Angular Distributions Of Protons Research Articles

Fluxes of =50-keV protons and =30-keV electrons at ∼35 RE , 1. Velocity anisotropies and plasma flow in the magnetotail

The NOAA/APL energetic particle experiment (EPE) on Imp 7 (Explorer 47) is capable of measuring hot plasma flow with a temporal resolution of 20 s if the densities exceed approx.0.1 cm/sup -3/. The lowest-energy electron channel (30--90 keV) can detect plasma with kTapprox.1 keV, while the lowest-energy proton channel (50--200 keV) can detect plasmas at similar temperatures if they have a bulk velocity of approximately-greater-than50 km s/sup -1/. The bulk velocities can be deduced from the measured proton angular distributions (16 sectors in the ecliptic) by using straightforward expressions derived from phase space transformations of a Maxwellian distribution. Representative examples are given for quiet time flow in the magnetosheath (Vapprox.500 km s/sup -1/, kTapprox. =5 keV) and the magnetotail (Vapprox.70 km s/sup -1/, kT/subp/approx.10 keV), with T/subp//T/sube/>3 in both cases. A detailed example of a class of high-intensity events that occur in the plasma sheet in the dusk sector of the magnetosphere is also presented. The 1-hour event (0520--0620 UT, October 3, 1973) was associated with a 1500-..gamma.. depression in the H component of the geomagnetic field at Barrow, Alaska. Tailward velocities of 1260 km s/sup -1/ were deduced during the expansive phase of the substorm, and sunward velocities ofmore » approx.950 km s/sup -1/ during the recovery. Comparison with higher-energy proton measurements on the same spacecraft over the first year of data (September 1972 to October 1973) reveals that the larger events often have a nonthermal tail, although bulk velocities, densities, and temperatures deduced from the smaller events are consistent with previous measurements of plasma flow by other workers. (AIP)« less

Three-nucleon transfer on 12C: The 12C(α, p) 15N reaction at 96.8 MeV

Angular distributions of protons from the 12C(α, p) 15N reaction have been measured over the angular range from 10–70° at an α-particle bombarding energy of 96.8 MeV. Well defined particle groups are observed up to an excitation energy of 18 MeV in 15N. The relatively small number of states excited implies a selectivity both in the reaction mechanism and in structure effects. DWBA calculations using a semi-microscopic three-nucleon form factor have been performed using several different sets of wave functions. Good agreement in the ratio σ exp/ σ th is obtained for most states using the 15N wave functions of de Meijer. The strongest state in the (α, p) spectrum is observed at 15.397 MeV in 15N and DWBA calculations give good agreement for a 13 2 + assignment. This state has been observed only in other three-nucleon transfer reactions involving heavy ions. The recent discovery of a 9 2 + state at 10.693 MeV in a p+ 14C resonance measurement is supported by our analysis.

Angular distributions of protons from the reaction 12C(d, p γ) 13C obtained by shape studies of γ-ray lines

A detailed study of the angular distributions of the emitted protons from the reaction 12C(d, p 1) 13C in the deuteron energy range 1.4 to 3.2 MeV is presented. The angular distributions are obtained from the line shape of the Doppler shifted γ-rays. The excitation function for the reaction shows strong intensity fluctuations which are superimposed on an energy dependent average behaviour. The reaction is therefore assumed to proceed through direct interaction as well as compound nucleus formation, and the amplitudes for the two different reaction mechanisms are added linearly to form the total reaction amplitude. The 14N resonance structure obtained is also based upon studies of the reactions (d, p 2γ) and (d, p 3γ).

Investigation of the 24Mg(d, p) 25Mg reaction

Proton angular distributions from the 24Mg(d, p) 25Mg reaction at E d = 12.0 MeV have been measured with a split-pole magnetic spectrograph for E x < 6 MeV at an average resolution (FWHM) of 7 keV. New l n values have been determined for three levels. A DWBA analysis yielded spectroscopic factors for 17 levels. A comparison has been made with shellmodel and collective model results.

Ti(τ, p) reactions at 15 MeV (II). 50Ti(τ, p) 52V

The 50ti(τ, p) 52V reaction has been studied at 15 MeV incident energy using a multiangle spectrograph. Seventy-seven transitions up to 8.84 MeV in excitation have been identified, and many of the corresponding proton angular distributions measured. The distribution shapes together with DWBA calculations allow the assignment of a number of new spin and parity values. The results of the present work are compared with other data on 52V. The isobaric spin (τ, p) intensity relations are applied to T = 3 and T = 4 states with J π = 0 + in 52 V , and it is found that the T = 3 levels take up only 18 % of the expected anti-analog strength.

Isospin conservation and the independence hypothesis in the decay of 49V, 52Cr and 55Mn

Energy spectra and angular distributions of protons and α-particles emitted in the decay of 49V, 52Cr and 55Mn produced by 14 MeV protons and 12–16 MeV α-particles were measured between 30° and 150°. The evaporation cross sections of the (p, p'), (p, α), (α, p) and (α, α') reactions were used to deduce the isospin mixing fractions, μ, between the T ⪢ and T < states of these compound nuclei and values of 0.2–0.3 were obtained. The ratio of upward to downward mixing was calculated to be ≈ 0.02. Values of the Coulomb matrix elements were deduced and found to range from ≈ 30 to 120eV. Measurements on the α and p ̃ exit channels permitted a test of the independence hypothesis and the latter was verified for 49V and 55Mn.

Extension of the isobar model for intranuclear cascades to 1 GeV

An intranuclear cascade model is proposed for studying pion and nucleon induced reactions in the region of single pion production. The model explicitly considers the production and subsequent interactions of (3,3) isobars. The predictions of the model are compared with experimental data from proton induced reactions such as pion production yields, pion and proton energy and angular distributions, and spallation yields. The model gives a fair to excellent representation of all these data.

Structure of 88Kr derived from the 86Kr(t, p) 88Kr reaction

The 86Kr(t, p) 88Kr has been used to measure the previously unknown 88Kr level spectrum. Comparison of the proton angular distributions to DWBA predictions leads to J π assignments for many observed levels.

Energetic particles in the Jovian magnetosphere

Detail account of the Pioneer 10 encounter with Jupiter as viewed by the Goddard-University of New Hampshire cosmic ray experiment. Flux time histories of electrons and protons are given over a wide energy band. These show a marked variation with magnetic latitude. Significant removal of low-energy protons by Io is apparent in the inner magnetosphere (less than or equal to 6 Jovian radii). Proton and electron energy spectra are given at various Jovicentric distances. The electron spectra are remarkably hard and constant in slope in the 0.12 to 8.0-MeV interval, the electron spectral index having a value of 1.5 to 2.0 in the region outside 25 Jovian radii. Proton spectra are shown to transform from a power law with indices in the 3 to 4.2 range to more nearly exponential forms in the inner regions (less than or equal to 40 Jovian radii). Extensive data are presented on the angular distributions of protons and electrons at various locations in the Jovicentric magnetosphere.

A study of 22Ne with the 20Ne(t, p) reaction

The 20Ne(t, p) 22Ne reaction has been studied at 15 and 20 MeV bombarding energies covering excitation energies up to 12 MeV. The protons were observed in a magnetic spectrograph with an energy resolution of 30–35 keV FWHM. The proton angular distributions are analyzed empirically as well as with DWBA methods and several final-state spin-parity assignments are made. The DWBA analysis shows that there are important higher-order contributions to the reaction mechanism. A comparison of the 15 MeV (t, p) data with corresponding (τ, p) data leads to the identification of 10 isobaric analog pairs in the mass-22 system. DWBA predictions based on theoretical wave functions are compared to the data and the overall trends agree reasonably well.

Ground State Radiation Width of the 10.18 MeV, Jπ = 3−, State in 28Si Deduced From 100 MeV Proton Inelastic Scattering

Differential cross section data for 100 MeV protons inelastically scattered from 6Li, 9Be, 12C, 24Mg, and 28Si are compared with the corresponding E2 and E3 transition rates and a strong correlation is shown to exist between (dσ/dΩ)max and Γγ0 if the shape of the proton angular distribution is characteristic of single excitation. The persistence of the correlation to transitions with Γγ0/Γγ &lt; 0.1 allows an estimate of Γγ0 = 8.6 ± 5 × 10−4 eV for the 10.18 MeV, Jπ = 3−, level in 28Si.

A Study of the Intermediate 5Li Ground State Produced in the 6Li(3He, αp)4He Reaction

An experiment has been performed on alpha–proton coincidences produced by the three body reaction 6Li(3He,αp)4He, at a bombarding energy of 1.25 MeV. Events ascribed to sequential breakup via the ground state of 5Li have been isolated with the aim of measuring the angular distribution of protons derived from 5Li. Difficulties are encountered because the alpha particle spectra in coincidence with the detected protons vary significantly with the proton angle. Possible interpretations of this effect are discussed. A tentative angular distribution, based on a compromise interpretation, shows a pronounced minimum which is shifted away from the 5Li recoil direction. Similar shifts have been detected in the 7Li(d,αn)4He reaction by Heggie and Martin, who explained the directional correlation effects in terms of a compound nucleus model. This model seems to be more applicable to these reactions than models based on stripping and pickup processes.

The study of the angular distributions of protons from the reaction162Dy(d,p)163Dy at 12·1 MeV

The angular distributions of protons from the reaction162Dy(d,p)163Dy were measured. The experimental results were analysed in a Distorted Waves Born Approximation theory and the transferred angular momentum and spectroscopic factors were determined for the stronger transitions. The experimental spectroscopic factors were compared with the Nilsson model including the pairing effect.

Photodisintegration of deuterium determined from the electrodisintegration process

The equivalent photon cross sections were extracted from deuteron electrodisintegration measurements over an energy range of 17 to 28 MeV. Proton angular distributions were measured at 12 photon energies and the total cross section determined with an experimental uncertainty of approximately ≲6%. The differential cross section at 90 ° c.m. was also measured. Satisfactory agreement is found between deuteron photodisintegration theory and our measurements. A comparison with other recent (γ,p) cross section measurements is made. [NUCLEAR REACTIONS H2(e,p)e′n, measured σ(Ep,θ), extracted H2(γ,p)n.]

Atmospheric spreading of protons in auroral arcs

A model is developed to calculate the effect of atmospheric spreading on the flux and angular distribution of protons in homogeneous auroral arcs. An expression is derived that indicates the angular distribution in the atmosphere as a function of distance from arc center, neutral scale height, arc width, and initial angular distribution. The results of the model agree favorably with those based on Monte-Carlo calculations. From these results the enhancement factors needed to compute the original proton current above the atmosphere are obtained. A technique is indicated for determining the incident angular distribution from rocket-based measurements of the arc width and angular distribution.

Experiment and theory for the 2H(e, p)e′n reaction

Differential cross sections and angular distributions of protons from the 2H(e, p)e′n reaction have been measured at four incident electron energies. The proton angular distributions were measured with the neutron-proton relative energy approximately constant, and an 85° differential cross section was measured as a function of the incident electron energy. The electrodisintegration cross section was calculated using the Hulthén wave function for the ground state with a plane wave for the final state. Reasonable agreement between experiment and theory is found.

Dissociative ionization by electron impact. I. Protons from H2

A new apparatus designed to investigate various aspects of the electron impact dissociative ionization process is described in detail. It is shown that the angular distributions obtained for protons from the 2 Sigma u+ state of H2+ are consistent with theoretical arguments and confirm the results of previous measurements. The first angular distribution of protons from the 2 Sigma g+ state of H2+ is also reported. Absolute cross sections for the production of protons from both the 2 Sigma g+ and 2 Sigma u+ state of H2+ at electron energies close to the respective thresholds are also presented. The ratio H+/H2+ is measured as a function of incident electron energy for ions originating from the 2 Sigma g+ state.

Test of the independence hypothesis and isospin conservation in compound-statistical reactions

Abstract Energy spectra and angular distributions of protons and α-particles emitted in the decay of 56 Fe, 60 Ni, 63 Cu, 64 Zn, and 66 Zn were measured. These compound nuclei were produced with a given excitation energy by irradiation of appropriate targets with 14.0 MeV protons and 15–19 MeV α-particles. The proton spectra featured a low-energy peak ascribable to the (p, np) or (α, np) reaction as well as a higher energy peak due to the (p, p') or (α, p) reaction. These peaks were sufficiently well resolved that differential cross sections could be obtained for the p, np, as well as α exit channels. The α and np exit channels were found to be free of precompound effects and are not affected by isospin conservation. Comparison of these particular cross sections for both entrance channels permits a test of the independence hypothesis provided a correction is made for the different angular momentum distributions in the entrance channels. When this correction is applied on the basis of the spin-dependent statistical theory it is found that the independence hypothesis is confirmed in all cases. Comparison of the p and α exit channels leads to values of the isospin mixing fraction, μ, between the T > and T states of the compound nucleus. The values of μ are 0.4±0.2 for all five compound nuclei and correspond to Coulomb mixing widths whose value is approximately 20 keV.

Simulation of Positron Channeling in Single Crystals

AbstractA simulation method of charged particle scattering in a crystal lattice is described. Angular distributions of protons and positrons leaving the crystal are calculated and the orientational distributions of axial channeling particles are received. The influence of the experimental geometry and the crystal condition on the obtained results is discussed. It is shown that binary collision calculation gives agreement with experimental results.

A study of nuclear structure in 59Ni from the (d, p) reaction on 58Ni

Level structure in 59Ni is studied from the (d, p) reaction in 58Ni using the Aldermaston tandem Van de Graaff accelerator and the multichannel magnetic spectrograph. Angular distributions of protons are measured over the angular range 5°–175° up to an excitation of ≈ 8 MeV and absolute cross sections are measured. The data are analysed in terms of the finite-range DWBA theory of direct reactions and spins, parities and spectroscopic factors are deduced for various levels. The summed spectroscopic factors and the single-quasiparticle energies of the shell-model states are obtained. Properties of the low-lying levels in 59Ni are compared with predictions based on exact shell-model calculations.