The Q value of the (76)Ge double beta decay has been determined by measuring the masses of (76)Ge and (76)Se in a Penning trap using neon- and fluorinelike ions. The obtained masses are 75.921 402 758(96) u and 75.919 213 795(81) u, respectively. The systematic errors of these two determinations are nearly equal, and therefore, the remaining systematic uncertainty of the Q value is drastically reduced. A Q value of 2 039.006(50) keV was obtained improving the accuracy of the accepted value by a factor of 6.
A high-accuracy mass measurement of 7Li was performed with the SMILETRAP Penning-trap mass spectrometer via a cyclotron frequency comparison of 7Li3+ and H2+. A new atomic-mass value of 7Li has been determined to be 7.016 003 425 6(45) u with a relative uncertainty of 0.63 ppb. It has uncovered a discrepancy as large as 14sigma (1.1 microu) deviation relative to the literature value given in the Atomic-Mass Evaluation AME 2003. The importance of the improved and revised 7Li mass value, for calibration purposes in nuclear-charge radii and atomic-mass measurements of the neutron halos 9Li and 11Li, is discussed.
High-spin states in 2~were populated in the 2~ 4n) reaction using e-particles in the energy region 42-51 MeV. Prompt and delayed y-rays as well as conversion electrons were studied in addition to excitation functions, angular distributions and 7-7 coincidences. In this way a stretched cascade of y-rays from a level at 8125.9 keV was found to feed the previously known isomeric 9-level at 2185.7 keV. Spins and parities were established for levels up to and including a 19-level at 6098.0 keV. The levels with J== 17-and 19-at excitation energies of 5664.3 and 6098.0 keV are likely to be due to the simple p~/1 i~z and f5721 ii-~2 configurations. The agreement between calculated and experimental energies for all observed levels in the region J=9-19 is very good in cases where the empirical two-particle interactions used are satisfactorily well known. Above the 19-level there are three weakly populated levels at 7402.1, 7849.2 and 8125.9 keV, which are likely to have J > 20. None of these energies agrees with the calculated value 7695 +20 keV for the 20 + state of the ila~2 configuration which has the highest angular momentum produced by the four valence neutron holes. This apparent anomaly can be understood if the yrast levels with J > 20 have angular momentum contribution from the core. It seems likely that the states at 7402.1, 7849.2 and 8125.9 keV are due to proton core excited states of the type Irh9/2 h11~/zXVp~/2 i1~/2 with J==20 + and J==21 + and =h9/2 h;11/2 x vpT/1 f57~ i~32/2 with J==22 + or 23 +, respectively. The state at 8126keV has the highest energy so far directly observed in a stretched cascade of y-rays from the decay of a heavy nucleus produced in (e, x n) reactions.
We report here the atomic masses of 3 H and 3 He determined by using the Penning trap mass spectrometer Smiletrap. The measurements are based on cyclotron frequency determinations of 3 H 1+ and 3 He 1+ using H + 2 ions as mass reference. The mass values for 3 H and 3 He are 3.016 049 278 7(25) u and 3.016 029 321 7(26) u, respectively. From these masses a new Q-value of the tritium β-decay was derived resulting in 18.589 8(12) keV, being the most accurate value at present. The Q-value of the tritium β-decay is related to the possible rest mass of the electron antineutrino. Introduction.-Q-values of nuclear decays and reactions involve masses of atoms in the initial and final states. In some cases such Q-values are related to fundamental questions in current physics requiring an extremely high mass precision. Such a case is the Q-value of the tritium β-decay. Neutrino oscillations, which recently have been observed [1-3], require the existence of rest masses for the three neutrinos but give only a lower limit of 0.05 eV to the mass of the electron antineutrino. By studying the shape of the β-spectrum of tritium in the region that refers to energy of the last 50 eV with electrostatic electron spectrometers, it has been possible to set an upper limit of the mass to about 2 eV for m(ν e) [4-7]. In the planned Katrin experiment [8] it will be possible to measure a neutrino mass as low as 0.3 eV. This method of determining m(ν e) could use a very accurate Q-value for calibration purpose. There are a number of Q-values available from end point determinations of the tritium β-decay. The uncertainty in the weighted average of these measurements is about 1 eV. These measurements should be checked by an independent and at least as accurate method, i.e. a Penning trap measurement. Already in 1993 a Q-value measurement using mass determinations in a Penning trap was reported [9], which was based on the mass measurement of 3 He and 3 H. However, 10 years later in ref. [10] we showed that the mass values of both 4 He and 3 He were too low by 7 nu and 14 nu, respectively (roughly a 5σ deviation in both cases). Therefore the Q-value reported in ref. [9] did not seem reliable and should thus be remeasured.
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