Takuji Yanabu

Augular Distributions of the Alpha Particles from the ( p , α) Reactions on Na 23 and K 39 at 6.9∼7.3 MeV

The angular distributions of the reactions Na 23 ( p , α)Ne 20 and K 39 ( p , α)A 36 leading to the ground and first excited states of the residual nuclei have been measured at 6.9, 7.1 and 7.3 MeV of the incident proton energy, respectively, by the use of a semiconductor detector. For the reaction Na 23 ( p , α)Ne 20 the angular distributions of these alpha particles are almost 90° symmetrical at 7.1 MeV of the incident proton energy, and they are slightly unsymmetrical about 90° at 7.3 and 6.9 MeV. For the reaction K 39 ( p , α)A 36 , the angular distributions are almost 90° symmetrical at all energies of the incident protons. It is considered that the reactions Na 23 ( p , α)Ne 20 and K 39 ( p , α)A 36 leading to the ground and first excited states of the residual nuclei, at around 7 MeV of incident proton energy, occur through a compound nucleus process and in the former reaction the number of the compound states excited by the about 7 MeV protons are probably not so many as to justify the statistical...

Elastic and Inelastic Scattering of 14.7 MeV Deuterons and of 29.4 MeV Alpha-Particles by Li 6 and Li 7

The angular distributions of alpha-particles and deuterons scattered elastically and inelastically by Li 6 and Li 7 were measured. The 2.18 MeV state of Li 6 , the 0.478 MeV and the 4.63 MeV states of Li 7 were appreciably excited. The experimental angular distributions were analysed with the DWBA theory, and the deformation parameters of the above mentioned states were determined. Experimental results and the DWBA analysis show the existence of some difference between the inelastic scattering of alpha-particles by Li 6 and by Li 7 , while no appreciable difference was observed in the case of the deuteron scattering. The DWBA calculation predicts larger quadrupole deformations of the excited states of Li 6 and Li 7 as compared with rotational model calculations of the energy levels.

( d , α) Reactions on O 16 , N 14 and C 12 by 14.7 MeV Deuterons

Angular distributions of α particles resulting from O 16 ( d , α 0 )N 14 (ground state), N 14 ( d , α 0 )C 12 (ground state), N 14 ( d , α 1 )C 12 (first excited state), C 12 ( d , α 0 )B 10 (ground state) and C 12 ( d , α 1 )B 10 (first excited state) reactions were studied, α particles from the O 16 ( d , α 0 )N 14 , C 12 ( d , α 0 )B 10 and C 12 ( d , α 1 )B 10 reactions exhibited forward peaks and backward peaks simultaneously, while α particles from N 14 ( d , α 0 )C 12 reaction showed forward peaks and oscillatory behavior. α particles leaving N 14 and C 12 nuclei in their T =1 state were also observed in the forward angle, and the isotopic spin conservation rule seemed to be violated. The reaction mechanism is then discussed on the basis of the surface direct reaction, the compound nucleus formation and α particle clustering in the target nucleus. It is concluded that α clustering may play an important role in the ( d , α) reaction.

Level structure of 80,82Sr via the 78,80Kr(α, 2nγ) reactions

Abstract The level structure of 80,82 Sr was studied with in-beam γ-ray spectroscopy via the 78,80 Kr(α, 2nγ) 80,82 Sr reactions at E α = 28.7 MeV. From the angular distributions and γ-γ coincidence measurements, the ground-state band up to (10 + ) and some other states were observed in both nuclei. The deduced levels are compared with current theoretical models. The observed level structure in neutron deficient Sr isotopes indicates a transition from spherical to deformed as neutron number decreases from 50 to 40.

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 differential cross sections for the D(d, d)D, D(d, p)T and D(d, 3 He)n reactions were measured at 13.2 MeV. The angular distributions of the differential cross sections were obtained from 12° to 90° in the c.m. system for the elastic scattering, from 3.6° to 90° for (d, p) and from 6.0° to 90° for (d, 3 He). The differential cross sections for the (d, n) reaction, deduced from the data on the (d, 3 He) reaction, coincide with those for the (d, p) reaction over the whole experimental angles. Analyses were made with the DWBA theory. The differential cross sections for the elastic scattering were well reproduced by using the optical model potential with the Majorana exchange term.

REACTION AT 14.7 Mev

Energy spectra of alpha particles from the 6 Li(d, α) 4 He * reaction at 13.6 MeV were observed at extremely forward angles. Angular correlations between alpha particles and deuterons were obtained for the 6 Li(d, αd)D reaction when the alpha particles were detected at 20° using coincidence method. Energy spectrum of alpha particles shows a broad peak corresponding to the excited state of 25.52 MeV in 4 He with the width of 2.26 MeV. The spin-parity of this state is assigned to be 0 + from the facts that the angular distributions of the emitted alpha particles are reproduced with DWBA theory assuming the angular momentum transfer of 2 and that the angular correlation function shows an isotropic distribution. In the coincidence energy spectrum of alpha particles a peak corresponding to the excited state of 27.5 MeV in 4 He was observed. The angular correlation for the excited state of 27.5 MeV is consistent with the assignment of odd parity.