H. H. Barschall

Scattering of neutrons by α-particles

Abstract The differential cross section for the scattering of neutrons by α-particles has been measured at neutron energies between 6 and 30 MeV. In the neighbourhood of the resonance at 22.16 MeV neutron energy, measurements were performed at closely spaced neutron energies. The present data as well as earlier measuremnts of elastic scattering and total cross sections, and previous polarization measurements were fitted with phase shifts which are based largely on the p-α phase shifts of Weitkamp and Haeberli. Satisfactory fits were obtained for neutron energies up to 30 MeV, including the region of the 22.16 MeV resonance. The analysing power of helium deduced from these phase shifts is presented in the form of a contour plot.

A consistent set of neutron kerma coefficients from thermal to 150 MeV for biologically important materials

Neutron cross sections for nonelastic and elastic reactions on a range of elements have been evaluated for incident energies up to 150 MeV. These cross sections agree well with experimental cross section data for charged-particle production as well as neutron and photon production. Therefore they can be used to determine kerma coefficients for calculations of energy deposition by neutrons in matter. Methods used to evaluate the neutron cross sections above 20 MeV, using nuclear model calculations and experimental data, are described. Below 20 MeV, the evaluated cross sections from the ENDF/B-VI library are adopted. Comparisons are shown between the evaluated charged-particle production cross sections and measured data. Kerma coefficients are derived from the neutron cross sections, for major isotopes of H, C, N, O, Al, Si, P, Ca, Fe, Cu, W, Pb, and for ICRU-muscle, A-150 tissue-equivalent plastic, and other compounds important for treatment planning and dosimetry. Numerous comparisons are made between our kerma coefficients and experimental kerma coefficient data, to validate our results, and agreement is found to be good. An important quantity in neutron dosimetry is the kerma coefficient ratio of ICRU-muscle to A-150 plastic. When this ratio is calculated from our kerma coefficient data, and averaged over the neutron energy spectra for higher-energy clinical therapy beams [three p (68) + Be beams, and a d (48.5) + Be beam], a value of 0.94 +/- 0.03 is obtained. Kerma ratios for water to A-150 plastic, and carbon to oxygen, are also compared with measurements where available.

Cost‐Effectiveness of Physics Journals

The rapid increase in the prices of physics journals has forced many physics libraries, in the face of static budgets, to cancel some of their subscriptions. Decisions on cancellations are usually based on the research interests of the users of the library, but the decision‐making process can be improved if a quantitative measure of the cost‐effectiveness of the journals is available. An often‐used measure is the cost per printed character; another is the frequency with which articles in the journal are cited, often referred to as the “impact.” The ratio of these two measures is perhaps the best indicator of a journals cost‐effectiveness.

Neutron evaporation spectra

Abstract Thin targets of Ni, Rh, Ta and Au were bombarded with protons of energies between 6 and 12 MeV. Neutrons emitted at angles up to 140° were observed. The neutron spectra were studied by time-of-flight spectroscopy. Except for Ni, continuous spectra resulted which had a Maxwellian energy distribution. The nuclear temperature showed, however, an anomalous increase with bombarding energy. Results consistent with the statistical theory could be obtained in the case of Rh by taking into account the energy dependence of the inverse reaction cross section.

Neutrons from protons on isotopes of tin

Abstract Neutron spectra resulting from the bombardment of eight isotopes of tin with protons of energies between 7 and 14 MeV have been obtained at a laboratory angle of 60°. At 10 and 14 MeV angular distributions were measured. The statistical model of nuclear reactions was used to deduce the dependence of the level densities in the residual nuclei on excitation energy, but contrary to the predictions of the model, the deduced level densities showed an apparent dependence on bombarding energy. The effect of the pairing energy on the neutron spectra from targets containing even and odd numbers of neutrons is discussed.

The Cost of Physics Journals

Science libraries all over the United States face serious financial problems associated with the increased costs of journals.

Reminiscences of the Early Days of Fission

Roger Stuewer has described how Leon Rosenfeld brought the news that uranium undergoes fission to Princetons Physics Journal Club on the evening of 16 January 1939—the day on which Niels Bohr and Rosenfeld had arrived in New York from Denmark. (See Stuewers article in PHYSICS TODAY, October 1985, page 48). Bohr had first learned of the discovery of fission from Otto Frisch on 3 January 1939, and Rosenfelds report was the first information received by physicists in the United States. I was in the audience and the news had an immediate impact on my own activities, and it continued to affect my work for the next six years. The following are some of my recollections of that period.

Neutrons from the bombardment of beryllium by deuterons.

Fast neutron spectra produced by the bombardment of thin and thick beryllium targets with deuterons have been measured at incident energies between 3 and 18 MeV. Total neutron yields and average neutron energies were determined from the data. The purpose of the measurements was to provide information from which dose rates and depth dose can be calculated for various conditions encountered in neutron radiotherapy with cyclotrons.

Detection system for charged particles produced by neutrons

Abstract Systems consisting of two or three magnetic quadropole lenses and detectors were developed for studying charged particles produced by 15 MeV neutrons. The lenses transport the charged particles from a radiator near the neutron source to the detectors located about 2.6 m away in order to reduce the neutron-induced background in the detectors.

High Energy - High Intensity Neutron Sources for Fusion Technology and Radiotherapy Applications

Abstract Instead of a preface we place this introductory paper in front of the contributions to this special issue. The article gives a brief review of the problems whose investigation and solution require intense high energy neutron generators. We also propose an economic strategy for the future development of high intensity sources.