-sections using an NaI(Tl) detector. The new method was tested by detecting γ-rays from standard γ-ray sources and neutron-induced reactions. Non-linear relation between the γ-ray energy and the pulse width of the detector output signal was studied. The neutron beam experiments were performed using a pulsed neutron beam from a spallation neutron source at the Japan Proton Accelerator Research Complex. Detector-deposited energy spectra were reconstructed from the pulse-width spectra using the parameterized relation between the pulse width and the γ-ray energy. Time response properties of the pulse-width analysis method were compared with the traditional pulse-height analysis method. Detailed analysis of the experimental results demonstrated that the present method was more resistive to intense γ-ray bursts from the spallation neutron source.

Quasi-differential neutron scattering from 238U from 0.5 to 20 MeV

The Rensselaer Polytechnic Institute Linear Accelerator was used to produce a pulsed neutron beam that was incident on a 238U scattering sample 30m from the source. Eight liquid scintillator (EJ-301) proton recoil fast neutron detectors located at several angles surrounding the sample were positioned at a distance 0.5m. Neutrons resulting from elastic scattering, inelastic scattering, and fission reactions were recorded as a function of time-of-flight. Pulse shape analysis including a new gamma misclassification correction was used to reduce erroneous counts from gamma events produced from fission and inelastic scattering reactions. The experimental data were simulated using an improved model of the Rensselaer Polytechnic Institute neutron scattering system that included individual detector efficiencies and neutron flux shape. The experimental data were compared with several evaluated nuclear data libraries using a figure-of-merit. Overall, the JENDL-4.0 evaluation provided the best agreement with the 238U experimental data. Furthermore, the Rensselaer Polytechnic Institute scattering model was used to constrain uncertainties that allowed for improvements to a new 238U evaluation.

Production of ultra cold neutrons by a doppler shifter with pulsed neutrons at J-PARC

Ultracold neutrons (UCNs) are neutrons whose kinetic energy is around a few hundred nanoelectronvolts. Neutrons with such small kinetic energy can be trapped in a material vessel or magnetic fields. Because of these unique characteristics, UCNs are used for some important experiments of fundamental physics. The Doppler shifter is a device to produce UCN by slowing them down by the reflection on a mirror moving with half of the velocity of incoming neutrons. A Doppler shifter using a quadruple-stack of monochromatic supermirrors that reflects neutrons with a velocity around 68m/s [1, Hino et al.(2010)] was fabricated, and operated with a pulsed neutron source of J-PARC. An important feature of the Doppler shifter is the use of a pulsed neutron beam. Unlike in continuous neutron beams, the neutron velocity can be selected by choosing a time slice in a pulsed neutron bunch. Thus the UCN production improves by ~80 times in the case of J-PARC. We successfully produced the UCNs by the Doppler shifter: the measured UCN production rate is consistent with the simulations.

A New Signal Processing Technique for Neutron Capture Cross Section Measurement Based on Pulse Width Analysis

A fast data acquisition method based on pulse width analysis was developed for γ-ray spectroscopy with an NaI(Tl) detector. The new method was tested in experiments with standard γ-ray sources and pulsed neutron beam from a spallation neutron source. Pulse height spectra were successfully reconstructed from pulse width distribution by use of an energy calibration curve. The 197Au(n, γ)198Au cross section was measured by this method to test the viability. The obtained experimental cross section showed a good agreement with a calculation using the resonance parameters of JENDL-4.0.

Time-of-flight measurement of fast neutrons with Timepix detectors

Timepix pixel detectors have been used to study theresponse of silicon hybrid pixel detectors to fast neutrons from a pulsedneutron beam at WNR FP30R, a 14 m long flight path, in the Los AlamosNeutron Science Center. Neutrons with kinetic energies up to 600 MeV wereavailable. In order to enhance the conversion of neutrons to energeticcharged particles, several converter foils and filters were attached to the300 μm thick silicon sensor, i.e. polyethylene, polyethylene withaluminum, 6LiF, 6LiF with aluminum, aluminum. The Time-of-Arrivalmode of the Timepix detectors has permitted the application of theTime-of-Flight (TOF) technique for the assignment of the detectedinteractions in the form of clusters (groups of adjacent pixels) in thepixel matrix, to the kinetic energies of the incident neutrons.It was found that, for lower neutron energies ( ∼ MeV range) the clusterrates below the polyethylene and the polyethylene and aluminum region,produced by recoil protons, are a good measure for the mean kinetic energiesof neutrons. For energies above 50 MeV nuclear reactions in the silicondominate the detector response. In this energy range the shape of theclusters indicates the neutron kinetic energy.

The Neutrons for Science Facility at SPIRAL-2

The Neutrons For Science (NFS) facility is a component of SPIRAL-2 laboratory under construction at Caen (France). SPIRAL-2 is dedicated to the production of high intensity Radioactive Ions Beams (RIB). It is based on a high-power linear accelerator (LINAG) to accelerate deuterons beams in order to produce neutrons by breakup reactions on a C converter. These neutrons will induce fission in 238U for production of radioactive isotopes. Additionally to the RIB production, the proton and deuteron beams delivered by the accelerator will be used in the NFS facility. NFS is composed of a pulsed neutron beam and irradiation stations for cross-section measurements and material studies. The beams delivered by the LINAG will allow producing intense neutron beams in the 100 keV–40 MeV energy range with either a continuous or quasi-mono-energetic spectrum. At NFS available average fluxes will be up to 2 orders of magnitude higher than those of other existing time-of-flight facilities in the 1 MeV – 40 MeV range. NFS will be a very powerful tool for fundamental physics and application related research in support of the transmutation of nuclear waste, design of future fission and fusion reactors, nuclear medicine or test and development of new detectors. The facility and its characteristics are described, and several examples of the first potential experiments are presented.

Partial Cross Sections of Neutron-Induced Reactions on [formula omitted]Cu at [formula omitted] = 6, 8, 10, 12, 14, and 16 MeV for 0νββ Background Studies

Partial cross-section measurements of (n,n'γ) reactions on natCu were carried out at tunl using monoenergetic neutrons at six energies of En = 6, 8, 10, 12, 14, 16 MeV. These studies were performed to provide accurate cross-section data on materials abundant in experimental setups involving HPGe detectors used to search for rare events, like the neutrino-less double-beta decay of 76Ge. Spallation and (α,n) neutrons are expected to cause the largest source of external background in the energy region of interest. At tunl pulsed neutron beams were produced via the 2H(d,n)3He reaction and the deexcitation γ rays from the reaction natCu(n,xγ) were detected with clover HPGe detectors. Cross-section results for the strongest transtions in 63Cu and 65Cu will be reported, and will compared to model calculations and to data recently obtained at lanl with a white neutron beam.

Measurements of Partial γ-ray Cross Sections in 60Ni([formula omitted]) Reactions

Absolute partial cross sections for production of discrete γ-rays using 60Ni(n,xnypzαγ) reactions with x≤3, y≤2 and z≤4 in a total of 20 reaction channels were measured. The data were taken using the GEANIE spectrometer comprised of 20 high-purity Ge detectors with BGO escape-suppression shields. The broad-spectrum pulsed neutron beam of the Los Alamos Neutron Science Center's (LANSCE) WNR facility provided neutrons in the energy range from 0.2 to 300 MeV. The time-of-flight technique was used to determine the incident neutron energies. Partial γ-ray cross sections have been measured for a total of 59 transitions and for neutron energies 1 MeV <En< 300 MeV. Hauser-Feshbach theoretical calculations with an improved cluster emission model in the pre-equilibrium process were performed up to En = 30 MeV and are compared to the experimental results.

Applications of a micro-pixel chamber (μPIC) based, time-resolved neutron imaging detector at pulsed neutron beams

The realization of high-intensity, pulsed spallation neutron sources such as J-PARC in Japan and SNS in the US has brought time-of-flight (TOF) based neutron techniques to the fore and spurred the development of new detector technologies. When combined with high-resolution imaging, TOF-based methods become powerful tools for direct imaging of material properties, including crystal structure/internal strain, isotopic/temperature distributions, and internal and external magnetic fields. To carry out such measurements in the high-intensities and high gamma backgrounds found at spallation sources, we have developed a new time-resolved neutron imaging detector employing a micro-pattern gaseous detector known as the micro-pixel chamber (μPIC) coupled with a field-programmable-gate-array-based data acquisition system. The detector combines 100μm-level (σ) spatial and sub-μs time resolutions with low gamma sensitivity of less than 10−12 and a rate capability on the order of Mcps (mega-counts-per-second). Here, we demonstrate the application of our detector to TOF-based techniques with examples of Bragg-edge transmission and neutron resonance transmission imaging (with computed tomography) carried out at J-PARC. We also consider the direct imaging of magnetic fields with our detector using polarized neutrons.

Neutron-decay Correlation Measurements with Polarized and Pulsed Beams

Abstract Neutron-decay polarization correlations arise due to the interference of amplitudes with different transformation properties, i.e. V, A, S, P, and T corresponding to vector, axial vector, scalar, pseudoscalar and tensor. Measurements of a number of these correlations are used to constrain fundamental parameters of the Standard Model as well as probe new physics. Recent and future efforts that I will discuss include time-reversal violating correlations, e.g. the D coefficient and its relation to the neutron EDM as well as the beta-neutrino correlation, with emphasis on systematic errors that could arise from residual polarization that can be measured with a pulsed neutron beam such as provided by the SNS or ESS.

Beam Line Parameters for PERC at the ESS

Abstract Precision measurements of correlations in neutron beta decay test the standard model of particle physics. Here, pulsed neutron beams are invaluable to fight systematic effects. We show that the Proton Electron Radiation Channel PERC in pulsed mode is particularly well suited for a long-pulse spallation source, due to its long decay volume. We indicate how the optimum beam line parameters to run PERC at the ESS can be derived and compare the performance with that at the most powerful continuous source, the reactor of the ILL.

Systematic Advantages of Pulsed Beams for Measurements of Correlation Coefficients in Neutron Decay

Abstract Measurements of correlation coefficients in neutron beta decay probe the structure of the weak interaction and serve to search for new physics beyond the standard model of particle physics. In this article we describe how pulsed cold neutron beams can be employed to effectively eliminate or control leading sources of systematic uncertainty. As two examples we introduce the existing instrument PERKEO III and the new instrument PERC.

Observation of the dependence on drift field of scintillation from nuclear recoils in liquid argon

We have exposed a dual-phase liquid argon time projection chamber (LAr-TPC) to a low energy pulsed narrow-band neutron beam, produced at the Notre Dame Institute for Structure and Nuclear Astrophysics, to study the scintillation light yield of recoiling nuclei. Liquid scintillation counters were arranged to detect and identify neutrons scattered in the LAr-TPC and to select the energy of the recoiling nuclei. We report the observation of a significant dependence (up to 32%) on the drift field of liquid argon scintillation from nuclear recoils of energies between 10.8 and 49.9 keV. The field dependence is stronger at lower energies. Since it is the first measurement of such an effect in liquid argon, this observation is important because, to date, estimates of the sensitivity of LAr-TPC dark matter searches are based on the assumption that the electric field has only a small effect on the light yield from nuclear recoils.Received 25 June 2013DOI:https://doi.org/10.1103/PhysRevD.88.092006© 2013 American Physical Society

Energy resolution of pulsed neutron beam provided by the ANNRI beamline at the J-PARC/MLF

We studied the energy resolution of the pulsed neutron beam of the Accurate Neutron–Nucleus Reaction Measurement Instrument (ANNRI) at the Japan Proton Accelerator Research Complex/Materials and Life Science Experimental Facility (J-PARC/MLF). A simulation in the energy region from 0.7meV to 1MeV was performed and measurements were made at thermal (0.76−62meV) and epithermal energies (4.8−410eV). The neutron energy resolution of ANNRI determined by the time-of-flight technique depends on the time structure of the neutron pulse. We obtained the neutron energy resolution as a function of the neutron energy by the simulation in the two operation modes of the neutron source: double- and single-bunch modes. In double-bunch mode, the resolution deteriorates above about 10eV because the time structure of the neutron pulse splits into two peaks. The time structures at 13 energy points from measurements in the thermal energy region agree with those of the simulation. In the epithermal energy region, the time structures at 17 energy points were obtained from measurements and agree with those of the simulation. The FWHM values of the time structures by the simulation and measurements were found to be almost consistent. In the single-bunch mode, the energy resolution is better than about 1% between 1meV and 10keV at a neutron source operation of 17.5kW. These results confirm the energy resolution of the pulsed neutron beam produced by the ANNRI beamline.

New concept for a neutron electric dipole moment search using a pulsed beam

A concept to search for a neutron electric dipole moment (nEDM) is presented, which employs a pulsed neutron beam instead of the nowadays established use of storable ultracold neutrons (UCN). The technique takes advantage of the high peak flux and the time structure of a next-generation pulsed spallation source like the planned European Spallation Source. It is demonstrated that the sensitivity for a nEDM can be improved by several orders of magnitude compared to the best beam experiments performed in the 1970's and can compete with the sensitivity of UCN experiments.

Small plasma focus as neutron pulsed source for nuclides identification

In this paper, we present preliminary results on the feasibility of employing a low energy (2 kJ, 31 kV) plasma focus device as a portable source of pulsed neutron beams (2.45 MeV) generated by nuclear fusion reactions D-D, for the "in situ" analysis of substances by nuclear activation. This source has the relevant advantage of being pulsed at requirement, transportable, not permanently radioactive, without radioactive waste, cheap, among others. We prove the feasibility of using this source showing several spectra of the characteristic emission line for manganese, gold, lead, and silver.

Two-dimensional differential calibration method for a neutron dosemeter using a thermal neutron beam

A new thermal neutron calibration method to experimentally determine the energy response function of a neutron detector using a pulse parallel beam and the time-of-flight (TOF) technique is developed. The calibration method was experimentally demonstrated for a (3)He proportional counter and an electric personal dosemeter using a pulsed thermal neutron beam from the research reactor JRR-3M. The responses of the detectors were successfully obtained as a function of neutron energy. However, detailed information on the detector structure is required to obtain the spatial response distribution for the detector. The authors further propose an improved calibration method obtaining the spatial response distribution using a pulsed narrow beam, the TOF technique and a beam scanning technique.

Measurement of235U(n,n′γ) and235U(n,2nγ) reaction cross sections

The design of generation IV nuclear reactors and the studies of new fuel cycles require knowledge of the cross sections of various nuclear reactions. Our research is focused on ($n,xn\ensuremath{\gamma}$) reactions occurring in these new reactors. The aim is to measure unknown cross sections and to reduce the uncertainty on present data for reactions and isotopes of interest for transmutation or advanced reactors. The present work studies the ${}^{235}$U($n,{n}^{\ensuremath{'}}\ensuremath{\gamma}$) and ${}^{235}$U($n,2n\ensuremath{\gamma}$) reactions in the fast neutron energy domain (up to 20 MeV). The experiments were performed with the Geel electron linear accelerator GELINA, which delivers a pulsed white neutron beam. The time characteristics enable measuring neutron energies with the time-of-flight (TOF) technique. The neutron induced reactions [in this case inelastic scattering and ($n,2n$) reactions] are identified by on-line prompt $\ensuremath{\gamma}$ spectroscopy with an experimental setup including four high-purity germanium (HPGe) detectors. A fission ionization chamber is used to monitor the incident neutron flux. The experimental setup and analysis methods are presented and the model calculations performed with the TALYS-1.2 code are discussed.