R.C. Jared

Application of High-Resolution Semiconductor Detectors in X-ray Emission Spectrography

Solid-state devices developed primarily for nuclear gamma spectroscopy have many potential uses in x-ray analysis.

A gas ionization counter for particle identification

Abstract A method is described for the identification of products from nuclear reactions. A gas ionization counter is used as a thin (0.8 mg/cm 2 ) transmission detector in a counter telescope particle-identification system. The response of the system is approximately linear in Z for the ions produced by heavy-ion-induced fission of medium- Z targets. Reaction products with Z up to ∽ 30 can be well resolved. Methods of fabrication of entrance windows for the counter are discussed and a procedure for determination of the window thickness is presented. Generally entrance windows were either Formvar or VYNS with a thickness of 40–60μg/cm 2 .

The TOPAZ Time Projection Chamber

Abstract A Time Projection Chamber (TPC) is under construction for the TOPAZ e + e − experiment at TRISTAN. The dimension of the TPC is 260 cm in diameter and 300 cm in axial length. Fin-type fine field cages are set inside GFRP insulator cylinders which also serve as the pressure container. The sector is made of multilayer G10 boards for better electric and thermal isolation. The cathode pads are substantially larger in area than those of the PEP4-TPC and having zigzag-shaped boundary. These serve to maintain high spatial resolution with fewer number of pad channels. Signals are amplified by low noise preamplifiers and shaping amplifiers, and, stored and digitized by FASTBUS based CCD-digitizers. Digitized information is preprocessed and sent to VAX 11/780 at a rate 2 MHz per 32 bit word. Nitrogen LASER beam will be used extensively with the LASER beacon system for calibration. Test results on production prototypes are also reported.

Evidence of incomplete relaxation in the reaction Ag+40Ar at 288 and 340 MeV bombarding energies☆

Abstract The particles emitted in the reaction induced by 40 Ar on natural Ag at 288 and 340 MeV bombarding energy have been studied. The fragments have been identified in atomic number, their kinetic energy distribution and their angular distributions have been measured. The kinetic energy spectra show two components: a high-energy component related to the beam energy, or “quasi-elastic” component, and a low kinetic energy component, close to the Coulomb energy called “relaxed” component. The relaxed component is present at all angles and for all particles. The quasi-elastic component is present close to the grazing angle for atomic numbers close to that of the projectile. The relaxed cross section increases with atomic number for Z > 9. The increase in cross section is sharper for the lower bombarding energy. The angular distributions are forward peaked, in excess of 1 sin θ for all the measured atomic numbers. The forward peaking is larger for particles close in Z to the projectile. The results are interpreted in terms of characteristic times associated with a short-lived intermediate complex. The cross sections and angular distributions are satisfactorily reproduced on the basis of a model accounting for a diffusion process occuring along the mass asymmetry coordinate of the intermediate complex.

Potential energy effects and diffusion in the relaxed components of the reaction 197Au + 40Ar at 288 and 340 MeV bombarding energies

Abstract The fragments emitted in the reaction between 197 Au and 40 Ar at 288 and 340 MeV bombarding energies have been studied. The fragments have been identified in atomic number up to Z = 32 by means of an E - Δ E telescope. The kinetic energy distributions, the cross sections and the angular distributions have been measured for each Z . The kinetic energy distributions show the typical quasielastic and relaxed components; the Z -distributions show a smooth increase in the cross section with increasing Z , interrupted at relatively forward angles by a fairly sharp peak close to Z = 18. The angular distributions are forward peaked in excess of 1 sin θ for atomic numbers as large as Z ≈ 30, as far as twelve atomic number units above the projectile; this is at variance with other reactions like Ag + 20 Ne, where the angular distributions become 1 sin θ four or five atomic number units above the projectile. This is interpreted in terms of an enhanced diffusion towards symmetry, possibly promoted by the potential energy in the intermediate complex corresponding to two fragments in contact.

Diffusion processes in the relaxed cross section for the reaction 107, 109Ag+20Ne

Abstract The fragments emitted in the reaction 107,109 Ag+ 20 Ne at 175 and 252 MeV bombarding energy have been identified in charge up to Z = 32. Kinetic energy distributions, cross sections and angular distributions have been measured for each Z . The kinetic energy spectra show the two usual components: the quasielastic component and the relaxed component. The Z -distribution of the latter is fairly flat, slowly decreasing up to Z ≈ 15 and then rising again up to Z = 30. The variations in the Z -distribution are more pronounced at the lower bombarding energy. The angular distributions associated with the relaxed component are forward peaked for Z -values close to that of the projectile and behave like 1 sinθ for larger Z -values. The forward peaking is very substantial for Z Z > 10 the forward peaking in excess of 1 sinθ disappears around Z = 15. These features are interpreted in terms of a diffusion process along the asymmetry coordinate of a short-lived intermediate complex.

Intermediate mass fragments emitted in the reaction Ag+14N at 100, 160 and 250 MeV bombarding energy

Abstract The fragments produced in the reaction between a 14 N beam of various energies and a natural Ag target have been studied. The atomic numbers of the fragments have been identified up to Z = 17 by means of a E - ΔE counter telescope. The cross sections, the kinetic energy distributions as well as the angular distributions have been measured for each atomic number. The kinetic energy distributions show two components: a high-energy component (quasi-elastic), prevailing at angles close to the grazing angles and for atomic numbers close to Z = 7, and a low-energy component (relaxed), at energies close to the Coulomb repulsion energy, present at all angles and for all the Z . A detailed study of the relaxed components of the kinetic energy seems to account for both them means and the widths of these distributions on a purely statistical basis. The cross sections of the relaxed components appear to be quite large at low Z and to decrease rapidly to a fairly constant value in the region of 10 ≦ Z ≦ 17. A marked even-odd alternation in the cross sections is observed. The angular distributions are strongly forward peaked for Z Z > 7 the forward peaking decreases rapidly until, for Z > 13, the limiting form 1/sin θ is attained. Evidence for the existence of a diffusion process along the mass asymmetry coordinate is discussed.

Analog Signal Processing for the Time Projection Chamber

The Time Projection Chamber (TPC) is a large gas filled cylindrical detector designed to provide 3-D images of tracks radiating from the center of the detector where e+ e- collisions occur. Ionization along the tracks is drifted in an electric field to the end planes which are equipped with a large array of proportional wires and position pads (17,000 channels). The wire signals are used to derive radial data while the pad signals provide the azmuthal information. The axial dimension is determined using the drift time of the ionization. Preamplifiers mounted in the ends of the chamber feed the signals to remote amplifiers whose outputs drive Charge Coupled Devices (CCD). The CCDs are normally clocked at 10 MHz and hold a 45.5 ¿s history (445 CCD buckets) of analog drift information from the TPC. During readout the clock is changed to 20 KHz and 17,000 CCD outputs are digitized (9 bits) in parallel. The non-zero data is then transferred to buffer memories associated with the digitizers. This paper emphasizes the analog signal processing part of the system.

A simple position-sensitive parallel-plate avalanche detector with 2-dimensional readout☆

A new design for an x−y position-sensitive avalanche detector is presented. The design is based on charge-division readout of resistive sheet electrodes. The position resolution is < 1 mm. In our application, the position-sensitive detector is operated in the transmission mode with a solid-state E-detector behind it.

Binary aspects and particle multiplicities of the fragments from natAg+340 MeV 40Ar deep inelastic collisions

Abstract Deep inelastic fragments from the reaction nat Ag+340 MeV 40 Ar have been studied in coincidence. Charged particles (10 ≦ Z ≦ 32) were detected and identified in Z by means of a ΔE − E telescope, while the complementary fragments were detected in a one-dimensional, solid-state position-sensitive detector. Both in-plane and out-of-plane correlations were measured. The results confirm the binary nature of the deep inelastic process for this reaction. From the measured energies and angles of the fragments and the atomic number of one of the fragments, it was possible to determine the total mass loss due to the de-excitation of the fragments as well as the total evaporated charge at symmetry. An iterative procedure is discussed which enables one to determine the masses and kinetic energies of the fragments before evaporation, as well as the total number of particles evaporated by each fragment. The widths of the in-plane and out-of-plane correlations agree with the results of the iterative calculations, as do evaporation calculations which are based on the charge equilibrium model. The experimental results support the charge equilibrium model and indicate that thermal equilibrium is achieved between the fragments at fixed mass asymmetry.