Calorimetric method for determination of <Superscript>51</Superscript>Cr neutrino source activity

Experimental study of nonstandard neutrino properties using high-intensity artificial neutrino sources requires the activity of the sources to be determined with high accuracy. In the BEST project, a calorimetric system for measurement of the activity of high-intensity (a few MCi) neutrino sources based on ⁵¹Cr with an accuracy of 0.5–1% is created. In the paper, the main factors affecting the accuracy of determining the neutrino source activity are discussed. The calorimetric system design and the calibration results using a thermal simulator of the source are presented.     

Precise determination of the neutron scattering length of lead isotopes <Superscript>204</Superscript>Pb, <Superscript>207</Superscript>Pb and <Superscript>208</Superscript>Pb by neutron interferometry

Excited states of ⁶⁸Ga have been investigated through the ⁵⁵Mn(¹⁶O, 2pn) reaction at projectile energy 55 MeV. The level scheme has been extended up to 7.8 MeV. Altogether six new excited levels could be identified and twelve previously unobserved γ-transitions have been placed in the modified level scheme. Received: 19 June 2000 / Accepted: 20 October 2000     

<Superscript>210</Superscript>Pb and <Superscript>210</Superscript>Po determination in environmental samples using liquid scintillation counting and alpha spectrometry

A simple radiochemical procedure has been developed to determine ²¹⁰Pb and ²¹⁰Po in environmental samples from the same matrix. Sediment samples are decomposed by leaching with mineral acids or by microwave digestion, while water samples are pre-concentrated. One part of the resulting solution, spiked with ²⁰⁹Po, is used for ²¹⁰Po determination by spontaneous deposition onto nickel disks (α-spectrometry). The other part is assayed for ²¹⁰Pb, separating the Pb either by anion-exchange (sediment samples), or by solvent extraction (water samples). The ²¹⁰Pb source is finally prepared by precipitation as oxalate and the chemical recovery determined by gravimetry. The ²¹⁰Pb activity concentration is determined by liquid scintillation. A standard sediment sample supplied by IAEA and spiked water samples were analysed to check the procedure. The ²¹⁰Pb and ²¹⁰Po measurements agreed well with the certifications, deviations being less than 10%. The mean recoveries for Pb and Po were (70±12)% and (77±8%) for sediments, and (70±10)% and (81±7)% for waters, respectively.     

Beta decay of <Superscript>115</Superscript>In to the first excited level of <Superscript>115</Superscript>Sn: Potential outcome for neutrino mass

Recent observation of β decay of ¹¹⁵In to the first excited level of ¹¹⁵Sn with an extremely low Q _β value (Q _β ≤ O(1) [keV]) could be used to set a limit on neutrino mass. To give a restriction potentially competitive with those extracted from experiments with ³H (≃2 eV) and ¹⁸⁷Re (≃15 eV), the atomic mass difference between ¹¹⁵In and ¹¹⁵Sn and energy of the first ¹¹⁵Sn level should be remeasured with higher accuracy (possibly of the order of ∼1 eV). The text was submitted by the authors in English.     

Dynamic polarization potentials for <Superscript>6</Superscript>He + <Superscript>209</Superscript>Bi and <Superscript>11</Superscript>Li + <Superscript>208</Superscript>Pb systems at near-barrier energies

The Coulomb dipole induced dynamic polarization potentials for ⁶He + ²⁰⁹Bi and ¹¹Li + ²⁰⁸Pb systems within the framework of Feshbach’s formalism with a motive to ascertain the presence or absence of threshold anomaly have been studied. As a result of this study, the threshold anomaly has been found to be present for both systems. It has also been found that at deep sub-barrier energies the imaginary part either starts increasing or at least remains unchanged which indicates the presence of the breakup threshold anomaly. In addition, the Coulomb breakup transmission factors for both systems have been found to have maximum value below and near-barrier energies, but at very high energies due to closure of the breakup channel the breakup transmission coefficients quickly becomes zero.     

Precise determination of neutron binding energy of <Superscript>64</Superscript>Cu

The neutron binding energy in ⁶⁴Cu has been accurately measured in thermal neutron capture. A composite target of natural Cu and NaCl was used on a high flux neutron beam using a large measuring time. The γ-ray spectrum emitted in the (n, γ) reaction was measured with a HPGe detector in large statistics (up to 10⁶ events per channel). Intrinsic limitations of HPGe detectors, which restrict the accuracy of energy calibration, were determined. The value B _n of ⁶⁴Cu was determined as 7915.867(24) keV.     

Limits of Majorana neutrino mass from combined analysis of data from <Superscript>76</Superscript>Ge and <Superscript>136</Superscript>Xe neutrinoless double beta decay experiments

We present effective Majorana neutrino mass limits <m _ββ> obtained from the joint analysis of the recently published results of ⁷⁶Ge and ¹³⁶Xe neutrinoless double beta decay (0νββ) experiments, which was carried out by using the Bayesian calculations. Nuclear matrix elements (NMEs) used for the analysis are taken from the works, in which NMEs of ⁷⁶Ge and ¹³⁶Xe were simultaneously calculated. This reduced systematic errors connected with NME calculation techniques. The new effective Majorana neutrino mass limits <m _ββ> less than [85.4–197.0] meV are much closer to the inverse neutrino mass hierarchy region.     

New approximations to the energy dependences of the total cross sections for the proton-induced fission of <Superscript>197</Superscript>Au, <Superscript>203</Superscript>Tl, <Superscript>nat</Superscript>Pb,and <Superscript>209</Superscript>Bi nuclei

The total cross sections for ¹⁹⁷Au and ²⁰³Tl fission induced by protons of energy varied from about 200 to 1000 MeV with a step of about 100 MeV are measured. New approximations to the energy dependences of the cross sections for the proton-induced fission of ¹⁹⁷Au, ²⁰³Tl, natPb, and ²⁰⁹Bi nuclei are presented and discussed. For all of these nuclei, exponential functions are used as approximations.     

Phase shift analysis of the <Superscript>6</Superscript>He+<Superscript>208</Superscript>Pb and the <Superscript>6</Superscript>He+<Superscript>197</Superscript>Au systems

We present the elastic scattering of the ⁶He+²⁰⁸Pb and the ⁶He+¹⁹⁷Au systems at the laboratory energy of E _lab=27 MeV within the framework of the McIntyre parametrization, and systematically investigate χ ²/N analysis of both systems to obtain an excellent agreement between the theoretical results and the experimental data. We find large diffusivity parameters indicating long range absorption mechanisms. We also show that both systems lack both the nuclear and the Coulomb rainbow scattering for obtained S-matrix parameters.     

Radiative strength function and the pygmy dipole resonance in <Superscript>208</Superscript>Pb and <Superscript>70</Superscript>Ni

The pygmy-resonance parameters and the E1 strength function are derived for ²⁰⁸Pb using a fully self-consistent microscopic formalism recently developed for magic nuclei, which takes into account quasiparticle phonon interactions (or coupling to phonons) in addition to the random phase approximation. For the radiative strength function of ²⁰⁸Pb at energies above 5 MeV, the experimental data of the Oslo group are adequately described by our predictions, whereby the important role of coupling to phonons is confirmed. By comparing the measurements based on the (³He, ³He′γ) and (γ, γ′) reactions, we discuss the physical properties of the radiative strength function measured for ²⁰⁸Pb. For the neutron-rich ⁷⁰Ni nucleus, predictions for the radiative strength function and the pygmy resonance are obtained using a partially self-consistent approach, which invokes the Skyrme forces in deriving the mean field, effective nucleon–nucleon interaction, and phonon characteristics.     

Precision electron-gamma spectroscopic measurements in <Superscript>75</Superscript>As

The decay of ⁷⁵Se to levels of ⁷⁵As has been studied using an HPGe detector for gamma-ray and a mini-orange electron spectrometer for conversion electron measurements. We identify 38 transitions in this decay, including 18 gamma rays and 16 conversion electron lines reported for the first time. New results also include E2 multipolarity assignment for the 81 keV transition, M1 assignment to three newly observed transitions and M1 + E2 for the 617 keV transition. A revised ⁷⁵As level scheme is constructed using the Ritz combination principle through the computer code GTOL. While confirming the existence of 10 well-established levels, two levels at 587 and 859 keV are newly placed into the decay scheme of ⁷⁵Se. The interpretation of the observed levels in terms of various theoretical approaches is briefly discussed. The newly placed 586.8 keV 1/2^- and 859.9 keV 1/2⁺ levels are studied in the light of the Interacting Boson-Fermion Model.     

High-precision mass measurements of hydrogen-like <Superscript>24</Superscript>Mg<Superscript>11+</Superscript> and <Superscript>26</Superscript>Mg<Superscript>11+</Superscript> ions in a Penning trap

For the determination of the bound-electron g factor in hydrogen-like heavy ions the mass of the ion is needed at a relative uncertainty of at least 1 ppb. With the SMILETRAP Penning trap mass spectrometer at the Manne Siegbahn Laboratory in Stockholm several mass measurements of ions with even-even nuclei at this level of precision have been performed so far, exploiting the fact that the mass precision increases linearly with the ion charge. Measurements of masses of the hydrogen-like ions of the two Mg-isotopes ²⁴Mg and ²⁶Mg are reported. The masses of the hydrogen-like ions are 23.979011054(14) u and 25.976562354(34) u, corresponding to the atomic masses 23.985041690(14) u and 25.982592986(34) u, respectively. The possibility to use these two isotopes for the first observation of an isotope effect in the bound-electron g factor in hydrogen-like heavy ions is discussed.     

Density-constrained time-dependent Hartree-Fock calculation of <Superscript>16</Superscript>O + <Superscript>208</Superscript>Pb fusion cross-sections

We present a fully microscopic study of the ¹⁶O + ²⁰⁸Pb fusion using the density-constrained time-dependent Hartree-Fock theory. The calculated fusion cross-sections are in good agreement with the experimental data for the entire energy range indicating that the incorporation of dynamical effects is crucial in describing heavy-ion fusion.     

Observation of a superdeformed band in <Superscript>190</Superscript>Pb

A superdeformed band has been observed in the N = 108 isotope ¹⁹⁰Pb. This is the most neutron-deficient Pb isotope in which superdeformed states have been observed. Several theoretical approaches have predicted that N = 108 will mark the limit of observable superdeformation in the Pb isotopes. The band, which consists of five (possibly six) transitions, is observed to feed at least one isomeric level in its decay to the ground state. This decay pattern supports a spin assignment of 10 for the lowest observed level.     

Multidimensional Langevin approach to describing the <Superscript>18</Superscript>O + <Superscript>208</Superscript>Pb fusion-fission reaction

The fusion-fission reaction is treated as a multistep process. Langevin equations are used to describe the evolution of the system at each reaction stage. The parameters of the fusion process are calculated at the first stage. The results obtained in the input channel are employed as initial conditions in calculating the features of the fission process. The cross sections for fusion and fission are successfully described, and the cross sections for the formation of evaporation residues are estimated. In addition, the procedure used makes it possible to describe the mass distribution of fission fragments and the fragment-mass dependence of the multiplicity of prefission neutrons and to determine the mass-energy distribution of fission fragments. From the calculations, it follows that all the fission features of the reaction in question can be reproduced without considering the formation of a classical compound nucleus. The reaction times are so long that it is impossible to separate experimentally such events from the case of true fission through a compound nucleus.     

On the flavor composition of the solar <Superscript>7</Superscript>Be neutrino

The flavor composition of the solar beryllium neutrino was analyzed using schemes that include the new (heavy) neutrino (ν₄) at a negligible angle of mixing with the light partners ν _e , ν_μ, and ν_τ.     

<Superscript>210</Superscript>Pb and <Superscript>210</Superscript>Po levels in sediments,water, and bioindicators in the Cananeia-Iguape estuary-Sao Paulo-Brazil

The purpose of this work was to determine levels of ²¹⁰Pb and ²¹⁰Po in seawater, sediment cores, fish and seafood as well as to estimate the concentration factors and the bioindicators for ²¹⁰Pb and ²¹⁰Po in marine organisms collected in the estuary. ²¹⁰Pb levels in seawater varied from 2.1 to 6.2 mBq.L^?1 and for ²¹⁰Po ranged from 1.6 to 4.1 mBq.L^?1. ²¹⁰Pb concentration factors in fish varied from 0.5×10² to 0.8×10³, in crustaceans from 0.5×10³ to 0.2×10⁴ and in shellfish from 0.2×10⁴ to 0.3×10⁴. ²¹⁰Po concentration factors in fish varied from 0.9×10² to 0.5×10⁴, in crustaceans from 0.5×10⁴ to 0.2×10⁵ and in shellfish from 0.3×10⁵ to 0.9×10⁵. The results obtained to the concentration factors indicated that shellfish and crustaceans are good bioindicators for the radionuclides studies. Some species of fish also accumulated significantly quantities of these radionuclides.