B. L. Beron

The Fluorescent Response of NaI(Tl), CsI(Tl), CsI(Na) and CaF2(Eu) to X-Rays and Low Energy Gamma Rays

The fluorescent response functions of NaI(Tl), CsI(Tl), CsI(Na) and CaF2(Eu) have been determined with thin crystals over the energy range from 3.3 keV to 840 keV. A pronounced nonlinear dependence on photon energy has been observed in this region for all four types of crystals investigated. Qualitatively the response functions for NaI(Tl), CsI(Tl) and CsI(Na) are similar down to a photon energy of about 20 keV, but major differences are observed at lower energies. The response function of CaF2(Eu) is very different from the response functions for the other three crystals over the entire energy range examined. Both K-shell and L-shell absorption edge discontinuities are evident in the fluorescent response curves for Na(Tl) and CsI(Tl). Only K-shell absorption edge discontinuities could be observed in the response curves for CsI(Na) and CaF2(Eu). A nonlinear fluorescent dependence on electron energy is indicated for all four types of crystals. Discontinuities in the spectral resolution function are observed in NaI(Tl) at energies corresponding to both the K-shell and L-shell absorption edges of iodine. A shift toward longer wavelengths in the light spectrum emitted by NaI(Tl) in response to excitation by X-rays with energies below about 10 keV may also be indicated by photomultiplier-dependent differences observed only at the lowest energies.

Design and Performance of a Modularized NaI(Tl) Detector (The Crystal Ball Prototype)

A prototye NaI(Tl) detector (the Cluster of 54) of spherical geometry subtending a solid angle of 7.5% of 4¿ at its center, has recently been assembled and tested. This detector consisted of 54 close-packed but optically isolated NaI(Tl) modules and the associated electronic circuitry. The Cluster of 54 is the predecessor of an almost complete spherical detector, the Crystal Ball, which will cover 94% of 4¿. The latter detector is now under construction and is especially designed for the study of ¿-rays produced in electron-positron collisions at colliding beam facilities. This article will outline the mechanical, optical, and electronic assembly of the prototype system. Cluster of 54 test data will be presented.

Performance of Large, Modularized NaI(Tl) Detectors

The properties of detector arrays made up of NaI(Tl) Polyscin modules 20 in. deep and of hexagonal cross section and the development of a Monte Carlo code of general use in the design of such detectors are described. The use of modularized NaI(Tl) detectors in the study of a new spectroscopy of ¿-rays in high energy physics is outlined.

The use of an active coded aperture for improved directional measurements in high energy γ-ray astronomy

The coded aperture, a refinement of the scatter-hole camera, offers a method for the improved measurement of γ-ray direction in γ-ray astronomy. Two prototype coded apertures have been built and tested. The more recent of these has 128 active elements of the heavy scintillator BGO. Results of tests for γ-rays in the range 50 - 500 MeV are reported and future application in space discussed.

Measurements of e+e− → e+e− →, e+e− → μ+μ− and e+e− → γγ at Center of Mass Energies Close to 3105 MeV

We report here independent evidence for the decay of the recently discovered ψ(3105) particle1–3 into electron-positron pairs and new evidence for the decay of this particle into muon pairs. We also report the results of a measurement of the reaction e+e− → γγ at center of mass energies in the vicinity of 3105 MeV. These measurements were begun immediately following the discovery of the ψ(3105) at SPEAR1. At that time an apparatus primarily designed for the study of quantum electrodynamics (QED) was operating in the second interaction region at SPEAR and was applied immediately thereafter to the study of the ψ(3105). This apparatus is very similar to that described recently by Beron, et al.,4 and is capable of identifying the reactions e+e− → e+e− →, e+e− → μ+μ− and e+e− → γγ. The detection apertures and procedures used to recognize each of these reactions are identical to those described by Beron et al.,4 except that the detection aperture for the reaction e+e− → μ+μ− is larger by a factor of 2.6. All of the measurements reported in this letter were made with the detection apparatus set to accept particles produced at angles 6 close to 90° with respect to the colliding beams.

Measurements of the reaction e/sup +/e/sup -/. -->. mu. /sup +/. mu. /sup -/ at center-of-mass energies in the range 6. 2--7. 4 GeV

Measurements of the cross section for the muon-pair-annihilation reaction e/sup +/e/sup -/ ..-->.. ..mu../sup +/..mu../sup -/, relative to Bhabha scattering at 4/sup 0/, are reported at center-of-mass energies in the range 6.2--7.4 GeV. These measurements provide a fundamental test of quantum electrodynamics (QED) for timelike values of the invariant four-momentum transfer q/sup 2/ as high as 54.8 (GeV/c)/sup 2/, which in this reaction is carried by the photon propagator. The results are in agreement with predictions of QED.