Recoil Particles Research Articles

The effect of energy of Ar recoil particles on the interfaces and micro-structure in Ni/Ti multilayer fabricated by direct current magnetron sputtering technique

Ni/Ti multilayers have been therefore widely used in neutron optics devices because of their excellent reflective properties for neutrons, which is strongly dependent to their interfaces and microstructure. Hence, there have been many attempts to improve the interfaces and microstructure of Ni/Ti multilayers, for example reactive sputtering, interlayers and so on. In this paper, the influence of energy of Ar recoil particles on the interface and micro-structure of Ni/Ti multilayers were completed, through varying the sputtering pressure. Firstly, the Simulation present that the decreasing of sputtering pressure would enlarge the number recoil particle proportion. Secondly, three Ni/Ti multilayers were fabricated by direct current sputtering technique with variable sputtering pressures (0.080Pa, 0.120Pa, 0.199Pa). Thirdly, the grazing incidence X-ray reflectometry (GIXRR), diffusing scattering, X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) were used to characterize the interfaces and micro-structure of these films. The measured results present that their interfacial width and roughness were variable as diseasing the sputtering pressure, and the micro-structure of Ni layers transform from (111) only to both (111) and (100). These experimental results could result from the effects of energy of both Ar recoil particles and the Ni, Ti depositing atoms.

Tungsten sputtering coefficients by light impurities of plasma

Calculations of the tungsten sputtering coefficients (the divertor material in the ITER tokamak) by He, Be, N, O – impurity atoms in the plasma – were carried out at collision energy of 0.010–100 keV using the Monte–Carlo method. To calculate the trajectory of the incident particle, pair potentials obtained within the framework of density functional theory were used. These potentials were corrected for the parameters of the potential well obtained from spectroscopic measurements. The target consisted of tungsten randomly oriented crystals the size of one lattice constant. Next, the trajectories of the recoil particles were calculated using many-particle potentials calculated using density functional theory. Thermal vibrations of target atoms were taken into account. The vibration amplitude was taken to be 0.05 Å, which corresponded to room temperature. The strong dependence of the results on the shape of the surface potential barrier is shown and the results are presented for two limiting cases of the surface state: a flat surface, when a planar surface potential barrier is realized, and a surface consisting of cones, when a spherical potential barrier occurs. In the experiment, the surface has some roughness, which depends on the experimental conditions. It is shown that the experimental results lie between the limiting cases we considered. Information was obtained on the average energy of sputtered atoms and angular distributions, necessary for calculating the entry of impurities into the tokamak plasma.

Characterization of 235U, 238U and 239Pu fission ionization chamber foils by [formula omitted] and [formula omitted]-ray spectrometry

The masses of thin, electroplated deposits of 235U, 238U and 239Pu on titanium backings have been determined to better than 1.3% precision by employing three complementary measurement techniques: α spectrometry, 2π gas counting, and γ-ray spectrometry. A dedicated α spectrometer was designed and calibrated to allow for repeatable, high-precision measurements of the absolute α activity of a sample. The isotopic composition of the sample was determined by fitting the peaks in the α spectrum, a technique which was demonstrated to be generally consistent with mass spectrometry. Independently, the total activity of the deposits were measured in a 2π gas flow proportional counter. A detailed study of the effects of α particle straggling in the actinide deposit and α particle recoil off the sample backing material was performed. The masses of these actinide deposits were also measured via γ-ray spectrometry. We found that all three systematically independent techniques produced consistent results, and could be combined into a weighted average with further reduced uncertainty. The mass ratios of these actinide deposits were determined to better than 1% precision via α spectrometry, enabling high-precision fission cross section ratio measurements.

Quantification of the light output anistropy in deuterated stilbene

Deuterated stilbene is an organic scintillator that is a desirable material for fast neutron spectroscopy using spectrum unfolding techniques without requiring time-of-flight information. Due to the crystal structure of the material, some anisotropy of the light output exists, which is dependent on the direction of heavy charged particle recoil relative to the crystal structure. The anisotropy of trans-stilbene (hereafter referred to as stilbene) has been well characterized in previous work, but for deuterated stilbene, the anisotropy has only been partially characterized along the a and b crystal axes, while the artificial c′ axis, which shows the largest anisotropy in stilbene, has not been characterized until this publication. In this work, two deuterated stilbene crystals were characterized with neutron energies up to 35 MeV at the Los Alamos Neutron Science Center. For one of the crystals, the response is characterized along the a, b, and c′ axes. This characterization shows a distinct anisotropy along the axes in deuterated stilbene, which is very similar to that found in regular stilbene, such that the a axis is the brightest, while the b and c′ axes are approximately 3% and 20%–35% lower relative to the a axis.

Radiative corrections to neutron and nuclear β-decays: a serious kinematics problem in the literature

We report a serious kinematics problem in the bremsstrahlung photon part of the order-α outer (model independent) radiative correction calculations for those neutron (and nuclear beta) decay observables (like electron-neutrino correlation parameter measurement) where the proton (recoil particle) is detected. The so-called neutrino-type radiative correction calculations, which fix the neutrino direction in the bremsstrahlung photon integrals, use 3-body decay kinematics to connect the unobserved neutrino direction with the observed electron and proton (recoil particle) momenta. But the presence of the bremsstrahlung photon changes the kinematics from 3-body to 4-body one, and the accurate information about the recoil particle momentum is lost due to the integration with respect to the photon momentum. Therefore the application of the abovementioned 3-body decay kinematics connection for the radiative correction calculations, rather prevalent in the literature, is not acceptable. We show that the correct, so-called recoil-type radiative correction calculations, which fix the proton (recoil particle) momentum instead of the neutrino direction and use rather involved analytical, semianalytical or Monte Carlo bremsstrahlung integration methods, result usually in much larger corrections than the incorrect neutrino-type analytical methods.

Cait: Analysis Toolkit for Cryogenic Particle Detectors in Python

Cryogenic solid state detectors are widely used in dark matter and neutrino experiments, and require a sensible raw data analysis. For this purpose, we present Cait, an open source Python package with all essential methods for the analysis of detector modules fully integrable with the Python ecosystem for scientific computing and machine learning. It comes with methods for triggering of events from continuously sampled streams, identification of particle recoils and artifacts in a low signal-to-noise ratio environment, the reconstruction of deposited energies, and the simulation of a variety of typical event types. Furthermore, by connecting Cait with existing machine learning frameworks we introduce novel methods, for better automation in data cleaning and background rejection.

Precision measurement of Compton scattering in silicon with a skipper CCD for dark matter detection

Experiments aiming to directly detect dark matter through particle recoils can achieve energy thresholds of $\mathcal{O}(1\,\mathrm{eV})$. In this regime, ionization signals from small-angle Compton scatters of environmental $\gamma$-rays constitute a significant background. Monte Carlo simulations used to build background models have not been experimentally validated at these low energies. We report a precision measurement of Compton scattering on silicon atomic shell electrons down to 23$\,$eV. A skipper charge-coupled device (CCD) with single-electron resolution, developed for the DAMIC-M experiment, was exposed to a $^{241}$Am $\gamma$-ray source over several months. Features associated with the silicon K, L$_{1}$, and L$_{2,3}$-shells are clearly identified, and scattering on valence electrons is detected for the first time below 100$\,$eV. We find that the relativistic impulse approximation for Compton scattering, which is implemented in Monte Carlo simulations commonly used by direct detection experiments, does not reproduce the measured spectrum below 0.5$\,$keV. The data are in better agreement with $ab$ $initio$ calculations originally developed for X-ray absorption spectroscopy.

Recoil and charged particle energy spectra from the natSi(n,x) reaction and the Si semiconductor detector response to the 14 MeV neutrons

The energy spectra of light and heavy charged particles generated by the 14 MeV neutrons in silicon nuclei and in the Si semiconductor detector (SSD) were analysed. The existing measurements were used to validate the corresponding energy differential cross sections from major evaluations ENDF/B-VIII.0 and JEFF-3.3. The required data were extracted by the various codes: NJOY21, SPKA and MCNP6. It was shown that both evaluations underestimate the high energy part of the 28Si(n,x)p- and α-particle spectra by ≤50%, whereas at smaller emission energies no experimental data even exist. The calculation of the atom displacement damage in SSD reveals that the secondary protons produce additionally ≈15% of damage, whereas the contribution from secondary alphas is impossible to estimate since the Si(α,x) recoil data are not available.The single experiment, carried out by K. Yageta and co-workers in 1988, reported the energy spectra in the Si semiconductor down to the rather low energy of ≈0.3 MeV, at which the production of reaction recoils dominates over the light ions. The Monte Carlo simulation of this experiment was performed by MCNP6. The generation and transport of all relevant ions were taken in account. The energy depositions from protons or alphas were summed with their associated recoils after correction for non-ionization losses. The neutron reactions in the dead layer of the SSD were shown to increase the counts in active layer by (1–20)% depending on sort of ions. The impact of the field funneling effect was studied. Consideration of all these underlying processes has eventually allowed a reasonable reproduction of this experiment.

The formation mechanisms of high burnup structure in UO2 fuel

The formation process of high burnup structure (HBS) in UO 2 fuel is accompanied by the subdivision of original grains and the formation of fission gas bubbles, which can accelerate the fission gas swelling and release, and correspondingly raises some safety concerns over the extension of operating life of the nuclear fuel in the reactor. The UO 2 fuel specimens were irradiated up to a maximum burnup of 120 GW·d/tU in High Flux Engineering Testing Reactor (HFETR) of Nuclear Power Institute of China (NPIC). High resolution scanning electron microscope (SEM) observations were carried out in the fuel specimens with different local burnups of 48–120 GW·d/tU. Our results show that there exist two restructuring mechanisms during the formation of the HBS in UO 2 fuel matrix: polygonization and recrystallization. Furthermore, a comparison with earlier experiments published at the CEA of France suggests that the deposition of fission fragments and recoil particles is the main mechanism responsible for the formation of small grains on the inner wall of large bubbles.

Simultaneous measurement of organic scintillator response to carbon and proton recoils

Background: Organic scintillators are widely used for neutron detection in both basic nuclear physics and applications. While the proton light yield of organic scintillators has been extensively studied, measurements of the light yield from neutron interactions with carbon nuclei are scarce.Purpose: Demonstrate a new approach for the simultaneous measurement of the proton and carbon light yield of organic scintillators. Provide new carbon light yield data for the EJ-309 liquid and EJ-204 plastic organic scintillators.Method: A 33-MeV $^{2}\mathrm{H}^{+}$ beam from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory was impinged upon a 3-mm-thick Be target to produce a high-flux, broad-spectrum neutron beam. The double time-of-flight technique was extended to simultaneously measure the proton and carbon light yields of the organic scintillators, wherein the light output associated with the recoil particle was determined using $np$ and $n\mathrm{C}$ elastic scattering kinematics.Results: The proton and carbon light yield relations of the EJ-309 liquid and EJ-204 plastic organic scintillators were measured over a recoil energy range of approximately 0.3 to 1 MeV and 2 to 5 MeV, respectively, for EJ-309, and 0.2 to 0.5 MeV and 1 to 4 MeV, respectively, for EJ-204.Conclusions: These data provide new insight into the ionization quenching effect in organic scintillators and key input for simulation of the response of organic scintillators for both basic science and a broad range of applications.

Study on flow field in Falcon separator by high-speed dynamic photography and CFD simulation

ABSTRACT This research builds an experimental test platform to verify practicability of theoretical calculation formula and CFD simulation (Fluent software) by comparison of measured value and calculated value, including flow film thickness, recoil water velocity, fluid velocity, and particle velocity. For liquid velocity test, 1 mm polystyrene foam beads are used as tracer particles, while solid velocity test uses fine coal with a density of 1800 kg/m3 and a particle size of 0.5 mm as observation object. Measurement results show that flow film thickness measured value is consisted of that of calculated value, all relative error is less than 5%. But increase of rotational frequency can make relative error increase slightly, this may be caused by instability of flow film due to increasing rotational frequency. In terms of recoil water velocity, its measured value is almost same as calculated value and its relative error is lower. Measurement results of fluid velocity and particle velocity indicate that variation trend of tangential and axial velocity simulation value is basically same as experimental value. However, relative error of axial tangential is greater than that of tangential by 10% for fluid velocity and relative error of axial tangential is greater than that of tangential by 20% for particle motion velocity. The large deviation of axial velocity is that direction of the axial acceleration changes easily relative to the stable tangential velocity, the “relaxation phenomenon” of tracer particles in the experiment and interference from other aspects of flow field make deviation increase slightly.

Axial and pseudoscalar form factors from charged current quasielastic neutrino-nucleon scattering

We study the scattering of neutrinos on polarized and unpolarized free nucleons, and also the polarization of recoil particles in these scatters. In contrast to electromagnetic processes, the parity-violating weak interaction gives rise to large spin asymmetries at leading order. Future polarization measurements could provide independent access to the proton axial structure and allow the first extraction of the pseudoscalar form factor from neutrino data without the conventional partially conserved axial current (PCAC) ansatz and assumptions about the pion-pole dominance. The pseudoscalar form factor can be accessed with precise measurements with muon (anti)neutrinos of a few hundreds $\mathrm{MeV}$ of energy or with tau (anti)neutrinos. The axial form factor can be extracted from scattering measurements using accelerator neutrinos of all energies.

Defect spectroscopy and non-ionizing energy loss analysis of proton and electron irradiated p-type GaAs solar cells

Admittance spectroscopy combined with non-ionizing energy loss (NIEL) analysis is shown to be a powerful tool for analyzing solar cell radiation degradation, not relying on the change of macroscopic cell parameters. GaAs component cells, representative of the middle sub-cell in Ga0.5In0.5P/GaAs/Ge solar cells, were irradiated with protons and electrons in the 0.5–3 MeV energy range. Four irradiation-induced defects are identified in the p-type base layer. The nature of each defect is assessed by analyzing the dependence of its introduction rate on the NIEL deposited by electrons in the semiconductor. The expected linear relationship is only achieved if a unique threshold energy Ed is ascribed to each defect, which ranges from 9 to 38 eV. An electron NIEL with Ed=21eV, customarily used for GaAs-based solar cell degradation analysis, is an approximation of the relative abundance of these four defects. The 21 eV value is thus a GaAs material-specific parameter, independent of the electrical device design. In addition, the type and energy of the incident particle is correlated with the relative abundance of high Ed defects. The impact of each defect on the macroscopic electrical parameters of the cell, namely, the open-circuit voltage VOC, the short-circuit current density JSC, and the recombination current density J02, is assessed with the help of a Pearson analysis. The different effectiveness of electron and proton irradiation on parameters dominated by recombination in the depleted region, such as VOC or J02, is attributed in part to the influence of the particle recoil spectra on the defect capture cross section.

Direct reconstruction of the pp – elastic scattering amplitudes at U70

The direct reconstruction of pp elastic scattering amplitudes at the SPASCHARM experiment is discussed. The observables are expressed in terms of invariant amplitudes. These amplitudes are deduced analytically by solving bilinear relations.Monte-Carlo simulations of elastic scattering as well background reactions were carried out. Elastic and diffraction interactions of protons were simulated by using PYTHIA generator for 16 GeV incident protons, designed Setup geometry and the resolution of the detectors. The criteria to select elastic processes are discussed and presented. Two-dimensional distributions of the product of the tangents of the polar angles of the recoil particle and the scattered particle versus difference of the azimuth angles of these particles, were obtained. The estimated ratio of the signal to background S/(S+B) is about 0.99.

Design and dosimetry of a facility to study health effects following exposures to fission neutrons at low dose rates for long durations

Purpose During extended missions into deep space, astronauts will be exposed to a complex radiation field that includes high linear energy transfer (LET) radiation from high energy, heavy ions (HZE particles) at low dose rates of about 0.5 mGy/d for long durations. About 20% of the dose is delivered by ions with LET greater than 10 keV/µm. There are sparse empirical data in any species for carcinogenic effects from whole-body exposures to external sources of mixed or high LET radiation at this level of dose rates. For the induction of solid tumors, acute exposures to HZE ions have been shown to be substantially more effective per unit dose than low LET exposures associated with photons. To determine the health effects of high LET radiation at space-relevant dose rates on experimental animals, we developed a vivarium in which rodents could be irradiated with Californium (252Cf) neutrons for protracted periods of time. Materials and methods The neutron source is a panoramic irradiator containing 252Cf located in a concrete shielded vault with a footprint of 53 m2. The vault can accommodate sufficient caging to simultaneously irradiate 900 mice and 60 rats for durations up to 400 d at a dose rate of 1 mGy/d and is approved for extended animal husbandry. Results The mixed field fluence is a combination of neutrons and photons emitted directly from the source and scattered particles from the concrete walls and floor. Mixed field dosimetry was performed using a miniature GM counter and CaF2:Dy thermoluminescent dosimeters (TLD) for photons and tissue-equivalent proportional counters (TEPC) for neutrons. TEPC data provided macroscopic dose rates as well as measurements of radiation quality based on lineal energy, y, and LET. The instantaneous dose rate from the source decreases with a half-life of 2.6 years. The exposure time is adjusted weekly to yield a total dose 1 mGy/d. The photon contribution is 20% of the total dose. The uncertainty in the delivered dose is estimated to be ±20% taking into account spatial variations in the room and random position of mice in each cage. The dose averaged LET for the charged particle recoil nuclei is 68 keV/µ. Conclusions We have developed a facility to perform high LET studies in mice and rats at space relevant dose rates and career-relevant doses using neutrons emitted from the spontaneous fission of 252Cf.

Jet modification with medium recoil in quark-gluon plasma

Jet energy transported to quark-gluon plasma during jet-medium interaction excites the QGP medium and creates energetic thermal partons – recoil particles or recoils. Modification of the jet structure in heavy ion collisions is studied using martini, in which recoil simulation is enabled. In large systems such as central Pb-Pb collisions, the recoil effect is expected to be critical due to strong jet-medium interaction. We show the results of the jet mass function and jet shape function are improved when the recoil particles are included in the reconstructed jets. We conclude that the energy carried by the recoil particles are regarded as a part of reconstructed jets and are necessary in studying jet modification in heavy ion collisions.

HCAL-J: hadron calorimeter for the study of nucleon form factors at Jefferson Lab

ABSTRACTHCAL-J is a hadron calorimeter under construction at JLAB in Newport News, VA (USA).The main interest of the JLAB physics is the study of the hadron matter properties, using a longitudinally polarised electron beam; in particular, researchers investigate the electromagnetic form factors of nuclei and nucleons using the Continuous Electron Beam Accelerator Facility (CEBAF) accelerator, which provides a beam of 12 GeV electrons. The upgrade to higher energies allows measurements at high values of Q2 and a more in-depth study of the internal structure of the hadron matter.To this purpose, Hall A collaboration is building the SuperBigBite Spectrometer (SBS), which consists of a series of elements including a dipole magnet to curve the trajectory of the recoil particles, and a series of Gas Electron Multiplier (GEM) to track the particles. Moreover, two analyzers for the measurement of the polarisation components and a hadron calorimeter, HCAL-J, to measure the particle energy, are used in order to apply the so-called recoil polarisation method, which consists in measuring both the longitudinal and transverse polarisation of the scattered nucleon.The study, through SBS, of the electromagnetic form factors of nucleons allows obtaining the ratio between these two components, which results to be proportional to the ratio between the electric and magnetic form factors of the nucleon.HCAL-J is a sampling calorimeter useful to measure the energy of the recoil nucleon; its active area consists of 288 modules that include a matrix with 24 modules in height and 12 in width. There are optical fibres in between each module, connected to a photomultiplier, in order to look at the light from the scintillating material and convert it into an electric signal, related to the energy of the incident particle.

Performance test of the MAIKo active target

A new active target named MAIKo (Mu-PIC based Active target for Inverse Kinematics∘) has been developed at Kyoto University and Research Center for Nuclear Physics (RCNP), Osaka University. MAIKo is suited for missing-mass spectroscopy of unstable nuclei at forward scattering angles in inverse kinematics. MAIKo consists of a time projection chamber (TPC), which incorporates a micro-pixel chamber (μ-PIC) as the electron multiplication and collection system. In MAIKo, the medium gas also plays the role of a reaction target, thus allowing detection of low-energy recoil particles with high position resolution. The MAIKo TPC was commissioned with He(93%)+iso-C4H10(7%) and He(93%)+CO2(7%) mixture gasses at 430 hPa. The gas gain and the angular resolution of MAIKo were evaluated with an alpha source and a 4He beam at 56 MeV. The TPC was stably operated up to 1000-kcps beam intensity. A tracking algorithm using the Hough transform method has been developed to analyze scattering events. An angular resolution of 1.3°was achieved for scattered 4He particles.

Measurement of 99Mo Yield in 100Mo(p, x) with 30 MeV Proton Irradiation of Multicomponent Submicron Particles

The radionuclide 99Mo was produced and separated in the process of irradiating powdered mixtures of molybdenum compounds and buffer particles by 30 MeV protons. The separation is based on the Szilard–Chalmers effect wherein 99Mo recoil particles are fixed in inert buffer particles. Two types of targets were investigated by using mixtures: soluble molybdenum compound–insoluble buffer and insoluble molybdenum compound–soluble buffer. 99Mo yield equal to 20% with enrichment coefficient 18.3 was obtained by using a target consisting of a mixture of submicron 100MoO3 and Al2O3 particles; the 99Mo yield was equal to 20% and the enrichment coefficient 18.3. For a target with the composition 100MoS2 + KCl, making it possible to separate 99Mo recoil atoms directly into solution, the 99Mo yield was equal to 8.7% and the enrichment coefficient 30.7.

COMPASS results on DVCS and exclusive π0 production

The high energy polarised muon beam available at CERN, with positive or negative charge, makes COMPASS a unique place for studies of General Parton Distributions (GPDs). The dedicated COMPASS GPD program started in 2012 with commissioning of a new long liquid hydrogen target and new detectors, such as the large recoil particle detector CAMERA and the large-angle electromagnetic calorimeter. It was followed by a short pilot ‘DVCS run’. The first results on DVCS and exclusive π0 channels have been obtained. From the sum of cross sections measured with positive and negative beam polarities the pure DVCS cross-section and its dependence on the squared four-momentum transfer t have been extracted. It allowed a first estimate of the transverse size of the partonic distribution of the nucleon in a range of intermediate xBj with a mean xBj value of 0.056. We report also on the absolute value of the cross section for exclusive π0 production and its dependence on t and azimuthal angle ϕ between the scattering plane and π0 production plane. These measurements are aiming to constrain the GPDs, in particular chiral-odd (transversity) GPDs. The full data taking for the GPD program approved within the COMPASS-II proposal continues in 2016 and 2017.