GRAIL, an omni-directional gravitational wave detector

A cryogenic spherical and omni-directional resonant-mass detector proposed by the GRAIL collaboration is described.Comment: 5 pages, 4 figs., contribution to proceedings GW Data Analysis Workshop, Paris, nov. 199

Feasibility of low energy radiative capture experiments at the LUNA underground accelerator facility

The LUNA (Laboratory Underground for Nuclear Astrophysics) facility has been designed to study nuclear reactions of astrophysical interest. It is located deep underground in the Gran Sasso National Laboratory, Italy. Two electrostatic accelerators, with 50 and 400 kV maximum voltage, in combination with solid and gas target setups allowed to measure the total cross sections of the radiative capture reactions $^2$H(p,$\gamma$)3He and $^{14}$N(p,$\gamma$)$^{15}$O within their relevant Gamow peaks. We report on the gamma background in the Gran Sasso laboratory measured by germanium and bismuth germanate detectors, with and without an incident proton beam. A method to localize the sources of beam induced background using the Doppler shift of emitted gamma rays is presented. The feasibility of radiative capture studies at energies of astrophysical interest is discussed for several experimental scenarios.Comment: Submitted to Eur. Phys. J.

Determination of 141Pr(alpha,n)144Pm cross sections at energies of relevance for the astrophysical p-process using the gamma-gamma coincidence method

The reaction 141Pr(alpha,n)144Pm was investigated between E_alpha=11 MeV and 15 MeV with the activation method using the gamma-gamma coincidence method with a segmented clover-type high-purity Germanium (HPGe) detector. Measurements with four other HPGe detectors were additionally made. The comparison proves that the gamma-gamma coincidence method is an excellent tool to investigate cross sections down to the microbarn range. The (alpha,n) reaction at low energy is especially suited to test alpha+nucleus optical-model potentials for application in the astrophysical p-process. The experimentally determined cross sections were compared to Hauser-Feshbach statistical model calculations using different optical potentials and generally an unsatisfactory reproduction of the data was found. A local potential was constructed to improve the description of the data. The consequences of applying the same potential to calculate astrophysical (gamma,alpha) rates for 145Pm and 148Gd were explored. In summary, the data and further results underline the problems in global predictions of alpha+nucleus optical potentials at astrophysically relevant energies.Comment: 13 pages, 9 figures, accepted in Phys. Rev.

First measurement of the 14N(p,gamma)15O cross section down to 70 keV

In stars with temperatures above 20*10^6 K, hydrogen burning is dominated by the CNO cycle. Its rate is determined by the slowest process, the 14N(p,gamma)15O reaction. Deep underground in Italy's Gran Sasso laboratory, at the LUNA 400 kV accelerator, the cross section of this reaction has been measured at energies much lower than ever achieved before. Using a windowless gas target and a 4pi BGO summing detector, direct cross section data has been obtained down to 70 keV, reaching a value of 0.24 picobarn. The Gamow peak has been covered by experimental data for several scenarios of stable and explosive hydrogen burning. In addition, the strength of the 259 keV resonance has been remeasured. The thermonuclear reaction rate has been calculated for temperatures 90 - 300 *10^6 K, for the first time with negligible impact from extrapolations