23690451
Systematics of inclusive pion double charge exchange in the delta resonance region.
A systematic study of inclusive pion double charge exchange is reported for nuclei between A=16 and A=208. The doubly differential cross sections for the A(${\mathrm{\ensuremath{\pi}}}^{+}$,${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$) and A(${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$,${\mathrm{\ensuremath{\pi}}}^{+}$) reactions in $^{16}\mathrm{O}$, $^{40}\mathrm{Ca}$, $^{103}\mathrm{Rh}$, and $^{208}\mathrm{Pb}$ were measured at incident energies between 120 and 270 MeV at three to five outgoing pion angles. Pion spectra were measured over the energy range from 10 MeV to the kinematic limit for double charge exchange. Integrating these spectra over outgoing pion energy generated angular distributions, and subsequently integrating these angular distributions generated total reaction cross sections. The shapes of the measured spectra are compared with those determined by the distribution of events in four-body phase space and with those predicted by a model in which the pion undergoes two sequential single charge exchanges on nucleons in a Fermi gas. The cross sections are compared with predictions of cascade calculations in which more than two interactions, including pion absorption and scattering without charge exchange, may occur.
54076839
Polarized electrons in the MIT-Bates South Hall Ring
The MIT-Bates facility is pursuing a vigorous spin physics program in its 1 GeV electron storage ring. The combination of polarized beams, polarized internal targets and a large acceptance spectrometer will allow world class measurements of important nuclear physics quantities including G/sup N//sub E/ and T/sub 20/. Toward this end we have constructed and installed a Siberian Snake to preserve longitudinal electron polarization at the internal target, a laser back-scattering Compton polarimeter to accurately measure the stored electron polarization and an RF coil for resonantly flipping the electron spin which will provide an important systematic check of all measured polarization dependent asymmetries. The status of the stored polarized beam and results from all these polarization handling devices are presented below.
117529021
Transmission Polarimetry at MIT Bates
The polarization dependence of Compton scattering in magnetized iron can be used to determine the polarization of an incident photon beam. This can in turn be related to the polarization of the electron beam which radiated the photons. It is difficult to calculate the analyzing power of these devices absolutely, however they are of great utility for rapid, relative measurements of electron beam polarization. These devices have been used at Bates as relative electron polarization monitors at 20 and 200 MeV. Efforts are now being made to use the device at 850 MeV as an online measure of the beam polarization in the South Hall Ring. A technique to calibrate these devices and build an affordable, absolute polarimeter is also being explored.
119811051
High energy photoprotons from light nuclei
Abstract In this paper we present (γ,p) measurements for the lithium, beryllium and carbon nuclei in the photon energy range 60–100 MeV. A single-difference bremsstrahlung unfolding technique is used to produce effectively monochromatic photons of energies 60±1, 80±1 and 100±1 MeV. At 60 MeV proton spectra were obtained at θ p = 45° over a range of residual nuclear excitation energies from 0 to 30 MeV for 6,7 Li and 0–20 MeV for 9 Be and 12 C. Also the angular distribution between 30° and 150° was measured for the highest energy protons from 6, 7 Li and 12 C at E γ = 60 MeV, for 7 Li and 12 C at E γ = 80 MeV and for 12 C at E γ = 100 MeV. Qualitative conclusions concerning the possible reaction mechanism may be drawn from the observed proton spectra, viz. that they support the hypothesis of a direct interaction of the photon with a proton in a shell-model (1s or 1p) orbit. However, simple shell-model wave functions are found to have insufficient amplitude in the high momentum region to account for the data. A phenomenological calculation which includes nucleon-nucleon correlations by means of the Jastrow model represents only approximately the energy and angular dependence of the measured cross sections.
121432461
New Results for Bremsstrahlung and Pion Production in the Neutron–Proton System
Differential cross sections for the neutron-proton bremsstrahlung (np → npγ) and pion production (np → npπ0 and np → ppπ-) processes have been measured for the first time at the Los Alamos Neutron Science Center. A pulsed neutron beam, produced by 800 MeV protons incident on a tungsten spallation target, bombarded a liquid hydrogen target. The outgoing neutrons and protons (in the first two reactions) or pairs of protons (in the third reaction) were observed in coincidence in organic liquid or plastic and CsI(pure) detectors at angles between 12° and 32° on opposite sides of the beam. For each pair of nucleon angles, the angular distribution of the unobserved photons or pions was deduced from the data.
121534175
Experimental test of virtual photon theory via electrodisintegration and photodisintegration of the deuteron
362446
Search for >200 TeV photons from Cygnus X-3 in 1988 and 1989.
Over a period of 16 months from April 1988 to August 1989, we have monitored the flux of cosmic-ray showers with energies above 2{times}10{sup 14} eV. We used a two-level array of scintillators covering an area of 3{times}10{sup 4} m{sup 2}. Counters on the surface measure the size and direction of each shower while counters buried 3 m beneath the surface sample the muons. By selecting showers with relatively few muons (less than one-tenth the average) the background of hadron-induced showers should be reduced by a factor of 150 or more while showers started by {gamma} rays should not be affected by this cut. We find no evidence for an excess from the direction of Cygnus X-3 either in ordinary showers or in muon-poor showers. For energies above 2{times}10{sup 14} eV, with 90% confidence, we find the excess flux of cosmic rays from the direction of Cygnus X-3 to be less than 1.3{times}10{sup {minus}13} cm{sup {minus}2}s{sup {minus}1} and the flux of photons (assuming they produce muon-poor showers) to be less than 1.5{times}10{sup {minus}14} cm{sup {minus}2}s{sup {minus}1}. This limit is substantially below the level of signals reported by earlier work. The period of observation included the intense radio bursts of Junemore » and July 1989. A portion of the data covering the 77-day period surrounding these events also showed no evidence for an excess.« less