Increasing Proton Energy Research Articles

A Monte Carlo model of auroral hydrogen emission line profiles

Abstract. Hydrogen line profiles measured from space-borne or ground-based instruments provide useful information to study the physical processes occurring in the proton aurora and to estimate the proton flux characteristics. The line shape of the hydrogen lines is determined by the velocity distribution of H atoms along the line-of-sight of the instrument. Calculations of line profiles of auroral hydrogen emissions were obtained using a Monte Carlo kinetic model of proton precipitation into the auroral atmosphere. In this model both processes of energy degradation and scattering angle redistribution in momentum and charge transfer collisions of the high-energy proton/hydrogen flux with the ambient atmospheric gas are considered at the microphysical level. The model is based on measured cross sections and scattering angle distributions and on a stochastic interpretation of such collisions. Calculations show that collisional angular redistribution of the precipitating proton/hydrogen beam is the dominant process leading to the formation of extended wings and peak shifts in the hydrogen line profiles. All simulations produce a peak shift from the rest line wavelength decreasing with increasing proton energy. These model predictions are confirmed by analysis of ground-based H-β line observations from Poker Flat, showing an anti-correlation between the magnitude of the peak shift and the extent of the blue wing of the line. Our results also strongly suggest that the relative extension of the blue and red wings provides a much better indicator of the auroral proton characteristic energy than the position of the peak wavelength.

Pinning energy of GdBa 2Cu 3O 7− δ—irradiation and magnetic field effects

We have investigated proton irradiation effects in GdBa 2Cu 3O 7− δ sintered polycrystalline samples with predominantly orthorhombic phase. The samples were irradiated with 0, 1.5, 2, and 2.5 MeV proton beams at 1×10 15 cm −2 dose. The magnetic and proton energy dependence of the effective pinning energy, U eff, have been determined from the corresponding electrical transport measurements under a magnetic field of up to 10 kOe. The magnetic dependence of U eff shows a progress of vortex localization in the vortex state, which varies from H −0.51 to H −0.37 with increasing proton energy. Our results also show a power law-like behavior for U eff as a function of proton energy.

Nuclear diagnostics for petawatt experiments (invited)

With the operation of successively more intense and powerful lasers, such as the NOVA petawatt laser with I∼3×1020 W/cm2, several novel (to laser physics) nuclear diagnostics were used to determine the nature of the laser/matter interaction at the target surface. A broad beam of hot electrons, whose centroid varied from shot to shot, width was remarkably constant, and intensity was about 40% of the incident laser energy was observed. New nuclear phenomenon included photonuclear reactions [e.g., (γ,xn)], photofission of U238 and intense beams of ions. Photonuclear reactions were observed and quantified in Cu, Ni, and Au samples, and produced activation products as neutron deficient as Au191 [a (γ,6n) reaction!], requiring gamma rays exceeding 50 MeV in energy. The spectral features of the gamma-ray source have been investigated by comparing activation ratios in Ni and Au samples, and angular distributions of higher energy photons have been measured with activation of spatially distributed Au samples. Extraordinarily intense beams of charged particles (primarily protons) were observed normal to the rear surface of the target and quantified using the charged particle reaction Ti48(p,n)48V, radiochromic film and CR39 plastic track detectors. Approximately 3×1013 protons, with energies up to 55 MeV were observed in some experiments. Collimation of this beam increases with increasing proton energy. Correlations of activation with laser performance will be discussed.

Neutron activation by neutrons produced via proton-induced spallation in a liquid-mercury target: Measurements and assessment of uncertainties

A preliminary test of a liquid mercury target for the production of neutrons by spallation was undertaken at the Alternating Gradient Synchrotron facility at Brookhaven National Laboratory. Neutron activation of elemental foils placed on the target demonstrates that a range of neutron energies does exist, as expected, and that the neutron flux is at a maximum 10–20 cm from the front of the target, moving deeper with increasing proton energy. Uncertainties in the activity calculations are in general significantly <10%. Impurities in some of the foils are a significant source of interference for some reactions, although there is no interference for most of the reactions. The presence of many interference-free reactions, along with the low uncertainties indicates that the foils will be useful benchmarks to validate the neutronics codes utilized in the target design.

Measurement of vector-tensor spin-transfer observables for the reaction [formula omitted] between 580 and 1300 MeV

The three polarization tensor components of the deuteron produced in the H( p, d)π + reaction have been measured for the first time. The experiment was performed using a vertically polarized proton beam produced by the SATURNE accelerator. The deuteron polarization was measured with the POLDER polarimeter. The three polarizing powers t 20 00, t 21 00 and t 22 00 and the three spin-transfer observables t 20 11, t 22 11 and t 22 11 have been extracted at a proton kinetic energy of 580 MeV over a wide angular range and at two fixed center-of-mass angles, 132° and 151°, between 800 and 1300 MeV. The six observables, calculated in the C.M. helicity frame, have been compared with predictions of the most refined partial-wave analyses and also with the predictions of a theoretical coupled-channel model which includes the NN-NΔ transition. The comparison between the data and the theory/partial-wave analyses shows some discrepancies which get worse with increasing proton energy. Adding these data to the world database should improve significantly future partial-wave analyses. The A y0 analyzing power has also been measured over the same kinematical range. The partial-wave analysis predictions are in good agreement with this observable.

On the relation between stopping power and electron yield for proton impact on aluminum

The ratio of total electron yield and stopping power (specific yield) is investigated. Both quantities are calculated using the same basic assumptions concerning the different interaction processes. We have taken into account all known excitation and scattering processes within the calculation of the electron yield. For proton impact on aluminum we obtain a decrease of the specific yield with increasing proton energy. This is in contrast to the observed independence of the specific yield of the impact energy but in accordance with the observed behaviour for heavier projectiles.

Experimental determination of relative light conversion factors of TLD-100 for protons with energies from 2.0 to 9.0 MeV

The efficiency of thermoluminescent (TL) detectors to heavy charged particles is described by the so-called light conversion factor η. Relative light conversion factors for protons, alphas and heavier recoils are needed for the calculation of the neutron sensitivity of TL detectors. Such light conversion factors can be determined experimentally. In this paper a method is presented for the experimental determination of relative light conversion factors. Using the experimental arrangement described, relative light conversion factors for LiF material (TLD-100) for protons were determined. In LiF the relative main peak (peak V) efficiency is always lower than 1. It increases with increasing proton energy whereas the relative efficiency of the high temperature peak (peak VI) shows an opposite dependence on the proton energy. Relative light conversion factors for peak VI clearly exceed 1.

Registration of low energy protons in CR-39 for use in fast neutron dosimetry

This paper gives some results on the registration of protons, in the energy range from 60 keV to 727 keV, incident normally on CR-39 detectors and etched chemically in 6N NaOH at 70°C. An increase in the track diameter ‘D’ with increasing proton energy ‘E p ’, has been observed. The response function V (=V t /V g ) for different energy protons has been experimentally determined and correlated with the calculated values of ‘V’ by the polynomial V =∑ a n V n . The variation in the response function ‘V’ with the proton range ‘R’ and REL (200) function are well described by the relations V=1+aR n and V= a n(REL) n , respectively. The critical angle, ϴ c ′, calculated as a function of the proton energy E p is given by the relation ϴ c = ∑a n (1n E p ) n .

Fragment emission in proton-xenon interactions in the near-threshold regime

Abstract Energy spectra of fragments, 3≤Z≤14, from the Interaction of 1–20 GeV protons with xenon have been measured over a nearly continuous range of proton energies using an Internal gas Jet target In the AGS. Analysis of the fragment energy spectra shows the presence of two distinct fragment production mechanisms below 6 GeV, which we Identify as binary and multi-fragment break up.The relative contribution of the binary process decreases with increasing proton energy and becomes negligible above 6 GeV. The data for the multi-fragment component above 4 GeV are consistent with the formation of fragments from a supersaturated gas of nucleons.The coexistence curve and the critical temperature are approached monotonically with increasing proton energy.

Electron capture in close collisions between protons and carbon (CH4)

The total probability for electron capture from CH4 by 200-2000 keV protons scattered through 15 or 20 degrees in the laboratory system by the carbon nucleus has been measured. The probability decreases strongly with increasing proton energy, and a clear structure is seen around 400 keV. Complementary differential coincidence measurements of capture by protons from the K shell of carbon (CH4) show that the structure is caused by the K-shell capture component of the total capture probability, which becomes significant in the energy range 200-500 keV. Above 1 MeV, the K-shell capture component dominates the total capture probability. The angular dependence (10-50 degrees ) of the total capture probability was determined at 500 keV, where the K-shell capture component at 20 degrees contributes with (80+or-15)%. An experimental measure of the widths of the impact parameter distributions for K-shell ionisation and capture, respectively, as functions of the collision energy, was obtained on the basis of the pertinent experimental total cross sections and measured probabilities for small impact parameter collisions with nearly straight-line trajectories. The width of the K-shell ionisation distribution increases with increasing projectile kinetic energy, whereas the width of the K-shell capture distribution exhibits a maximum. Particular attention has been paid to the capture probabilities in an energy region around the elastic scattering resonances 12C(p,p)12C near 1.7 MeV.

Polarization of preequilibrium proton emission in the 93Nb + 14N reaction

Spin polarization of protons emitted at 20° and 40° in the 93Nb + 14N reaction at 95 MeV has been measured by the double scattering method using a polarimeter particularly designed for protons having a continuous energy distribution.The result shows that the polarization is small for low-energy protons, but increases smoothly with the increase of proton energy, reaching around + 20 % at about 20 MeV in the center-of-mass system. Energy and angular distributions of protons measured in the same reaction indicate coexistence of equilibrium and preequilibrium components in the proton emission of interest, the fraction of the preequilibrium component increasing with the increasing proton energy. If we assume that protons emitted in equilibrium are completely unpolarized, and that the value of polarization ( P) for the preequilibrium component is independent of proton energy, the present result is consistent with P ⋍ + 22 % for the emission at 20° and P ⋍ + 38 % for the emission at 40°.The result is discussed in terms of the hot-spot model for precompound decay.

Radiochemical study of the combined (p,π0) and (p,γ) reactions on bismuth with protons from 62 to 480 MeV

The excitation function for the combined /sup 209/Bi(p,..gamma..)/sup 210/Po and /sup 209/Bi(p,..pi../sup 0/)/sup 210/Po reactions was measured for proton energies from 62 to 480 MeV. The measurements were made using standard radiochemical and residual ..cap alpha..-counting techniques. Below pion-production threshold the radiative proton-capture cross section was observed to decrease with increasing proton energy. Above threshold the combined cross section increases to about 10 ..mu..b at 170 MeV. From a smooth extrapolation of the (p,..gamma..) cross section to energies above pion-production threshold, an estimate of a cross section for the (p,..pi../sup 0/) process is obtained. A theoretical fit of the summed total cross section into all particle bound states was made using a density of states factor, a two nucleon t matrix, and by taking into account the initial state (proton) and final state (pion) distortions using optical potentials.

Angular distributions and differential ranges of Ba products from the interactions ofU238with 0.8-400-GeV protons

Angular distributions and differential ranges at ${90}^{0}$ to the beam of $^{128}\mathrm{Ba}$, $^{131}\mathrm{Ba}$, $^{135}\mathrm{Ba}^{m}$, and $^{140}\mathrm{Ba}$ emitted in the interaction of $^{238}\mathrm{U}$ with 0.8-400 GeV protons have been measured. The angular distributions of $^{128}\mathrm{Ba}$ and $^{131}\mathrm{Ba}$ change from forward-peaked to sideward-peaked between 3 and 11.5 GeV, while those of $^{135}\mathrm{Ba}^{m}$ and $^{140}\mathrm{Ba}$ are sideward-peaked and independent of bombarding energy in the above regime. Momentum distributions of all products are Gaussian at 0.8 GeV with a mean value increasing from 120 ${(\mathrm{M}\mathrm{e}\mathrm{V}\phantom{\rule{0ex}{0ex}}\mathit{A})}^{1/2}$ for $^{128}\mathrm{Ba}$ to 139 ${(\mathrm{M}\mathrm{e}\mathrm{V}\phantom{\rule{0ex}{0ex}}\mathit{A})}^{1/2}$ for $^{140}\mathrm{Ba}$. The momenta of the neutron-deficient products decrease by nearly a factor of 2 with increasing proton energy and the distributions broaden and become asymmetric. On the other hand, the momentum distributions of $^{135}\mathrm{Ba}^{m}$ and $^{140}\mathrm{Ba}$ are independent of proton energy. The results are analyzed with the two-step model and compared with the kinematics of the coherent interaction model. The implications of the results and comparisons for the reaction mechanism are considered.NUCLEAR REACTIONS $^{238}\mathrm{U}(p,X)^{128}\mathrm{Ba}$, $^{131}\mathrm{Ba}$, $^{135}\mathrm{Ba}^{m}$, $^{140}\mathrm{Ba}$. ${T}_{p}=0.8\ensuremath{-}400$ GeV. Measured angular distributions and differential ranges at 90\ifmmode^\circ\else\textdegree\fi{} to the beam, deduced two-step model parameters.

Changes in lifetime and diffusion length due to the electron and proton bombardment of silicon solar cells

The degradation by 1 and 4.5 MeV electrons and 10–600 MeV protons of conventional n+-p cells designed for space was studied using separate measurements of the carrier diffusion length, lifetime and mobility and their variation with the carrier injection level. The following comparisons were made. 1.(a) The cell base degradation was compared with theoretical calculations of the number of atoms displaced as a function of particle energy.2.(b) The changes in lifetime of bulk samples were compared with the changes in lifetime of the base of cells made of the same silicon material.3.(c) The degradation of the emitter region and of the region close to the space charge region was investigated.In all the solar cells irradiated with 10–600 MeV protons a large room temperature recovery was observed. After the recovery the cell base lifetime damage agreed with (a) the variation in damage with increasing proton energy predicted theoretically and (b) the amount and quality of lifetime damage induced in the bulk samples. No room temperature recovery was observed after electron irradiation; however, the 4.5 MeV bulk sample degradation agreed with the smooth increase predicted theoretically, in contrast with the 1 MeV cell base degradation. Moreover, noticeable changes in the “operational” carrier lifetime of the emitter region and in the carrier mobility of the region close to the space charge region were recorded in cells irradiated with 10 MeV protons, especially for the lowest fluence range.

Angular distributions of Sc fragments from the interaction ofU238with 0.8-400 GeV protons

Angular distributions of $^{44}\mathrm{Sc}^{m}$, $^{46}\mathrm{Sc}$, $^{47}\mathrm{Sc}$, and $^{48}\mathrm{Sc}$ emitted in the interaction of $^{238}\mathrm{U}$ with 0.8, 3.0, 11.5, and 400 GeV protons have been measured. The angular distributions peak at forward angles at 0.8 and 3 GeV but are sideward-peaked at 11.5 and 400 GeV. At 400 GeV, fewer fragments are emitted at forward than at backward angles. Isotopic differences were found to be small. The data were fitted with the function ${F}_{L}({\ensuremath{\theta}}_{L})=1+{A}_{1}{cos\ensuremath{\theta}}_{L}+{A}_{2}{{cos}^{2}\ensuremath{\theta}}_{L}$ and were also analyzed in terms of the two-step model. The values of ${A}_{1}$ peak at 3 GeV, go through zero at 11.5 GeV, and become negative at 400 GeV. The values of ${A}_{2}$ are zero at 0.8 GeV and become increasingly negative with increasing proton energy. A qualitative explanation in terms of a possible change in the nature of proton-nucleus interactions at high energies is presented.

Formation of isobaric nuclides withA=131in the interaction ofU238with 0.8-11.5 GeV protons

Cross sections and thick-target recoil properties of $^{131}\mathrm{Ce}$, $^{131}\mathrm{La}$, $^{131}\mathrm{Ba}$, and several neighboring Ba nuclides formed in the interaction of $^{238}\mathrm{U}$ with 0.8-11.5 GeV protons have been determined. The results reveal a dichotomy between $^{131}\mathrm{Ba}$ and the more neutron-rich products on the one hand, and the more neutron-deficient ones on the other. The latter have rising excitation functions, forward-to-backward ratios (F/B) that peak at 3 GeV, and ranges that decrease abruptly just below this energy. The former have decreasing excitation functions as well as F/B and ranges that decrease slowly and featurelessly with increasing proton energy. The energy dependence of F/B as well as the changes in the angular distributions of the very neutron deficient products observed between 3 and 11.5 GeV are explained in terms of a change in the nature of near-central proton-nucleus interactions. At the lower energies the interaction consists of a series of nucleon-nucleon collisions while at high energies the proton interacts collectively with all the nucleons lying in its path. The dropoff in the mean ranges of these same nuclides and the accompanying broadening of the spectra indicate a transition between fission and deep spallation. The possible connection between these two effects is discussed. Several experiments to test the proposed model are suggested.NUCLEAR REACTIONS Measured $\ensuremath{\sigma}$, range, and F/B of $^{131}\mathrm{Ce}$, $^{131}\mathrm{La}$, $^{131}\mathrm{Ba}$, $^{128}\mathrm{Ba}$, $^{133}\mathrm{Ba}^{m}$, $^{135}\mathrm{Ba}^{m}$, and $^{140}\mathrm{Ba}$ formed in interaction of $^{238}\mathrm{U}$ with 0.8-11.5 GeV protons. Proposed explanation for change in properties of very neutron deficient products.

Compound nucleus (α, p) and (p, p′) reactions on odd-Anuclei in the Ni region

Experimental compound nucleus cross sections are obtained for (p,p') and (..cap alpha..,p) reactions induced by 12 MeV protons and 15 and 18 MeV ..cap alpha.. particles on /sup 55/Mn, /sup 57/Fe, /sup 59/Co, /sup 61/Ni, and /sup 63/Cu. The noncompound nucleus cross sections, estimated from the spectra from /sup 64/Ni, are found to account for at least 20% of the total proton cross sections and also soften the spectra in the (p,p') cases. When these are subtracted off, good agreement in spectral intensities is found between experimental compound nucleus cross sections and predictions using Hauser-Feshbach calculations with Gilbert-Cameron level density parameters. No adjustable parameters were used. The slopes of the proton energy spectra from both (p,p') and (..cap alpha..,p) reactions are consistently flatter (i.e., decrease less rapidly with increasing proton energy) for odd-A than for even-even targets.

Independent yields of Rb and Cs isotopes from the fission of natural uranium induced by protons of energy 80 and 100 MeV

The independent yields or production cross sections of rubidium isotopes from mass 86 to 97, and of cesium isotopes from mass 129 to 144, have been measured for the fission of natural uranium induced by 80 and 100 MeV protons. The results were obtained by means of an on-line mass spectrometer. The rubidium distributions are quite symmetric, whereas the cesium distributions show a definite skewness toward the heavy mass side. Comparison with other results at 40, 50, 60 and 150 MeV proton energies shows that the heavy mass sides of the isotopic distributions are relatively insensitive to proton energy, whereas the light mass sides shift downward with increasing proton energy. The average total number of neutrons emitted has been estimated for each fission reaction. The mechanism of nuclear charge division in 80 and 100 MeV proton fission in the mass split studied here appears to be similar to that operating in thermal-neutron and low-energy proton fission.

Auger decay of neon following energetic ion bombardment

A high-resolution double-focusing electrostatic electron analyzer has been used to resolve Ne Auger electrons produced by 0.15-6.0-MeV ${\mathrm{H}}^{+}$, 1.0-MeV ${\mathrm{He}}^{+}$, and 33-MeV ${0}^{5+}$ bombardment. Individual $K$-Auger satellite lines stemming from the decay of multiply ionized neon have been observed. The energies, relative intensities, and production probabilities of these satellite lines were measured as a function of the projectile $Z$ and as a function of proton bombarding energy. Tentative identifications for all observed lines were made by comparison with calculated Auger satellite transition energies. The reliability of the Hartree-Fock calculations used was demonstrated by comparison with ${e}^{\ensuremath{-}}+\mathrm{Ne}$ data and by comparing calculated x-ray transition energies for multiply ionized neon to recent measurements of O + Ne x-ray lines. A rough estimate of the probability of single- and double-$2s$ orbital vacancy production as a function of $L$-shell defect was obtained. With proton bombardment, the satellite-production probability ${Q}_{s}$ was observed to decrease smoothly with increasing proton energy. The observation that ${Q}_{s}$ for 6-MeV proton bombardment was approximately equal to that obtained with equal-velocity electrons is believed to imply that electron shakeoff is the dominant $L$-shell ionization mechanism for high-energy proton bombardment.

A phenomenological woods-saxon potential for p-shell nuclei

The parameters of a Woods-Saxon potential well have been determined for ten p-shell nuclei by fitting the electron scattering form factors and single-particle binding energies. The resulting radius shows, for all but very light nuclei, a regular A 1 3 dependence while the depth smoothly decreases with the increasing proton energy. The observed energy dependence may be ascribed to the non-locality of the HF potential. An energy-independent non-local potential, compatible with elastic electron and proton scattering, is proposed in the energy range −50 to +50 MeV.