36631133
Pion-induced single charge exchange in deuterium.
We report the measurement of the differential cross section for [sup 2]H([pi][sup [minus]],[pi][sup 0]) for laboratory angles 0[degree]--145[degree], at incident pion energies of 164, 263, and 371 MeV. A Faddeev calculation at 164 MeV incorporating Pauli-blocking and multiple-scattering effects describes those data well. At the two higher energies the [sup 2]H([pi][sup [minus]],[pi][sup 0]) cross section is essentially identical to the [sup 1]H([pi][sup [minus]],[pi][sup 0]) cross section, except at forward angles where the former is suppressed by the Pauli principle. This experiment was the first to make use of a major component of the Neutral Meson Spectrometer at the Los Alamos National Laboratory.
121534175
Experimental test of virtual photon theory via electrodisintegration and photodisintegration of the deuteron
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.
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.
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
28295913
Search for compact sources of cosmic photons above 200 TeV.
From April 1988 to February 1990 we used a two-level array of scintillators to search in the cosmic radiation for compact sources of {gamma} rays above 200 TeV. Counters on the surface measured the size and direction of extensive air showers while counters buried 3 m below ground measured their muon content. Showers induced by {gamma} rays are expected to have many fewer muons than those initiated by hadrons so the selection of muon-poor showers should greatly reduce the background of hadronic showers. Three objects, Cygnus X-3, the Crab nebula, and Hercules X-1, were examined in detail. Searches were made on short and long time scales and source periodicity was used, where applicable, to enhance any possible signals. We found no evidence for any compact sources.