No abstract

12 C( 7 Li,␣) angular distributions have been obtained for 16 states in 15 N at E( 7 Li)ϭ52.5 MeV. Also, 12 C( 6 Li ជ , 3 He) angular distributions and vector analyzing powers have been measured at E( 6 Li ជ )ϭ50 MeV. Finite-range distorted-wave Born-approximation ͑FRDWBA͒ triton cluster transfer calculations are able to describe the ( 7 Li,␣) data for transfer to states with known J values. Comparison with known levels in 19 F suggests that the 12 C( 7 Li,␣) reaction selectively populates negative parity states. FRDWBA calculations support this idea. Several previously suggested J levels are confirmed and new J values are proposed for six other levels. The previously observed ( 6 Li ជ , 3 He) J dependence has been used along with coupled-channel Born-approximation calculations to confirm the J values for states in 15 N.

The LLNL Crystal Driven Neutron Source is operational and has produced record ion currents of approximately 10 nA and neutron output of 1.9(+/-0.3)x10(5) per thermal cycle using a crystal heating rate of 0.2 degrees C/s from 10 to 110 degrees C. A 3 cm diameter by 1 cm thick LiTaO(3) crystal with a socket secured field emitter tip is thermally cycled with feedback control for ionization and acceleration of deuterons onto a deuterated target to produce D-D fusion neutrons. The entire crystal and temperature system is mounted on a bellows which allows movement of the crystal along the beam axis and is completely contained on a single small vacuum flange. The modular crystal assembly permitted experimental flexibility. Operationally, flashover breakdowns along the side of the crystal and poor emitter tip characteristics can limit the neutron source. The experimental neutron results extend earlier published work by increasing the ion current and pulse length significantly to achieve a factor-of-two higher neutron output per thermal cycle. These findings are reviewed along with details of the instrument.

One-dimensional scattering of a particle or a wave packet by a finite number of periodic potential barriers is studied. The fundamental physical mechanism that determines the transmission coefficient is shown to be quantum interference between waves with different numbers of inner reflections. The tendency of the transmission coefficient to saturate with respect to an increase in the number of barriers is due to the free-particle nature of a particle subject to a completely periodic potential.

Data for the elastic scattering of 27.8 MeV polarized 6 Li from 4 He and new data for the 6 Li→␣ϩd sequential breakup have been analyzed using the coupled-channels ͑CC͒ method with potentials derived via the cluster-folding ͑CF͒ procedure. The three low-lying Tϭ0 resonant excited states of 6 Li as well as nonresonant continuum states were taken into account in the calculations by means of the continuum-discretized coupledchannels ͑CDCC͒ method. No adjustable parameters were used. The analysis shows a dominant role of the projectile breakup into ␣ϩd in the 6 Liϩ 4 He elastic scattering. The deuteron transfer process is found to be of less importance. The calculations reproduce the values of the differential cross section for the sequential breakup channels at forward scattering angles. Predictions for the direct breakup near the 6 Li→␣ϩd breakup threshold are made. ͓S0556-2813͑97͒00210-0͔