Publications (22)31.04 Total impact
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Article: Observation of a low-lying neutron-unbound state in 19C
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ABSTRACT: Proton removal reactions from a secondary 22N beam were utilized to populate unbound states in neutron-rich carbon isotopes. Neutrons were measured with the Modular Neutron Array (MoNA) in coincidence with carbon fragments. A resonance with a decay energy of 76(14) keV was observed in the system 18C+n corresponding to a state in 19C at an excitation energy of 653(95)keV. This resonance could correspond to the first 5/2+ state which was recently speculated to be unbound in order to describe 1n and 2n removal cross section measurements from 20C.05/2013; -
Article: Search for $^{21}$C and constraints on $^{22}$C
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ABSTRACT: A search for the neutron-unbound nucleus $^{21}$C was performed via the single proton removal reaction from a beam of 22 N at 68 MeV/u. Neutrons were detected with the Modular Neutron Array (MoNA) in coincidence with $^{20}$C fragments. No evidence for a low-lying state was found, and the reconstructed $^{20}$C+n decay energy spectrum could be described with an s-wave line shape with a scattering length limit of |as| < 2.8 fm, consistent with shell model predictions. A comparison with a renormalized zero-range three-body model suggests that $^{22}$C is bound by less than 70 keV.04/2013; -
Article: Exploring the Low-$Z$ Shore of the Island of Inversion at $N = 19$
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ABSTRACT: The technique of invariant mass spectroscopy has been used to measure, for the first time, the ground state energy of neutron-unbound $^{28}\textrm{F},$ determined to be a resonance in the $^{27}\textrm{F} + n$ continuum at $2\underline{2}0 (\underline{5}0)$ keV. States in $^{28}\textrm{F}$ were populated by the reactions of a 62 MeV/u $^{29}\textrm{Ne}$ beam impinging on a 288 $\textrm{mg/cm}^2$ beryllium target. The measured $^{28}\textrm{F}$ ground state energy is in good agreement with USDA/USDB shell model predictions, indicating that $pf$ shell intruder configurations play only a small role in the ground state structure of $^{28}\textrm{F}$ and establishing a low-$Z$ boundary of the island of inversion for N=19 isotones.Physical Review Letters 01/2012; 108(3). · 7.37 Impact Factor -
Article: Neutron knockout of^{12} Be populating neutron-unbound states in^{11} Be
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ABSTRACT: Neutron-unbound resonant states of 11Be were populated in neutron knockout reactions from 12Be and identified by 10Be–n coincidence measurements. A resonance in the decay-energy spectrum at 80(2) keV was attributed to a highly excited unbound state in 11Be at 3.949(2) MeV decaying to the 2+ excited state in 10Be. A knockout cross section of 15(3) mb was inferred for this 3.949(2) MeV state, suggesting a spectroscopic factor near unity for this 0p3/2- level, consistent with the detailed shell model calculations.Phys. Rev. C. 05/2011; 83(5). -
Article: Neutron knockout of 12Be populating neutron-unbound states in 11Be
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ABSTRACT: Neutron-unbound resonant states of 11Be were populated in neutron knock-out reactions from 12Be and identified by 10Be-n coincidence measurements. A resonance in the decay-energy spectrum at 80(2) keV was attributed to a highly excited unbound state in 11Be at 3.949(2) MeV decaying to the 2+ excited state in 10Be. A knockout cross section of 15(3) mb was inferred for this 3.949(2) MeV state suggesting a spectroscopic factor near unity for this 0p3/2- level, consistent with the detailed shell model calculations.04/2011; -
Article: Doubly-magic nature of 56Ni: measurement of the ground state nuclear magnetic dipole moment of 55Ni
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ABSTRACT: The nuclear magnetic moment of the ground state of $^{55}$Ni ($I^{\pi}=3/2^{-}, T_{1/2}=204$ ms) has been deduced to be $|\mu$^{55}Ni)$|=(0.976 \pm 0.026)$ $\mu_N$ using the $\beta$-NMR technique. Results of a shell model calculation in the full \textit{fp} shell model space with the GXPF1 interaction reproduce the experimental value. Together with the known magnetic moment of the mirror partner $^{55}$Co, the isoscalar spin expectation value was extracted as $<\sum \sigma_z >=0.91 \pm 0.07$. The $<\sum \sigma_z>$ shows a similar trend as that established in the \textit{sd} shell. The present theoretical interpretations of both $\mu(^{55}$Ni) and $<\sum \sigma_z>$ for the $T=1/2$, A=55 mirror partners support the softness of the $^{56}$Ni core. Comment: 13 pages, 1 figure, accepted for publication in Phys. Rev. C05/2009; -
Article: Evidence for a doubly magic $^24O$
Phys. Lett. B. 01/2009; 672(1):17 - 21. -
Article: Determination of the N=16 shell closure at the oxygen drip line.
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ABSTRACT: The neutron unbound ground state of (25)O (Z=8, N=17) was observed for the first time in a proton knockout reaction from a (26)F beam. A single resonance was found in the invariant mass spectrum corresponding to a neutron decay energy of 770_+20(-10) keV with a total width of 172(30) keV. The N=16 shell gap was established to be 4.86(13) MeV by the energy difference between the nu1s(1/2) and nu0d(3/2) orbitals. The neutron separation energies for (25)O agree with the calculations of the universal sd shell model interaction. This interaction incorrectly predicts an (26)O ground state that is bound to two-neutron decay by 1 MeV, leading to a discrepancy between the theoretical calculations and experiment as to the particle stability of (26)O. The observed decay width was found to be on the order of a factor of 2 larger than the calculated single-particle width using a Woods-Saxon potential.Physical Review Letters 04/2008; 100(15):152502. · 7.37 Impact Factor -
Article: Production of nuclei in neutron unbound states via primary fragmentation of $^48Ca$
Nuc. Phys. A. 01/2008; 801(3-4):101 - 113. -
Article: Nuclear magnetic moment of 57Cu ground state
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ABSTRACT: The nuclear magnetic moment of the ground state of 57Cu(Iπ = 3/2-, T1/2 = 196.3 ms) has been measured to be |μ(57Cu)| = (2.00 ±0.05) μN using the β-NMR technique. Together with the known magnetic moment of the mirror partner 57Ni, the spin expectation value was extracted as áåszñ\langle\sum\sigma_z\rangle = -0.78 ± 0.13. Discrepancy between present results and shell model calculations in the full fp shell implies significant shell breaking at 56Ni with the neutron number N = 28.The European Physical Journal Special Topics 10/2007; 150(1):145-146. · 1.56 Impact Factor -
Article: Nuclear magnetic moment of the 57Cu ground state.
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ABSTRACT: The nuclear magnetic moment of the ground state of (57)Cu(Iota(pi) = 3/2(-), T(1/2) = 196.3 ms) has been measured to be /mu((57)Cu)/ = (2.00 +/- 0.05)mu(N) using the beta-NMR technique. Together with the known magnetic moment of the mirror partner (57)Ni, the spin expectation value was extracted as <Sigmasigma(z)> = -0.078 +/- 0.13. This is the heaviest isospin mirror T = 1/2 pair above the (40)Ca region for which both ground state magnetic moments have been determined. The discrepancy between the present results and shell-model calculations in the full f p shell giving mu((57)Cu) approximately 2.4mu(N) and <Sigmasigma(z)> approximately 0.5 implies significant shell breaking at (56)Ni with the neutron number N = 28.Physical Review Letters 03/2006; 96(10):102501. · 7.37 Impact Factor -
Article: Spin polarization of 37K produced in a single-proton pickup reaction at intermediate energies.
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ABSTRACT: Spin polarization of 37K nuclei produced via single proton pickup from a 9Be target by a beam of 150 MeV/nucleon 36Ar has been observed. Positive spin polarization with magnitude (8.5+/-0.6)% was deduced near the peak of the 37K momentum distribution. The variation of the spin polarization as a function of outgoing 37K momentum is explained by a classical conservation model, as previously applied to describe the induced spin polarization observed for fragments produced in intermediate-energy heavy-ion reactions, with the condition that the picked-up proton has an average momentum equal to the Fermi momentum and is aligned along the incident beam direction.Physical Review Letters 06/2003; 90(20):202502. · 7.37 Impact Factor -
Article: Ground-state magnetic moment of the T= 1 nucleus^{32} Cl using on-line β-NMR spectroscopy
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ABSTRACT: The magnetic dipole moment of the 1+ ground state of the T=1 nucleus 1732Cl15 has been measured to be μ=1.114(6)μN using conventional β-NMR spectroscopy. Polarized 32Cl nuclei were produced by fragmentation of a 100 MeV/nucleon 36Ar beam in a 642 mg/cm2 93Nb target, where the beam was incident on the target at an angle 2.5° to the normal beam axis. The desired 32Cl fragments were filtered from other fragmentation products using the A1200 fragment separator and implanted in a NaCl single crystal, maintained at room temperature, at the center of a β-NMR apparatus. The Larmor frequency was determined by measuring the β-decay asymmetry as a function of the applied radio-frequency field. Isoscalar and isovector moments for the A=32, T=1 isospin multiplet are extracted and compared with large-basis shell model calculations.Phys. Rev. C. 09/2000; 62(4). -
Article: Disappearance of the N= 14 shell
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ABSTRACT: An excited state of 22N unbound with respect to neutron emission was observed in a stripping reaction from a 85 MeV/nucleon 26F beam. The observed decay energy of 650(50) keV places the level, which is interpreted to be the first 3- state, at an excitation energy of 1.93(22) MeV. Together with the previously measured bound states of 22N, reduction of the N=14 shell gap compared to less neutron-rich nitrogen isotopes at the neutron dripline is observed. Based on the magnitude of the reduction of the shell gap for 22N, a disappearance of the gap and even a level inversion of the ν1s1/2 and the ν0d5/2 levels in the neutron-unbound nucleus 21C seems likely.Phys. Rev. C. 80(2). -
Article: Observation of a two-neutron cascade from a resonance in^{24} O
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ABSTRACT: A new resonance having a relative decay energy of ~0.6 MeV has been observed above the two-neutron separation energy in 24O at an excitation energy of ~7.5 MeV. The new level was found to directly feed the first excited state in 23O, an E=0.045(2)-MeV resonance, through the measurement of neutron-neutron correlations. Energy level comparisons with 23O suggest that this new level in 24O is dominated by an unpaired neutron in the ν0d3/2 single-particle orbital coupled to a single hole in the ν0d5/2 single-particle orbital. Establishment of this two-neutron discrimination technique provides a means for investigating high-lying excited states in neutron-rich nuclei.Phys. Rev. C. 83(3). -
Article: Reply to “Comment on 'Neutron knockout of^{12} Be populating neutron-unbound states in^{11} Be'”
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ABSTRACT: In the preceding Comment, Fortune argues that, in our original paper [ Peters et al. Phys. Rev. C 83 057304 (2011)], we did not or could not separate the two neutron-unbound states in 11Be near 4 MeV. However, including the suggested contribution of the 3.887-MeV state decaying via 18 keV to the 2+ state in 10Be does not fit the data; neither do any other attempts incorporating any contribution of this decay channel. The best fit was achieved with a single resonance of decay energy 80(2) keV.Phys. Rev. C. 86(1). -
Article: Spin Polarization of $^37$K Produced in a Single-Proton Pickup Reaction at Intermediate Energies
Phys. Rev. Lett. 90(20):202502-. -
Conference Proceeding: Nuclear magnetic moment of $^57$Cu ground state
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ABSTRACT: The nuclear magnetic moment of the ground state of 57 Cu(I? = 3/2-, T1/2 = 196.3 ms) has been measured to be ?(57Cu) = (2.00 ± 0.05) ?N using the ?-NMR technique. Together with the known magnetic moment of the mirror partner 57Ni, the spin expectation value was extracted as ?? ?z? = -0.78 ± 0.13. Discrepancy between present results and shell model calculations in the full fp shell implies significant shell breaking at 56Ni with the neutron number N = 28. © EDP Sciences/Societe? Italiana di Fisica/Springer-Verlag 2007. -
Article: Nuclear magnetic moment of the $^57$Cu ground state (I=3/2$^-$, T$_1/2$=199.4 ms)
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ABSTRACT: The nuclear magnetic moment of the ground state of Cu57(I?=3/2-,T1/2= 196.3ms) has been measured to be |?(Cu57)|=(2.00±0.05)?N using the ?-NMR technique. Together with the known magnetic moment of the mirror partner Ni57, the spin expectation value was extracted as ??z =-0.78±0.13. This is the heaviest isospin T=1/2 mirror pair above the Ca40 region for which both ground state magnetic moments have been determined. The discrepancy between the present results and shell-model calculations in the full fp shell giving ?(Cu57)?2.4?N and ??z ?0.5 implies significant shell breaking at Ni56 with the neutron number N=28. © 2006 The American Physical Society.Phys. Rev. Lett. 96(10):1-4. -
Article: Evidence for 2f$_1/2$ neutron strength in the low-energy structure of $^144,146,148,150Nd isotopes
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ABSTRACT: The Bardeen model - the first regular black hole model in General Relativity - is reinterpreted as the gravitational field of a nonlinear magnetic monopole, i.e., as a magnetic solution to Einstein equations coupled to a nonlinear electrodynamics. (C) 2000 Elsevier Science B.V.Phys. Lett. B. 493(1-2):7-11.
Top Journals
Institutions
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2000–2011
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Westmont College
- Physics
Santa Barbara, CA, USA
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2007
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Santa Barbara College Of Law
Santa Barbara, CA, USA
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2006–2007
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Michigan State University
- Department of Chemistry
East Lansing, MI, USA
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