arXiv subjects

J. C. Hardy

Publications and source records attributed to J. C. Hardy.

At least 19 recordsLinked to original sources

arXiv2018

Precise measurement of $α_K$ and $α_T$ for the 39.8-keV $E$3 transition in $^{103}$Rh: Test of internal-conversion theory

Neutron-activated sources of $^{103}$Ru and $^{103}$Pd both share the isomeric first-excited state in $^{103}$Rh as a daughter product. From independent measurements of both decays, we have measured the $K$-shell and total internal conversion coefficients, $α_K$ and $α_T$, for the 39.8-keV $E$3 transition, which de-excites that state in $^{103}$Rh, to be 141.1(23) and 1428(13), respectively. When compared with Dirac-Fock calculations, our new results disagree with the version of the theory that ignores the $K$-shell atomic vacancy, which is consistent with our conclusion drawn from a series of measurements on high multipolarity transitions in nuclei with higher $Z$. Calculations that include the atomic vacancy indicate that the transition actually has a small $M$4 component with mixing ratio $δ$ = 0.023(5).

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arXiv2018

Nuclear beta decays and CKM unitarity

Nuclear beta decays between (J^pi,T) = (0^+,1) analog states yield the best value for the Vud element of the Cabibbo-Kobayashi-Maskawa matrix. Current world data establish the corrected Ft values of 14 separate superallowed transitions to a precision of order 0.1% or better. The validity of the small theoretical correction terms is confirmed by excellent consistency among the 14 Ft values and by recent measurements that compare pairs of mirror superallowed transitions. With consistency established, the results now yield |Vud| = 0.97420(21). This value is consistent with the considerably less precise results obtained from beta decays of the neutron, the pion and T=1/2 mirror nuclei, which are hampered by experimental challenges.

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arXiv2018

Precise half-life measurement of the superallowed emitter 30S

We have measured the half-life of 30S, the parent of a superallowed 0+-to-0+ beta transition, to high precision using very pure sources and a 4pi proportional gas counter to detect the decay positrons. Our result for the half-life is 1.17992(34) s. As a byproduct of this measurement, we determined the half-life of its daughter, 30P, to be 2.501(2) min.

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arXiv2017

Precise Test of Internal-Conversion Theory: alpha_K Measurements for Transitions in Nine Nuclei Spanning Z values from 45 to 78

We have been testing the theory used to calculate internal-conversion coefficients (ICCs) by making a series of measurements of alpha_K values with precision better than +/-2%. So far we have measured E3 transitions in three nuclei, 103Rh, 111Cd and 134Cs; and M4 transitions in six nuclei, 119Sn, 125Te, 127Te, 137Ba, 193Ir and 197Pt. Together, these span a wide range of A and Z values. In all cases, the results strongly favor Dirac-Fock calculations in which the final-state electron wave function has been computed in an atomic field that includes the vacancy created by the internal-conversion process.

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arXiv2017

Precise measurement of alpha_K and alpha_T for the 109.3-keV M4 transition in 125Te: Test of internal-conversion theory

We have measured the K-shell and total internal conversion coefficients (ICCs), alpha_K and alpha_T, for the 109.3-keV M4 transition in 125Te to be 185.0(40) and 350.0(38), respectively. Previously this transition's ICCs were considered anomalous, with alpha values lying below calculated values. When compared with Dirac-Fock calculations, our new results show good agreement. The alpha_K result agrees well with the version of the theory that takes account of the K-shell atomic vacancy and disagrees with the one that does not. This is consistent with our conclusion drawn from a series of high multipolarity transitions.

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arXiv2017

Precise measurement of alpha_K for the 88.2-keV M4 transition in 127Te: Test of internal-conversion theory

We have measured the K-shell internal conversion coefficient, alpha_K, for the 88.2-keV M4 transition from the 106-day isomer to the ground state in 127Te to be 484(6). When compared with Dirac-Fock calculations of alpha_K, this result agrees well with the version of the theory that incorporates the effect of the K-shell atomic vacancy and disagrees with the one that does not. As a byproduct of this measurement, we have determined the beta branching from the isomer to be 2.14(3)%.

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arXiv2015

Precise measurement of alpha_K and alpha_T for the 150.8-keV E3 transition in 111Cd: Test of internal-conversion theory

We have measured the K-shell and total internal conversion coefficients, alpha_K and alpha_T, for the 150.8-keV E3 transition in 111Cd to be 1.449(18) and 2.217(26) respectively. The alpha_K result agrees well with Dirac-Fock calculations in which the effect of the K-shell atomic vacancy is accounted for; it extends our precision tests of alpha_K calculations to Z = 48, the lowest Z yet measured. However, the result for alpha_T disagrees by about two standard deviations from the calculated alpha_T value, whether or not the atomic vacancy is included.

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arXiv2015

Theoretical corrections and world data for the superallowed ft values in the beta decays of 42Ti, 46Cr, 50Fe and 54Ni

Prompted by recent measurements, we have surveyed world data and calculated radiative and isospin-symmetry breaking corrections for the superallowed 0+ -to- 0+ Fermi transitions from 42Ti, 46Cr, 50Fe and 54Ni. This increases the number of such transition with a complete set of calculated corrections from 20 to 23. The results are compared with their equivalents for the mirror superallowed transitions from 42Sc, 46V, 50Mn and 54Co. The predicted ft-value asymmetries of these mirror pairs are sensitive to the correction terms and provide motivation for improving measurement precision so as to be able to test the corrections. To aid in that endeavor, we present a parameterization for calculating the f values for the new transitions to plus/minus 0.01%.

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arXiv2015

The current evaluation of Vud

The Vud element of the Cabibbo-Kobayashi-Maskawa matrix can be determined from several different experimental approaches: either 0+-to-0+ superallowed nuclear beta decays, neutron decay, nuclear mirror decays, or pion beta decay. Currently all give consistent results but, because the nuclear superallowed value has an uncertainty at least a factor of seven less than all other results, it dominates the result. A new survey of world superallowed-decay data establishes the Ft values of 14 separate superallowed transitions to a precision of order 0.1% or better; and all 14 are statistically consistent with one another. This very robust data set yields the result Vud = 0.97417(21), the value we recommend.

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arXiv2015

Precise measurement of branching ratios in the beta decay of 38Ca

We present the full description of a measurement of the branching ratios for the beta-decay of 38Ca. This decay includes five allowed 0+ --> 1+ branches and a superallowed 0+ --> 0+ one. With our new result for the latter, we determine its ft value to be 3062.3(68) s, a result whose precision (0.2%) is comparable to the precision of the thirteen well known 0+ --> 0+ transitions used up till now for the determination of Vud, the up-down quark-mixing element of the CKM matrix. The 38Ca superallowed transition thus becomes the first addition to this set of transitions in nearly a decade and the first for which a precise mirror comparison is possible, thus enabling an improved test of the isospin-symmetry-breaking corrections required for the extraction of Vud.

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arXiv2014

Parameterization of the statistical rate function for select superallowed transitions

We present a parameterization of the statistical rate function, f, for 20 superallowed 0+-to-0+ nuclear beta transitions between T=1 analog states, and for 18 superallowed "mirror" transitions between analog T=1/2 states. All these transitions are of interest in the determination of V_{ud}. Although most of the transition Q_{EC} values have been measured, their precision will undoubtedly be improved in future. Our parameterization allows a user to easily calculate the corresponding new f value to high precision (+/-0.01%) without complicated computing.

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arXiv2014

Superallowed 0+ --> 0+ nuclear beta decays: 2014 critical survey, with precise results for Vud and CKM unitarity

A new critical survey is presented of all half-life, decay-energy and branching-ratio measurements related to 20 superallowed 0+ --> 0+ beta decays. Included are 222 individual measurements of comparable precision obtained from 177 published references. Compared with our last review in 2008, we have added results from 24 new publications and eliminated 9 references, the results from which having been superseded by much more precise modern data. We obtain world-average ft-values for each of the eighteen transitions that have a complete set of data, then apply radiative and isospin-symmetry-breaking corrections to extract corrected Ft values. Fourteen of these Ft values now have a precision of order 0.1% or better. In the process of obtaining these results we carefully evaluate the available calculations of the isospin-symmetry-breaking corrections by testing the extent to which they lead to Ft values consistent with conservation of the vector current (CVC). Only one set of calculations satisfactorily meets this condition. The resultant average Ft value, when combined with the muon liftime, yields the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, Vud = 0.97417 +/- 0.00021. The unitarity test on the top row of the matrix becomes |Vud|^2 + |Vus|^2 + |Vub|^2 = 0.99978 +/- 0.00055 if the Particle Data Group recommended value for Vus is used. However, recent lattice QCD calculations, not included yet in the PDG evaluation, have introduced some inconsistency into kaon-decay measurements of Vus and Vus/Vud. We examine the impact of these new results on the unitarity test and conclude that there is no evidence of any statistically significant violation of unitarity. Finally, from the Ft-value data we also set limits on the possible existence of scalar interactions.

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arXiv2014

Precision half-life measurement of the \boldmath$β^+$ decay of \tsups{37}K

The half-life of \tsups{37}K has been measured to be $1.23651(94)~\mathrm{s}$, a value nearly an order of magnitude more precise than the best previously reported. The $β^+$ decay of \tsups{37}K occurs mainly via a superallowed branch to the ground-state of its $T=1/2$ mirror, \tsups{37}Ar. This transition has been used recently, together with similar transitions from four other nuclei, as an alternative test of CVC and method for determining $V_{ud}$, but the precision of its $ft$ value was limited by the relatively large half-life uncertainty. Our result corrects that situation. Another motivation for improving the $ft$ value was to determine the standard-model prediction for the $β$-decay correlation parameters, which will be compared to those currently being measured by the \trinat{} collaboration at \triumf. The new $ft$ value, $4605(8)~\mathrm{s}$, is now limited in precision by the $97.99(14)\%$ ground-state branching ratio.

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arXiv2014

The beta decay of 38Ca: Sensitive test of isospin symmetry-breaking corrections from mirror superallowed 0+-to-0+ transitions

We report the first branching-ratio measurement of the superallowed 0+-to-0+ beta transition from 38Ca. The result, 0.7728(16), leads to an ft value of 3062.3(68)s with a relative precision of +/-0.2%. This makes possible a high-precision comparison of the ft values for the mirror superallowed transitions, 38Ca-to-38mK and 38mK-to-38Ar, which sensitively tests the isospin symmetry-breaking corrections required to extract Vud, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, from superallowed beta decay. The result supports the corrections currently used, and points the way to even tighter constraints on CKM unitarity.

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arXiv2013

Precise measurement of alpha-K for the 65.7-keV M4 transition in 119Sn: Extended test of internal-conversion theory

We have measured the K-shell internal conversion coefficient, alpha-K, for the 65.7-keV M4 transition in 119Sn to be 1621(25). This result agrees well with Dirac-Fock calculations in which the effect of the K-shell atomic vacancy is accounted for, and disagrees with calculations in which the vacancy is ignored. This extends our precision tests of theory to Z = 50, the lowest Z yet measured.

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arXiv2013

The measurement and interpretation of superallowed 0+ to 0+ nuclear beta decay

Measurements of the decay strength of superallowed 0+ to 0+ nuclear beta transitions shed light on the fundamental properties of weak interactions. Because of their impact, such measurements were first reported 60 years ago in the early 1950s and have continued unabated ever since, always taking advantage of improvements in experimental techniques to achieve ever higher precision. The results helped first to shape the Electroweak Standard Model but more recently have evolved into sensitively testing that model's predictions. Today they provide the most demanding test of vector-current conservation and of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. Here, we review the experimental and theoretical methods that have been, and are being, used to characterize superallowed 0+ to 0+ beta transitions and to extract fundamentally important parameters from their analysis.

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arXiv2011

Precise Half-Life Measurement of the Superallowed Beta+ Emitter 46V

The half-life of 46V has been measured to be 422.66(6) ms, which is a factor of two more precise than the best previous measurement. Our result is also consistent with the previous measurements, with no repeat of the disagreement recently encountered with Q_{EC} values measured for the same transition. The Ft value for the 46V superallowed transition, incorporating all world data, is determined to be 3074.1(26) s, a result consistent with the average Ft value of 3072.08(79) s established from the 13 best-known superallowed transitions.

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arXiv2011

The beta Decay of 32Cl: Precision gamma-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 32Cl decay provides such a test case. Purpose: To improve the gamma yields following the beta decay of 32Cl and to determine the ft values of the the beta branches, particularly the one to the isobaric-analogue state in 32S. Method: Reaction-produced and recoil-spectrometer-separated 32Cl is collected in tape and transported to a counting location where beta-gamma coincidences are measured with a precisely-calibrated HPGe detector. Results: The precision on the gamma yields for most of the known beta branches has been improved by about an order of magnitude, and many new transitions have been observed. We have determined 32Cl-decay transition strengths extending up to E_x~11 MeV. The ft value for the decay to the isobaric-analogue state in 32S 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 (δ_C-δ_NS)_exp=5.4(9)%, significantly larger than for any other known superallowed Fermi transition. This correction agrees with a shell-model calculation, which yields δ_C-δ_NS=4.8(5)%. Our results also provide a way to improve the measured ft values for the beta decay of 32Ar.

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