J. Reginald Richardson

Differential cross sections and polarizations in elastic p-d scattering at medium energies

Abstract Differential cross sections for p-d elastic scattering have been measured at 22.0, 35.0 and 46.3 MeV using the energy-analysed external proton beam of the UCLA sector-focussed cyclotron. The angular distributions cover centre-of-mass angles between 9° and 168°. At forward angles both protons and deuterons were observed using a d E /d x - E telescope counter consisting of a fully depleted surface-barrier detector ( ΔE ) and a NaI(Tl) scintillation detector. ( E ). At larger angles, protons were observed using an array of four NaI(Tl) scintillation detectors. The differential cross sections have in general a relative uncertainty less than 2%, while the absolute scale of the measurements has an uncertainty of 1.7%. The proton polarization angular distributions at 35.0 and 40.0 MeV were also measured. In this part of the experiment, the polarized proton beam facility was used. The polarized proton beam was obtained by scattering the internal beam of the cyclotron from a carbon scatterer. At 35.0 MeV, the polarization angular distribution covers centre-of-mass angles between 20° and 164°. At 40.0 MeV, measurements were made for centre-of-mass angles greater than 130° only. Scattered particles were observed using six NaI(Tl) scintillation detectors placed in groups of three on either side of the incident beam. The target used when detecting elastically scattered protons was deuterium gas. The backward part of the angular distribution was measured by detecting recoil deuterons from a deuterated polythylene target. The available proton polarization data for p-d elastic scattering have been used to construct a polarization contour diagram for the energy range of 10–400 MeV.

Two Electron Models of a Constant‐Frequency Relativistic Cyclotron

Two model constant‐frequency cyclotrons based on the principle of L. H. Thomas, as extended by David L. Judd, are described. Both accelerated electrons to speeds of half that of light in magnetic fields of three‐fold azimuthal periodicity. Three 60°‐wide wedge‐shaped electrodes, driven 120° out of phase, provided an energy gain per revolution of 3 eV0, where V0 is the peak electrode‐to‐ground voltage. Electrons were accelerated to 75 kv with V0=23 v, implying a minimum of one thousand revolutions in the cyclotron. The beam reached full energy without axial loss and it was demonstrated that essentially all of the circulating current will emerge from this type of accelerator without the use of additional deflecting systems. The success of this development program has shown the feasibility of a high‐current, high‐energy cyclotron based on the Thomas principle.

Neutron-proton scattering cross sections between 200 and 500 MeV

Abstract The n-p total cross section has been measured in a transmission experiment in which a neutron beam produced by the 2 H(p,n) reaction was incident on a liquid-hydrogen target. Results are presented at 212, 268, 319, 369, 417 and 495 MeV; the overall uncertainties average ±1.9%. The n-p differential elastic cross section between 10° and 180° c.m. was measured at 212, 319, 418 and 493 MeV using the same beam and target. Different techniques were used in two overlapping angular regions, the relative normalisation being fixed by a calibrated monitor of neutron beam intensity. Point-to-point uncertainties in the forward region vary from ±1.4% to ±9.5%, but are generally close to ±2.0%. In the backward region the uncertainties average ±1.5%. Relative normalisation between the two regions has an uncertainty of about ±3% at each energy, and a further normalisation uncertainty of ±1.6% is common to all the data.

Measurement of the angular distribution of 4He(p, d)3He, 4He(p, 3He)pn and 4He(p, t)pp reactions

Abstract We have measured the angular distribution of the reaction 4 He(p, d) 3 He at 47 MeV over the center-of-mass angular range of 12–166°. We have also measured the angular distributions of the reactions 4 He(p, 3 He)pn and 4 He(p, t)pp in the region of the nucleon-nucleon final state interaction at the same bombarding energy over an angular range of 7.5° to 50.0° in the laboratory. The 3 He and triton energy spectra are also presented and Watson-Migdal fits to these data in the region of the nucleon-nucleon final state interaction are shown.

Decay of 102Ag and levels in 102Pd

Abstract The decay of the 102 Ag isomers has been investigated using magnetic-lens, scintillation and solid-state spectrometers. Half-lives of 13±0.4 and 7.7±0.5 min were assigned to the 5 + and 2 + spin isomers, respectively. Beta rays of 4.06, 3.37, 3.07, 2.26, 1.90, 1.50, 1.00 and 0.65 MeV end-points and gamma rays of 0.558, 0.727, 0.86, 1.01, 1.28, 1.60, 1.70, 1.80, 2.07, 2.79, 3.23 and 3.33 MeV were observed, and a large amount of K-capture was found. The isomeric tansition proceeds by means of the internal conversion process. A partial decay scheme has been proposed on the basis of the γ-γ, γ-γ-γ, β-γ, and X-ray-γ coincidences.

Inelastic scattering of 46 MeV protons from 12C

Abstract The differential cross sections for the excitation of nine levels of carbon have been measured each at 35 angles from 15° to 150°. The cross sections for the 4.4 and 9.6 MeV levels have a typical relative accuracy of 3%, while the measurements for the 7.7, 10.8, 11.8, 12.7, 14.1, 15.1 and 16.1 MeV levels have a typical accuracy of 10%. The cross sections decrease by from one to three orders of magnitude through the measured angular range. Levels at 13.3 and 16.6 MeV were not observed. The angular distributions have been compared with distorted wave calculations using both macroscopic and microscopic approaches.

Delayed heavy-particle emission from 24Al and 32Cl

Abstract The energy spectra of the delayed heavy particles emitted from levels in 24Mg and 32S following the beta decay of 24Al and 32Cl, respectively, are presented. Alpha transitions were found from the 11.23 MeV, 11.70 MeV and 12.13 MeV levels of 24Mg and from the 8.79 MeV and 9.47 MeV levels of 32S. Proton transitions were measured from the 9.65 MeV, 9.91 MeV and 10.26 MeV levels of 32S. The relative intensities of the positon decays to the heavy particle emitting levels of 32S were measured as well as the absolute positon branching ratio to the alpha particle unstable levels of 24Mg. The energy levels deduced in 24Mg and 32S are compared with known energy levels and their spin and parity assignments are discussed.

The new radioisotope 99Ag and some measurements on 100Ag

Abstract Production of 99 Ag with a (p, 4n) reaction on 102 Pd targets has been observed. A half-life of 106±10 sec has been measured for gamma transition at 660(30), 750(15), 1040(100), 1525 (30), 1700(90) and 3315(35) keV. The growth and decay of the daughter 99 Pd has been observed. A positon spectrum was resolved into three branches at 3.32(59.2), 2.43(23.9) and 1.69(16.9) MeV. A level scheme has been proposed for the levels in 99 Pd. A high-energy positon branch at 6.5±0.5 MeV with a 7.5±1 min half-life was observed and has been ascribed to 100 Ag. The threshold for this production indicates a (p, 3n) reaction. In addition, two intense gamma transitions at 556 and 728 keV with the same half-life are ascribed to the decay of 100 Ag.

Design and operation of the U.C.L.A. 50 MeV spiral-ridge cyclotron

The design and operation of the U.C.L.A. 50 Mev cyclotron is described. The magnetic field is presented in a series of graphs and orbit calculations on beam stability are given. The results of experimental observations and measurements on the internal beam include beam intensity graphs and photographs, piots of / nu /sub z/ and nu /sub r/ from r.f. knockout measurements, beam intensity as a function of dee voltage, and radial oscillation amplitude of the beam. Because of iack of shielding, the beam has been restricted to 2 mu a of 50 Mev protons by use of a 5% duty cycle. An increased intensity is expected when a puller electrode is used at the source. The tuning up of the beam by means of the eight circular coils for trimming the magnetic field has been found to be quite simple in practice. Efforts to get an external beam are now proceeding in the permanent shielding vault. (auth)

A technique for measuring proton total reaction cross sections at medium energies

Abstract Total proton reaction cross sections between 20 and 50 MeV have been measured at the UCLA 50 MeV Cyclotron Laboratory. Our method, a variation of the attenuation technique first proposed by Gooding and Eisberg, is described. Features include a tightly collimated and well defined beam, the ability to use either solid or gaseous targets, and rapid accumulation of the data.