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Register a new userMeasurements of the 48Ca({gamma},n) Reaction
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The 48Ca({gamma},n) cross section was measured using {gamma}-ray beams of energies between 9.5 and 15.3 MeV generated at the Triangle Universities Nuclear Laboratory (TUNL) high-intensity {gamma}-ray source (HI{gamma}S). Prior to this experiment, no direct measurements had been made with {gamma}-ray beams of sufficiently low energy spread to observe structure in this energy range. The cross sections were measured at thirty-four different {gamma}-ray energies with an enriched 48Ca target. Neutron emission is the dominant decay mechanism in the measured energy range that spans from threshold, across the previously identified M1 strength, and up the low-energy edge of the E1 giant dipole resonance (GDR). This work found B(M 1) = 6.8 pm 0.5 {mu}N2 for the 10.23 MeV resonance, a value greater than previously measured. Structures in the cross section commensurate with extended random-phase approximation (ERPA) calculations have also been observed whose magnitudes are in agreement with existing data.
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We have searched for the production of element 112 in the reaction of 231 MeV 48Ca with 238U. We have not observed any events with a one event upper limit cross section of 1.6 pb for EVR-fission events and 1.8 pb for EVR-alpha events.
We report new p$(vec{e},e^prime p)pi^circ$ measurements in the $Delta^{+}(1232)$ resonance at the low momentum transfer region utilizing the magnetic spectrometers of the A1 Collaboration at MAMI. The mesonic cloud dynamics are predicted to be dominant and appreciably changing in this region while the momentum transfer is sufficiently low to be able to test chiral effective calculations. The results disagree with predictions of constituent quark models and are in reasonable agreement with dynamical calculations with pion cloud effects, chiral effective field theory and lattice calculations. The reported measurements suggest that improvement is required to the theoretical calculations and provide valuable input that will allow their refinements.
The total cross sections for the $^{152}$Gd(p,$gamma$)$^{153}$Tb and $^{152}$Gd(p,n)$^{152}$Tb reactions have been measured by the activation method at effective center-of-mass energies mbox{$3.47 leq E_mathrm{c.m.}^mathrm{eff}leq 7.94$ MeV} and mbox{$4.96 leq E_mathrm{c.m.}^mathrm{eff} leq 7.94$ MeV}, respectively. The targets were prepared by evaporation of 30.6% isotopically enriched $^{152}$Gd oxide on aluminum backing foils, and bombarded with proton beams provided by a cyclotron accelerator. The cross sections were deduced from the observed $gamma$-ray activity, which was detected off-line by a HPGe detector in a low background environment. The results are presented and compared with predictions of statistical model calculations. This comparison supports a modified optical proton+$^{152}$Gd potential suggested earlier.
A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the r-process. As a proof-of-principle, the $gamma$-spectra from the $beta$-decay of $^{76}$Ga have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and $gamma$-ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the $^{75}$Ge($n,gamma$)$^{76}$Ge cross section and reaction rate.
The interpretation of the most recent solar neutrinos experiments requires a good knowledge of the cross section of the reaction 7Be(p,gamma)8B at very small energy (Ecm=18 keV). We have recently measured this cross section for Ecm=0.35-1.4 MeV and for Ecm=0.112-0.190 MeV. We report here on the description of the preparation of the radioactive targets of 7Be used in these experiments.
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