N. Nica

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

Are you N. Nica?

Claim your profile

Publications (69)95.1 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Precise measurements are being used to test theoretical K-shell internal conversion coefficients (ICCs): in particular, our program has focused on examining whether the atomic K-vacancy formed during the conversion process must be incorporated into the calculations. We report here a measurement on the 65.66-keV, 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. · 2.67 Impact Factor
  • Article: β
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the first branching-ratio 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 high-precision comparison of the ft values for the mirror superallowed transitions, Ca38→38mK and K38m→Ar38, 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 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
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    01/2014; 112(10).
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Physical Review C 12/2013; 89(1). · 3.72 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In a research program aimed at testing calculated internal-conversion coefficients (ICCs), we have made precise measurements of αK values for transitions in five nuclei, (197)Pt, (193)Ir, (137)Ba, (134)Cs and (119)Sn, which span a wide range of A and Z values. In all cases, the results strongly favor calculations in which the final-state electron wave function has been computed using a potential that includes the atomic vacancy created by the internal-conversion process.
    Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine 11/2013; · 1.09 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Because of angular-momentum 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 half-lives to ±0.03% and branching ratios to ±0.1% or better, for cyclotron-produced activities with half-lives 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; · 1.09 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A digital β-counting method has been developed for high-precision nuclear β-decay half-life experiments that use a gas proportional counter. An 8-bit, 1-GS/s sampling-rate digitizer was used to record the waveforms from the detector and a software filter was designed, tested and applied successfully to discriminate genuine β-decay events from spurious signals by pulse-shape analysis. The method of using a high-speed digitizer for precision β counting is described in detail. We have extensively tested the digitizer and the off-line filter by analyzing saved waveforms from the decay of Alm26 acquired at rates up to 10,000 per second. The half-life 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 high-speed digitizer and off-line digital signal processing techniques for high-precision nuclear β-decay half-life measurements.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 11/2013; · 1.14 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We made a preliminary measurement of the K-shell 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 γ-ray and K x-rays from ^119mSn with an efficiency-calibrated high-purity 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 x-rays. Despite this, our preliminary measurement indicates better agreement with the calculation that includes the vacancy, as is physically expected.
    10/2012;
  • Source
  • [Show abstract] [Hide abstract]
    ABSTRACT: Currently, the most stringent test of the unitarity of the CKM matrix depends on results from precise ft-value measurements of superallowed beta decays. One of the key elements of this test is the calculated isospin-symmetry-breaking (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 odd-odd TZ=0 daughter, it has multiple beta-decay branches. This presentation focuses on progress in our measurement of the branching-ratio 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.
    03/2012;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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: 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 isobaric-analog state in 32S.Method: Reaction-produced and recoil-spectrometer-separated 32Cl is collected in a tape and transported to a counting location where β-γ coincidences are measured with a precisely calibrated high-purity 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 32Cl-decay transition strengths extending up to Ex∼11 MeV. The ft value for the decay to the isobaric-analog 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 (δC−δNS)exp=5.4(9)%, significantly larger than for any other known superallowed Fermi transition. This correction agrees with a shell-model 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). · 3.72 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Physical Review C 12/2011; · 3.72 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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 (\delta_C-\delta_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 \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.
    12/2011;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A precision measurement of the γ yields following the β decay of (32)Cl has determined its isobaric-analogue branch to be (22.47(-0.18)(+0.21))%. Since it is an almost pure-Fermi decay, we can also determine the amount of isospin-symmetry breaking in this superallowed transition. We find a very large value, δ(C) = 5.3(9)%, in agreement with a shell-model calculation. This result sets a benchmark for isospin-symmetry-breaking 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. · 7.73 Impact Factor
  • [Show abstract] [Hide abstract]
    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 65.7-keV M4 transition in ^119Sn. However, the energy of the ^119Sn x-rays is below the energy range that our HPGe detector is accurately calibrated for. The β-decay 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 x-rays, which is an essential requirement for the measurement of the ^119Sn ICC.
    10/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: To test the unitarity of the CKM matrix via precise measurements of superallowed 0^+->0^+ nuclear &+circ; decay, accurate calculations of small nuclear- structure-dependent 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 nuclear-structure-dependent correction term is calculated to be one of the largest in the sd shell [1]. We report our measured half-life to be 443.88(36) ms and the first preliminary results from a branching-ratio measurement. Combined with the well-known 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- structure-dependent 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.
    04/2011;
  • [Show abstract] [Hide abstract]
    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 Cabibbo-Kobayashi-Maskawa matrix. Recent Penning-trap QEC measurements of the superallowed beta decay of ^46V showed an earlier reaction-based result to be wrong and raised the Ft value by nearly three standard deviations from the average of all other well-known superallowed transitions. This anomaly raised the possibility of systematic effects for all reaction-based Q- value measurements and led to a theoretical reexamination of the isospin-symmetry-breaking 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 half-life of ^46V. The preliminary result, 422.67(10) ms, agrees with but is more precise than previous values.
    11/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have measured the half-life 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 half-life we measured previously with a metallic environment, we find the half-lives in both environments to be the same within 0.04%, thus contradicting a prediction that screening from a "plasma" of quasi-free electrons in a metal increases the half-life by as much as 7%.
    Physical Review C 09/2010; · 3.72 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We measured the half-life of the superallowed 0{sup +â}0{sup +} β{sup +} emitter ²⁶Si to be 2245.3(7) ms. We used pure sources of ²⁶Si and employed a high-efficiency gas counter, which was sensitive to positrons from both this nuclide and its daughter ²⁶Al{sup m}. The data were analyzed as a linked parent-daughter decay. To contribute meaningfully to any test of the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, the ft value of a superallowed transition must be determined to a precision of 0.1% or better. With a precision of 0.03%, the present result is more than sufficient to be compatible with that requirement. Only the branching ratio now remains to be measured precisely before a {+-}0.1% ft value can be obtained for the superallowed transition from ²⁶Si.
    Physical Review C - PHYS REV C. 08/2010; 82(3):035502-035502.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Indirect techniques have been used to obtain information about reaction rates for several proton capture reactions that occur on short-lived nuclei. The techniques used to carry out the measurements are reviewed and the results obtained are presented. Also future prospects for further measurements with a new facility, T-REX are discussed.
    08/2010;

Publication Stats

137 Citations
95.10 Total Impact Points

Institutions

  • 2004–2014
    • Texas A&M University
      • Cyclotron Institute
      College Station, Texas, United States
    • Idaho State University
      • Idaho Accelerator Center
      Pocatello, ID, United States
  • 2005–2009
    • Horia Hulubei National Institute of Physics and Nuclear Engineering
      Bucureşti, Bucureşti, Romania
  • 2007–2008
    • Petersburg Nuclear Physics Institute
      Krasnogwardeisk, Leningrad, Russia