R. Eisberg

The nuclear reaction efficiency correction for silicon and germanium detectors

Abstract The proton total-reaction cross section of silicon has been measured to be 732 ±20mb at 28 ±1MeV. The efficiency corrections for nuclear reactions in silicon and germanium detectors for protons from 5 to 150 MeV have been calculated using the energy dependence of the proton total-reaction cross sections. These calculations are shown to be in excellent agreement with direct measurements of the efficiency of silicon detectors.

Total reaction cross sections for 29 MeV protons

Abstract The USC proton linear accelerator is being used in a programme of measuring the energy dependence of proton total reaction cross sections. As a first step in this programme measurements were made using the full beam energy. The anticoincidence beam attenuation technique was used. The following cross sections were obtained for 29 MeV protons: C, 418 ± 18 mb; Al, 775± 37 mb; 1023 ± 40 mbAg, 1471 ± 71 mb; and Au, 2209 ± 118 mb. These cross sections are compared to other measurements and optical model analyses.

Reaction cross sections for 26.5 MeV deuterons

Abstract By using an attenuation technique, total reaction cross sections were measured for 26.5 MeV incident deuteron energy on Be, C, Mg, Al, Ti, V, Fe, Ni, Co, Cu, Zn, Zr, Rh, Ag, Sn, Ta, Au, and Pb. The main feature of the data is the presence of a minimum in the nickel region in agreement with surface absorption optical model calculations performed on elastic scattering data at 27.5 MeV. In general surface absorption calculations predict σ R values in better agreement with experimental data than volume absorption calculations.

PROTON TOTAL REACTION CROSS SECTIONS OF CARBON FROM 16 to 28 Mev

Abstract Optical model analysis of the elastic scattering of 18 to 31 MeV protons from carbon has shown that fairly wide variations in the optical model parameters are necessary to reproduce the data. A later analysis of these data in which it was assumed that the scattering amplitude is described by the sum of optical model and Breit-Wigner terms has indicated possible resonances at 19.8, 20.01, and 24.9 MeV (c.m.). The later analysis predicts an inflection point in the proton total reaction cross section at about 21 MeV (lab). In this work the reaction cross sections were measured in the energy range 16 to 28 MeV using the anti-coincidence beam attenuation technique, and the energy variation was achieved with beryllium absorbers and subsequent magnetic analysis. The measured reaction cross section agrees well with the cross section predicted by the later analysis except that there is a weak maximum instead of an inflection point at about 21 MeV (lab).

Design and performance of an 8 cm thick intrinsic germanium detector telescope

Abstract A detector telescope consisting of eight 1 cm thick intrinsic Ge diodes is described. The diodes have thin dead layer Li junctions (∼15 ωm ) and are mounted in interchangeable holders. Designs of the holders and the mounting assembly are presented. The major problem in using stopping detectors at medium energies is the tail of low pulse height events produced by nuclear reactions and scattering out. A technique for rejecting these events is described and the results obtained with deuterons from p-d elastic scattering of 800 MeV protons are presented. Analysis of the nuclear reaction tail for 120, 220, and 250 MeV deutrons yields an average total reaction cross section for deuterons on Ge of σ R = (1490±130) mb.

The effect of nuclear reactions in the response of stacked silicon detectors

Abstract Measurements are reported of the percentage of pulses of reduced height due to nuclear reactions in Si detectors bombarded by monoenergetic protons. The results of these measurements are: 45.3 MeV, 3.39 ± 0.04%; 37.5 MeV, 2.51 ± 0.04%; 27.5 MeV, 1.39 ± 0.04%; 12.9 MeV, 0.215 ± 0.022%. These results are compared to values predicted from proton total reaction cross sections.

Nuclear interaction correction for deuteron scintillation counting

Abstract Charged particles entering a thick scintillation counter occasionally suffer a nuclear interaction before they are stopped by electronic interactions, thereby producing pluses of smaller than maximum height. This effect, which can contribute an important correction to certain experiments, has been measured for 26.8 MeV deuterons incident upon NaI and plastic scintillators.

Semiconductor detector telescopes for measuring proton energies up to 300 MeV — problems and solutions

Abstract The major problem in measuring the energy of a medium energy particle in a semiconductor (or scintillation) detector is the high probability that it will experience a nuclear reaction or scattering in the detector material, before it goes through its range and stops. This problem can be solved by dividing the stopping detector into a number of laminae, measuring the pulse height produced by each lamina, and comparing with predictions obtained from integrations of the range-energy relation. We will present results obtained in using such a technique with 45 MeV protons, and considerations involved in extending the technique to 300 MeV protons.

A method for reducing the effect of nuclear reactions in stopping detectors

Abstract The tail of lower energy pulses due to nuclear reactions of incident particles in a stopping detector causes difficulty in the measurement of inelastically scattered particles. But it is possible to separate lower pulse height events arising from nuclear reactions from those due to “true” low energy particles by comparing the spatial energy loss distribution observed in the detector to that predicted from the range-energy relation for “true” particles. This is accomplished by dividing the detector into a number of laminae, and recording the energy loss in each. Two methods of treating the information that is obtained are described in this paper. Results are presented for protons of energies up to 45 MeV incident on a Si detector stack consisting of four equal laminae.

Small-angle inelastic scattering of 40 MeV protons by 12C, 40Ca, 56Fe and 58Ni

Abstract Angular distributions have been measured for inelastic scattering of 40 MeV protons to several states of 12 C, 40 Ca, 56 Fe and 58 Ni in the angular range of 4–20°. In a special small-angle scattering chamber, the inelastic protons were detected with a telescope consisting of three passing-geometry 3 mm Si(Li) detectors. Spurious events, produced when some of the very numerous elastic protons bombarding the detector produce nuclear reactions in it, were eliminated in a computer analysis. The experimental results are compared to DWBA and coupled-channel calculations, and to McCarthys parity rule.