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تسجيل مستخدم جديدFirst direct determination of the superallowed $beta$-decay $Q_{EC}$-value for $^{14}$O
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We report the first direct measurement of the $^{14}text{O}$ superallowed Fermi $beta$-decay $Q_{EC}$-value, the last of the so-called traditional nine superallowed Fermi $beta$-decays to be measured with Penning trap mass spectrometry. $^{14}$O, along with the other low-$Z$ superallowed $beta$-emitter, $^{10}$C, is crucial for setting limits on the existence of possible scalar currents. The new ground state $Q_{EC}$ value, 5144.364(25) keV, when combined with the energy of the $0^+$ daughter state, $E_x(0^+)=2312.798(11)$~keV [Nucl. Phys. A {bf{523}}, 1 (1991)], provides a new determination of the superallowed $beta$-decay $Q_{EC}$ value, $Q_{EC}(text{sa}) = 2831.566(28)$ keV, with an order of magnitude improvement in precision, and a similar improvement to the calculated statistical rate function $f$. This is used to calculate an improved $mathcal{F}t$-value of 3073.8(2.8) s.
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B. E. Glassman (Department of Physics
, Astronomy
, Nationaln Superconducting Cyclotron Laboratory
2019
textbf{Background}: Superallowed $0^+ rightarrow 0^+$ $beta$ decays of isospin $T=2$ nuclides can be used to test theoretical isospin symmetry breaking corrections applied to extract the CKM matrix element $V_{ud}$ from $T = 0,1$ decays by measuring
precise $ft$ values and also to search for scalar currents using the $beta- u$ angular correlation. Key ingredients include the $Q_{textrm{EC}}$ value and branching of the superallowed transition and the half life of the parent. textbf{Purpose}: To determine a precise experimental $Q_{textrm{EC}}$ value for the superallowed $0^+ rightarrow 0^+$ $beta$ decay of $T=2$ $^{20}$Mg and the intensity of $^{20}$Mg $beta$-delayed $gamma$ rays through the isobaric analog state in $^{20}$Na. textbf{Method}: A beam of $^{20}$Mg was produced using the in-flight method and implanted into a plastic scintillator surrounded by an array of high-purity germanium detectors used to detect $beta$-delayed $gamma$ rays. The high-resolution $gamma$-ray spectrum was analyzed to measure the $gamma$-ray energies and intensities. textbf{Results}: The intensity of $^{20}$Mg $beta$-delayed $gamma$ rays through the isobaric analog state in $^{20}$Na was measured to be $(1.60 pm 0.04_{textrm{stat}} pm 0.15_{textrm{syst}} pm 0.15_{textrm{theo}}) times 10^{-4}$, where the uncertainties are statistical, systematic, and theoretical, respectively. The $Q_{textrm{EC}}$ value for the superallowed transition was determined to be $4128.7 pm 2.2$ keV based on the measured excitation energy of $6498.4 pm 0.2_{textrm{stat}} pm 0.4_{textrm{syst}}$ keV and literature values for the ground-state masses of $^{20}$Na and $^{20}$Mg. textbf{Conclusions}: The $beta$-delayed $gamma$-decay branch and $Q_{textrm{EC}}$ value are now sufficiently precise to match or exceed the sensitivity required for current low-energy tests of the standard model.
A direct $Q_{EC}$-value measurement of the superallowed $beta^+$ emitter $^{22}$Mg was performed using TRIUMFs Ion Trap for Atomic and Nuclear science (TITAN). The direct ground-state to ground-state atomic mass difference between $^{22}$Mg and $^{22
}$Na was determined to be $Q_{EC}=4781.40(22)$~keV, representing the most precise single measurement of this quantity to date. In a continued push towards calculating superallowed isospin-symmetry-breaking (ISB) corrections from first principles, ab-initio shell-model calculations of the $A=22$ IMME are also presented for the first time using the valence-space in-medium similarity renormalization group formalism. With particular starting two- and three-nucleon forces, this approach demonstrates a level of agreement with the experimental data that suggests reliable ab-initio calculations of superallowed ISB corrections are now possible.
Masses of the radioactive isotopes 62Ga, 62Zn and 62Cu have been measured at the JYFLTRAP facility with a relative precision of better than 18 ppb. A Q_EC value of (9181.07 +- 0.54) keV for the superallowed decay of 62Ga is obtained from the measured
cyclotron frequency ratios of 62Ga-62Zn, 62Ga-62Ni and 62Zn-62Ni ions. The resulting Ft-value supports the validity of the conserved vector current hypothesis (CVC). The mass excess values measured were (-51986.5 +-1.0) keV for 62Ga, (-61167.9 +- 0.9) keV for 62Zn and (-62787.2 +- 0.9) keV for 62Cu.
The cyclotron frequency ratio of $^{187}mathrm{Os}^{29+}$ to $^{187}mathrm{Re}^{29+}$ ions was measured with the Penning-trap mass spectrometer PENTATRAP. The achieved result of $R=1.000:000:013:882(5)$ is to date the most precise such measurement pe
rformed on ions. Furthermore, the total binding-energy difference of the 29 missing electrons in Re and Os was calculated by relativistic multiconfiguration methods, yielding the value of $Delta E = 53.5(10)$ eV. Finally, using the achieved results, the mass difference between neutral $^{187}$Re and $^{187}$Os, i.e., the $Q$ value of the $beta^-$ decay of $^{187}$Re, is determined to be 2470.9(13) eV.
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 measureme
nt 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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