K. Bethge

Break-up of 6Li and 7Li on tin and nickel nuclei

Abstract The break-up of the stable lithium nuclei on 58Ni and 118Sn has been investigated in the bombarding energy range 12–24 MeV. The emerging α-particles have been analysed showing that the cross sections peak at the angle of grazing collisions. Inspection of the present data suggests the conclusion that several different reaction mechanisms contribute to the continuous spectrum of the α-particles.

Investigation of the reaction 12C(7Li, t)16O

Abstract Angular distributions of the reaction 12 C( 7 Li, t) 16 O have been measured at E lab = 15, 21.1 and 24 MeV with a magnetic spectrograph and a d E /d x — E telescope. From the shape of the angular distributions and the weak excitation of the 2 − state at E x = 8.87 MeV in 16 O it is concluded that the reaction proceeds dominantly by a direct α-transfer. Contributions from compound nucleus formation were estimated from a Hauser-Feshbach calculation. The angular distributions were analysed by means of the DWBA, which has been modified to take into account the relative p-state between the α-particle and the triton in 7 Li. Approximations valid for a surface reaction were used to simplify the theory. The calculations are able to reproduce the essential features of the angular distributions. Reduced α-widths were extracted for some states in 16 O.

Angular correlations from 6Li break-up near the Coulomb barrier of 118Sn and 208Pb

Abstract Absolute coincidence cross sections for three-particle final states have been measured inplane in the 6 Li + 118 Sn and 6 Li + 208 Pb reactions at incident energies of 22.2 and 23.0 MeV, respectively. Most strongly populated is the α + d branch, proceeding sequentially through the first excited state ( E x = 2.18 MeV, J π = 3 + ) of 6 Li. The angular distributions are fitted by DWBA calculations including Coulomb interaction in the excitation of the projectile. The main competing reaction channels above and at the Coulomb barrier ( 118 Sn: E / E c ≈ 1.3; 208 Pb: E / E c ≈ 0.9) are: neutron transfer ( 6 Li, αp) and the non-sequential α + d break-up of 6 Li. The latter spectra are consistent with a quasi-free break-up mechanism. No 3 He or tritons have been found in the coincidence spectra, as well as no evidence for a three-particle dissociation of 6 Li into α + p + n.

6Li induced reactions on 12C at Elab = 20 MeV

Abstract Differential cross sections for the reactions 12 C( 6 Li, d) 16 O, 12 C ( 6 Li , α) 14 N and 12 C( 6 Li, p) 17 O, were measured at E lab = 20 MeV. The angular distributions exhibit neither pure direct nor pure compound nuclear reaction mechanisms. It is assumed that the excitation of the 8.88(2−) MeV level in 16 O is due to a pure compounf nuclear reaction. To estimated the compound nucleus contribution for some of the low-lying levels in 16 O, Hauser-Feshbach calculations were carried out. The strong excitation of some rotational states in 16 O can be explained by a good angular momentum match for a direct α-particle capture. A similar explanation fails for the states in 14 N.

A source for a vector-polarized lithium-6 beam at an en-tandem

Abstract A source for vector-polarized 6Li ions produced by the atomic-beam method was installed at the Heidelberg EN-tandem accelerator. The first results are reported. ( i target max = 40 nA 6 Li 3+ ; 0.1 Li )

Molecular and atomic ions of the elements of the sub-groupsA of the periodic system

The production of positive and negative ions of all elements of the sub-groupsA and some of the sub-groupsB has been investigated as an extension of previous work on Penning sources. Molecular ions of the typeXn±,n>1 and ions of hydride moleculesXnHm±,n,m>1 have been found. The maximum numbermmax of the H atoms bound in the cluster is determined by the position of the element in the periodic system.The yield of the atomic and molecular beams has been measured as a function of the electric source parameters and the different gases maintaining the discharge to establish the production mechanism. The data on ion beam intensities and the state of clustering of molecules are listed in tables.

Three-particle correlations from208Pb+6Li

AbstractThree-particle correlations in the reaction208Pb+6Li were studied near the Coulomb threshold betweenn

Elastic scattering of 7Li from light target nuclei

E_{6_{Li} } = 24