[en] Excited states of nuclei in the vicinity of ¹⁰⁰Sn have been studied in a series of experiments using three different experimental setups. The first experiment utilized the NORDBALL detector array where for the first time excited states in the T_z=-3/2 nuclei ⁹⁹Cd and ¹⁰¹In were identified. The following experiments used a recoil catcher setup in combination with two EUROBALL cluster detectors, where for the first time excited states in the T_z=1 nuclei ⁹⁸Cd and ¹⁰²Sn were identified. These two nuclei are now the nearest neighbors of ¹⁰⁰Sn with known excited states. The last three experiments used the Fragment Mass Analyzer at Argonne National Laboratory to study ¹⁰²Sn in more detail. In all experiments a beam of ⁵⁸Ni ions was used to bombard targets of ⁴⁶Ti and ⁵⁰Cr. The experimental level schemes of ⁹⁸Cd, ⁹⁹Cd, ¹⁰²Sn and ¹⁰³In are well reproduced by the shell model calculations. Isomeric states were found in ⁹⁸Cd, ⁹⁹Cd and ¹⁰²Sn and their half-lives were measured. The isomeric states in all three nuclei decay via low energy E2 transitions. The deduced E2 transition rates lead to controversial results for the proton and neutron effective charges, which are also basic shell model parameters. In ¹⁰²Sn the measured B(E2;6⁺→4⁺) value leads to a neutron effective charge of 2.0^+0.5_-0.3e, which is a fairly large value. The analysis of the isomeric 17/2⁺ state in ⁹⁹Cd suggests a proton effective charge of 1.4(1)e, whereas the measured B(E2;8⁺→6⁺) value in ⁹⁸Cd requires a proton effective charge of only 0.93^+0.14_-0.10e. The small proton effective charge in ⁹⁸Cd is very surprising, since it is even smaller than the bare proton charge. In all other nuclei studied so far, the effective charges are larger than the bare nucleon charges, and usually the neutron effective charge is lower than the proton effective charge. The large neutron effective charge points to a softness of the ¹⁰⁰Sn core with respect to quadrupole shape changes, whereas the two proton holes weakly polarize the core in ⁹⁹Cd and not at all in ⁹⁸Cd

[en] Careful measurements of activity concentrations of ¹³⁷Cs in soil samples taken layer by layer in autumn of 1999 in Slovenia are confronted with a prediction based on the diffusion-convection equation with a boundary condition which - unlike the boundary conditions applied in the literature so far - conserves the deposited activity over time, except for the natural decay. It is shown that it is essential to consider the deposits from atmospheric nuclear weapons tests and the Chernobyl accident to arrive at a good fit to the measured data. The corresponding Green's function as well as the diffusion constant and migration speed based on the analysis are given

[en] We present a method for the synthesis of entire in situ gamma-ray spectra based on Monte Carlo calculations and measured data that characterize the detector properties. The method can serve for the determination of the effective depth of ¹³⁷Cs in soil based on the information contained in the low-energy part of an in situ spectrum. Effective depth is defined as the depth of a plane distribution of ¹³⁷Cs beneath the surface that reproduces the fluence energy and angular distribution at 1 m above the ground of gamma rays belonging to the real ¹³⁷Cs distributions. We managed to reproduce the measured in situ spectra with our method and to demonstrate that the method allows the determination of the effective depth of ¹³⁷Cs with a precision of 10^-2 m. The method requires minimal experimental characterization of the detector and is not sensitive to the details of the detector model and the soil composition and density employed in the Monte Carlo calculations

[en] Electron screening enhances cross sections for nuclear reactions at low energies. We have studied the ¹H(⁷Li,α)⁴He reaction in inverse kinematics and observed large electron screening only when the metallic targets were under tensile stress. Hydrogen was loaded into Pd and PdAg alloy foils from gas phase and concentrations reached about 0.6 protons per metallic atom. Mechanical pressure creates stress induced states in the metal. Without pressure hydrogen occupies octahedral interstitial positions in the fcc Pd lattice. Under stress some protons move to dislocated octahedral (dis-O) sites in the lattice. We believe that the magnitude of screening in various metals depends on the electron density on dis-O sites in case of fcc lattices or dislocated tetrahedral sites in bcc metals. We are currently trying to confirm the above by determining the electron density at the sites occupied by protons via the measurement of proton Knight's shift with ¹H nuclear magnetic resonance technique.

[en] Electron screening has been studied in the ¹H(⁷Li, α)⁴He fusion reaction at lithium beam energies from 0.34 to 2.07 MeV for hydrogen-implanted Pd, Pt, Zn and Ni targets. A large electron screening has been observed in all the targets. However, no large electron screening has been observed in the following proton-induced reactions: ⁵⁵Mn(p, γ)⁵⁶Fe, ⁵⁵Mn(p, n)⁵⁵Fe, ¹¹³Cd(p, n)¹¹³In, ¹¹⁵In(p, n)¹¹⁵Sn, ⁵⁰V(p, n)⁵⁰Cr and ⁵¹V(p, γ)⁵²Cr. Moreover, no shift in the resonance energy for the metallic compared to the insulator environment has been observed within our uncertainties for the studied (p,n) and (p, γ) reactions. These results raise the question about the validity of the measurements that showed large electron screening potentials in nuclear reactions involving high-Z targets, and point to a dependence of the electron screening potential on the position of the target nuclei in the metallic lattice. (orig.)

[en] Activity concentrations of ⁴⁰K and ³H in drinking water from four sources in the vicinity of NPP Krsko and their correlation with geological data are presented. The data extends from the year 1996 until present. In addition, activity concentrations of ⁴⁰K in drinking water at randomly selected sources in Slovenia are presented on a map. These activity concentrations vary by more than an order of magnitude with the largest values in northeastern part of the country. (author)

[en] We have measured the cross-section for the ¹H(⁷Li, α)⁴He reaction at lithium beam energies from 0.34 to 1.05MeV. Hydrogen was forced by diffusion into Pd and PdAg alloy foils. A large electron screening effect was observed only when foils were under tensile stress. A dependence of the screening potential on hydrogen concentration or Hall coefficient of the metallic host could not be established. (orig.)

[en] Electron screening effect was studied on different hydrogen containing targets with the ⁷Li, ¹¹B and ¹⁹F ion beams. Results show large electron screening potentials strongly dependent on the proton number Z of the projectile. The largest ever measured screening potential with a value of about 50 times the result given by calculations from the model in adiabatic limit was observed in the graphite target containing hydrogen as an impurity. (authors)

[en] Due to Coulomb repulsion the cross section for charged particle induced nuclear reactions drops rapidly with decreasing beam energy. It is known that the cross section increases at low energies when the interacting nuclei are not bare, i.e. are in the form of atoms and molecules or in plasma [1]. The enhancement ratio could be written as f(E) where U_e is the screening potential energy. It was recently observed by two independent groups that the cross section for fusion of two deuterons increases even more when deuterium is implanted into a metal [2,3]. A similar increase was subsequently observed in other nuclear reactions [4,5]. The cross section increase was attributed to metallic valence electrons, which may come closer to the deuteron and more effectively screen its charge than in a hydrogen atom. However, the size of the screening effect strongly depends on the host material and the reason for this dependence is not known. Raiola et al. [6] have observed a connection between U_e and the Hall coefficient of the metallic host, while Kasagi [2] suggested that U_e depends on deuterium concentration in the metal. We have studied the reaction 1^H(7^Li,α)4^He in inverse kinematics, which simplified the experimental setup. The emitted ,α particles were measured in a silicon detector at a backward angle of 150^o. The lithium ions delivered by the 2 MV Tandetron at Jozef Stefan Institute had energies between 0.34 and 4.3 MeV. We used 6 different targets from polymer Kapton to metallic Pd and various PdAg alloys. The PdAg alloys have a crystalline structure similar to Pd but their Hall coefficients differ considerably. Hydrogen was forced into the metallic targets by pressure gradient. Our preliminary results indicate that the U_e does not depend strongly on the Hall coefficient of PdAg alloys. The dependence on hydrogen concentration, however, is much stronger. We have observed large U_e values only in foils that contained less than a few percent of hydrogen per metallic atom.(author)

[en] We have measured the cross section for the ¹H(⁷Li,α)⁴He reaction at lithium beam energies from 0.34 to 1.05 MeV. Hydrogen was forced by diffusion into Pd and PdAg alloy foils. A large electron screening effect was not observed at high hydrogen concentrations, while at low H/metal ratio the results are inconclusive. A dependence of the screening potential on Hall coefficient of the metallic host could not be confirmed.