The Coincident Measurement of Neutron-Proton Pairs from the Photodisintegration of LITHIUM-6

A 100% duty cycle bremsstrahlung beam with a 67 Mev endpoint energy was used to produce neutron-proton coincidences from the photodisintegration of ('6)Li. The proton energy was measured with a (DELTA)E-E scintillator telescope; the neutron energy was determined by measuring its time of flight across two meters. The energy and angle of the np pair were used to determine the photon energy for each event through the use of ('6)Li((gamma),np)(alpha) kinematics. A ('2)H target was used to calibrate the detector system and to normalize the ('6)Li data. Quasideuteron correlations between the neutron and proton momenta (direction and magnitude) were observed. The ratio of the quasideuteron photodisintegration cross section for ('6)Li, d(sigma)(,qd)/d(OMEGA)(,p), to that of ('2)H, d(sigma)(,d)/d(OMEGA)(,p), was found to have the values .084 (+OR-) .009, .17 (+OR-) .01, .31 (+OR-) .02 and .43 (+OR-) .04 at photon energies of 30, 40, 50 and 60 Mev, respectively (at 90(DEGREES) in the center of mass systems of both the deuteron and quasideuteron). A 2S harmonic oscillator momentum distribution of the form (3 - 2q('2)/q(,o)('2))('2) exp(-q('2)/q(,o)('2)) was fit to the measured distribution of np pair momentum transverse to the photon beam, which was assumed to be equal to the transverse momentum of the quasideuteron inside the nucleus. A value of q(,o) = 84.5 (+OR-) 5.3 Mev/c was obtained, which corresponds to a FWHM of 89.4 (+OR-) 5.6 Mev/c. This was in good agreement with values obtained in ('6)Li((pi)('-),np) and ('6)Li(p,p'd) experiments. The same momentum distribution used to calculate np angular correlations predicted widths greater than those observed at photon energies less than 45 Mev. Events consistent with the two-body photodisintegration of ('6)Li into a proton and ('5)He were also observed (('5)He decays to an alpha and a neutron). The ratio of the cross section for this two-body break up of ('6)Li, d(sigma)(,2)/d(OMEGA)(,p), to that of ('2)H was found to have the values 1.18 (+OR -) .26, l.00 (+OR-) .23, 0.87 (+OR-) .22 and 0.19 (+OR-) .07 at photon energies of 30, 40, 50 and 60 Mev, respectively (at 84(DEGREES) in the laboratory).