() reaction studies of Dy and Hf

Angular distributions for the ¹⁶³Dy(t,p) and ¹⁷⁷Hf(t,p) reactions were measured using 17 MeV tritons from the McMaster University Tandem Van de Graaff accelerator. Reaction products were analyzed with a magnetic spectrograph and detected with photographic emulsions. Favored L=0 transitions confirmed assignments of the 5/2⁻[523] band in ¹⁶⁵Dy and 7/2⁻[514] band in ¹⁷⁹Hf. Additional L=0 transitions in each nuclide identified previously unknown 5/2⁻ levels in ¹⁶⁵Dy and 7/2⁻ ones in ¹⁷⁹Hf. Overall trends of L=0 strengths support the existence of subshell closures at neutron numbers 98 and 108. On the basis of a relatively strong L=2 transition, the K^π=11/2⁻ γ-vibration based on the 7/2⁻[514] state is identified at 1689 keV in ¹⁷⁹Hf, about 440 keV above its previously-assigned K^π=3/2⁻ partner.     

Investigation of two- and three-nucleon transfer reactions in12C +56Fe

Multi-nucleon transfer reactions⁵⁶Fe(¹²C, X) have been studied at an incident¹²C energy of 60 MeV. Angular distributions of¹⁰Be and⁹Be corresponding to 2p and 2p 1n transfer reactions in transition to low-lying states in the residual nuclei have been measured. The angular distribution data for 2p transfer have been analysed in terms of finite range DWBA calculations assuming a one-step transfer of two protons. The spectroscopic factors for three low-lying transitions observed in⁵⁶Fe(¹²C,¹⁰Be)⁵⁸Ni have been extracted. Transfer probabilities for the ground state transition in two- and three-nucleon stripping channels have been obtained and compared with the corresponding sequential transfer probabilities in order to emphasise the role of direct transfer of nucleons vis-a-vis sequential transfer.     

Observation of the hot GDR in neutron-deficient thorium evaporation residues

The giant dipole resonance built on excited states was observed in very fissile nuclei in coincidence with evaporation residues. The reaction ⁴⁸Ca + ¹⁷⁶Yb populated evaporation residues of mass A=213–220 with a cross section of 200 μb at 259 MeV. The extracted giant dipole resonance parameters are in agreement with theoretical predictions for this mass region.     

Compton scattering by the proton through θcms = 75° and 90° in the Δ-resonance region

Differential cross sections for Compton scattering by the proton have been measured in the energy interval between 200 and 500 MeV at scattering angles of θcms = 75° and θcms = 90° using the CATS, the CATS/TRAJAN, and the COPP setups with the Glasgow Tagger at MAMI (Mainz). The data are compared with predictions from dispersion theory using photo-meson amplitudes from the recent VPI solution SM95. The experiment and the theoretical procedure are described in detail. It is found that the experiment and predictions are in agreement as far as the energy dependence of the differential cross sections in the Δ-range is concerned. However, there is evidence that a scaling down of the resonance part of the M1+3/2 photo-meson amplitude by (2.8 ± 0.9)% is required in comparison with the VPI analysis. The deduced value of the M1+3/2-photoproduction amplitude at the resonance energy of 320 MeV is: |M1+3/2| = (39.6 ± 0.4) × 10−3 mπ+−1.     

Double-electron capture of Se and the search for neutrinoless decay

Experimental results on the measurement of the double-electron capture (εε) decay process of ⁷⁴Se are described. This decay is particularly interesting, because ⁷⁴Se is almost degenerate to the second excited state at 1204 keV in the daughter nucleus ⁷⁴Ge. Such a degeneracy favors a neutrinoless decay because of the large phase-space suppression for a decay with two neutrinos. Subsequent de-excitation would generate a 2γ-ray cascade of 608 and 596 keV, whose coincident detection provides a unique signature for this particular εε process. The 2γ-ray cascade has been searched for by a HPGe γ-ray detector in coincidence with a NaI detector using 3 kg of natural selenium.     

Study of Be + C elastic scattering at energies near the Coulomb barrier

In this work, angular distribution measurements for the elastic channel were performed for the ⁹Be + ¹²C reaction at the energies ELab=13.0$E_{\mathit{Lab}}=13.0$, 14.5, 17.3, 19.0 and 21.0 MeV, near the Coulomb barrier. The data have been analyzed in the framework of the double folding São Paulo potential. The experimental elastic scattering angular distributions were well described by the optical potential at forward angles for all measured energies. However, for the three highest energies, an enhancement was observed for intermediate and backward angles. This can be explained by the elastic transfer mechanism.     

First search for double β decay of dysprosium

A search for double β decay of dysprosium was realized for the first time with the help of an ultra-low background HP Ge γ detector. After 2512 h of data taking with a 322 g sample of dysprosium oxide limits on double beta processes in ¹⁵⁶Dy and ¹⁵⁸Dy have been established on the level of T_1/2?¹⁰¹⁴–¹⁰¹⁶ yr$T_{1/2}?{10}^{14}\text{–}{10}^{16}\text{yr}$. Possible resonant double electron captures in ¹⁵⁶Dy and ¹⁵⁸Dy were restricted on a similar level. As a by-product of the experiment we have measured the radioactive contamination of the Dy₂O₃ sample and set limits on the α   decay of dysprosium isotopes to the excited levels of daughter nuclei as T_1/2?¹⁰¹⁵–¹⁰¹⁷ yr$T_{1/2}?{10}^{15}\text{–}{10}^{17}\text{yr}$.