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Register a new userSimulations of beta-decay of 6He in an Electrostatic Ion Trap
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S. Vaintraub
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Trapped radioactive atoms present exciting opportunities for the study of fundamental interactions and symmetries. For example, detecting beta decay in a trap can probe the minute experimental signal that originates from possible tensor or scalar terms in the weak interaction. Such scalar or tensor terms affect, e.g., the angular correlation between a neutrino and an electron in the beta-decay process, thus probing new physics of beyond-the-standard-model nature. The present system focuses on a novel use of an innovative ion trapping device, the Electrostatic Ion Beam Trap. Such a trap has not been previously considered for Fundamental Interaction studies and exhibits potentially very significant advantages over other schemes. These advantages include improved injection efficiency of the radionuclide under study, an extended field-free region, ion-beam kinematics for better efficiency and ease-of operation and the potential for a much larger solid angle for the electron and recoiling atom counters. The beta-decay of trapped 6He is discussed and preliminary Monte-Carlo (MC) simulation and error-analysis considerations are presented.
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We demonstrate that abundant quantities of short-lived beta unstable ions can be trapped in a novel transparent Paul trap and that their decay products can directly be detected in coincidence. Low energy 6He+ (807 ms half-life) ions were extracted from the SPIRAL source at GANIL, then decelerated, cooled and bunched by means of the buffer gas cooling technique. More than 10^8 ions have been stored over a measuring period of six days and about 10^5 decay coincidences between the beta particles and the 6Li^{++} recoiling ions have been recorded. The technique can be extended to other short-lived species, opening new possibilities for trap assisted decay experiments.
Trapped radioactive atoms present exciting opportunities for the study of fundamental interactions and symmetries. For example, detecting beta decay in a trap can probe the minute experimental signal that originates from possible tensor or scalar terms in the weak interaction. Such scalar or tensor terms affect, e.g., the angular correlation between a neutrino and an electron in the beta-decay process, thus probing new physics of beyond-the-standard-model nature. In particular, this article focuses on a novel use of an innovative ion trapping device, the Electrostatic Ion Beam Trap (EIBT). Such a trap has not been previously considered for Fundamental Interaction studies and exhibits potentially very significant advantages over other schemes. These advantages include improved injection efficiency of the radionuclide under study, an extended field-free region, ion-beam kinematics for better efficiency and ease-of-operation and the potential for a much larger solid angle for the electron and recoiling atom counters.
We present a microscopic calculation of the 6He beta-decay into the ground state of 6Li. To this end, we use chiral perturbation theory at next-to-next-to-next-to-leading order to describe the nuclear weak-currents. The nuclear wave functions are derived from the J-matrix inverse scattering nucleon-nucleon potential (JISP), and the Schroedinger equation is solved using the hyperspherical-harmonics expansion. Our calculation brings the theoretical decay-rate within 3% of the measured one. This success is attributed to the use of chiral-perturbation-theory based mesonic currents, whose contribution is qualitatively different compared to standard nuclear physics approach, where the use of meson exchange currents worsens the comparison to experiment. The inherent inconsistency in the use of the JISP potential together with chiral-perturbation-theory based is argued not to affect this conclusion, though a more detailed investigation is called for. We conclude that any suppression of the axial constant in nuclear matter is included in this description of the weak interaction in the nucleus.
A new technique has been developed at TRIUMFs TITAN facility to perform in-trap decay spectroscopy. The aim of this technique is to eventually measure weak electron capture branching ratios (ECBRs) and by this to consequently determine GT matrix elements of $betabeta$ decaying nuclei. These branching ratios provide important input to the theoretical description of these decays. The feasibility and power of the technique is demonstrated by measuring the ECBR of $^{124}$Cs.
Background: The understanding and description of forbidden decays provides interesting challenges for nuclear theory. These calculations could help to test underlying nuclear models and interpret experimental data. Purpose: Compare a direct measurement of the $^{138}$La $beta$-decay $Q$ value with the $beta$-decay spectrum end-point energy measured by Quarati et al. using LaBr$_3$ detectors [Appl. Radiat. Isot. 108, 30 (2016)]. Use new precise measurements of the $^{138}$La $beta$-decay and electron capture (EC) $Q$ values to improve theoretical calculations of the $beta$-decay spectrum and EC probabilities. Method: High-precision Penning trap mass spectrometry was used to measure cyclotron frequency ratios of $^{138}$La, $^{138}$Ce and $^{138}$Ba ions from which $beta$-decay and EC $Q$ values for $^{138}$La were obtained. Results: The $^{138}$La $beta$-decay and EC $Q$ values were measured to be $Q$ = 1052.42(41) keV and $Q_{EC}$ = 1748.41(34) keV, improving the precision compared to the values obtained in the most recent atomic mass evaluation [Wang, et al., Chin. Phys. C 41, 030003 (2017)] by an order of magnitude. These results are used for improved calculations of the $^{138}$La $beta$-decay shape factor and EC probabilities. New determinations for the $^{138}$Ce 2EC $Q$ value and the atomic masses of $^{138}$La, $^{138}$Ce, and $^{138}$Ba are also reported. Conclusion: The $^{138}$La $beta$-decay $Q$ value measured by Quarati et al. is in excellent agreement with our new result, which is an order of magnitude more precise. Uncertainties in the shape factor calculations for $^{138}$La beta-decay using our new $Q$ value are reduced by an order of magnitude. Uncertainties in the EC probability ratios are also reduced and show improved agreement with experimental data.
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