J. Jänecke

Updated mass predictions from the Garvey-Kelson mass relations

Abstract Part A, Neutron-Rich Nuclides, describes the procedures for estimating masses of neutron-rich nuclei from the transverse Garvey-Kelson mass relation. This relation represents a homogeneous partial difference equation. The most general solutions have been subjected to a χ2-minimization procedure (boundary condition) based on the new atomic mass adjustment of Wapstra and Bos. The resulting solution can be viewed as a many-parameter mass equation with about 500 parameters. About 5000 mass values have been calculated for nuclei with 2 ≤ Z ≤ 100, 4 ≤ N ≤ 156, and N > Z (or N = Z= even). The standard deviation between calculated and experimental mass-excess values is σm = 118 keV. Part B, Proton-Rich Nuclides, describes the procedure for estimating masses of proton-rich nuclei with T ≥ 1 based on the charge-symmetric mass relation of Kelson and Garvey. Use is made of the experimental Coulomb energy differences between T = 1 2 mirror nuclei (A ≤ 55) together with a few estimated values (57 ≤ A ≤ 71). Mass values have been calculated for about 120 nuclei with 1 ≤ T ≤ 5 2 and A ≤ 70. The standard deviation between calculated and experimental mass-excess values is σm ≈ 100 keV.

Mass predictions from the Garvey-Kelson mass relations

Abstract Part A: The transverse Garvey-Kelson mass relation represents a homogeneous third-order partial difference equation. Procedures are described for estimating masses of nuclei with N ⩾ Z from the most general solution of this difference equation subject to a χ2 minimization, using the recent atomic mass adjustment of Wapstra, Audi, and Hoekstra as a boundary condition. A judicious division of the input data into subsets of neutron-rich and proton-rich nuclei had to be introduced to reduce systematic errors in long-range extrapolations. Approximately 5600 mass-excess values for nuclei with 2 ⩽ Z ⩽ 103, 4 ⩽ N ⩽ 157, and N ⩾ Z (except N = Z = odd for A Part B: The charge-symmetric mass relation of Kelson and Garvey for estimating masses of nuclei with Z > N and T ⩾ 1 is described. The calculations make use of the experimental Coulomb energy differences between T = 1 2 mirror nuclei for A ⩽ 59 and of estimated values for A > 59. Some 250 mass-excess values have been calculated. The standard deviation for reproducing the known values is σm ≈ 231 keV.

6 Li elastic scattering ON 12 C, 16 O, 40 Ca, 58 Ni, 74 Ge, 124 Sn, 166 Er and 208 Pb at E( 6 Li ) = 50.6 MeV

Abstract The elastic scattering of 6 Li ions from a variety of targets, A = 12 to 208, has been measured at a bombarding energy of 50.6 MeV. The angular distributions are characteristic of strongly absorbed particles, such as 3 He and heavy ions, and less diffractive than for 4 He. A simple optical model with Woods-Saxon real and imaginary volume potentials is adequate to fit the data. Spin-orbit effects are not apparent in the data.

6Li elastic scattering ON 12C, 16O, 40Ca, 58Ni, 74Ge, 124Sn, 166Er and 208Pb at E(6Li) = 50.6 MeV

Abstract The elastic scattering of 6 Li ions from a variety of targets, A = 12 to 208, has been measured at a bombarding energy of 50.6 MeV. The angular distributions are characteristic of strongly absorbed particles, such as 3 He and heavy ions, and less diffractive than for 4 He. A simple optical model with Woods-Saxon real and imaginary volume potentials is adequate to fit the data. Spin-orbit effects are not apparent in the data.

Gamow-Teller strengths from (t,3He) charge-exchange reactions on light nuclei

Abstract Zero-degree cross sections have been measured for (t, 3 He) reactions on the light target nuclei 9 Be, 10 B, 11 B, 12 C, and 13 C at a bombarding energy of 127 MeV/A. The triton beam was produced by ( 4 He,t+p) breakup on a Be production target using a 4 He beam of 155 MeV/A. Dispersion matching was applied to obtain good energy resolution ( Δ E/E=0.002, Δ E=780 keV). The zero-degree (t, 3 He) cross sections are used to discuss Gamow-Teller strengths in 10 Be and 11 Be.

On isobaric analogue states

Abstract The excitation energies of isobaric analogue states, i.e. the energetically lowest states with a given isobaric spin T , have been related to the symmetry and pairing energies of the respective nuclei. Symmetry parameters a ( A ) and pairing energies δ ( A ) were extracted from the experimental data. The parameter a ( A ) exhibits shell structure. An expression for the energetic difference between isobaric analogue states was established which reproduces the over 200 known values (known experimentally or calculated from the known masses of neighbouring isobars) up to A = 80 with a standard deviation of about 0.5 MeV. The same formula can be used to predict excitation energies of unknown isobaric analogue states and the masses of unknown neutron-rich and proton-rich nuclei. The above expression is in accordance with a theoretical expression based on an effective two-nucleon interaction. There exist small but systematic deviations from the supermultiplet model.

A radioactive beam facility using a large superconducting solenoid

Abstract A facility for producing well-focussed (~ 5 mm diameter) secondary beams of ≤ 20 MeV 6 He, 7 Be, 8 Li, and similar ions has been implemented. The heart of the apparatus is a superconducting solenoid operating in an asymmetric lens configuration, with large solid angle (dΩ ≥ 100 msr) for the collection of reaction products. A beam of 15-MeV 8 Li ions ( ΔE ≤ 0.6 MeV) of intensity 5 × 10 4 ions/s, produced via the 9 Be( 7 Li, 8 Li) 8 Be reaction, was scattered from targets of CH 2 , CD 2 , 9 Be, 12 C, 27 l, and 197 Au. Elastic scattering and ( 8 Li, 7 Li) reaction products are unambiguously identified. Preliminary results of measurements on the 2 H( 8 Li, 9 Be)n reaction, as well as the status of a project to upgrade the 8 Li beam intensity to ≥ 1 ×10 6 ions/s, are reported. ft]∗|Permanent address: Physics Department, Oberlin College, Oberlin, OH 44074, USA.

The emission of protons from light neutron-deficient nuclei

Abstract The properties of the processes which lead to the emission of protons from light neutron-deficient nuclei are discussed. These processes are in particular proton decay, double proton decay and β-delayed emission of protons.and di-protons. Masses of light nuclei with Z ≦ 14 were calculated and a limit of stability with regard to the emission of protons is given. Candidates for double proton decay are the following light even- Z nuclei: O 12 , Ne 16 , Mg 19 and possibly Si 23 . The β-delayed emission of protons should occur subsequently to the β + -decays of C 9 , Ne 17 , (Mg 19 ) and Mg 20 . Emission of weak proton groups may also follow the β + -decays of (O 12 ), O 13 , Mg 21 , Si 24 and Si 25 . Several of these proton groups have been observed. The findings of this paper supplement and extend previous predictions.

The Ca40(d, α)K38 reaction and the nuclear structure of K38

Abstract Natural Ca-targets were bombarbarded with 7.7 MeV deutereons. Magnetic analysis was used to obtain α-particle spectra at angles of 50°, 70° and 90°. About 35 levels in K38 were found up to an excitation energy of 4.8 MeV. There are the following low-lying states: (Eexc, Jπ, T) = (0.00 MeV, 3+, 0); (0.12 MeV, 0+, 1); (0.43 MeV, 1+, 0); (1.69 MeV, 1+, 0); (2.41 MeV, 2+, 1). They are in agreement with recent intermediate coupling shell model calculations. Most of the levels above 2.5 MeV result from configurations with one or more nucleons raised into the f 7 2 shell. The nuclear temperature derived from an Ericson plot is 1.05 ± 0.15 MeV. Angular distributions for the low excited states were measured from 10° to 165°. The angular distributions and the total cross section show the effect of the ΔT = 0 isobaric spin selection rule which inhibits direct interaction leading to T = 1 final states. Compound nucleus transitions to the T = 1 states take place, however, because of isobaric spin mixing in the intermediate nucleus, and the selection rule seems to be completely violated. The total cross sections are in agreement with the theory of Hauser and Feshbach. This theory also makes it possible to estimate the compound nucleus contributions for the transitions leading to T = 0 states. About 2 3 of the total cross section for these transitions are due to direct interaction, which produces a pronounced structure of the angular distributions in the forward and backward hemisphere. The significance of this structure in terms of the various direct interaction modes is discussed.

Isospin decomposition of the Gamow-Teller strength in Cu-58

Abstract The Gamow-Teller (GT) strength excited by a (p, n)-type reaction on a nucleus with isospin T0 and N > Z is shared by isospin components T0 − 1, T0 and T0 + 1. A good energy resolution (3He, t) reaction on 58Ni revealed the fine structure of the GT strength in 58Cu. The isospin of each level constituting the fine structure was assigned by comparing to results from inelastic electron and proton scatterings and (n, p)-type reactions, thus resolving the isospin structure of the GT strength in 58Cu. The ratio of the summed GT strengths among the three isospin components is well described by a shell-model calculation.