Energy Spectra Of Α-particles Research Articles

Observation of near-scission “polar” and “equatorial” proton emission in heavy-ion induced fission

Proton and α-particle energy spectra were measured in coincidence with fission fragments at different relative angles in 16O (96 MeV) + 232Th reaction. The multiplicity spectra were analyzed within the framework of a Moving Source Disentangling Analysis (MSDA) to determine contributions from different emission stages. The MSDA conclusively shows “Near Scission Emission (NSE)” as an essential component in the multiplicity spectra. In contrast to NSE α particles which emit mainly perpendicular (“equatorial emission”), the NSE protons are observed to be emitted perpendicular as well as parallel (“polar emission”) to the fission axis with similar intensities (~20% for each). Thus, around 40% of total pre-scission protons are emitted near the scission stage, whereas the same fraction for α particles is only around 10%. The inevitable presence of “polar” and “equatorial” NSE protons in a heavy-ion induced fission has been observed for the first time. Present results open up a new avenue to study the heavy-ion induced fission dynamics.

Single nucleation of Cl-doped FAPbBr3 with inhibited ion migration for ambipolar radiation detection

High-quality and dopant-compensated FAPbBr3−xClx single crystals were demonstrated. The as-grown FAPbBr2.9Cl0.1 prevented halide migration appreciably and exhibited well-defined α-particle energy spectra of both electrons and holes.

The New Physics in LILITA_N21: An Improved Description of the Reaction 190 MeV 40Ar + 27Al

In this paper, light charged particle emission in the evaporation residue channel for the 190 MeV 40Ar + 27Al reaction leading to 67Ga composite nuclei at Ex = 91 MeV and angular momentum up to 46 ℏ has been re-analyzed. The main goal was to study the decay of 67Ga on the basis of an extended set of observables in order to provide a description of the evaporative decay cascades using the multistep Monte Carlo approach. The proton and α-particle energy spectra along with their angular distributions and ratios of differential multiplicities have been considered. The measured observables were compared with statistical model calculations. Having used a single-step Monte Carlo approach and standard parameters decades ago, the model does not provide a good description of the full dataset. Only a subset of the data was reproduced by assuming emitting nuclei with very large deformed shapes in a previous work published in the late 1980s. In the reported analysis, better agreement has been observed. Using the new transmission coefficients from the Optical Model, the parameters of which have recently been derived, the multi-step approach and the introduction of a nuclear shape description based on the nuclear stratosphere allowed us to realize a significant improvement.

LILITA_N21: Updated version of the Monte Carlo fusion–evaporation code

Since the code LILITA was presented in 1981 by Gomez Del Campo and Stockstad (1981)[1] and used to simulate the emission of light particles in the decay of a compound nucleus, relevant improvements have been made. Revisions leading to LILITA_N97 were begun by G. La Rana (Naples), M. Kaplan (CMU, Pittsburgh, PA), J.M. Alexander (Stony Brook, NY) and continued by the Naples Group (Moro et al., 2012) [2]. In this work new key features of the code consisting of the implementation of transmission coefficients based on global parametrization of the optical model potential, a description of the nuclear shape based on the nuclear stratosphere model, the parallelization of the code and a graphical user interface are presented. We expect that the new code version, LILITA_N21, makes it possible a better reproduction of wide data set from literature. In order to illustrate how this could be achieved, the standard statistical model predictions have been compared with those obtained with the new code features. A single set of parameters of the new code simultaneously well reproduces the neutron, proton and α-particle energy spectra, angular distributions, and multiplicities in the fusion–evaporation channel. By way of example, here the calculations are compared with experimental data of the reaction 60Ni+100Mo at the excitation energy of about 280MeV (Charity et al., 2003) [3]. The capability to reduce the execution time by exploiting the code parallelization is also discussed.

Effective neutron detection using vertical-type BGaN diodes

In this study, vertical-type thick BGaN PIN diodes were successfully fabricated to improve the neutron capture rate of BGaN diodes by improving the BGaN epitaxial growth technique. In this technique, 5-μm-thick epitaxial growth was achieved using trimethylboron as a B metal-organic source, which suppressed the gas-phase reaction. The α-particle energy spectrum, the neutron pulse signal, and the residual energy of particles emitted from a neutron capture reaction were measured using the fabricated BGaN diodes by performing radiation detection measurements. The detected signal position in the neutron detection signal spectrum was similar to that of 2.3 MeV α-particles. These results indicate that vertical-type BGaN diodes can be used as effective neutron detectors.

Diagnostic of fast-ion energy spectra and densities in magnetized plasmas

The measurement of the energy spectra and densities of α-particles and other fast ions are part of the ITER measurement requirements, highlighting the importance of energy-resolved energetic-particle measurements for the mission of ITER. However, it has been found in recent years that the velocity-space interrogation regions of the foreseen energetic-particle diagnostics do not allow these measurements directly. We will demonstrate this for γ-ray spectroscopy (GRS), collective Thomson scattering (CTS), neutron emission spectroscopy and fast-ion Dα spectroscopy by invoking energy and momentum conservation in each case, highlighting analogies and differences between the different diagnostic velocity-space sensitivities. Nevertheless, energy spectra and densities can be inferred by velocity-space tomography which we demonstrate using measurements at JET and ASDEX Upgrade. The measured energy spectra agree well with corresponding simulations. At ITER, α-particle energy spectra and densities can be inferred for energies larger than 1.7 MeV by velocity-space tomography based on GRS and CTS. Further, assuming isotropy of the α-particles in velocity space, their energy spectra and densities can be inferred by 1D inversion of spectral single-detector measurements down to about 300 keV by CTS. The α-particle density can also be found by fitting a model to the CTS measurements assuming the α-particle distribution to be an isotropic slowing-down distribution.

Alpha-particle velocity-space diagnostic in ITER

We discuss α-particle velocity-space diagnostic in ITER based on the planned collective Thomson scattering (CTS) and γ-ray spectrometry (GRS) systems as well as ASCOT simulations of the α-particle distribution function. GRS is sensitive to α-particles with energies MeV at all pitches p, and CTS for MeV and . The remaining velocity space is not observed. GRS and CTS view the plasma (almost) perpendicularly to the magnetic field. Hence we cannot determine the sign of the pitch of the α-particles and cannot distinguish co- and counter-going α-particles with the currently planned α-particle diagnostics. Therefore we can only infer the sign-insensitive 2D distribution function by velocity-space tomography for MeV. This is a serious limitation, since co- and counter-going α-particle populations are expected to have different birth rates and neoclassical transport as well as different anomalous transport due to interaction with modes such as Alfvén eigenmodes. We propose the installation of an oblique GRS system on ITER to allow us to diagnostically track such anisotropy effects and to infer the full, sign-sensitive for MeV. α-particles with MeV are diagnosed by CTS only, which does not allow velocity-space tomography on its own. Nevertheless, we show that measurements of the α-particle energy spectrum, which is an ITER measurement requirement, are now feasible for MeV using a velocity-space tomography formalism assuming isotropy in velocity space.

Investigation of thickness uniformity of thin metal films by using α-particle energy loss method and successive scanning measurements

The metal films are widely used in the Inertial Confinement Fusion (ICF) experiments to obtain the radiation opacity, and the accuracy of the measuring results mainly depends on the accuracy of the film thickness and thickness uniformity. The traditional used measuring methods all have various disadvantages, the optical method and stylus method cannot provide mass thickness which reflects the internal density distribution of the films, and the weighing method cannot provide the uniformity of the thickness distribution. This paper describes a new method which combines the α-particle energy loss (AEL) method and the successive scanning measurements to obtain the film thickness and thickness uniformity. The measuring system was partly installed in the vacuum chamber, and the relationship of chamber pressure and energy loss caused by the residual air in the vacuum chamber was studied for the source-to-detector distance ranging from 1 to 5 cm. The results show that the chamber pressure should be less than 10 Pa for the present measuring system. In the process of measurement, the energy spectrum of α-particles transmitted through each different measuring point were obtained, and then recorded automatically by a self-developed multi-channel analysis software. At the same time, the central channel numbers of the spectrum (CH) were also saved in a text form document. In order to realize the automation of data processing and represent the thickness uniformity visually in a graphic 3D plot, a software package was developed to convert the CH values into film thickness and thickness uniformity. The results obtained in this paper make the film thickness uniformity measurements more accurate and efficient in the ICF experiments.

Study on the Measurement of U-238 Neutron Yield Base on the Fission Chamber

This paper discusses a variety of fission neutron yield measurement method, a D-T / D-D neutron yield monitoring of U-238 fission ionization chamber measuring system, the application of spontaneous decay of U-238 α-particles for initial debugging of the system. At different voltage on the α-particle energy spectrum and α particle counts were measured, given the U-238 fission chamber curve to determine the U-238 fission chamber measurement system the best operating parameters.

Calibration of an alpha particle irradiator for in vitro cells irradiation

An alpha particle irradiator using 210Po radioactive sources was calibrated under specific conditions for cell irradiation. The energy spectrum of α-particles hitting the cell monolayer was measured by a surface barrier detector. The simulation of the results obtained with this detector was performed using the MCNPX Monte Carlo code with the same conditions used during the experimental measurements. Based on the experimental results the LET spectrum at the cell monolayer was extracted using the published Stopping Power and Range tables from the National Institute of Standards and Technology database. From this spectrum the average LET value was calculated to be (154 ± 9) keV/μm. In order to calculate the dose value at the cell monolayer, the alpha particle count rate hitting the cells was also estimated from the experimental measurements and compared with the activity of the source. Finally, the dose rate value at cell monolayer was calculated using the measured particle fluence.

Internal conversion and summing effects in heavy-nuclei spectroscopy

Internal conversion of low-energy nuclear transitions occurs with a high probability in heavy nuclei. After the emission of the conversion electron, a cascade of X-rays, Auger or Coster–Krönig electrons takes place. In α-decay experiments in which the nuclei of interest are implanted into a silicon detector, these atomic processes contribute to the detected energy. To understand the distortions of the α-particle energy spectra, knowledge of the various atomic yields is required. Using state-of-the-art calculations, new atomic yields are computed in 99Es and compared to those available in the literature. Detailed simulations of the Md101251α decay are performed and compared to experimental data. Possible ways to discriminate between the available atomic yields are also discussed.

Design, spectrum measurements and simulations for a 238Pu α-particle irradiator for bystander effect and genomic instability experiments

Design, spectrum measurements and simulations for an α-particle irradiator for bystander effect and genomic instability experiments are presented. Measured α-particle energy spectra were used to confirm the characteristics of the source of the irradiator specified by the manufacturer of the source. The spectra were measured in vacuum with a high-resolution spectrometer and simulated with an AASI Monte Carlo code. As a next step, we simulated α-particle energy spectra at the target plane of the irradiator for three different source-to-target distances. In these simulations, helium was used as the medium between the source and the exit window of the irradiator; its pressure and temperature corresponded to those of the ambient air. Mean energies and full-widths at half-maximum (FWHM) were calculated for the three different helium gas tracks.

STUDY OF STATISTICAL EMISSIONS IN 28Si+natSi AND 28Si+27Al REACTIONS AT 4–5 MeV/A INCIDENT ENERGIES

We measure the energy spectra of α-particles and protons in 28 Si + nat Si and 28 Si +27 Al reactions at 4–5 MeV/A for both forward and backward angles. We show with a statistical model that the choice of the level density parameter plays a very crucial role in explainning the evaporation spectra. The shell corrected Gilbert Cameron level density parameter is found to give satisfactory results.

Search for entrance channel effects in the decay of compound nucleus

The α-particle energy spectra have been measured at different laboratory angles from the fusion reaction 12 C + 45 Sc at 83 and 97 MeV incident energies. These spectra are consistent with the predictions of the statistical model calculations using the Rotating Liquid Drop Model (RLDM) values of the moment of inertia and the optical model transmission coefficients for the respective inverse absorption channels. The results of 12 C + 45 Sc asymmetric system were compared with the 28 Si + 27 Al symmetric system at 140 MeV studied earlier as both the systems lead to the formation of nearly same compound nucleus ( Z=27) with the same angular momentum and the excitation energy. The comparison was made in order to understand the symmetric and the asymmetric entrance channel effects in the formation and the decay of the compound system. In the case of 28 Si + 27 Al symmetric system, the experimental spectra deviate at higher as well as at lower energies from the statistical model calculations. Alterations were required in the moment of inertia as well as in the calculation of the transmission coefficients to explain the experimental data. However, in the case of 12 C + 45 Sc asymmetric system there was no need for such changes and the experimental spectra can be well explained by the statistical model calculation using RLDM values of moment of inertia and the optical model transmission coefficients. The dynamical trajectory model calculations are done to explain the experimental data. The comparison of the decay times with the formation times implies that the light charged particles are preferentially emitted prior to the full relaxation of the compound nucleus in the case of 28 Si + 27 Al symmetric system. The results of the present study suggest an entrance channel dependence in the formation and the decay of the compound nucleus.

Fabrication and testing of a microstrip particle detector based on highly oriented diamond films

A particle detector for high flux applications has been fabricated based on highly oriented diamond (HOD) films. Relatively thick HOD films were achieved by combining the bias enhanced nucleation (BEN) in a microwave plasma chemical vapor deposition (MPCVD) reactor and high rate growth process in a low pressure combustion flame (LPCF) reactor. Following the diamond deposition, Si substrate was etched away to obtain a free standing, 4 mm diameter diamond membrane. A Ti/Au microstrip electrode pattern was applied to one side of the detector to provide spatial resolution. The detector performance was tested by measuring the energy spectra of α-particles emitted from an 241 Am source. As compared to the performance of a polycrystalline diamond detector, the HOD detector showed a three to four fold improvement in performance, which was close to that obtained for single crystalline diamond detectors.

Binary dissipative processes and formation of hot nuclei in reactions from 55 to 95 MeV/u

A 4π multidetector array with a high efficiency has been used to detect the charged products from reactions induced by 36 Ar on 27 Al at energies ranging from 55 to 95 MeV/u. Well-characterized events were selected and sorted as a function of the impact parameter. Fusion or full stopping events have a very small cross section. Dissipative binary collisions accompanied by pre-equilibrium (mid-rapidity) emission, and followed by de-excitation of the quasi-projectile and quasi-target, were found to dominate for all impact parameters. The mass of the quasi-projectile has been reconstructed from its products and found to be slighty below the projectile mass. Isotropic emission in its rest frame has been observed at all energies and impact parameters, indicating that equilibrated nuclei may have been formed. The excitation energy of the quasi-projectile, determined via calorimetry, and the slope of kinetic energy spectra of α-particles were found to increase with incident energy and with decreasing impact parameter. Excitation energies per nucleon above 11 MeV are reached in a sizable cross section (70 mb). The mass distribution and kinetic energy spectra of emitted particles and fragments are essentially governed by the excitation energy, with a weak dependence on the impact parameter. The evolution of dissipative processes from deep inelastic collisions to the participant-spectator regime is discussed.

Mechanisms of non-equilibrium light-particle emission in 32S + Ag reactions at 30 A · MeV

Energy spectra of light charged particles ( Z = 1,2) observed at θ LP = 5°−150° in coincidence with fragments of Z = 5–14 at θ F = ±9° are examined. The fragment-energy spectra show two components, one with a projectile-like velocity and another with a much lower velocity. Light particles in coincidence with fragments of projectile-like velocity show a very strong left-right asymmetry in the forward hemisphere. At very forward angles the asymmetry is essentially dominated by a recoil effect of the ejectile emitted from the fragment. The asymmetry at intermediate angles (27°⩽ θ ⩽ 60°) shows a strong dependence on the charge of the fragments and the asymmetry is similar among those for the composite particles, whereas the asymmetry is much smaller for protons. Light particles in coincidence with the lower-energy component of the fragment spectra show much less asymmetry. For such fragments α-particle energy spectra are reproduced without an intermediate-velocity source of high apparent temperature, whereas this high temperature source is needed for the proton spectra. These facts may indicate that the dominant emission mechanism of the intermediate-velocity protons and α-particles is different. Possible mechanisms for the production of these particles are discussed.

The distribution of emergent flight path lengths from homogeneous spheres

Empirical as well as formal arguments are used to show that the probability, P ( x) ddx, for particles born uniformly and emitted isotropically throughout a sphere of radius a, to have an escape flight path length L which lies in the interval ad x, about ax is given by P(x) dx = ( 3 4 )[1−(x/2) 2] dx where 0 ≤ x ≤ 2 is distribution may be used directly in the algebraic formulation of a number of interesting physical problems or else conveniently sampled numerically according to the expression x = −4 sos[(2 π − cos −1 ( ξ))/3], where ξ is a random number between 0 and 1. As an example of how the analytical form may be used a general expression for the energy spectrum of α-particles emerging from small, homogeneous, spherical particles of α-emitter is derived.

The energy spectrum of α-particles emitted from used CANDU™ fuel

α-radiolysis could affect the dissolution behaviour of used UO 2 fuel. To model this effect, one must first determine the α-radiation dose absorbed by the water near the fuel surface, e.g. in fuel cracks. This is the purpose of our paper. First, using the actinide inventories of used UO 2 fuel, we calculate the number and energies of the α-particles created in various used fuels. However, the α-particles created in the fuel deposit a large fraction of their energy in the fuel matrix before reaching the fuel surface. In this paper, we show that the self-shielding by the surface layer of the fuel reduces the α-particle dose rate at the fuel surface by about a factor of seven.

Production and characterization of hot nuclei in the reactions of 19 and 35 MeV/u 14N with 145Sm

Hot nuclei produced in the reactions of 261 MeV and 490 MeV 14N with 154Sm have been studied. The initial properties of these nuclei; excitation energies, angular momenta and temperatures, have been characterized through measurements of residue velocities, gamma ray multiplicities and α-particle energy spectra. Nuclei with excitation energies as high as 400 MeV and temperatures as high as 6 MeV are produced. Determinations of the variation of temperature with excitation energy for nuclei of A ⋍ 160 indicate that the apparent level density parameter a, defined as E ∗|T 2 changes from A/8 at low energies to ≈ A/13 at 400 MeV excitation energy. Effective particle emission barriers suggest large shape fluctuations during the de-excitation cascade. At 35 MeV/u the variation of angular momentum transfer with linear momentum transfer in incomplete fusion reactions is in reasonable agreement with values calculated using a geometric overlap model.