Publications (70)115.95 Total impact

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ABSTRACT: We present the full description of a measurement of the branching ratios for the betadecay 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 updown quarkmixing 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 isospinsymmetrybreaking corrections required for the extraction of Vud. 
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ABSTRACT: Precise measurements are being used to test theoretical Kshell internal conversion coefficients (ICCs): in particular, our program has focused on examining whether the atomic Kvacancy formed during the conversion process must be incorporated into the calculations. We report here a measurement on the 65.66keV, M4 isomeric transition in 119Sn. Our preliminary result is αK=1610(27)αK=1610(27), which confirms the importance of including the vacancy in the ICC calculations.Nuclear Data Sheets 06/2014; 120:91–94. DOI:10.1016/j.nds.2014.07.015 · 3.35 Impact Factor 
Article: β
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ABSTRACT: We report the first branchingratio measurement of the superallowed 0+→0+β transition from Ca38. 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 highprecision comparison of the ft values for the mirror superallowed transitions, Ca38→38mK and K38m→Ar38, which sensitively tests the isospin symmetrybreaking corrections required to extract Vud, the updown quarkmixing element of the CabibboKobayashiMaskawa (CKM) matrix, from superallowed β decay. The result supports the corrections currently used and points the way to even tighter constraints on CKM unitarity.Physical Review Letters 03/2014; 112(10):102502. · 7.73 Impact Factor 
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ABSTRACT: We report the first branchingratio measurement of the superallowed 0+to0+ 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 highprecision comparison of the ft values for the mirror superallowed transitions, 38Cato38mK and 38mKto38Ar, which sensitively tests the isospin symmetrybreaking corrections required to extract Vud, the updown quarkmixing element of the CabibboKobayashiMaskawa (CKM) matrix, from superallowed beta decay. The result supports the corrections currently used, and points the way to even tighter constraints on CKM unitarity.Physical Review Letters 01/2014; 112(10). DOI:10.1103/PhysRevLett.112.102502 · 7.73 Impact Factor 
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ABSTRACT: We have measured the Kshell internal conversion coefficient, alphaK, for the 65.7keV M4 transition in 119Sn to be 1621(25). This result agrees well with DiracFock calculations in which the effect of the Kshell 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.Physical Review C 12/2013; 89(1). DOI:10.1103/PhysRevC.89.014303 · 3.88 Impact Factor 
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ABSTRACT: In a research program aimed at testing calculated internalconversion coefficients (ICCs), we have made precise measurements of a(K) values for transitions in five nuclei, Pt197, Ir193; Ba137, Cs134 and Sn119, which span a wide range of A and Z values. In all cases, the results strongly favor calculations in which the finalstate electron wave function has been computed using a potential that includes the atomic vacancy created by the internalconversion process. (c) 2013 Elsevier Ltd. All rights reserved.Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine 11/2013; 87. DOI:10.1016/j.apradiso.2013.11.033 · 1.09 Impact Factor 
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ABSTRACT: Because of angularmomentum conservation, superallowed β decay between 0(+) analog states involves only the vector part of the weak interaction, so its measured ft value can be used to determine the vector coupling constant, GV. If many such transitions are measured, then the constancy of GV can be established and several important tests made on fundamentals of the electroweak Standard Model. We have developed apparatus that allows us to measure halflives to ±0.03% and branching ratios to ±0.1% or better, for cyclotronproduced activities with halflives as short as 100ms. We present an overview of the equipment and a summary of more than 10 years of results.Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine 11/2013; 87. DOI:10.1016/j.apradiso.2013.11.018 · 1.09 Impact Factor 
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ABSTRACT: A digital βcounting method has been developed for highprecision nuclear βdecay halflife experiments that use a gas proportional counter. An 8bit, 1GS/s samplingrate digitizer was used to record the waveforms from the detector and a software filter was designed, tested and applied successfully to discriminate genuine βdecay events from spurious signals by pulseshape analysis. The method of using a highspeed digitizer for precision β counting is described in detail. We have extensively tested the digitizer and the offline filter by analyzing saved waveforms from the decay of Alm26 acquired at rates up to 10,000 per second. The halflife we obtain for Alm26 is 6345.30±0.90 ms, which agrees well with previous published measurements and is as precise as the best of them. This work demonstrates the feasibility of applying a highspeed digitizer and offline digital signal processing techniques for highprecision nuclear βdecay halflife measurements.Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 11/2013; 728:8191. DOI:10.1016/j.nima.2013.06.039 · 1.32 Impact Factor 
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ABSTRACT: We made a preliminary measurement of the Kshell internal conversion coefficient, αK, for the 65.7 keV M4 transition from ^119mSn, with the result 1645±27. This result agrees with 1618, the value obtained with the ``Frozen Orbital'' method to describe the electron vacancy when calculating the ICC. If the vacancy is not included, the calculated value of the ICC is 1544, nearly four standard deviations away from our preliminary result. Our value was achieved by a measurement of the γray and K xrays from ^119mSn with an efficiencycalibrated highpurity Germanium detector. However, work is still needed to include the effects of scattering in our detector's efficiency calibration in the range of the K xrays. Despite this, our preliminary measurement indicates better agreement with the calculation that includes the vacancy, as is physically expected. 
Dataset: savedrecs(4)

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ABSTRACT: Currently, the most stringent test of the unitarity of the CKM matrix depends on results from precise ftvalue measurements of superallowed beta decays. One of the key elements of this test is the calculated isospinsymmetrybreaking (ISB) correction that must be applied to each experimental ft value in order to extract a corrected Ft value. According to conserved vector current, the Ft values for all such transitions should be the same, so the efficacy of a particular set of ISB correction terms can be judged by whether they satisfy this condition. This test becomes even more demanding if additional superallowed ft values can be measured, especially for cases where the ISB correction is expected to be unusually large. The case of ^38Ca is particularly interesting because its total ISB correction is calculated to be one of the largest in the sd shell. However, being a TZ=1 nucleus decaying to an oddodd TZ=0 daughter, it has multiple betadecay branches. This presentation focuses on progress in our measurement of the branchingratio for the superallowed 0^+>0^+ transition from ^38Ca. The challenges remaining before we reach our goal of 0.1% precision will be discussed, and preliminary results presented. 
Article: β decay of^{32} Cl: Precision γray spectroscopy and a measurement of isospinsymmetry breaking
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ABSTRACT: Background: Models to calculate small isospinsymmetrybreaking 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: The purpose of this paper is to improve the γ yields following the β decay of 32Cl and to determine the ft values of the the β branches, particularly the one to the isobaricanalog state in 32S.Method: Reactionproduced and recoilspectrometerseparated 32Cl is collected in a tape and transported to a counting location where βγ coincidences are measured with a precisely calibrated highpurity germanium detector.Results: The precision on the γ yields for most of the known β branches has been improved by about an order of magnitude, and many new transitions have been observed. We have determined 32Cldecay transition strengths extending up to Ex∼11 MeV. The ft value for the decay to the isobaricanalog state in 32S has been measured. A comparison to a shellmodel calculation shows good agreement.Conclusions: We have experimentally determined the isospinsymmetrybreaking correction to the superallowed transition of this decay to be (δC−δNS)exp=5.4(9)%, significantly larger than for any other known superallowed Fermi transition. This correction agrees with a shellmodel calculation, which yields δC−δNS=4.8(5)%. Our results also provide a way to improve the measured ft values for the β decay of 32Ar.Physical Review C 02/2012; 85(2). DOI:10.1103/PhysRevC.85.025501 · 3.88 Impact Factor 
Article: Nuclear Data Sheets for A=36
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ABSTRACT: Nuclear spectroscopic information for experimentally investigated nuclides of mass 36 (Mg, Al, Si, P, S, Cl, Ar, K, Ca) has been evaluated. The principal sources of the 'adopted levels' presented for nuclides close to the stability line are Endt's evaluations (1990En08, 1978En02). The data sets for reactions and decays, including all available gammaray data, are based mostly on the original literature. The Â³â¶Na has been looked for but not yet experimentally detected. There are no data available for the excited states in Â³â¶Al, and for Â³â¶Mg and Â³â¶Ca, only one excited state is known.Nuclear Data Sheets 01/2012; 113(1). DOI:10.1016/j.nds.2012.01.001 · 3.35 Impact Factor 
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ABSTRACT: The halflife 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 bestknown superallowed transitions.Physical Review C 12/2011; DOI:10.1103/PhysRevC.84.065502 · 3.88 Impact Factor 
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ABSTRACT: Background: Models to calculate small isospinsymmetrybreaking 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 isobaricanalogue state in 32S. Method: Reactionproduced and recoilspectrometerseparated 32Cl is collected in tape and transported to a counting location where betagamma coincidences are measured with a preciselycalibrated 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 32Cldecay transition strengths extending up to E_x~11 MeV. The ft value for the decay to the isobaricanalogue state in 32S has been measured. A comparison to a shellmodel calculation shows good agreement. CONCLUSIONS: We have experimentally determined the isospinsymmetrybreaking correction to the superallowed transition of this decay to be (\delta_C\delta_NS)_exp=5.4(9)%, significantly larger than for any other known superallowed Fermi transition. This correction agrees with a shellmodel calculation, which yields \delta_C\delta_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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ABSTRACT: A precision measurement of the γ yields following the β decay of (32)Cl has determined its isobaricanalogue branch to be (22.47(0.18)(+0.21))%. Since it is an almost pureFermi decay, we can also determine the amount of isospinsymmetry breaking in this superallowed transition. We find a very large value, δ(C) = 5.3(9)%, in agreement with a shellmodel calculation. This result sets a benchmark for isospinsymmetrybreaking calculations and lends support for similarly calculated, yet smaller, corrections that are currently applied to 0+ → 0 + transitions for tests of the standard model.Physical Review Letters 10/2011; 107(18):182301. DOI:10.1103/PhysRevLett.107.182301 · 7.73 Impact Factor 
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ABSTRACT: Precise internal conversion coefficients (ICCs) are vital to the study of nuclear decay schemes, determining transition rates, spin and parity designations, and branching ratios. However, there are very few experimental tests of the calculated ICC's and in fact there are only ˜10 measurements available with errors of less than 1%. Such a paucity of data complicates scientists' efforts to determine what theoretical calculations should be used to model the ICC. The goal of our present experiment is to determine the αk for the 65.7keV M4 transition in ^119Sn. However, the energy of the ^119Sn xrays is below the energy range that our HPGe detector is accurately calibrated for. The βdecay of ^116In populates states in ^116Sn which produce a few strong transitions with well established conversion coefficients. This allows us to calibrate our detector at the energy of the Sn xrays, which is an essential requirement for the measurement of the ^119Sn ICC. 
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ABSTRACT: To test the unitarity of the CKM matrix via precise measurements of superallowed 0^+>0^+ nuclear &+circ; decay, accurate calculations of small nuclear structuredependent corrections are essential. Currently, uncertainties in these calculations are comparable to the present level of experimental precision. However, these theoretical uncertainties can, in principle, be reduced by experiment. ^38Ca is a particularly favorable case for this purpose because its nuclearstructuredependent correction term is calculated to be one of the largest in the sd shell [1]. We report our measured halflife to be 443.88(36) ms and the first preliminary results from a branchingratio measurement. Combined with the wellknown QEC value [1,2], these two results will ultimately lead to a precise Ft value for ^38Ca, and a valuable test of the calculated nuclear structuredependent correction term.[4pt] [1] J.C. Hardy and I.S. Towner, Phys. Rev. C 79, 055502 (2009).[0pt] [2] T. Eronen et al., to be published. 
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ABSTRACT: The ^46V is one of the key superallowed transitions contributing to precision tests of the conserved vector current hypothesis and the unitarity of the CabibboKobayashiMaskawa matrix. Recent Penningtrap QEC measurements of the superallowed beta decay of ^46V showed an earlier reactionbased result to be wrong and raised the Ft value by nearly three standard deviations from the average of all other wellknown superallowed transitions. This anomaly raised the possibility of systematic effects for all reactionbased Q value measurements and led to a theoretical reexamination of the isospinsymmetrybreaking corrections for superallowed decays. The improved corrections removed the anomalous result of ^46V and restored agreement among the corrected Ft values. Throughout these changes, the previously accepted half life of ^46V was assumed to be completely correct. We have now tested this assumption by measuring a new precise halflife of ^46V. The preliminary result, 422.67(10) ms, agrees with but is more precise than previous values. 
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ABSTRACT: We have measured the halflife of the beta decay of 198Au to be 2.6948(9) d, with the nuclide sited in an insulating environment. Comparing this result with the halflife we measured previously with a metallic environment, we find the halflives in both environments to be the same within 0.04%, thus contradicting a prediction that screening from a "plasma" of quasifree electrons in a metal increases the halflife by as much as 7%.Physical Review C 09/2010; 82(4). DOI:10.1103/PHYSREVC.82.044320 · 3.88 Impact Factor
Publication Stats
256  Citations  
115.95  Total Impact Points  
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Institutions

2004–2015

Texas A&M University
 Cyclotron Institute
College Station, Texas, United States


2005–2009

Horia Hulubei National Institute of Physics and Nuclear Engineering
Bucureşti, Bucureşti, Romania


2001

French National Centre for Scientific Research
Lutetia Parisorum, ÎledeFrance, France
