J. D. Fox

COMPARATIVE PULSE-HEIGHT ANOMALY FOR PROTONS AND ALPHA-PARTICLES IN SILICON SURFACE BARRIER DETECTORS.

Abstract It has been observed experimentally that the pulse-height obtained from a Si surface barrier detector for 9.500 MeV incident alpha particles and protons is different by 56±9 keV, with the alpha particle appearing to have the higher energy. This result indicates that Q -value determinations obtained by comparing the energy of different particles can be seriously in error.

A scattering chamber using junction counters

Abstract The specifications and characteristics of a versatile scattering chamber are presented. The chamber is designed for use with solid state detectors. It became necessary in the course of a study of the fission of U 238 and Th 232 by a proton beam from the Florida State University Tandem Van de Graaff to design a small scattering chamber in which solid state junction counters could be positioned precisely at various angles around the target. The following features were desirable in the scattering chamber: (a) precise positioning of the target; (b) precise positioning of counters both with respect to the distance from the target and the angle to the beam; (c) ease of rotation of the counters to different angles; (d) provision for both movable and fixed counters; (e) precise positioning of the chamber about the beam tube; (f) precise defining slits for both the beam and the particles to be counted; (g) freedom from trailing lead wires as the counters are rotated; (h) a Faraday cup which provided accurate measurements of the beam current. The chamber which was designed possesses all of these features and has proven to be of sufficient usefulness to warrant journal description.

The Florida State University quadrupole spectrometer

Abstract A quadrupole doublet lens refocuses particles of rigidities up to 400 MeV/c per unit charge scattered within an angular range of −15° to +140° from a 30 cm chamber onto a detection surface 3.0 m removed from the target. This system, herein to be called the quadrupole spectrometer, has been developed for the purpose of (1) reduction of noise and background during detection of charged particles, (2) magnetic rigidity band pass filtering and reduction of unwanted or overprolific beam species, (3) small-angle cross section measurements, (4) charge state determinations, and (5) time-of-flight measurements. A general description of the quadrupole spectrometer, discussion of its intended uses and examples of data obtained are presented.

Status report on the Florida State linac project

The Florida State University superconducting linear accelerator booster will consist of three cryostat modules, each with four β=0.105 resonators and two superconducting solenoids, and buncher and rebuncher resonators in individual cryostats. The first cryostat module was recently completed and is described.

Targets and target wheel mechanism for APEX

Abstract A rotating target wheel system built for the Atlas Positron Experiment (APEX) is described. It is designed so that targets could withstand the heating caused by the energy loss of intense heavy ion beams. A unique feature is the use of a digital encoder to provide logic trigger signals for beam sweeping and event-by-event target location information. Techniques for fabricating targets of tantalum, lead, thorium and uranium and the behaviour of the targets during beam exposure are also discussed.

Energy dependence of the elastic scattering 40Ca(3He, 3He) in the energy range 10.0 to 18.0 MeV

Abstract Differential cross sections for the elastic scattering of 18, 16, 14, 12 and 10 MeV 3 He particles by 40 Ca were measured and analyzed in terms of the optical model with volume imaginary and real spin-orbit potentials. Angular distributions have been measured in 5° steps between 25° and 175°. Four sets of optical model parameters were established and in two of these, sets A and B, systematic variations with energy of the real, volume imaginary and spin-orbit potentials were obtained. The geometrical parameters were not varied as a function of energy. The effect of the matching radius R M on the optical model calculations, was investigated. It was found that the matching radius should be calculated using the geometrical parameters of the potential that yields the largest value for R M according to the receipe R M = R + 7 a where R is the nuclear radius and a is the diffuseness.

Study of structure in the 28Si(p, n)28P and 28Si(p, α)25Al excitation functions

Abstract The 28 Si(p, n) 28 P and 28 Si(p, α) 25 Al reactions have been studied over the energy range of 16.0 to 18.2 MeV incident proton energy. Fluctuations appear in the excitation functions over the entire range with widths of 100 keV and 48 keV for the neutron and alpha channels, respectively. The energy averaged 28 Si(p, α) 25 Al angular distributions are not reproduced by Hauser-Feshbach compound nucleus calculations but do resemble DWBA calculations. Because of the complex nature of the reaction mechanism in this energy range, it could not be concluded whether the structure in the excitation functions is due to doorway states or Ericson fluctuations.

A large general purpose scattering chamber

An inexpensive charged-particle scattering chamber has been constructed from a large obsolete dry ice trap. A removable platform mounted on a linear bearing contributes to the chambers versatility and convenience. The chambers construction permits cooling of solid state detectors to improve resolution and to make possible the utilization of marginal detectors. Electrical motors are used to change beam defining apertures, targets and detector angles. No movable vacuum seals are used in this design.

Status of the Florida State University superconducting linear accelerator

Abstract The Florida State University Superconducting Linac has completed its first year of operation. The accelerator consists of 14 independently phased niobium (explosively bonded to copper), superconducting, rf cavities, injected by a FN tandem Van de Graaff. The history of the project, its present status and recent developments are outlined.

First tests of the liquid‐helium distribution line for the FSU linac

The liquid‐helium distribution system for the FSU superconducting linear accelerator has been installed and a preliminary evaluation of the system performance has been made. A heat leak of about 30 W was anticipated for the entire system. With two of the five cryostats in place, we estimate an overhead heat leak for the piping system of about 37 W.