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Experiment TGV-2 and Search for Double Electron Capture of 106 Cd

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Experiment TGV-2 and Search for Double Electron Capture of 106 Cd Section III. Rare Nuclear Processes ' UA0700259 NUCLEAR EXCITATION AT THE POSITRON - ATOMIC ELECTRON ANNIHILATION S. N. Fedotkin, V. A. Zheltonozhskii Institute for Nuclear Research, National Academy of Sciences of Ukraine, Kyiv, Ukraine The process of nuclear excitation at the annihilation of the positrons and atomic shell electrons is well enough explored experimentally [1, 2]. The theoretical calculations of the cross section of this process are on 3 - 5 orders smaller than experimental values. Two different mechanisms are considered herewith: resonant (radiationless) and nonelastic ones. Only positrons with the energies £+ in the interval ER < E+ < ER + Г excite the nuclei in the resonant processes. Here Г and ER are the linewidth of the K- shell electron and the resonance energy of positron. The correct estimation of the share of positrons which excite a nuclei in this process is necessary for the determination of the cross section from the experimental data. The detectors of the particles have a finite resolving capacity ДЕ « E+ or there is the energy spread AE of the particles beam in any process of the scattering of the electrons and positrons. Because of this never manages to separate the contributions of the elastic processes from inelastic ones in which photons with energy smaller than AE are radiated. The cross section a is defined in this case according to method offered in [3] as a sum of the cross sections of elastic process ael and inelastic one in which the photon with energy smaller than AE is emitted: а-Ф-ln— , where a andO are the fine structure constant and the some function of momentum of particles. The cross section a weakly differs herewith from crel . But the share of positrons participating at the nuclear excitation increases in AEJT times in contrast to the purely elastic process. At the excitation of nuclei U5In in [4] was used the monoenergetic positron beam with energy £. = 89 keV. In this case the energy spread of positrons due to their motion through the target is AE ~ E+ - ER - 5 keV. As far as the linewidth F = 7eV the value of the cross section defined from experiment will decreases in Л£/Г~103 times and becomes close to theoretical meaning of the cross section of resonant process. Similarly we can interpret the experimental data of papers [1, 2]. The cross sections approach significantly in this case to the theoretical values. 1. Микоуата Т., Shimizu S. II Phys. Rev. - 1972. - Vol. C5. - P. 95. 2. Vishnevskii IN, Zheltonozhskii V.A., Svyato V.P., Trishin V. V. //JETP Lett. - 1979. - Vol. 30. - P. 366. 3. Schwinger J. // Phys. Rev. - 1949. - Vol. 75. - P. 898. 4. Cassidy D., Hunt A. et al. //Phys. Rew. - 2001. - Vol. C64. - 054603. UA0700260 EXPERIMENT TGV-2 AND SEARCH FOR DOUBLE ELECTRON CAPTURE OF 106Cd V. B. Brudanin1, N. I. Rukhadze1, V. G. Egorov1, Ch. Briancon2, P. Benes3, P. Cermak3, K. N. Gusev1, F. A. Danevich4, A. A. Klimenko1, V. E. Kovalenko1, A. Kovalik1, A. V. Salamatin1, I. Stekl3, V. V. Timkin1, V. I. Tretyak4, Ts. Vylov1, V. V. Kobvchev4 1 Joint Institute for Nuclear Research, Dubna, Russia 2 Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse, Orsay, France 3 Institute of Experimental and Applied Physics, Prague, Czech Republic 4 Institute for Nuclear Research, National Academy of Sciences of Ukraine, Kyiv, Ukraine Double electron capture (2є) of 106Cd has been searched for using the low-background spectrometer TGV-2 placed in the Modane underground laboratory in France (depth 4800 m of water equivalent). The spectrometer includes 32 HPGe detectors (the total sensitive volume is about 400 cm3) mounted one over 96 Section III. Rare Nuclear Processes another in a common cryostat. The source is presented by 16 thin foils of cadmium with a thickness of ~50 u-m inserted between pairs of neighboring detectors. The signature of the double electron capture of a I06Cd nucleus is coincidence between two characteristic KX-rays of palladium detected by two detectors neighboring one source. Several long-term measurements were made with 16 samples of natural Cd with a total mass of 14.5 g and without any sample to obtain the background conditions of TGV-2. Three long-term runs were performed in searching for double electron capture of 106Cd with different samples of enriched 106Cd (with enrichment of 60%, 68% and 75%). The third run lasted at present by more than 1000 hours has the best background characteristics. In the third run, the limit of Tm > 5 x io"y (90% CL) was obtained for two-neutrino double electron capture (0T —»• 0+, ground state) of 106Cd from the preliminary calculations of the data accumulated for 900 hours. The model of the detector was created using GEANT4 package, and Monte-Carlo simulations of 2v2e decay of 106Cd were performed in order to calculate the efficiency of the detector to the sought process. IIIIL UA0700261 THE MUON DECAY AND MUON CAPTURE DETECTION WITH LVD N. Agafonova Institute for Nuclear Research, Russian Academy of Sciences, Moscow, Russia A purpose of the measurements is evaluation of the charge composition of primary cosmic rays at energy higher than 10 TeV using the pi+ I/.Г ratio for muon flux underground. The method of the muon capture detection with LVD and preliminary results are presented. UA0700262 PRODUCTION OF THE Hf ISOMERS IN REACTOR IRRADIATIONS S. A. Karamian', J. J. Carroll2, J. Adam1'3, E. N. Kulagin1, E. P. Shabalin1 1 Joint Institute for Nuclear Research, Dubna, Moscow region, Russia 2 Youngstown State University, Ohio, USA J Institute Nuclear Physics, Rez, Prague, Czech Republic Metal natHf samples were activated with neutron flux of Dubna IBR-2 reactor at the positions corresponded to different flux magnitudes without filters or using Cd and CB4 layers. Gamma-activity of samples has been extensively analyzed with the Ge gamma-spectrometers during two years past irradiation. In presence of the dominant radioactive products of 175Hf and mHf, the high-spin 17S^Hf and I79m2Hf isomers have also been detected, despite relatively low level of their activity. With the reactor neutrons, it is established now that 178m2Hf is produced due to the slow neutron capture (n, y) reaction, while 179m2Hf explicitly due to the (n, n'f) reaction with fast neutrons. The production cross-sections are also very different; allowing the accumulation of I79m2Hf in a microgram amount after standard irradiation, while 17Sm2Hf only in a quantity of nanograms. From the comparison of obtained results with published data [1], the destruction (burn-up) cross-section is deduced for I78m2Hf due to the second neutron capture at the reactor flux. At neutron fluence > 1021 n/cm2 [1], the burn-up effect must be significant. In the present work, the partial <7lh and lr values are specified for the burn-up process leading to both m2 and g states in Hf. The isomer-to-ground state ratios for Hf isomer in neutron induced reactions are systematized and discussed. The 178m2Hf isomers application as a reservoir for energy storage and pulsed release are extensively discussed in literature, and grams of the isomeric material are required for that. However, the known until now and present results do not support optimistic perspectives for using the reactor neutrons as an appropriate projectile for solving the problem. For 178m2Hf, the production and destruction cross-sections in (n, у) reactions are presented in Table 1. This work has been supported by US AFOSR Grant: F49620-02-01-0187. 97.
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