Kiyohiko Takimoto

Quasi-Free α-α Scattering in Be9 and C12 at 37 MeV

Energy and angular correlations between two alpha particles from the Be 9 (α, 2α)He 5 and C 12 (α, 2α)Be 8 reactions were investigated. The incident alpha particle energies were 32.3 MeV and 37.4 MeV for Be 9 and 37.4 MeV for C 12 . It is concluded that the quasi-free scattering of incident alpha particles from alpha clusters in Be 9 is the main process of the (α, 2α) reaction on Be 9 . It remains some ambiguity for the mechanism of the (α, 2α) reaction on C 12 to be explained as a simple quasi-free scattering process.

Al

The angular distributions have been measured for the eight groups of alpha particles leading to the ground state and the excited states of Mg 25 from the reaction Al 27 ( d , α)Mg 25 with 14.7 MeV deuterons, by using a semiconductor detector of p - n junction. The differential cross-sections of the reactions leading to the single levels of Mg 25 are compared with a formula obtained from the two-nucleon pick-up theory. The experimental angular distribution for each alpha group with a comparatively large cross-section is in agreement, at least in forward angle, with the theoretical curve. The alpha group leading to the 3.40 MeV level of Mg 25 is considered to come from the transition to the 9/2+ state rather than to the 3/2- state. The total cross-sections for the levels of Mg 25 corresponding to the same K -band 5/2+ as that of the ground state of Al 27 are larger than the others.

sup 27

Angular distributions and total cross sections of the C 12 ( d , α)B 10 and O 16 ( d , α)N 14 reactions were obtained in the deuteron energy range from 15 MeV to 20 MeV. Deuteron energies were 15.1, 15.9, 16.7, 17.5, 18.2, 19.0 and 19.7 MeV in the C 12 ( d , α)B 10 reaction, and were 14.9, 15.4, 15.7, 16.0, 16.5, 16.9, 17.3, 18.1, 18.8 and 19.6 MeV in the O 16 ( d , α)N 14 reaction. Alpha particle groups leaving the residual nuclei in their low-lying states showed pronounced forward and backward peaks simultaneously in the whole energy range. Total cross sections decreased gradually with increasing deuteron energies, but some anomalies were found. Reaction mechanism is discussed under the assumptions of knock-out and heavy-particle stripping processes, and it is indicated that the clustering of nucleons at the surface of the target and or the residual nuclei seems to play an important role in these reactions.

(d,/cap alpha/)Mg

Angular distributions of alpha particles from the O/sup 16/(d, alpha )N/ sup 14/ reaction were measured. Results from the ground-state and second-excited- state reactions are presented in graphical form. The absolute cross section calculated from C/sub 8/H/sub 4/O/sub 2/ agreed reasonably with that from the O/ gas target. The principle of isotopic spin conservation was violated in this reaction. Comparison is made with previous experiments (T. Yanabu, J. Phys. Soc. Japan 16, 2118(1961); NSA, 15i 2l556; NSA, 15: 26972). (L.N.N.)

sup 25

The angular distributions have been obtained for alpha-particles from the reactions Be 9 ( p , α) Li 6 (ground state), Be 9 ( d , α) Li 7 (ground, first and second excited states), B 10 ( p , α) Be 7 (ground state), B 10 ( d , α) Be 8 (ground state), B 11 ( p , α) Be 8 (ground state) and B 11 ( d , α) Be 9 (ground and second excited states), and from the elastic and inelastic (second excited state) scatterings of alpha-particles by Be 9 . Besides, the angular distribution of deuterons from the reaction Be 9 ( p , d ) Be 8 (ground state) was measured. The energies of incident beams were nearly 7 MeV for protons, 14 MeV for deuterons and 28 MeV for alpha-particles. The results, except for B 10 ( p , α)Be 7 and B 11 ( p , α)Be 8 , show forward and/or backward rises and may be interpreted by direct interactions. The integrated cross sections of the reactions ( p , α) and ( d , α) on Be 9 are larger than those on B 10 and B 11 .

REACTION AT 14.7 Mev

The angular distributions have been obtained for alpha-particles from the reactions Be 9 ( p , α) Li 6 (ground state), Be 9 ( d , α) Li 7 (ground, first and second excited states), B 10 ( p , α) Be 7 (ground state), B 10 ( d , α) Be 8 (ground state), B 11 ( p , α) Be 8 (ground state) and B 11 ( d , α) Be 9 (ground and second excited states), and from the elastic and inelastic (second excited state) scatterings of alpha-particles by Be 9 . Besides, the angular distribution of deuterons from the reaction Be 9 ( p , d ) Be 8 (ground state) was measured. The energies of incident beams were nearly 7 MeV for protons, 14 MeV for deuterons and 28 MeV for alpha-particles. The results, except for B 10 ( p , α)Be 7 and B 11 ( p , α)Be 8 , show forward and/or backward rises and may be interpreted by direct interactions. The integrated cross sections of the reactions ( p , α) and ( d , α) on Be 9 are larger than those on B 10 and B 11 .