Angular anisotropy in the /sup 6/Li(n,. cap alpha. )/sup 3/H reaction at 25 keV

The angular anisotropy in the /sup 6/Li(n,..cap alpha..)/sup 3/H reaction at 25 keV has been measured in two sets of experiments performed at an iron-filtered beam facility (99 percent of the flux at 25 keV) at the NBS Reactor. First, a surface-barrier detector coated with 80 ..mu..g/cm/sup -2/ of /sup 6/LiF (front face) was used as a 2..pi.. detector. This detector was placed in four different angular positions with respect to the neutron beam: front face at 90/sup 0/ and 45/sup 0/ to the beam; back face at 90/sup 0/ and 45/sup 0/ to the beam. The pulse-height distributions of both the /sup 3/H and /sup 4/He were recorded for these four positions yielding a forward-to-backward asymmetry of 1.59 +- 0.11 in the center-of-mass system. A second detector was placed coaxially with the first (at 90/sup 0/ to the beam) and in such a way as to substend a 45/sup 0/ cone. Coincidence measurements, that simultaneously recorded the distributions in both detectors, yielded an asymmetry in the backward-to-forward 45/sup 0/ cone of 1.80 +- 0.06 in the center-of-mass system. The existence of such a large anisotropy at this low energy and the possibility of similar behavior at still lower energiesmore » (i.e., 1 to 2 keV) should result from s--p wave interference. This would give rise to a constant anisotropy that is experimentally masked by the 1/v behavior of the isotropic s--s interference terms at lower energies. 5 figures, 1 table. (auth)« less