Z. Elekes

Collapse of the N=28 shell closure in (42)Si.

The energies of the excited states in very neutron-rich (42)Si and (41,43)P have been measured using in-beam gamma-ray spectroscopy from the fragmentation of secondary beams of (42,44)S at 39A MeV. The low 2(+) energy of (42)Si, 770(19) keV, together with the level schemes of (41,43)P, provides evidence for the disappearance of the Z=14 and N=28 spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that (42)Si is best described as a well-deformed oblate rotor.

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.

Anomalously hindered E2 strength B(E2;2+(1)-->0+) in 16C.

The electric quadrupole transition from the first 2(+) state to the ground 0(+) state in 16C is studied through measurement of the lifetime by a recoil shadow method applied to inelastically scattered radioactive 16C nuclei. The measured mean lifetime is 77+/-14(stat)+/-19(syst) ps. The central value of mean lifetime corresponds to a B(E2;2+(1)-->0(+)) value of 0.63e(2) fm(4), or 0.26 Weisskopf units. The transition strength is found to be anomalously small compared to the empirically predicted value.

Thick target γ-ray yields for light elements measured in the deuteron energy interval of 0.7–3.4 MeV

Abstract With the aim of providing missing basic data for deuteron-induced γ-ray emission (DIGE, or d-PIGE) analysis a completion of our earlier work (Kiss et al., 1994) has been performed. Typical γ-ray spectra, tables for the most suitable γ-ray lines for elemental analysis and a complete series of absolute thick-target yields for the most characteristic γ-rays of elements with Z=3–20 (except for Be, Ne, P and Ar) in the deuteron energy range of 0.7–3.4 MeV are presented. An analytical formula fitting well the measured yield curves is suggested for the yield calculations in elemental analysis, and also for the effective design and operation of low background experiments. The capability of this method is illustrated in the examples by spectra taken on an industrial glass and an obsidian sample.

Magnetic spherules: Cosmic dust or markers of a meteoritic impact?

Abstract Magnetic spherules from several localities in Hungary were analyzed and the results were compared to analytical data of similar objects found in Japan, Slovakia and Hawaii. The studies were carried out using micro-PIXE technique. On the basis of morphological features and elemental compositions it was concluded that signs of a new meteoritic impact could be found.

First Direct Measurement of the 17O(p,γ)18F Reaction Cross Section at Gamow Energies for Classical Novae

Classical novae are important contributors to the abundances of key isotopes, such as the radioactive (18)F, whose observation by satellite missions could provide constraints on nucleosynthesis models in novae. The (17)O(p,γ)(18)F reaction plays a critical role in the synthesis of both oxygen and fluorine isotopes, but its reaction rate is not well determined because of the lack of experimental data at energies relevant to novae explosions. In this study, the reaction cross section has been measured directly for the first time in a wide energy range E(c.m.)~/= 200-370 keV appropriate to hydrogen burning in classical novae. In addition, the E(c.m.)=183 keV resonance strength, ωγ=1.67±0.12 μeV, has been measured with the highest precision to date. The uncertainty on the (17)O(p,γ)(18)F reaction rate has been reduced by a factor of 4, thus leading to firmer constraints on accurate models of novae nucleosynthesis.

Direct measurement of the 15N(p,γ)16O total cross section at novae energies

The 15N(p,gamma)16O reaction controls the passage of nucleosynthetic material from the first to the second carbon-nitrogen-oxygen (CNO) cycle. A direct measurement of the total 15N(p,gamma)16O cross section at energies corresponding to hydrogen burning in novae is presented here. Data have been taken at 90-230 keV center-of-mass energy using a windowless gas target filled with nitrogen of natural isotopic composition and a bismuth germanate summing detector. The cross section is found to be a factor two lower than previously believed.

Application of a Clover-Ge-BGO detector system for PIGE measurements at a nuclear microprobe

Abstract The application of a high efficiency Clover–Ge–BGO detector system for PIGE elemental analysis at the Debrecen nuclear microprobe is demonstrated. Advantages and disadvantages of this facility are discussed. Detection limits for Li, B, F, Na, Al and Si in different sample matrixes are presented.

A new study of the 22Ne(p, γ)23Na reaction deep underground: Feasibility, setup and first observation of the 186 keV resonance

The 22Ne(p,γ)23Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle is active in asymptotic giant branch stars as well as in novae and contributes to the nucleosythesis of neon and sodium isotopes. In order to reduce the uncertainties in the predicted nucleosynthesis yields, new experimental efforts to measure the 22Ne(p,γ)23Na cross section directly at the astrophysically relevant energies are needed. In the present work, a feasibility study for a 22Ne(p,γ)23Na experiment at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400 kV accelerator deep underground in the Gran Sasso laboratory, Italy, is reported. The ion-beam-induced γ-ray background has been studied. The feasibility study led to the first observation of the Ep=186 keV resonance in a direct experiment. An experimental lower limit of 0.12 × 10−6 eV has been obtained for the resonance strength. Informed by the feasibility study, a dedicated experimental setup for the 22Ne(p,γ)23Na experiment has been developed. The new setup has been characterized by a study of the temperature and pressure profiles. The beam heating effect that reduces the effective neon gas density due to the heating by the incident proton beam has been studied using the resonance scan technique, and the size of this effect has been determined for a neon gas target.

The N14(p,γ)O15 reaction studied with a composite germanium detector

The rate of the carbon-nitrogen-oxygen (CNO) cycle of hydrogen burning is controlled by the N14(p,γ)O15 reaction. The reaction proceeds by capture to the ground states and several excited states in ...