E. Somorjai

Measurements of relative thick target yields for PIGE analysis on light elements in the proton energy interval 2.4–4.2 MeV

In order to extend the energy range of the systematic investigation on relative thick target yields performed by ANTTILA et al2 for 1≤Ep≤2.4 MeV bombarding energies, gamma spectra and yield data are presented for elements Z=3–9, 11–17, 19–21 in the energy range 2.4≤Ep≤4.2 MeV and the results are discussed from the point of view of PIGE analysis.

Enhanced electron screening in d(d, p)t for deuterated Ta

Abstract:The recent observation of a large electron screening effect in the d(d, p)t reaction using a deuterated Ta target has been confirmed using somewhat different experimental approaches: Ue = 309±12 eV for the electron screening potential energy. The high Ue value arises from the environment of the deuterons in the Ta matrix, but a quantitative explanation is missing.

S-factor of 14N(p,γ)15O at astrophysical energies⋆

Abstract.The astrophysical S(E) factor of 14N(p,γ)15O has been measured for effective center-of-mass energies between Eeff = 119 and 367 keV at the LUNA facility using TiN solid targets and Ge detectors. The data are in good agreement with previous and recent work at overlapping energies. R-matrix analysis reveals that due to the complex level structure of 15O the extrapolated S(0) value is model dependent and calls for additional experimental efforts to reduce the present uncertainty in S(0) to a level of a few percent as required by astrophysical calculations.

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

Abstract 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, γ)15O reaction. Deep underground in Italys 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 4π 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.

Activation measurement of the He3(α,γ)Be7 cross section at low energy

The nuclear physics input from the 3He(alpha,gamma)7Be cross section is a major uncertainty in the fluxes of 7Be and 8B neutrinos from the Sun predicted by solar models and in the 7Li abundance obtained in big-bang nucleosynthesis calculations. The present work reports on a new precision experiment using the activation technique at energies directly relevant to big-bang nucleosynthesis. Previously such low energies had been reached experimentally only by the prompt-gamma technique and with inferior precision. Using a windowless gas target, high beam intensity, and low background gamma-counting facilities, the 3He(alpha,gamma)7Be cross section has been determined at 127, 148, and 169 keV center-of-mass energy with a total uncertainty of 4%. The sources of systematic uncertainty are discussed in detail. The present data can be used in big-bang nucleosynthesis calculations and to constrain the extrapolation of the 3He(alpha,gamma)7Be astrophysical S factor to solar energies.

Electron screening in d(d, p)t for deuterated metals and the periodic table ✩

The electron screening effect in the d(d, p)t reaction has been studied for 29 deuterated metals and 5 deuterated insulators/semiconductors. As compared to measurements performed with a gaseous D2 target, a large effect has been observed in the metals V, Nb, and Ta, which belong to group 5 of the periodic table, as well as in Cr, Mo, and W (group 6), Mn and Re (group 7), Fe and Ru (group 8), Co, Rh, and Ir (group 9), Ni, Pd, and Pt (group 10), Zn and Cd (group 12), and Sn and Pb (group 14). In contrast, a comparatively small effect is found in group 4 (Ti, Zr, Hf), group 11 (Cu, Ag, Au), group 13 (B, Al), for the insulator BeO, and for the semiconductors C, Si, and Ge. An explanation of this apparently novel feature of the periodic table is missing.  2002 Elsevier Science B.V. All rights reserved.

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

Abstract.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 ^2H2H(p, γ)^3He3Heand ^14N14N(p, γ)^15O15Owithin 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.

Electron screening effect in the reactions 3He(d, p)4He and d(3He, p)4He

The cross section of the reactions 3He(d, p)4He and d(3He, p)4He has been measured at the center-of-mass energies E=5 to 60 keV and 10 to 40 keV, respectively. The experiments were performed to determine the magnitude of the electron screening effect leading to the respective electron-screening potential energy Ue=219±7 and 109±9 eV, which are both significantly higher than the respective values from atomic physics models, Ue=120 and 65 eV.

{sup 144}Sm-{alpha} optical potential at astrophysically relevant energies derived from {sup 144}Sm({alpha},{alpha}){sup 144}Sm elastic scattering

For the determination of the {sup 144}Sm-{alpha} optical potential we measured the angular distribution of {sup 144}Sm({alpha},{alpha}){sup 144}Sm scattering at the energy E{sub lab}=20 MeV with high accuracy. Using the known systematics of {alpha}-nucleus optical potentials we are able to derive the {sup 144}Sm-{alpha} optical potential at the astrophysically relevant energy E{sub c.m.}=9.5 MeV with very limited uncertainties. {copyright} {ital 1997} {ital The American Physical Society}

Electron screening effect in the reactions 3 He(d, p) 4 He and d( 3 He, p) 4 He ☆ ☆ Supported in part by INFN, BMBF (06BO812), DFG (436UNG113-146) and OTKA (T025465).

The cross section of the reactions 3He(d, p)4He and d(3He, p)4He has been measured at the center-of-mass energies E=5 to 60 keV and 10 to 40 keV, respectively. The experiments were performed to determine the magnitude of the electron screening effect leading to the respective electron-screening potential energy Ue=219±7 and 109±9 eV, which are both significantly higher than the respective values from atomic physics models, Ue=120 and 65 eV.