Superallowed Fermi Decay Research Articles

Status of the TAMUTRAP facility and initial characterization of the RFQ cooler/buncher

The Texas A&M University Penning Trap experiment (TAMUTRAP) is an upcoming ion trap facility that will be used to search for possible scalar currents in T = 2 superallowed pure Fermi decays (utilizing β-delayed proton emitters), which, if found, would be an indication of physics beyond the standard model. In addition, TAMUTRAP will provide a low-energy, point-like source of ions for various other applications at the Cyclotron Institute at Texas A&M University. The experiment is centered around a unique, compensated cylindrical Penning trap that employs a specially optimized length/radius ratio in the electrode structure that is not used by any other facility. The radioactive beam, provided by the Texas A&M University Re-accelerated Exotics (T-REX) program at the Cyclotron Institute, will be prepared for loading in the measurement trap via a specially designed Radio Frequency Quadrupole (RFQ) cooler/buncher. These proceedings will describe the current status of the TAMUTRAP facility, paying particular attention to the design and initial characterization of the RFQ cooler/buncher. Future plans will also be discussed.

High-precision half-life and branching-ratio measurements for superallowed Fermiβ+emitters at TRIUMF – ISAC

A program of high-precision half-life and branching-ratio measurements for superallowed Fermi emitters is being carried out at TRIUMF's Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. Recent half-life measurements for the superallowed decays of 14 O, 18 Ne, and 26 Al m , as well as branching-ratio measurements for 26 Al m and 74 Rb are reported. These results provide demanding tests of the Standard Model and the theoretical isospin symmetry breaking (ISB) corrections in superallowed Fermi decays.

βdecay of32Cl: Precisionγ-ray spectroscopy and a measurement of isospin-symmetry breaking

Background: Models to calculate small isospin-symmetry-breaking effects in superallowed Fermi decays have been placed under scrutiny in recent years. A stringent test of these models is to measure transitions for which the correction is predicted to be large. The decay of ${}^{32}$Cl decay provides such a test case.Purpose: The purpose of this paper is to improve the $\ensuremath{\gamma}$ yields following the $\ensuremath{\beta}$ decay of ${}^{32}$Cl and to determine the $ft$ values of the the $\ensuremath{\beta}$ branches, particularly the one to the isobaric-analog state in ${}^{32}$S.Method: Reaction-produced and recoil-spectrometer-separated ${}^{32}$Cl is collected in a tape and transported to a counting location where $\ensuremath{\beta}\ensuremath{-}\ensuremath{\gamma}$ coincidences are measured with a precisely calibrated high-purity germanium detector.Results: The precision on the $\ensuremath{\gamma}$ yields for most of the known $\ensuremath{\beta}$ branches has been improved by about an order of magnitude, and many new transitions have been observed. We have determined ${}^{32}$Cl-decay transition strengths extending up to ${E}_{x}\ensuremath{\sim}11$ MeV. The $ft$ value for the decay to the isobaric-analog state in ${}^{32}$S has been measured. A comparison to a shell-model calculation shows good agreement.Conclusions: We have experimentally determined the isospin-symmetry-breaking correction to the superallowed transition of this decay to be ${({\ensuremath{\delta}}_{C}\ensuremath{-}{\ensuremath{\delta}}_{\mathrm{NS}})}_{\mathrm{exp}}=5.4(9)%$, significantly larger than for any other known superallowed Fermi transition. This correction agrees with a shell-model calculation, which yields ${\ensuremath{\delta}}_{C}\ensuremath{-}{\ensuremath{\delta}}_{\mathrm{NS}}=4.8(5)%$. Our results also provide a way to improve the measured $ft$ values for the $\ensuremath{\beta}$ decay of ${}^{32}$Ar.

Q-value for the Fermi beta-decay of 46V

By comparing the Q -values for the 46Ti ( 3He , t 46V and 47Ti ( 3He , t 47V reactions to the isobaric analogue states the Q -value for the superallowed Fermi decay of 46V has been determined as Q EC( ^46V ) = (7052.11±0.27) keV. The result is compatible with the values from two recent direct mass measurements but is at variance with the previously most precise reaction Q -value. As additional input quantity we have determined the neutron separation energy S n( ^47Ti ) = (8880.51±0.25) keV.

QValue of the Superallowed Decay ofV46and Its Influence onVudand the Unitarity of the Cabibbo-Kobayashi-Maskawa Matrix

The masses of the radioactive nuclei (46)V and its decay daughter (46)Ti have been measured with the Canadian Penning Trap on-line Penning trap mass spectrometer to a precision of 1 x 10(-8). A Q(EC) value of 7052.90(40) keV for the superallowed beta decay of (46)V is obtained from the difference of these two masses. With this precise Q value, the Ft value for this decay is determined with improved precision. An investigation of an earlier Q-value measurement for (46)V uncovers a set of 7 measurements that cannot be reconciled with modern data and affects previous evaluations of V(ud) from superallowed Fermi decays. A new evaluation, adding our new data and removing the discredited subset, yields new values for G(V) and V(ud). When combined with recent results for V(us), this yields modified constraints for the unitarity of the Cabibbo-Kobayashi-Maskawa matrix and other extensions of the standard model.

Gamow-Teller strength in theO14→N14(3.948 MeV) beta decay

The Gamow-Teller ..beta.. decay from the /sup 14/O 0/sup +/ ground state to the 3.948 MeV 1/sup +/ level in /sup 14/N has been studied by observing ..gamma.. rays from the deexcitation of the 3.948 and 2.313 MeV levels in /sup 14/N. We measured a branching ratio of (5.28 +- 0.23) x 10/sup -4/ relative to the superallowed Fermi decay to the 2.313 MeV level, and deduce ft = 1446 +- 63. The corresponding Gamow-Teller transition strength is B(GT) = 2.73 +- 0.12. This value is about 40% lower than that predicted by several widely used shell model calculations, and may suggest appreciable quenching by mesonic currents.

New Isotopes of Interest to Explosive Nucleosynthesis

A number of new isotopes in the iron region, both neutron-rich and proton-rich, have been produced at the Argonne FN tandem using heavy-ion beams. On the neutron-rich side, masses and beta-decay schemes have been obtained, and the masses will be compared with various mass formulae used in nucleosynthesis calculations. Several heavy proton-rich N = Z odd-odd nuclei extending up from 62Ga have been investigated with the aim of measuring the ft-values of their superallowed Fermi decays. The resulting ft-values will be compared with those found for the well-studied lighter nuclei between 14O and 54Co.

The end-point energy of the superallowed Fermi decay of38mK

The threshold for the 38Ar(p,n)38K reaction has been measured relative to the thresholds for 10B(p,n)10C and 14N(p,n)14O. The value deduced for the 38mK beta endpoint energy, 5020.71+or-0.85 keV, enhances the evidence for a trend of ft with Z.

A measurement of the half-life of the superallowed Fermi decay [formula omitted] and a study of some systematic errors involved

The half-life for 46V positon decay has been determined with high precision. Particular care has been taken to eliminate systematic effects introduced by inappropriate data analysis methods, by the presence of contaminant activities and by the occurrence of pulse pile-up in the electronic system. The final result obtained is 422.28 ± 0.23 ms, which is significantly lower than the presently accepted value.

The ft value of the superallowed Fermi decay [formula omitted

The 46 Ti(p, n) 46 V reaction threshold has been measured as 8007.7 ± 1.8 keV, equivalent to an energy release of 6030.6 ± 1.8 keV in the beta decay 46 V(β +) 46 Ti . The 46 V half-life has been measured as 422.28 + 0.23 ms. The corresponding ft value is reasonably consistent with those of other superallowed Fermi decays.

The half-life for the superallowed fermi beta decay 50Mn(β +) 50Cr

The half-life for the decay 50Mn(β +) 50Cr has been measured to be 282.8 ± 0.3 ms. This result is ≈ 1% lower than the accepted value. It would bring the ft value for 50Mn decay into agreement with recent measurements for other superallowed Fermi decays.

The ft value for the superallowed fermi decay [formula omitted

The threshold for the reaction 54Fe(p,n) 54Co has been measured as 9192.4±1.8 keV. The corresponding end-point energy for the superallowed Fermi decay 54Co(β +) 54Fe is 7218.5 ± 1.8 keV. The half-life for 54Co decay was found to be 193.0 ± 0.3 ms. The calculated “effective” ft value is in good agreement with those of 14O, 26Al m and 34Cl.

The half-life of 14O and the ft value of the superallowed Fermi decay

A series of experiments has been carried out to measure the half-life for 14O decay, using different reactions and a variety of techniques, in two laboratories. Considerable care has been taken in the experiments, and in the data analyses, to reduce the possibility of systematic errors. The final result obtained is 70.588 ± 0.028 s, where the error is the statistical standard deviation (external error) of the weighted mean. This leads to an ft value for the 0 + → 0 + superallowed 14O Fermi decay of 3050 ± 11 s, excluding electromagnetic radiative corrections; the corresponding “effective” ft value is 3090 ± 11 s, allowing for the first-order outer radiative correction. The error quoted for the ft value is determined very largely by the error in the f-value. This result for the 14O Fermi decay is consistent with the ft values for the 26mAl and 34Cl decays.

The superallowed Fermi decay of 34Cl and the vector weak interaction

The half-life for the superallowed Fermi decay of 34 Cl has been measured to be 1.526 ± 0.002 s, and the beta end-point energy, 4467.4 ± 1.9 keV. The deduced ft value is in good agreement with that for 26 Al m . The result provides no evidence for mirror asymmetry in mass 34 Fermi decays.

A new measurement of the branching ratio for 10C superallowed Fermi decay and its significance for the weak vector interaction

Abstract The branching ratio for the pure Fermi decay 10 C(β + ) 10 B ∗∗ to the second excited state of 10 B has been measured by an accurate determination of the ratio of the intensities of 1.022 and 0.718 MeV γ-rays following this decay and the Gamow-Teller transition to the first excited state of 10 B. Computer programmes were devised for accurate analysis of the intensities of the full energy peaks obtained with a Ge(Li) detector, and for deducing the detector relative efficiency from calibration source data. The results were averaged with those from previous measurements of comparable accuracy to give β 1 = (98.53 ±0.02) % and β 2 = (1.465 ± 0.014) % as the best values of the branching ratios for positon decay to the first and second excited states of 10 B respectively. The ft value of the Fermi transition was deduced as 3155±40 s with radiative corrections, and the corresponding vector coupling constant as G β V = (1.396 ± 0.009) × 10 −49 erg · cm 3 .

Superallowed Fermi decay of 14O and its relevance to weak interaction theory

A new measurement of the half-life for 14O decay has been made, giving the result 70.580 ± 0.035 s. This brings the ft value for the pure Fermi decay of 14O into agreement with the value for 26Al m, and gives support to the recent estimate of a lower limit to the mass of the intermediate vector boson.

The ft value of the superallowed fermi beta decay 26mAl( β+) 26Mg

The threshold for the reaction 26Mg(p, n) 26mAl has been measured in terms of the accurately known energies of the α-particle groups from a ThC source. The result E th = 5208.5 ± 1.7 keV corresponds to a Q-value of −5013.5 ± 1.6 keV. The weighted mean of this and an earlier independent Q-value measurement gives for the end-point in the beta decay 26mAl( β +) 26Mg the result 3208.6±1.3 keV. The half-life for the beta decay has been measured as 6.346±0.005 sec. The ft value for the transition is thus found to be 3081±7 sec, including radiative corrections. This result is lower than those for other superallowed Fermi decays. It corresponds to a value for the vector coupling constant G β v = (1.4129±0.0016) x 10 −49 erg · cm 3. The value inferred for the Cabibbo angle is cos θ β v = 0.985±0.001, excluding uncertainties in the radiative corrections. This result appears to differ appreciably from the value inferred from the rate of K + → π 0e + v decay.