U. Schmidt-Rohr

Elastic scattering of 52 MeV deuterons

Abstract Strongly excited levels of the nuclei 12 C, 14 N, 20 Ne, 22 Ne, 27 Al, 28 Si, 32 S, 40 Ar, 48 Ti, 54 Fe, 58 Ni, 64 Ni, 208 Pb and 209 Bi have been investigated by means of inelastic scattering of 52 MeV deuterons. The angular distributions have been analysed in terms of the DWBA. The description of the excited states in the collective model yields good fits and values of the deformation parameter β L which agree with independent measurements. Satisfactory fits are obtained in an attempt to apply a microscopic theory of inelastic deuteron scattering. An effective nucleon-nucleon interaction of Wigner type V ( r ) = V N exp(− r 2 / γ 2 ) is assumed to induce the scattering. From target nuclei where shell-model functions for the ground and excited states are available, we deduce the parameters V N = 38±5 MeV and γ = 1.7 fm. For other target nuclei, information about the collective enhancement of the excited states is obtained which is more sensitive to the details of the nuclear structure than the β L values.

Proton separation energies derived from the (d, 3He) reaction on f-p shell nuclei at 52 MeV

Abstract The (d, 3 He) reaction was investigated by 52 MeV deuterons on 45 Sc, 54 Fe, 58 Ni, 60 Ni, 63 Cu, and 65 Cu. The measured angular distributions were compared with local zero-range DWBA calculations from which the angular momenta of the transfered protons and the spectroscopic factors were deduced. The centres of gravity of the binding energies were determined for the 1 f 7 2 , 1 d 3 2 and 2 s 1 2 proton hole states. Taking into consideration the results of proton pick-up experiments on ten other f-p shell nuclei partly investigated by us previously, it was possible to study the systematic behaviour of the binding energies. In the lower f-p shell for nuclei with A ⩽ 48, the 2 s 1 2 protons are in the average more tightly bound than the 1 d 3 2 protons, and the reverse is true for A > 48. A Bansal and French type calculation based on an average particle-hole interaction E ph = − E + ΔE (t p ·t h proved to reproduce the observed data. The parameters E and ΔE have been determined for the 1 d 3 2 − f 7 2 and the 2 s 7 2 − f 7 2 interaction by means of a least-squares fit procedure considering the experimental binding energies in altogether 16 nuclei.

SHELL STRUCTURE STUDIES IN THE TITANIUM REGION WITH 52-MeV DEUTERONS.

The (d,3He)-reactions on the target nuclei48,50Ti and51V have been studied with 52 MeV deuterons. The data were analyzed by means of the DWBA which is shown to be applicable at this energy. All our results agree well with the assumption of pure (f7/2)n proton configurations for these nuclei.The inelastic scattering of 52 MeV deuterons from the lowest 2+ state in48Ti has been described in terms of the collective model as well as of the microscopic shell model. Good fits to the measured angular distributions have been obtained with reasonable values for the deformation parameters and the basic nucleon-nucleon interaction.

Proton pick-up from 19F, 20Ne and 22Ne

Abstract Energy spectra and angular distributions of the 3He particles from the (d, 3He) reactions on 19F, 20Ne and 22Ne have been measured at an incident energy of 52 MeV. Excitation energies up to 15 MeV (18O), 7 MeV (19F) and 9 MeV (21F) and pick-up from seven different shell-model orbits have been observed. Several previously unknown negative parity states have been found in 18O. A ( 3 2 , 1 2 ) − level at 4.56 MeV was found in 19F, while the known J = 3 2 level at 3.91 MeV was not observed which suggests a positive parity assignment. The hole state spectrum of 21F resembles closely that of 19F. The spectroscopic factors are compared to the predictions from a simple rotational model and from various effective shell-model calculations. All models describe the positive parity transitions leading to 19, 21F reasonably well, but those leading to 18O are only understood by the inclusion of excited core contributions of 4p-2h character in 18O. The low-lying negative parity states, containing essentially the 1p 1 2 hole strengths, are also nicely described by the weak coupling calculations. Higher excited negative parity states show deviations which are discussed in terms of 2p particle-1p hole admixtures.

Investigation of the ββ decay of 116Cd into excited states of 116Sn

Abstract The double-beta decay of 116Cd into excited states of 116Sn is experimentally and theoretically investigated. From an inclusive experiment, using an external source of isotopically enriched Cd, new most stringent limits for the allowed and non-standard-model decays into excited states are derived. It is further investigated whether the bremsstrahlung emitted by the ββ electrons can be used to derive information on the ground-state decay. For the two-neutrino-decay mode a calculation, using the quasiparticle random-phase approximation, shows that the disadvantage in phase space, in comparison to the ground-state decay, is partially compensated through the nuclear-matrix element. Experimental perspectives for other ββ-unstable nuclides are discussed.

Proton pick-up from the 1p and 2s-1d shells of 27Al

Energy spectra and angular distributions of 3He particles from the 27Al(d, 3He)26Mg reaction have been measured at an incident energy of 52 MeV. An 11 MeV excitation range in 26Mg has been covered. Below 4 MeV final excitation, the DWBA spectroscopic factors agree with shell-model predictionsbut disagree with those from a simple rotational model. Above 4 MeV, we have found some evidence in favour of a rotational band structure of the hole states. Negative-parity hole states have been observed at an energy much lower than expected from (p, 2p) experiments. The application of the DWBA to the pick-up of strongly bound protons requires optical potentials with modified radii in the exit channel.

Die winkelverteilungen der protonen aus den reaktionen Be9(d, p)Be10, C12(d, p)C13, O16(d, p)O17 und Ca40(d, p)Ca41 bei 11.8 MeV

Abstract To determine the absolute total cross sections of (d, p) reactions, the angular distributions of protons from 10° to 165° have been measured for the following reactions: Be 9 (d, p)Be 10 , C 12 (d, p)C 13 , O 16 (d, p)O 17 and Ca 40 (d, p)Ca 41 . The deuteron energy was 11.8 MeV. The angular momenta of the captured neutrons were estimated by comparison of the experimental angular distributions with those calculated in the plane wave Born approximation. It is found that the neutron captured into the 7.37 MeV level of Be 10 contributes l = 2 and that, therefore, this level has negative parity. For all levels studied the reduced widths were calculated. A comparison with measurements at other energies showed that a systematic dependence of the reduced widths with energy is rarely noticeable. The reduced width of the 6.28 MeV level of Be 10 is θ 2 = 0.032, which is considerably less than the value reported by Macfarlane. Our reduced widths of Ca 40 (d, p)Ca 41 are in better agreement with the values of Nemets et al. than with those of Macfarlane. The reduced width of the 2.47 MeV level of Ca 41 is relatively small which is an indication that the Ca 40 core is excited during the (d, p) process.

Proton particle-hole states in 208Pb

Abstract Differential cross sections for the 209Bi(d, 3He)208Pb transitions to the proton particle-proton hole states in 208Pb were obtained with the 45 MeV analyzed deuteron beam from the JULIC cyclotron and the high resolution spectrograph BIG KARL. 72 states up to 6.6 MeV were studied with an overall resolution of 12 to 15keV. Spectroscopic factors were extracted relative to the simultaneously measured calibration reaction 208Pb(d, 3He)207Tl. For 26 states new parity assignments were possible on the basis of the measured angular distributions. The deduced inclusion into one of the four multiplets put limits on the possible spins of the states in question. With the help of sum rule arguments the spins of 12 states were assigned. The comparison with shell model calculations give only rough agreement as they predict the energies of the respective states about 300 keV too high. The magnetic dipole state at 5.846 MeV was observed with a Spectroscopic factor C2S = 0.17. From this, together with the transition probability B(M1↑) = (1.6 ± 0.5) μN2 from a ( γ , γ′) experiment we derived size and relative sign of the dominant neutron and proton spin-flip amplitudes. The result gives clear evidence for the isoscalar character of this state in accordance wtih TDA and RPA predictions. The matrix elements of the two-body residual interaction were derived unambiguously for the h 9 2 ∗ s 1 2 and h 9 2 ∗ d 3 2 multiplets. For the h 9 2 ∗ h 11 2 and h 9 2 ∗ d 5 2 multiplets uncertainties are larger because of assumptions of some of the spins for the states of high excitation energy. The four monopole terms are found close to the average of −308 keV. They are dominated by the Coulomb contributions of ≈ − 216 keV. The deduced J-dependence of the matrix elements differs from those found in other systematic investigations indicating more complicated underlying nuclear forces must contribute.

β-zerfall des N13 und fierz-interferenz bei fermiwechselwirkung

Abstract The β-ray spectrum of the mirror transition N13 → C13 has been investigated with an iron-free lens spectrometer. No deviation from the allowed shape was observed. The Fierz coefficient was measured to be b=(0.14 ± 2.37)% (standard deviation). Taking into account that only 70% of the transition rate are due to Fermi interaction an upper limit of 11 % is found for |bF|, bF being the Fierz coefficient for pure Fermi interaction.

Shell effects in potential radii deduced from (d, 3He) angular distributions

Abstract Systematic phase displacements between measured (d, 3He) angular distributions and conventional DWBA calculations are observed. They can be removed by shell-dependent optical parameters. The j-effect on l = 2 angular distributions is interpreted as a shell effect. Arguments are given that there is some geometrical shell structure nuclei.