N. Nica

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

Are you N. Nica?

Claim your profile

Publications (74)124.53 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    No preview · Article · Dec 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Preview · Article · Mar 2015 · Physical Review C

  • No preview · Article · Jan 2015 · The European Physical Journal Conferences
  • N. Nica · J.C. Hardy · V.E. Iacob
    [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.
    No preview · Article · Jun 2014 · Nuclear Data Sheets
  • 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.
    No preview · Article · Mar 2014 · Physical Review Letters
  • 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.
    Preview · Article · Jan 2014 · Physical Review Letters
  • 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.
    Preview · Article · Dec 2013 · Physical Review C
  • [Show abstract] [Hide abstract]
    ABSTRACT: In a research program aimed at testing calculated internal-conversion coefficients (ICCs), we have made precise measurements of a(K) values for transitions in five nuclei, Pt-197, Ir-193; Ba-137, Cs-134 and Sn-119, 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. (c) 2013 Elsevier Ltd. All rights reserved.
    No preview · Article · Nov 2013 · Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine
  • [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.
    No preview · Article · Nov 2013 · Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine
  • [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.
    No preview · Article · Nov 2013 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
  • Molly Maguire · N. Nica · J. C. Hardy
    [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.
    No preview · Article · Oct 2012
  • Source

    Full-text · Dataset · Aug 2012
  • Ninel Nica · John Cameron · Balraj Singh
    [Show abstract] [Hide abstract]
    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 gamma-ray data, are based mostly on the original literature. The ³⁶Na has been looked for but not yet experimentally detected. There are no data available for the excited states in ³⁶Al, and for ³⁶Mg and ³⁶Ca, only one excited state is known.
    No preview · Article · Jun 2012 · Nuclear Data Sheets
  • [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.
    No preview · Article · Mar 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.
    Full-text · Article · Feb 2012 · Physical Review C
  • 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.
    Full-text · Article · Dec 2011 · Physical Review C
  • 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.
    Full-text · Article · Dec 2011
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A precision measurement of the gamma yields following the beta decay of 32Cl has determined its isobaric analogue branch to be (22.47^{+0.21}_{-0.19})%. 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, delta_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.
    Full-text · Article · Oct 2011 · Physical Review Letters
  • Sondra Miller · John Hardy · Ninel Nica · John Goodwin
    [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.
    No preview · Article · Oct 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.
    No preview · Article · Apr 2011

Publication Stats

366 Citations
124.53 Total Impact Points

Institutions

  • 2004-2015
    • Texas A&M University
      • Cyclotron Institute
      College Station, Texas, United States
  • 2010
    • Queen's University
      Kingston, Ontario, Canada
  • 2007
    • Brookhaven National Laboratory
      New York, New York, United States
  • 2005
    • Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering
      București, Bucureşti, Romania
  • 2001
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France