Elastic Scattering of 20.6-Mev Protons by Deuterons

The absolute differential cross section for the elastic scattering of 20.6-Mev protons by deuterons was measured by using the external beam of the U.C.L.A. synchrocyclotron. A triplecoincidence proportional counter telescope, with variable absorbers between the second and third counters and differential pulseheight discriminators (set by a new method) on the first two counters, was used to select the desired particle by range and specific ionization. Deuterium gas at atmospheric pressure provided the target for the proton beam, which was collimated to $\frac{1}{8}$ in. diameter, with a maximum angular divergence of ½°. An interchangeable slit system gave angular resolutions of 0.9° or 1.8°. Absolute measurements were made at 22 angles from 12° to 164° (center-of-mass) with an accuracy varying approximately from 1 percent to 3 percent, depending upon the angle. The cross section shows the familiar deep minimum (near 130° in the present case), but in addition a shallower minimum near 18°, due to Coulomb-nuclear interference. This latter minimum should allow fitting the data with a unique set of phase shifts, unlike previous nucleon-deuteron scattering experiments, and thus provide a more stringent test for theories.