An earlier experiment has been modified by the addition of a spin-precessing solenoid to permit an improved measurement of the polarization of the neutrons from photodisintegration of deuterium. Monoenergetic 2.75-MeV gamma rays were obtained from Na 24 and the neutron polarization was analyzed by scattering from magnesium. The polarization normal to the reaction plane was measured for y-n laboratory angles from 30 to 150°. Empirical corrections were derived for neutron scattering in the deuterium source as well as in the Mg analyzer. Within the errors the polarization is found to be symmetric about 90°, consistent with the absence of noncentral forces. The magnitude is, however, (12=fc7)% smaller than that calculated by Kramer from El-M 1 interference using effective-range theory. A major source of uncertainty in the experiment is the analyzing power of Mg. For a y-n laboratory angle of 90°, the neutron polarization was also determined in the direction of the incident gamma ray. The result P<0.01 is consistent with the conservation of parity in the reaction.

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The binding energy of the deuteron has been determined by measuring the energy of the neutron-proton capture gamma ray with a 2-meter bent quartz crystal spectrometer in the Cauchois geometry. A polyethylene target in the through-tube of a reactor supplied the n-p capture gamma rays. The 411.77-kev gamma ray of Hg 138 and the annihilation radiation were used to calibrate the spectrometer. The average of the results of four plates gives 2.225±0.003 Mev for the binding energy of the deuteron. O NE of the most direct methods to determine the binding energy of the deuteron consists of measuring the energy of the neutron-proton capture gamma ray. The use of a bent quartz crystal spectrometer for this purpose affords high absolute precision. We have employed a 2-meter spectrometer 1 ' 2 in the Cauchois geometry to diffract the n-p capture gamma rays from a polyethylene target in the through-tube of the Livermore pool-type reactor. The present measurements are a continuation of earlier work 3 done in this laboratory.The experimental arrangement is illustrated in Fig. 1. The polyethylene provides an effective source strength of one kilocurie. The beam is defined by a lead collimator which reduces from a width of 1.2 cm at the source to 3 mm at the crystal. This collimator remains fixed to insure that the same portion of the bent crystal is used throughout the experiment. The spectrometer is aligned with the center of the crystal and the conjugate focus on the axis of the collimator. The focussed gamma-ray line is produced at twice the Bragg angle from the beam axis. 600 JJL Ilford G-5 emulsions mounted on glass are used to record the lines. The spectrometer is then rotated about the center of the crystal to reflect the gamma rays from the other side of the (310) crystal planes, forming the line pattern shown in Fig. 2. Each deuteron line required an exposure of ^140 hours.A gold target was used to provide calibration lines. The gamma rays were the 411.770±0.036 kev gamma ray 4 from Hg 198 and the 510.976-kev 5 annihilation radiation. The latter is presumably the result of pair production by high-energy gold-capture gamma rays in the gold target. The distances between the lines were measured with a precision comparator.Bragg angles involved here, the energy of the deuteron formation gamma ray ED may simply be calculated fromwhere Ec is the energy of the calibration gamma ray, and A