Angular Distributions Of Protons Research Articles

(h, p) Reactions on Cr

Abstract The reaction 50 Cr(h, p) 52 Mn has been studied at 16.5 MeV incident energy and with a resolution of ≈ 15 keV FWHM. Forty-nine transitions were observed up to 5.87 MeV of excitation and proton angular distributions were extracted. The distribution shapes in conjunction with DW calculations are used for assignments of spin and parity of many final states. The data are compared to previous information on 52 Mn and two states at 2.929 MeV and 5.491 MeV are assigned as isobaric analogues of the two lowest 0 + states in 52 Cr. The strength of the 0 + → 1 + excitations is commented upon.

Spectroscopy of 22Na with the 20Ne( 3He, p) and 20Ne( 6Li, α) reactions

The 22Na nucleus has been studied by means of the 20Ne( 3He, p) reaction at 15 MeV incident energy and the 20Ne( 6Li, α) reaction at 18 MeV bombarding energy. Levels up to 10 MeV of excitation were measured with energy resolutions of 25 keV in the ( 3He, p) case and of 40 keV in the 6Li induced reaction using the University of Pennsylvania tandem Van de Graaff and multi-angle spectrograph. The systematics of the proton and α-particle angular distribution shapes allow the assignment of values of the transferred angular momentum for a number of transitions, resulting in several new spin-parity assignments. Comparison of the proton and α-particle spectra reveals that T = 1 levels are extremely weakly excited in the ( 6Li, α) reaction and this fact is used for assigning several T = 1 states. A distorted wave calculation of relative intensities was performed based on a description of the 22Na levels in terms of pure two-particle Nilsson states with associated rotational bands. This analysis is consistent with the ground state K = 3 band and the K = 0, T = 1 band built on the first 0 + state having simple two-Nilsson-particle character whereas the properties of the second (1.93 MeV) 1 + state are inconsistent with such a description. It is concluded that the combination of ( 3He, p) and ( 6Li, α) reactions employed in the present study provides a powerful spectroscopic tool.

Energetic particle measurements in a pulsating aurora

Electron and proton precipitation at energies greater than 25 kev were measured in an early morning pulsating aurora by rocket-borne particle detectors. Pulsations found in the lower energy (25≤E≤80 kev) electron precipitation were in phase with ground-based photometric observations of the 3914-A emission. In the intervals between the trains of pulsations, (hard) electron and more intense (soft) proton precipitation was reasonably stable. During the pulsations large increases (factors of 4 or 5) in lower energy electron intensities were measured, which resulted in nearly identical electron and proton spectral distributions at the pulsation peak, whereas proton and energetic (E>100 kev) electron precipitation exhibited no detectable variation. Upper limits on intensity fluctuations of protons and energetic electrons were set at 5% and 10%, respectively. Lower energy electrons were found to have anisotropic pitch angle distributions peaked at 90° going isotropic during a pulsation and were responsible for a significant fraction of the 3914-A intensity modulation. Angular distributions of protons and energetic electrons were isotropic for the duration of the flight. These measurements indicate that auroral pulsations result primarily from increases in pitch angle diffusion that cause large electron precipitation enhancements in the energy range 15 to 80 kev. Certain requirements of theoretical pulsation models are discussed.

2H(d, p) 3H anisotropy at low energies

The angular distribution of protons from the 2H(d, p) 3H reaction has been measured for deuteron lab energies in the range 90 to 120 keV in steps of 2 keV and with a resolution of less than 3 keV. A resonance as reported in other measurements was not reproduced.

Electroproduction of π o mesons in the region of the first pion-nucleon resonance

The reaction e −+p→e −+p+ π o has been studied in the π−N centre of mass range from 1130 to 1340 MeV/ c 2 by detecting the final proton in coincidence with the scattered electron. The four-momentum transfer to the pion-nucleon system was between 0.40 and 0.50 (GeV/ c) 2 and the polarisation of the exchanged virtual photon near unity. The proton angular distribution is analysed phenomenologically in terms of the multipoles M 1+, E 1+, S 1+ contributing to the resonant partial wave and E o+, S o+ contributing to the s-wave background. The magnetic dipole excitation M 1+ is shown to dominate the cross section but clear evidence is obtained for a significant contribution from the scalar multipole S 1+.

A study of the level structure in 57Fe from the (d, p) reaction on 56Fe

Abstract The reaction 56 Fe(d, p) 57 Fe is investigated at 12 MeV using the Aldermaston multi-channel magnetic spectrograph. The angular distributions of protons leading to various states in 57 Fe upto an excitation of 6.7 MeV are measured over an angular range 5°–175°. The data are analysed with the distorted wave Born approximation calculations; a satisfactory agreement is found in most cases upto about 100°. Spin, parity and the spectroscopic factors for various states are obtained and the positions of the single-quasiparticle energies determined. The results are compared with those for the isotonic nuclei 55 Cr and 59 Ni and with the pairing theory.

Angular and energy distribution of photoprotons from27Al

The angular and energy distribution of photoprotons from27Al irradiated with 85 MeV bremsstrahlung has been measured using two different techniques, solid-state detectors telescope and diffusion cloud chamber in magnetic field. There is some experimental evidence of high-energy excited levels beyond the giant resonance. The proton angular distribution suggests a rather important interference between the mainE1 andE2 orM1 photonuclear excitations. We have also compared our results with the theoretical predictions of the quasi-deuteron and one-particle interaction models. This latter model is in good agreement with experimental data.

Proton energy distributions from 0.060 to 3.3 Mev at 6.6 Earth radii

Proton differential fluxes are reported for 12 energies from 0.060 to 3.3 Mev at 6.6 earth radii for the time period of October 2 to 13, 1968. The proton energies were measured with a surface barrier semiconductor detector and a stacked discriminator pulse height analyzer on the Air Force Office of Aerospace Research Satellite OV2-5 (1968-81A). The typical quiettime fluxes decreased by 8 orders of magnitude over the measured energy interval. During this time the energy spectrum varied from E−3.5 to E−6.0. Below 200 kev the energy distributions flatten but never peak above the energy of the lowest channel, 68 kev. Energy spectra associated with the two magnetic storms on October 2 and 12 are presented. After the storms the fluxes were higher than before; this is particularly true at the lower energies measured. Quiettime pitch angle distributions near the local noon-midnight meridian clearly show the east-west effect caused by the radial gradient in the fluxes. The pitch angle distributions at local midnight show the ‘drift loss cone’ predicted by Roederer. This experiment provides the first confirmation of the Roederer [1967] model of shell splitting in the earth's magnetic field by measured proton angular distributions.

Structure of 51Cr via 48Ti( 4He, nγ) and 51V(p, nγ) prompt γ-ray spectrometry

The level structure of 51Cr has been studied in some detail via prompt γ-ray energy and intensity measurements utilizing a NaI(Tl)-Ge(Li) anti-Compton spectrometer and a 511-γ-511 escape peak spectrometer via the 51V(p, nγ) reaction with proton energies in the range 2.6–6.0 MeV and via the 48Ti( 4He, nγ) reaction with t4He ++ energies in the range 12.0–15.0 MeV. Many of the γ-rays associated with levels in 51Cr were identified with the ( 4He, nγ) or the (p, nγ) reaction by means of nγ coincidence measurements employing an organic phosphor as the fast neutron detector and a Ge(Li) γ-ray detector. Characterization of many levels populated in the (p, nγ) reaction was achieved by means of thresholds for individual γ-rays obtained from measurement of excitation functions of individual γ-rays and from the γγ coincidence relationships established in on-beam γγ coincidence measurements in the 51V(p, nγ) reaction at E p = 5.0 MeV employing a NaI(Tl) and a Ge(Li) detector. It was thus established that 39 levels in 51Cr are populated in these reactions. The levels at 2255.7, 2385.6, 2767.1 and 3001.6 or 3004.1 keV which were observed in these experiments have not been reported previously. The rest of the levels studied in this work have been studied previously by means of (d, p), (p, d) and ( n th , γ) reactions. With the exception of the first six levels, the levels reported here have not been reported previously in the (p, nγ) or the ( 4He, nγ) reactions. For the levels below 2704 keV in 51Cr branching ratios for deexcitation of these levels by γ-decay were obtained by averaging the measured angular correlation of each γ-ray about the beam direction. The new γ-ray information from the present study was used in conjunction with the results of previously reported (d, p) reaction studies to make definite J π assignments to many stripping levels in 51Cr and to place limits to the J π values for many levels which were reported earlier to exhibit proton angular distribution patterns from the (d, p) reaction non-characteristic of a stripping reaction. In this work a number of γ-rays were assigned to deexcite levels in 51V that are populated via the 51V(p, p'γ) and 48Ti( 4He, pγ) reactions and which were found to compete to a small extent with the (p, nγ) and (4He, nγ) reactions. A tentative decay scheme for the deexcitation of levels in 51V is offered. The level structure of 51Cr and of 51V is compared with previously reported results of the Coriolis coupling model for the f 7 2 . shell and good qualitative agreement in the level ordering is found.

Further evidence of a [formula omitted] band in the mirror nuclei 25Al and 25Mg

A new level in 25Al at E x = 6328 ± 3 keV has been located as a resonance in the 24Mg(p, p′γ) reaction at E p = 4227 ± 2 keV. From proton and γ-ray angular distributions J = 7 2 is assigned to the resonance. Very low limits ( θ l 2 ≈ 10 −4) on the proton reduced widths are imposed by the intensities of the resonant elastic and inelastic scattering. The reduced widths are similar to those of the known E p = 2.007 MeV, J π = 3 2 + and the E p = 2.408 MeV, J π = 5 2 6+ resonances. The three levels are suggested to be the lowest members of a K π = 3 2 + band. The corresponding J π = 3 2 +, 5 2 + levels in the mirror nucleus 25Mg have been investigated with the 23Na( 3He, p) reaction. A L = 0 two-particle transfer was observed to the J π = 3 2 + level. The relevance of this result is discussed.

Study of the (d, p) Reaction on the Even-ABarium Isotopes 130-138

The ($d, p$) reactions on ${\mathrm{Ba}}^{130,132,134,136,138}$ have been investigated with 12.0-MeV deuterons from the Argonne Tandem Van de Graaff accelerator. Proton spectra were recorded in a broad-range magnetic spectrograph. Many new levels were observed. The ground-state $Q$ values (in MeV) for the ($d, p$) reactions (including the odd-$A$ targets) are found to be 5.269 for $A=130, 4.977$ for $A=132, 4.746$ for $A=134, 6.886$ for $A=135, 4.680$ for $A=136, 6.398$ for $A=137, \mathrm{and} 2.493$ for $A=138$. Proton angular distributions were measured for states up to an excitation energy of about 3 MeV. The observed angular momentum transfers were ${l}_{n}=0, 1, 2, 3, \mathrm{and} 5$, which correspond to the population of states of the $3{s}_{\frac{1}{2}}$ and $2{d}_{\frac{3}{2}}$ configurations below the closed neutron shell at $N=82$ and the $2{f}_{\frac{7}{2}}$, $3{p}_{\frac{3}{2}}$, $3{p}_{\frac{1}{2}}$, $1{h}_{\frac{9}{2}}$, and $2{f}_{\frac{5}{2}}$ configurations above it. From the observed $l$ values, it was possible to assign spins in some isotopes from a knowledge of the spin in other isotopes by taking account of systematic shifts in the $Q$ values of levels and also from shell-model expectations. Distorted-wave Born-approximation calculations were used to extract absolute spectroscopic factors. The problems and uncertainties arising in such calculations were studied in some detail. They derive, in part, from the need to use a sharp radial cutoff to fit the experimental angular distributions; calculations with nonlocal potentials and finite-range approximations did not yield satisfactory fits. Another source of uncertainty is the dependence of the spectroscopic factors upon the geometric parameters of the bound-state potential well. The results are interpreted with the help of pairing theory; centers of gravity and single-particle energies are deduced.

Angular distribution of protons from the reaction Co59(n, p) Fe59 forE n ∼6·3 MeV

The energy and angular distributions of protons in the reaction Co59 (n, p) Fe59 have been measured forEp=6·3 MeV. The results show the presence of other mechanism than compound nucleus.

Models for High-Energy Processes

Recent developments in the concepts and models used to describe high-energy collisions of fundamental particles are reviewed. The areas of appreciable activity in research in high-energy physics are surveyed briefly and the general framework for the description of processes at high energies is outlined. There follows a sampling of recent experimental data designed to show the extent and detail of present-day experimental results. Recent applications of Regge pole models are reviewed with emphasis on the difficulties as well as the successes of models employing only Regge poles. The various multiple-scattering models are then discussed and correlated by means of the methods of Glauber. The connection of these models with amplitudes having branch cuts in the angular-momentum plane (Regge cuts) is described, as well as some comparisons with experiment. Finite energy sum rules as a means of relating the low-energy and high-energy domains are discussed in some detail. Next, the far-reaching concept of duality whereby the direct-channel resonances are (in some sense) the crossed-channel Regge exchanges is described, along with the related ideas of exchange degeneracy, the special role of the Pomeranchon Regge pole, and duality diagrams. An explicit realization of duality is achieved in the Veneziano model. This model is discussed in some detail for the relatively simple and interesting example of pion-pion scattering. Brief mention is also made of the extensions of the Veneziano model to the $n$-particle amplitude, attempts at unitarization, and various applications. The topic of multiparticle final states is covered relatively briefly with emphasis on the applications of double Regge pole exchange to three-body final states, the calculation of proton and pion energy and angular distributions in proton-proton collisions by means of the multi-Regge exchange model, and the generation of self-consistent Regge singularities with the multi-Regge exchange model and unitarity. The final section of the review concerns recent results on pion-pion scattering phase shifts and also $K\ensuremath{-}\ensuremath{\pi}$ phase shifts, and some remarks on theorems connecting decay correlations of resonances with the mechanism of production. The literature survey ended, with a few exceptions, in May 1969.

Experimental Investigations of theC12(h,p)N14Reaction Mechanism

Systematic studies on proton angular distribution and proton-$\ensuremath{\gamma}$-radiation angular correlations have been carried out on the ${\mathrm{C}}^{12}(h,p){\mathrm{N}}^{14}$ reaction throughout the energy range $4.62\ensuremath{\le}{E}_{h}\ensuremath{\le}11.0$ MeV. ($h\ensuremath{\equiv}{\mathrm{He}}^{3}$.) Both direct and compound-system reaction amplitudes are present; however, the latter appear to dominate. Striking resonant phenomena are observed, and it is suggested that these correspond to quasigiant resonances in the excitation-energy range from 17 to 23 MeV in ${\mathrm{O}}^{15}$ having a particularly simple structure involving singleproton orbitals coupled to excited ${\mathrm{N}}^{14}$ core configurations. A systematic correlation has been observed between the population of $|m|=1$ magnetic substates of the 7.03-MeV state in the residual nucleus and the appearance of backward peaking in the corresponding proton angular distributions. A crude argument relating these phenomena to the participation of a heavy-particle direct stripping mechanism is suggested.

Study of Protons and Alpha Particles Emitted fromBr75Compound Nuclei with Differing Angular-Momentum Distributions

The energy spectra and angular distributions of protons and $\ensuremath{\alpha}$ particles emitted from the compound nucleus ${\mathrm{Br}}^{75}$ formed at the excitation energies of 49 and 88 MeV have been studied. The ${\mathrm{Br}}^{75}$ compound nuclei were formed in three different ways: ${\mathrm{B}}^{11}$+${\mathrm{Zn}}^{64}$, ${\mathrm{C}}^{12}$+${\mathrm{Cu}}^{63}$, and ${\mathrm{O}}^{16}$+${\mathrm{Co}}^{59}$. The differences in the angular-momentum distributions of the compound nuclei formed in each of the entrance channels permitted the study of the particles emitted from specific ranges of angular momentum of the compound nuclei. The yield of $\ensuremath{\alpha}$ particles from the high-angular-momentum states was found to be significantly enhanced relative to that from the low-angular-momentum states and the average energy of the $\ensuremath{\alpha}$ particles emitted increased with the angular momentum of the compound nucleus. The yield of protons and their average energy was not significantly affected by angular momentum. These results are consistent with results calculated using an angular-momentum-dependent statistical theory of nuclear reactions.

Nuclear structure studies in the tellurium isotopes: The 124Te(d, p)125Te reaction

The reaction 124Te(d, p)125Te has been studied at a bombarding energy of 7.5 MeV in order to get information about the 125Te nuclear level scheme. The protons were recorded simultaneously at 23 angles in a multiple-gap magnetic spectrograph. One hundred and fifty two levels were observed below an excitation energy of 6.2 MeV, and the proton angular distribution for 55 of these transitions were compared to DWBA calculations in order to determine the transferred orbital angular momentum, ln, and to measure spectroscopic factors. The lower part of the level scheme was compared to the results from studies of 125Sb decay, and to theoretical pairing-theory calculations. A sum-rule analysis of the holes in the 50–82 neutron shell gave 7.95 vacancies while the expected value is 10. Single-quasiparticle energies for 125Te, 127Te, 129Te and 131Te are listed. A comparison is made with the isobaric analogue states in 125I observed elsewhere in the 124Te(p, p) reaction.

Reaction Mechanisms inFe56(p,p′)from 5 to 6 MeV

Proton angular distributions and spin-flip angular correlations have been measured as absolute cross sections for inelastic scattering of 4.96-, 5.58-, and 5.88-MeV protons to the first excited (${2}^{+}$) state at 0.847 MeV in $^{56}\mathrm{Fe}$. The spin-flip measurements involve directional correlation of the 0.847-MeV $\ensuremath{\gamma}$ rays, detected along a perpendicular to the reaction plane, with the inelastic protons observed at angles from 30\ifmmode^\circ\else\textdegree\fi{} to 150\ifmmode^\circ\else\textdegree\fi{} in the reaction plane. The spin-flip probability was determined for the three energies studied. The measured cross sections are compared with the predictions of the statistical model and the direct-interaction model. The compound-nucleus mechanism appears to dominate the reaction in this energy range. The statistical-model predictions, which are based on optical-model parameters obtained at somewhat higher energies, give the correct shape and order of magnitude, but fail to fit simultaneously both the angular distributions and the spin-flip correlation data.

Niveaux excités de 19O étudiés par la réaction 18O(d, p) 19O

A Buechner-type magnetic spectrograph has been used to study the 18O(d, p) 19O reaction between 20° and 130° with respect to the incident deuteron beam at E d = 5 MeV. Proton groups corresponding to previously reported levels, up to 4.118 MeV excitation energy in 19O, have been observed and the energies of nine excited states are determined. No evidence is found for the previously reported levels at 0.348, 1.257 and 3.791 MeV. Comparison of the proton angular distributions with PWBA predicted shapes indicates l n = 2 for the levels at 0.097, 2.370, 3.160 and 3.237 MeV. Gamma radiation was observed with Ge(Li) detectors. Particle-γ and γ−γ coincidence measurements were performed at E d = 3 MeV. The gamma branching ratio of the 1.468 MeV state to the ground state has been found to be (3.1±1.7)%. The present results are compared with previous work and discussed in the frame of the shell model.

Low-Lying States inRb86from (d, p), (d, t), and (n, γ) Reactions

The energy levels of ${\mathrm{Rb}}^{86}$ have been studied through the neutron stripping and pickup reactions ${\mathrm{Rb}}^{85}(d, p){\mathrm{Rb}}^{86}$ and ${\mathrm{Rb}}^{87}(d, t){\mathrm{Rb}}^{86}$, and the thermal-neutron-capture reaction ${\mathrm{Rb}}^{85}(n, \ensuremath{\gamma}){\mathrm{Rb}}^{86}$. Enriched targets were bombarded with 12-MeV deuterons, and proton and triton spectra were observed with a magnetic spectrograph; proton angular distributions were compared with a distorted-wave Born-approximation (DWBA) calculation. Thermal-neutron-capture $\ensuremath{\gamma}$-ray spectra from both enriched ${\mathrm{Rb}}^{85}$ and natural rubidium targets have been studied in the energy intervals 50-2000 keV and 5000-8500 keV with a Ge(Li) spectrometer system. 32 low-energy $\ensuremath{\gamma}$-ray transitions were incorporated into a level scheme defined by the combined ($d, p$), ($d, t$), and the primary ($n, \ensuremath{\gamma}$) measurements. Tentative spin and parity assignments for 18 levels below 1505 keV are proposed on the basis of assigned orbital angular momentum transfers and $\ensuremath{\gamma}$-ray population and decay modes. The low-lying states of ${\mathrm{Rb}}^{86}$ are discussed in terms of shell-model proton-neutron configurations; comparison is made with a zero-range spin-dependent calculation. Although correlation between the data and positive parity levels predicted by the simple model is not entirely satisfactory, reasonable agreement has been found for low-lying negative parity levels.

Isobaric analogue states of 10Be- 10B

A study has been made of the 5.96 and 6.26 MeV levels of 10Be. Electromagnetic transitions following the 9Be(d,p) 10Be reaction were examined. Spectra in coincidence with the proton groups were analysed to determine γ-ray branching ratios. The result of a γ-γ correlation measurement upon the cascade γ-rays from both states was consistent with J = 2 for both states. The correlation observed for the decay of the 5.96 MeV states is not consistent with that of a 1 − state. However, it is suggested that a 1 −−2 + doublet exists at 5.96 MeV in 10Be with the J = 2 member decaying predominately by cascade through the 3.37 MeV state; and the J = 1 member decaying predominately by a direct ground state transition. Experimental confirmation of the doublet structure at 5.96 MeV was obtained and a level separation of 1.6±0.5 keV determined with the 2 + level being lower in excitation. Proton angular distributions at 2.8 MeV deuteron energy were determined for the individual members of the doublet to establish the parities of the states. Spectroscopic factors and reduced widths for the individual members of the doublet were extracted from plane-wave and distorted-wave analyses of the angular distributions.