Gamma-Beams at the HIγS facility in the USA and anticipated at the ELI-NP facility, now constructed in Romania, present unique new opportunities to advance research in nuclear astrophysics; not the least of which is resolving open questions in oxygen formation during stellar helium burning via a precise measurement of the 12 C(α, γ) reaction. Time projection chamber (TPC) detectors operating with low pressure gas (as an active target) are ideally suited for such studies. We review the progress of the current research program and plans for the future at the HIγS facility with the optical readout TPC (O-TPC) and the development of an electronic readout TPC for the ELI-NP facility (ELITPC).
An active-target Time Projection Chamber (ELITPC) is being developed at the University of Warsaw to investigate the photo-disintegration reaction 16 O(γ,α) 12 C at energies relevant for nuclear astrophysics (down to ∼ 1 MeV in the centre of mass). Selected results from ongoing R&D activities are presented in this paper.
The designed and constructed at the University of Lodz an electron spectrometer is devoted to "in-beam" measurements. The apparatus is characterized by high efficiency up to 9%, good energy resolution (FWHM = 5 keV at 482 keV) and, what is very important good suppression of delta electrons, positrons, and photons emitted by the targets. This achievement was obtained using a combination of magnetic field in two different layouts: perpendicular and parallel to the axis of the spectrometer being orthogonal to the beamline. The conversion-electron spectrometer coupled to the EAGLE array was successfully tested in an "in-beam" measurement.
The 134 Nd required for studies of the violation of the K selection rule for electromagnetic transitions in nuclei with mass numbers around 130 can be produced in the reaction of 122 Te with 16 O. The 122 Te target was prepared by the evaporation in a high vacuum. The deposition of the Te isotope on the backing was performed from the very close distance to economize the usage of the isotopic material. The thickness distribution of the target material determined by measurements of the alpha particles energy loss was estimated as 32%. The first test of the target on the 16 O beam with energy of 80 MeV and intensity of 40 enA proved that target prepared by the Te deposition on the Au backing in vacuum is stable in the in-beam conditions and in spite of its relatively high inhomogeneity is suitable for the planned studies.
Background: Investigation of the 140 62 Sm 78 nucleus, situated in the area close to the magic N = 82 neutron shell, offers the opportunity to find and study interesting phenomena resulting from the interplay of collective and other degrees of freedom. Purpose: Experimental identification of low-spin low-energy levels, particularly 0 + , in 140 Sm and theoretical interpretation within the collective general Bohr Hamiltonian (GBH) model. Method: The γ -γ angular correlation technique for γ radiation after the β/EC decay of 140 Eu → 140 Sm and 140 Gd → 140 Eu → 140 Sm was used to determine spins of excited states of 140 Sm. The 140 Gd and 140 Eu nuclei were produced in the 104 Pd + 40 Ar reaction at the HIL UW cyclotron. In the theoretical part the full five-dimensional GBH model was applied in two variants: the simple phenomenological Warsaw model and the microscopic version with six inertial functions and a potential calculated from mean-field theory.
Results:The spin and parity of six low spin (0,1,2) low lying excited levels of 140 Sm were measured. Two new states at around 2 MeV were identified. A analysis of the consequences of possible admixtures on the determination of the spin of a level was performed. The theoretical models applied successfully describe most of the spectrum of 140 Sm giving hints on the origin of the states observed in the experiment. Conclusions: Significant softness against nonaxial deformation seems to be essential to interpret the properties of 140 Sm. Further experimental studies are needed to check if some low-energy excitations are not deformation driven.
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