Deuteron photodisintegration at intermediate energies

Abstract

Measurements were made using the LEALE photon beam facility at Frascati. Positrons produced by the linear accelerator (LINAC) were annihilated in a liquid hydrogen target having a thickness of 0.0 1 18 radiation lengths. The size and position of the beam on the target were controlled by a beam profile monitor; beam spot semi-axes were 6 mm horizontally by 4 mm vertically. Photon beam energy spectra were measured by a pair spectrometer; spectra so obtained showed an annihilation peak (-4 MeV full width half maximum (FWHM) at 10 MeV and -12 MeV FWHM at 240 MeV) plus a bremsstrahlung tail. The photon beam then passed through a liquid deuterium target and into a quantameter. Protons from the deuteron photodisintegration were detected by counter telescopes at 32.5, 55, 80°, 105, and 130. Each telescope consisted of a 3-mm-thick dE/dx scintillator and a 10-cm-@ by 12-cm NaI crystal as E the counter. The gain stability of the detectors was checked every 5 min with light pulsers and with 4.43-MeV gamma rays from an Am-Be source. Measurements at 100, 120, 140, 200, 224, and 255 MeV were made in several runs over a period of 24 years; results of different runs are consistent to within 5%. A Monte Carlo program, having as input the measured photon energy spectrum and the system geometry, was able to reproduce the observed proton spectra in the peak region. It was also possible to use this program to extend cross-section determination to the bremsstrahlung tail of the spectrum. This allowed a cross check on consistency of cross sections obtained at different positron beam energies; good agreement was found between values obtained from the annihilation peaks and those from the bremsstrahlung tails. Differential cross-section plots for yd + pn were shown for 20-MeV steps from E, = 100-260 MeV. Good agreement is found with data from the Indiana University Cyclotron Facility, (IUCF), Mainz, Bonn (1983), and the Massachusetts Institute of Technology -(MIT).