Louis Rosen

Elastic scattering of 10.5- and 14.5-MeV polarized protons from nuclei and the optical model potential at intermediate energies

Abstract The results of extensive measurements of the angular distributions and azimuthal asymmetries for elastic scattering of 10.5 and 14.5 MeV polarized protons, from a wide range of nuclei, are presented. Attention is focused on the general features of these angular distributions and certain deviations from the general trends. The interpretations of both these aspects of the data are discussed. In addition, results are presented from an extensive search program designed to obtain fits to the data with a six-parameter local “optical” potential. From these individual fits to each nuclide have been obtained a set of average parameters at 10.5 MeV and another set at 14.5 MeV. The predictions of the optical model with the average parameters are compared not only to the polarization data but also to elastic differential cross sections and reaction cross sections for protons. With a modification of the magnitudes of the refractive and absorptive central potentials, as required to fit 14.5 MeV neutron elastic scattering cross sections, the potential has been used to predict differential elastic cross sections, reaction cross sections, total cross sections, and polarizations for neutrons, and the results compared with available experimental data. A study has been made of the dependence of the refractive central potential depth on proton energy and on the nuclear symmetry parameter, (N−Z) A , obtaining reasonable agreement with the results of other workers.

Elastic scattering of polarised protons by C12

Abstract The angular dependence of the polarization resulting from the elastic scattering of protons by C12 has been measured for 8 protons energies between 5.4 and 19.7 MeV. Optical model analysis has been performed and is able to reproduce the experimental results except for two energy regions, around 10 and 20 MeV. Inelastic scattering polarization has also been obtained at 19.7 MeV for the first C12 excited level at 4.4 MeV.

Angular and energy distributions of neutrons from the interaction of 14 MeV neutrons with Li6 and Li7

The angular and energy distributions from the interaction of 14 Mev neutrons with /sup 6/Li and /sup 7/Li were determined from analysis of nuclear plate detectors placed at 10 deg intervals from 10 deg to 160 deg . The angular distributions of the elastically scattered neutrons are similar not only to those expected on the basis of diffraction scattering, but also to those obtained from an optical model analysis with parameters identical to those used for fitting medium-weight and heavy nuclei. The total elastic scattering cross section for 6/sup Li/ is 883 plus or minus 95 mb; for 7/sup Li/, 969 plus or minus 110 mb. The neutrons from inelastic collisions are much less peaked in the forward direction and exhibit a considerable isotropic component. The measured value for the total cross section for the emission of neutrons for /sup 6/Li is 1.44 plus or minus 0.16 b; for /sup 7/Li, 1.61 plus or minus 0.2 b. (auth)

Mechanism of the Zn64(n, p)Cu64 reaction at incident neutron energies of 8 and 14 MeV

The Zn/sup 64/(n,p)Cu/sup 64/ reaction was studied at incident neutron energies of 8 and l4 Mev. These experiments were part of an investigation of the adequacy of the statistical model concept of the compound nucleus to describe interactions when complex nuclei are bombarded by neutrons at energies in the region of nuclear binding energies. The spectral and spatial distributions of most of the protons indicated that the compound-nucleus hypothesis may be satisfied. The high-energy proton distributions are in sharp contrast with the predictions of the statistical model and contradict the compound-nucleus hypothesis. For 8 Mev neutronbombarding energy, there is an inordinately large probability for the emission of protons with energies considerably lower than that of the Coulomb barrier. (auth)

Nuclear Multiple Plate Camera

A nuclear multiple plate camera has been devised which permits observations to be made on scattering and reaction processes resulting from the bombardment of gas targets with a charged particle beam. Sixty‐nine photographic plates are held in a rigid geometry which allows simultaneous measurements of interaction differential cross sections at 2.5° intervals from 10° to 170° in the laboratory system. Because of the precision with which the camera is machined, relative cross‐section measurements can be made essentially within the statistical error of the number of particle tracks counted at each angle. As a check of the apparatus, measurements were made on the p—p and p—He4 elastic scattering processes. The results are in excellent agreement with previously reported counter data.

On the Use of Photographic Plate Detectors in Neutron Experiments

A technique is discussed for utilizing photographic plate detectors in an evacuated camera, containing an appropriate radiator, to make precise determinations of the range distributions of the disintegration products of slow neutron reactions. The same technique is applied to the problem of measuring neutron energies by making range measurements on the forward recoil protons projected by fast neutrons from a thin polyethylene radiator. As an indication of the accuracy attainable with photographic plates when used in this manner, determinations have been carried out for the Q values of the Li6(n, α)H3 reaction and the B10(n, α)Li7 reaction.

Some Medical Applications of Accelerators

The present uses of accelerators in nuclear medicine and radiation therapy are summarized. Attention is called to the widespread use of these devices for production of radioisotopes for diagnostic purposes and of x rays for treatment of cancer. Developments presently underway to make use of high energy heavy nuclear particles for both isotope production and therapy are discussed and an overview is presented of one of a new family of accelerators nearing completion. In view of the large fraction of the total population who stand to benefit from better diagnostic and therapy modalities, the question is posed whether more adequate resources should not be made available for improving diagnostic and therapeutic capabilities while minimizing radiation dose to the patient.

The responsibility of the scientific community in matters of national security

Abstract Scientists must provide more and better leadership in the debate over how to avoid catastrophe, whether it be through war, or starvation, or plague, or environmental degradation. Scientists should be vigilant about challenging false perceptions and defending the truth. They should alert our citizenry to major dangers—such as those brought about by weapons of great destructive potential—whether they be nuclear, biological, chemical, or even psychological. The scientific community needs to provide accurate and understandable analyses of these issues. It is their duty to develop and disseminate factual information by engaging in research, teaching, public outreach, and even lobbying. The scientific community has an obligation to identify and challenge muddled thinking. It is absolutely essential that the quality of public debate be raised well above where it now resides, in this election year. Some years ago, the American Physical Society created a Panel on Public Affairs. It has sponsored in-depth studies on critical national concerns such as energy and the environment. In this connection, I quote from a letter to the membership from Sid Drell, when he was President of the American Physical Society: As a result of the great impact of technology on our conditions of life and especially the threat of nuclear holocaust, there has never been a greater need for scientists, and physicists in particular, to be involved with public policy. The Society can and should play a constructive and instructive role in informing its members and in supporting and presenting appropriate studies to members of government and to the public. The council and officers of the Society have an important trust in protecting a high standard for such studies. The APS directedenergy weapons study stands out as the most pressing item on the societys agenda this year. I hope that by this coming summer the council will be able to release a report which will contribute significantly to the national dabate on the strategic defense initiative. The above report has, indeed, been released. But scientists have not yet done enough to make it understandable to the public.

LAMPF—Its Origins, History, and Accomplishments

The main vehicle for bringing the pion to bear on a vast array of problems, has been the meson factories. Today there exist such facilities in Switzerland (SIN), in Canada (TRIUMF), and in the USA (LAMPF). A fourth is just now being completed in the Soviet Union. They are enormous enterprises - the current replacement value of LMPF is

Status of the Clinton P. Anderson Meson Physics Facility (LAMPF)

350 million, not including the part devoted to national security problems. But they accommodate hundreds of scientists from around the world and by so doing generate political as well as intellectual and economic capital. Proton facilities, together with heavy-ion accelerators and electron facilities, form a triad on which stands the present edifice of experimental nuclear science. Each leg of this triad is dependent, to a greater or lesser extent, on the other two. However, in terms of versatility, the size of the community it serves, and the relatively short-term application of the knowledge base and people base for which nuclear science is responsible, the meson factory part of the above triad is by no means the least important component. I discuss this component from the standpoint of the facility I know best, namely LAMPF. 33 refs., 36 figs.