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Allmond JM, Stuchbery AE, Baktash C, Gargano A, Galindo-Uribarri A, Radford DC, Bingham CR, Brown BA, Coraggio L, Covello A, Danchev M, Gross CJ, Hausladen PA, Itaco N, Lagergren K, Padilla-Rodal E, Pavan J, Riley MA, Stone NJ, Stracener DW, Varner RL, Yu CH. Electromagnetic Moments of Radioactive ^{136}Te and the Emergence of Collectivity 2p⊕2n Outside of Double-Magic ^{132}Sn. PHYSICAL REVIEW LETTERS 2017; 118:092503. [PMID: 28306272 DOI: 10.1103/physrevlett.118.092503] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Indexed: 06/06/2023]
Abstract
Radioactive ^{136}Te has two valence protons and two valence neutrons outside of the ^{132}Sn double shell closure, providing a simple laboratory for exploring the emergence of collectivity and nucleon-nucleon interactions. Coulomb excitation of ^{136}Te on a titanium target was utilized to determine an extensive set of electromagnetic moments for the three lowest-lying states, including B(E2;0_{1}^{+}→2_{1}^{+}), Q(2_{1}^{+}), and g(2_{1}^{+}). The results indicate that the first-excited state, 2_{1}^{+}, composed of the simple 2p⊕2n system, is prolate deformed, and its wave function is dominated by excited valence neutron configurations, but not to the extent previously suggested. It is demonstrated that extreme sensitivity of g(2_{1}^{+}) to the proton and neutron contributions to the wave function provides unique insight into the nature of emerging collectivity, and g(2_{1}^{+}) was used to differentiate among several state-of-the-art theoretical calculations. Our results are best described by the most recent shell model calculations.
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Schwengner R, Frauendorf S, Brown BA. Low-Energy Magnetic Dipole Radiation in Open-Shell Nuclei. PHYSICAL REVIEW LETTERS 2017; 118:092502. [PMID: 28306274 DOI: 10.1103/physrevlett.118.092502] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Indexed: 06/06/2023]
Abstract
Low-energy M1 strength functions of ^{60,64,68}Fe are determined on the basis of large-scale shell-model calculations with the goal to study their development from the bottom to the middle of the neutron shell. We find that the zero-energy spike, which characterizes nuclei near closed shells, develops toward the middle of the shell into a bimodal structure composed of a weaker zero-energy spike and a scissorslike resonance around 3 MeV, where the summed strengths of the two structures change within only 8% around a value of 9.8 μ_{N}^{2}. The summed strength of the scissors region exceeds the total γ absorption strength from the ground state by a factor of about three, which explains the discrepancy between total strengths of the scissors resonance derived from (γ, γ^{'}) experiments and from experiments using light-ion induced reactions.
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Dietz B, Heusler A, Maier KH, Richter A, Brown BA. Chaos and Regularity in the Doubly Magic Nucleus ^{208}Pb. PHYSICAL REVIEW LETTERS 2017; 118:012501. [PMID: 28106417 DOI: 10.1103/physrevlett.118.012501] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Indexed: 06/06/2023]
Abstract
High-resolution experiments have recently lead to a complete identification (energy, spin, and parity) of 151 nuclear levels up to an excitation energy of E_{x}=6.20 MeV in ^{208}Pb [Heusler et al., Phys. Rev. C 93, 054321 (2016)PRVCAN2469-998510.1103/PhysRevC.93.054321]. We present a thorough study of the fluctuation properties in the energy spectra of the unprecedented set of nuclear bound states. In a first approach, we group states with the same spin and parity into 14 subspectra, analyze standard statistical measures for short- and long-range correlations, i.e., the nearest-neighbor spacing distribution, the number variance Σ^{2}, the Dyson-Mehta Δ_{3} statistics, and the novel distribution of the ratios of consecutive spacings of adjacent energy levels in each energy sequence, and then compute their ensemble average. Their comparison with a random matrix ensemble which interpolates between Poisson statistics expected for regular systems and the Gaussian orthogonal ensemble (GOE) predicted for chaotic systems shows that the data are well described by the GOE. In a second approach, following an idea of Rosenzweig and Porter [Phys. Rev. 120, 1698 (1960)PHRVAO0031-899X10.1103/PhysRev.120.1698], we consider the complete spectrum composed of the independent subspectra. We analyze their fluctuation properties using the method of Bayesian inference involving a quantitative measure, called the chaoticity parameter f, which also interpolates between Poisson (f=0) and GOE statistics (f=1). It turns out to be f≈0.9. This is so far the closest agreement with a GOE observed in the spectra of bound states in a nucleus. The same analysis is also performed with spectra computed on the basis of shell model calculations with different interactions (surface-delta interaction, Kuo-Brown, Michigan-three-Yukawa). While the simple surface-delta interaction exhibits features typical for nuclear many-body systems with regular dynamics, the other, more realistic interactions yield chaoticity parameters f close to the experimental values.
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Goigoux T, Ascher P, Blank B, Gerbaux M, Giovinazzo J, Grévy S, Kurtukian Nieto T, Magron C, Doornenbal P, Kiss GG, Nishimura S, Söderström PA, Phong VH, Wu J, Ahn DS, Fukuda N, Inabe N, Kubo T, Kubono S, Sakurai H, Shimizu Y, Sumikama T, Suzuki H, Takeda H, Agramunt J, Algora A, Guadilla V, Montaner-Piza A, Morales AI, Orrigo SEA, Rubio B, Fujita Y, Tanaka M, Gelletly W, Aguilera P, Molina F, Diel F, Lubos D, de Angelis G, Napoli D, Borcea C, Boso A, Cakirli RB, Ganioglu E, Chiba J, Nishimura D, Oikawa H, Takei Y, Yagi S, Wimmer K, de France G, Go S, Brown BA. Two-Proton Radioactivity of ^{67}Kr. PHYSICAL REVIEW LETTERS 2016; 117:162501. [PMID: 27792367 DOI: 10.1103/physrevlett.117.162501] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Indexed: 06/06/2023]
Abstract
In an experiment with the BigRIPS separator at the RIKEN Nishina Center, we observed two-proton (2p) emission from ^{67}Kr. At the same time, no evidence for 2p emission of ^{59}Ge and ^{63}Se, two other potential candidates for this exotic radioactivity, could be observed. This observation is in line with Q value predictions which pointed to ^{67}Kr as being the best new candidate among the three for two-proton radioactivity. ^{67}Kr is only the fourth 2p ground-state emitter to be observed with a half-life of the order of a few milliseconds. The decay energy was determined to be 1690(17) keV, the 2p emission branching ratio is 37(14)%, and the half-life of ^{67}Kr is 7.4(30) ms.
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Spyrou A, Liddick SN, Naqvi F, Crider BP, Dombos AC, Bleuel DL, Brown BA, Couture A, Crespo Campo L, Guttormsen M, Larsen AC, Lewis R, Möller P, Mosby S, Mumpower MR, Perdikakis G, Prokop CJ, Renstrøm T, Siem S, Quinn SJ, Valenta S. Strong Neutron-γ Competition above the Neutron Threshold in the Decay of ^{70}Co. PHYSICAL REVIEW LETTERS 2016; 117:142701. [PMID: 27740831 DOI: 10.1103/physrevlett.117.142701] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Indexed: 06/06/2023]
Abstract
The β-decay intensity of ^{70}Co was measured for the first time using the technique of total absorption spectroscopy. The large β-decay Q value [12.3(3) MeV] offers a rare opportunity to study β-decay properties in a broad energy range. Two surprising features were observed in the experimental results, namely, the large fragmentation of the β intensity at high energies, as well as the strong competition between γ rays and neutrons, up to more than 2 MeV above the neutron-separation energy. The data are compared to two theoretical calculations: the shell model and the quasiparticle random phase approximation (QRPA). Both models seem to be missing a significant strength at high excitation energies. Possible interpretations of this discrepancy are discussed. The shell model is used for a detailed nuclear structure interpretation and helps to explain the observed γ-neutron competition. The comparison to the QRPA calculations is done as a means to test a model that provides global β-decay properties for astrophysical calculations. Our work demonstrates the importance of performing detailed comparisons to experimental results, beyond the simple half-life comparisons. A realistic and robust description of the β-decay intensity is crucial for our understanding of nuclear structure as well as of r-process nucleosynthesis.
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Bennett MB, Wrede C, Brown BA, Liddick SN, Pérez-Loureiro D, Bardayan DW, Chen AA, Chipps KA, Fry C, Glassman BE, Langer C, Larson NR, McNeice EI, Meisel Z, Ong W, O'Malley PD, Pain SD, Prokop CJ, Schatz H, Schwartz SB, Suchyta S, Thompson P, Walters M, Xu X. Isospin Mixing Reveals ^{30}P(p,γ)^{31}S Resonance Influencing Nova Nucleosynthesis. PHYSICAL REVIEW LETTERS 2016; 116:102502. [PMID: 27015475 DOI: 10.1103/physrevlett.116.102502] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2015] [Indexed: 06/05/2023]
Abstract
The thermonuclear ^{30}P(p,γ)^{31}S reaction rate is critical for modeling the final elemental and isotopic abundances of ONe nova nucleosynthesis, which affect the calibration of proposed nova thermometers and the identification of presolar nova grains, respectively. Unfortunately, the rate of this reaction is essentially unconstrained experimentally, because the strengths of key ^{31}S proton capture resonance states are not known, largely due to uncertainties in their spins and parities. Using the β decay of ^{31}Cl, we have observed the β-delayed γ decay of a ^{31}S state at E_{x}=6390.2(7) keV, with a ^{30}P(p,γ)^{31}S resonance energy of E_{r}=259.3(8) keV, in the middle of the ^{30}P(p,γ)^{31}S Gamow window for peak nova temperatures. This state exhibits isospin mixing with the nearby isobaric analog state at E_{x}=6279.0(6) keV, giving it an unambiguous spin and parity of 3/2^{+} and making it an important l=0 resonance for proton capture on ^{30}P.
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Meisel Z, George S, Ahn S, Bazin D, Brown BA, Browne J, Carpino JF, Chung H, Cole AL, Cyburt RH, Estradé A, Famiano M, Gade A, Langer C, Matoš M, Mittig W, Montes F, Morrissey DJ, Pereira J, Schatz H, Schatz J, Scott M, Shapira D, Smith K, Stevens J, Tan W, Tarasov O, Towers S, Wimmer K, Winkelbauer JR, Yurkon J, Zegers RGT. Mass Measurement of 56Sc Reveals a Small A = 56 Odd-Even Mass Staggering, Implying a Cooler Accreted Neutron Star Crust. PHYSICAL REVIEW LETTERS 2015; 115:162501. [PMID: 26550869 DOI: 10.1103/physrevlett.115.162501] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2015] [Indexed: 06/05/2023]
Abstract
We present the mass excesses of (52-57)Sc, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The masses of 56Sc and 57Sc were determined for the first time with atomic mass excesses of -24.85(59)((-54)(+0)) MeV and -21.0(1.3) MeV, respectively, where the asymmetric uncertainty for 56Sc was included due to possible contamination from a long-lived isomer. The 56Sc mass indicates a small odd-even mass staggering in the A = 56 mass chain towards the neutron drip line, significantly deviating from trends predicted by the global FRDM mass model and favoring trends predicted by the UNEDF0 and UNEDF1 density functional calculations. Together with new shell-model calculations of the electron-capture strength function of 56Sc, our results strongly reduce uncertainties in model calculations of the heating and cooling at the 56Ti electron-capture layer in the outer crust of accreting neutron stars. We find that, in contrast to previous studies, neither strong neutrino cooling nor strong heating occurs in this layer. We conclude that Urca cooling in the outer crusts of accreting neutron stars that exhibit superbursts or high temperature steady-state burning, which are predicted to be rich in A≈56 nuclei, is considerably weaker than predicted. Urca cooling must instead be dominated by electron capture on the small amounts of adjacent odd-A nuclei contained in the superburst and high temperature steady-state burning ashes. This may explain the absence of strong crust Urca cooling inferred from the observed cooling light curve of the transiently accreting x-ray source MAXI J0556-332.
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Midgley CM, Watson JT, Nix WA, Curns AT, Rogers SL, Brown BA, Conover C, Dominguez SR, Feikin DR, Gray S, Hassan F, Hoferka S, Jackson MA, Johnson D, Leshem E, Miller L, Nichols JB, Nyquist AC, Obringer E, Patel A, Patel M, Rha B, Schneider E, Schuster JE, Selvarangan R, Seward JF, Turabelidze G, Oberste MS, Pallansch MA, Gerber SI. Severe respiratory illness associated with a nationwide outbreak of enterovirus D68 in the USA (2014): a descriptive epidemiological investigation. THE LANCET RESPIRATORY MEDICINE 2015; 3:879-87. [PMID: 26482320 PMCID: PMC5693332 DOI: 10.1016/s2213-2600(15)00335-5] [Citation(s) in RCA: 153] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Revised: 08/14/2015] [Accepted: 08/17/2015] [Indexed: 01/08/2023]
Abstract
BACKGROUND Enterovirus D68 (EV-D68) has been infrequently reported historically, and is typically associated with isolated cases or small clusters of respiratory illness. Beginning in August, 2014, increases in severe respiratory illness associated with EV-D68 were reported across the USA. We aimed to describe the clinical, epidemiological, and laboratory features of this outbreak, and to better understand the role of EV-D68 in severe respiratory illness. METHODS We collected regional syndromic surveillance data for epidemiological weeks 23 to 44, 2014, (June 1 to Nov 1, 2014) and hospital admissions data for epidemiological weeks 27 to 44, 2014, (June 29 to Nov 1, 2014) from three states: Missouri, Illinois and Colorado. Data were also collected for the same time period of 2013 and 2012. Respiratory specimens from severely ill patients nationwide, who were rhinovirus-positive or enterovirus-positive in hospital testing, were submitted between Aug 1, and Oct 31, 2014, and typed by molecular sequencing. We collected basic clinical and epidemiological characteristics of EV-D68 cases with a standard data collection form submitted with each specimen. We compared patients requiring intensive care with those who did not, and patients requiring ventilator support with those who did not. Mantel-Haenszel χ(2) tests were used to test for statistical significance. FINDINGS Regional and hospital-level data from Missouri, Illinois, and Colorado showed increases in respiratory illness between August and September, 2014, compared with in 2013 and 2012. Nationwide, 699 (46%) of 1529 patients tested were confirmed as EV-D68. Among the 614 EV-D68-positive patients admitted to hospital, age ranged from 3 days to 92 years (median 5 years). Common symptoms included dyspnoea (n=513 [84%]), cough (n=500 [81%]), and wheezing (n=427 [70%]); 294 (48%) patients had fever. 338 [59%] of 574 were admitted to intensive care units, and 145 (28%) of 511 received ventilator support; 322 (52%) of 614 had a history of asthma or reactive airway disease; 200 (66%) of 304 patients with a history of asthma or reactive airway disease required intensive care compared with 138 (51%) of 270 with no history of asthma or reactive airway disease (p=0·0004). Similarly, 89 (32%) of 276 patients with a history of asthma or reactive airway disease required ventilator support compared with 56 (24%) of 235 patients with no history of asthma or reactive airway disease (p=0·039). INTERPRETATION In 2014, EV-D68 caused widespread severe respiratory illness across the USA, disproportionately affecting those with asthma. This unexpected event underscores the need for robust surveillance of enterovirus types, enabling improved understanding of virus circulation and disease burden. FUNDING None.
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Kusoglu A, Stuchbery AE, Georgiev G, Brown BA, Goasduff A, Atanasova L, Balabanski DL, Bostan M, Danchev M, Detistov P, Gladnishki KA, Ljungvall J, Matea I, Radeck D, Sotty C, Stefan I, Verney D, Yordanov DT. Magnetism of an excited self-conjugate nucleus: precise measurement of the g factor of the 2(1)(+) state in (24)Mg. PHYSICAL REVIEW LETTERS 2015; 114:062501. [PMID: 25723214 DOI: 10.1103/physrevlett.114.062501] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Indexed: 06/04/2023]
Abstract
A precise measurement of the g factor of the first-excited state in the self-conjugate (N=Z) nucleus (24)Mg is performed by a new time-differential recoil-in-vacuum method based on the hyperfine field of hydrogenlike ions. Theory predicts that the g factors of such states, in which protons and neutrons occupy the same orbits, should depart from 0.5 by a few percent due to configuration mixing and meson-exchange effects. The experimental result, g=0.538±0.013, is in excellent agreement with recent shell-model calculations and shows a departure from 0.5 by almost 3 standard deviations, thus achieving, for the first time, the precision and accuracy needed to test theory. Proof of the new method opens the way for wide applications including measurements of the magnetism of excited states of exotic nuclei produced as radioactive beams.
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Meisel Z, George S, Ahn S, Browne J, Bazin D, Brown BA, Carpino JF, Chung H, Cyburt RH, Estradé A, Famiano M, Gade A, Langer C, Matoš M, Mittig W, Montes F, Morrissey DJ, Pereira J, Schatz H, Schatz J, Scott M, Shapira D, Smith K, Stevens J, Tan W, Tarasov O, Towers S, Wimmer K, Winkelbauer JR, Yurkon J, Zegers RGT. Mass measurements demonstrate a strong N=28 shell gap in argon. PHYSICAL REVIEW LETTERS 2015; 114:022501. [PMID: 25635542 DOI: 10.1103/physrevlett.114.022501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2014] [Indexed: 06/04/2023]
Abstract
We present results from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. We report the first mass measurements of ^{48}Ar and ^{49}Ar and find atomic mass excesses of -22.28(31) MeV and -17.8(1.1) MeV, respectively. These masses provide strong evidence for the closed shell nature of neutron number N=28 in argon, which is therefore the lowest even-Z element exhibiting the N=28 closed shell. The resulting trend in binding-energy differences, which probes the strength of the N=28 shell, compares favorably with shell-model calculations in the sd-pf shell using SDPF-U and SDPF-MU Hamiltonians.
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Brown BA, Horoi M, Sen'kov RA. Nuclear structure aspects of neutrinoless double-β decay. PHYSICAL REVIEW LETTERS 2014; 113:262501. [PMID: 25615313 DOI: 10.1103/physrevlett.113.262501] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Indexed: 06/04/2023]
Abstract
We decompose the neutrinoless double-β decay matrix elements into sums of products over the intermediate nucleus with two less nucleons. We find that the sum is dominated by the J(π)=0(+) ground state of this intermediate nucleus for both the light and heavy neutrino decay processes. This provides a new theoretical tool for comparing and improving nuclear structure models. It also provides the connection to two-nucleon transfer experiments.
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Gallant AT, Brodeur M, Andreoiu C, Bader A, Chaudhuri A, Chowdhury U, Grossheim A, Klawitter R, Kwiatkowski AA, Leach KG, Lennarz A, Macdonald TD, Schultz BE, Lassen J, Heggen H, Raeder S, Teigelhöfer A, Brown BA, Magilligan A, Holt JD, Menéndez J, Simonis J, Schwenk A, Dilling J. Breakdown of the isobaric multiplet mass equation for the A = 20 and 21 multiplets. PHYSICAL REVIEW LETTERS 2014; 113:082501. [PMID: 25192091 DOI: 10.1103/physrevlett.113.082501] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Indexed: 06/03/2023]
Abstract
Using the Penning trap mass spectrometer TITAN, we performed the first direct mass measurements of (20,21)Mg, isotopes that are the most proton-rich members of the A = 20 and A = 21 isospin multiplets. These measurements were possible through the use of a unique ion-guide laser ion source, a development that suppressed isobaric contamination by 6 orders of magnitude. Compared to the latest atomic mass evaluation, we find that the mass of (21)Mg is in good agreement but that the mass of (20)Mg deviates by 3 σ. These measurements reduce the uncertainties in the masses of (20,21)Mg by 15 and 22 times, respectively, resulting in a significant departure from the expected behavior of the isobaric multiplet mass equation in both the A = 20 and A = 21 multiplets. This presents a challenge to shell model calculations using either the isospin nonconserving universal sd USDA and USDB Hamiltonians or isospin nonconserving interactions based on chiral two- and three-nucleon forces.
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Langer C, Montes F, Aprahamian A, Bardayan DW, Bazin D, Brown BA, Browne J, Crawford H, Cyburt RH, Domingo-Pardo C, Gade A, George S, Hosmer P, Keek L, Kontos A, Lee IY, Lemasson A, Lunderberg E, Maeda Y, Matos M, Meisel Z, Noji S, Nunes FM, Nystrom A, Perdikakis G, Pereira J, Quinn SJ, Recchia F, Schatz H, Scott M, Siegl K, Simon A, Smith M, Spyrou A, Stevens J, Stroberg SR, Weisshaar D, Wheeler J, Wimmer K, Zegers RGT. Determining the rp-process flow through 56Ni: resonances in 57Cu(p,γ)58Zn identified with GRETINA. PHYSICAL REVIEW LETTERS 2014; 113:032502. [PMID: 25083636 DOI: 10.1103/physrevlett.113.032502] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2014] [Indexed: 06/03/2023]
Abstract
An approach is presented to experimentally constrain previously unreachable (p, γ) reaction rates on nuclei far from stability in the astrophysical rp process. Energies of all critical resonances in the (57)Cu(p,γ)(58)Zn reaction are deduced by populating states in (58)Zn with a (d, n) reaction in inverse kinematics at 75 MeV/u, and detecting γ-ray-recoil coincidences with the state-of-the-art γ-ray tracking array GRETINA and the S800 spectrograph at the National Superconducting Cyclotron Laboratory. The results reduce the uncertainty in the (57)Cu(p,γ) reaction rate by several orders of magnitude. The effective lifetime of (56)Ni, an important waiting point in the rp process in x-ray bursts, can now be determined entirely from experimentally constrained reaction rates.
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Noji S, Zegers RGT, Austin SM, Baugher T, Bazin D, Brown BA, Campbell CM, Cole AL, Doster HJ, Gade A, Guess CJ, Gupta S, Hitt GW, Langer C, Lipschutz S, Lunderberg E, Meharchand R, Meisel Z, Perdikakis G, Pereira J, Recchia F, Schatz H, Scott M, Stroberg SR, Sullivan C, Valdez L, Walz C, Weisshaar D, Williams SJ, Wimmer K. β+ Gamow-Teller transition strengths from 46Ti and stellar electron-capture rates. PHYSICAL REVIEW LETTERS 2014; 112:252501. [PMID: 25014806 DOI: 10.1103/physrevlett.112.252501] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2014] [Indexed: 06/03/2023]
Abstract
The Gamow-Teller strength in the β(+) direction to (46)Sc was extracted via the (46)Ti(t,(3)He + γ) reaction at 115 MeV/u. The γ-ray coincidences served to precisely measure the very weak Gamow-Teller transition to a final state at 991 keV. Although this transition is weak, it is crucial for accurately estimating electron-capture rates in astrophysical scenarios with relatively low stellar densities and temperatures, such as presupernova stellar evolution. Shell-model calculations with different effective interactions in the pf shell-model space do not reproduce the experimental Gamow-Teller strengths, which is likely due to sd-shell admixtures. Calculations in the quasiparticle random phase approximation that are often used in astrophysical simulations also fail to reproduce the experimental Gamow-Teller strength distribution, leading to strongly overestimated electron-capture rates. Because reliable theoretical predictions of Gamow-Teller strengths are important for providing astrophysical electron-capture reaction rates for a broad set of nuclei in the lower pf shell, we conclude that further theoretical improvements are required to match astrophysical needs.
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40
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Gade A, Janssens RVF, Weisshaar D, Brown BA, Lunderberg E, Albers M, Bader VM, Baugher T, Bazin D, Berryman JS, Campbell CM, Carpenter MP, Chiara CJ, Crawford HL, Cromaz M, Garg U, Hoffman CR, Kondev FG, Langer C, Lauritsen T, Lee IY, Lenzi SM, Matta JT, Nowacki F, Recchia F, Sieja K, Stroberg SR, Tostevin JA, Williams SJ, Wimmer K, Zhu S. Nuclear structure towards N = 40 60Ca: in-beam γ-ray spectroscopy of 58,60Ti. PHYSICAL REVIEW LETTERS 2014; 112:112503. [PMID: 24702356 DOI: 10.1103/physrevlett.112.112503] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2013] [Indexed: 06/03/2023]
Abstract
Excited states in the neutron-rich N = 38, 36 nuclei (60)Ti and (58)Ti were populated in nucleon-removal reactions from (61)V projectiles at 90 MeV/nucleon. The γ-ray transitions from such states in these Ti isotopes were detected with the advanced γ-ray tracking array GRETINA and were corrected event by event for large Doppler shifts (v/c ∼ 0.4) using the γ-ray interaction points deduced from online signal decomposition. The new data indicate that a steep decrease in quadrupole collectivity occurs when moving from neutron-rich N = 36, 38 Fe and Cr toward the Ti and Ca isotones. In fact, (58,60)Ti provide some of the most neutron-rich benchmarks accessible today for calculations attempting to determine the structure of the potentially doubly magic nucleus (60)Ca.
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Horoi M, Brown BA. Shell-model analysis of the 136Xe double beta decay nuclear matrix elements. PHYSICAL REVIEW LETTERS 2013; 110:222502. [PMID: 23767716 DOI: 10.1103/physrevlett.110.222502] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/24/2012] [Revised: 03/18/2013] [Indexed: 06/02/2023]
Abstract
Neutrinoless double beta decay, if observed, could distinguish whether the neutrino is a Dirac or a Majorana particle, and it could be used to determine the absolute scale of the neutrino masses. 136Xe is one of the most promising candidates for observing this rare event. However, until recently there were no positive results for the allowed and less rare two-neutrino double beta decay mode. The small nuclear matrix element associated with the long half-life represents a challenge for nuclear structure models used for its calculation. We report a new shell-model analysis of the two-neutrino double beta decay of 136Xe, which takes into account all relevant nuclear orbitals necessary to fully describe the associated Gamow-Teller strength. We further use the new model to analyze the main contributions to the neutrinoless double beta decay matrix element, and show that they are also diminished.
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Papuga J, Bissell ML, Kreim K, Blaum K, Brown BA, De Rydt M, Garcia Ruiz RF, Heylen H, Kowalska M, Neugart R, Neyens G, Nörtershäuser W, Otsuka T, Rajabali MM, Sánchez R, Utsuno Y, Yordanov DT. Spins and magnetic moments of 49K and 51K: establishing the 1/2+ and 3/2+ level ordering beyond N = 28. PHYSICAL REVIEW LETTERS 2013; 110:172503. [PMID: 23679713 DOI: 10.1103/physrevlett.110.172503] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Indexed: 06/02/2023]
Abstract
The ground-state spins and magnetic moments of (49,51)K have been measured using bunched-beam high-resolution collinear laser spectroscopy at ISOLDE CERN. For 49K a ground-state spin I = 1/2 was firmly established. The observed hyperfine structure of 51K requires a spin I > 1/2 and strongly suggests I = 3/2. From its magnetic moment μ(51K) = +0.5129(22)μ(N) a spin-parity I(π) = 3/2+ with a dominant π1d(3/2)(-1) hole configuration was deduced. This establishes for the first time the reinversion of the single-particle levels and illustrates the prominent role of the residual monopole interaction for single-particle levels and shell evolution.
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Lepailleur A, Sorlin O, Caceres L, Bastin B, Borcea C, Borcea R, Brown BA, Gaudefroy L, Grévy S, Grinyer GF, Hagen G, Hjorth-Jensen M, Jansen GR, Llidoo O, Negoita F, de Oliveira F, Porquet MG, Rotaru F, Saint-Laurent MG, Sohler D, Stanoiu M, Thomas JC. Spectroscopy of 26F to probe proton-neutron forces close to the drip line. PHYSICAL REVIEW LETTERS 2013; 110:082502. [PMID: 23473138 DOI: 10.1103/physrevlett.110.082502] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Indexed: 06/01/2023]
Abstract
A long-lived J(π) = 4(1)(+) isomer, T(1/2) = 2.2(1) ms, has been discovered at 643.4(1) keV in the weakly bound (9)(26)F nucleus. It was populated at Grand Accélérateur National d'Ions Lourds in the fragmentation of a (36)S beam. It decays by an internal transition to the J(π) = 1(1)(+) ground state [82(14)%], by β decay to (26)Ne, or β-delayed neutron emission to (25)Ne. From the β-decay studies of the J(π) =1(1)(+) and J(π) = 4(1)(+) states, new excited states have been discovered in (25,26)Ne. Gathering the measured binding energies of the J(π) = 1(1)(+) -4(1)(+) multiplet in (9)(26)F, we find that the proton-neutron π0d(5/2)ν0d(3/2) effective force used in shell-model calculations should be reduced to properly account for the weak binding of (9)(26)F. Microscopic coupled cluster theory calculations using interactions derived from chiral effective field theory are in very good agreement with the energy of the low-lying 1(1)(+), 2(1)(+), 4(1)(+) states in (26)F. Including three-body forces and coupling to the continuum effects improve the agreement between experiment and theory as compared to the use of two-body forces only.
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Zhang YH, Xu HS, Litvinov YA, Tu XL, Yan XL, Typel S, Blaum K, Wang M, Zhou XH, Sun Y, Brown BA, Yuan YJ, Xia JW, Yang JC, Audi G, Chen XC, Jia GB, Hu ZG, Ma XW, Mao RS, Mei B, Shuai P, Sun ZY, Wang ST, Xiao GQ, Xu X, Yamaguchi T, Yamaguchi Y, Zang YD, Zhao HW, Zhao TC, Zhang W, Zhan WL. Mass measurements of the neutron-deficient 41Ti, 45Cr, 49Fe, and 53Ni nuclides: first test of the isobaric multiplet mass equation in f p-shell nuclei. PHYSICAL REVIEW LETTERS 2012; 109:102501. [PMID: 23005283 DOI: 10.1103/physrevlett.109.102501] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2012] [Indexed: 06/01/2023]
Abstract
Isochronous mass spectrometry has been applied to neutron-deficient 58Ni projectile fragments at the HIRFL-CSR facility in Lanzhou, China. Masses of a series of short-lived T(z)=-3/2 nuclides including 41Ti, 45Cr, 49Fe, and 53Ni have been measured with a precision of 20-40 keV. The new data enable us to test for the first time the isobaric multiplet mass equation (IMME) in fp-shell nuclei. We observe that the IMME is inconsistent with the generally accepted quadratic form for the A=53, T=3/2 quartet. We perform full space shell model calculations and compare them with the new experimental results.
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45
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Brodeur M, Brunner T, Ettenauer S, Lapierre A, Ringle R, Brown BA, Lunney D, Dilling J. Elucidation of the anomalous A=9 isospin quartet behavior. PHYSICAL REVIEW LETTERS 2012; 108:212501. [PMID: 23003246 DOI: 10.1103/physrevlett.108.212501] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2012] [Indexed: 06/01/2023]
Abstract
Recent high-precision mass measurements of 9Li and 9Be, performed with the TITAN Penning trap at the TRIUMF ISAC facility, are analyzed in light of state-of-the-art shell model calculations. We find an explanation for the anomalous isobaric mass multiplet equation behavior for the two A=9 quartets. The presence of a cubic d=6.3(17) keV term for the J(π)=3/2(-) quartet and the vanishing cubic term for the excited J(π)=1/2(-) multiplet depend upon the presence of a nearby T=1/2 state in 9B and 9Be that induces isospin mixing. This is contrary to previous hypotheses involving purely Coulomb and charge-dependent effects. T=1/2 states have been observed near the calculated energy, above the T=3/2 state. However, an experimental confirmation of their J(π) is needed.
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46
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Winkler R, Gade A, Baugher T, Bazin D, Brown BA, Glasmacher T, Grinyer GF, Meharchand R, McDaniel S, Ratkiewicz A, Weisshaar D. Quadrupole collectivity beyond N = 28: intermediate-energy Coulomb excitation of (47,48)Ar. PHYSICAL REVIEW LETTERS 2012; 108:182501. [PMID: 22681067 DOI: 10.1103/physrevlett.108.182501] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Indexed: 06/01/2023]
Abstract
We report on the first experimental study of quadrupole collectivity in the very neutron-rich nuclei (47,48)Ar using intermediate-energy Coulomb excitation. These nuclei are located along the path from doubly magic Ca to collective S and Si isotopes, a critical region of shell evolution and structural change. The deduced B(E2) transition strengths are confronted with large-scale shell-model calculations in the sdpf shell using the state-of-the-art SDPF-Uand EPQQM effective interactions. The comparison between experiment and theory indicates that a shell-model description of Ar isotopes around N=28 remains a challenge.
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Meharchand R, Zegers RGT, Brown BA, Austin SM, Baugher T, Bazin D, Deaven J, Gade A, Grinyer GF, Guess CJ, Howard ME, Iwasaki H, McDaniel S, Meierbachtol K, Perdikakis G, Pereira J, Prinke AM, Ratkiewicz A, Signoracci A, Stroberg S, Valdez L, Voss P, Walsh KA, Weisshaar D, Winkler R. Probing configuration mixing in 12Be with Gamow-Teller transition strengths. PHYSICAL REVIEW LETTERS 2012; 108:122501. [PMID: 22540576 DOI: 10.1103/physrevlett.108.122501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Indexed: 05/31/2023]
Abstract
We present a novel technique for studying the quenching of shell gaps in exotic isotopes. The method is based on extracting Gamow-Teller (ΔL=0, ΔS=1) transition strengths [B(GT)] to low-lying states from charge-exchange reactions at intermediate beam energies. These Gamow-Teller strengths are very sensitive to configuration mixing between cross-shell orbitals, and this technique thus provides an important complement to other tools currently used to study cross-shell mixing. This work focuses on the N=8 shell gap. We populated the ground and 2.24 MeV 0+ states in 12Be using the 12B(1+) (7Li, 7Be) reaction at 80 MeV/u in inverse kinematics. Using the ground-state B(GT) value from β-decay measurements (0.184±0.007) as a calibration, the B(GT) for the transition to the second 0+ state was determined to be 0.214±0.051. Comparing the extracted Gamow-Teller strengths with shell-model calculations, it was determined that the wave functions of the first and second 0+ states in 12Be are composed of 25±5% and 60±5% (0s)4(0p)8 configurations, respectively.
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48
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Spyrou A, Kohley Z, Baumann T, Bazin D, Brown BA, Christian G, DeYoung PA, Finck JE, Frank N, Lunderberg E, Mosby S, Peters WA, Schiller A, Smith JK, Snyder J, Strongman MJ, Thoennessen M, Volya A. First observation of ground state dineutron decay: 16Be. PHYSICAL REVIEW LETTERS 2012; 108:102501. [PMID: 22463404 DOI: 10.1103/physrevlett.108.102501] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2011] [Indexed: 05/31/2023]
Abstract
We report on the first observation of dineutron emission in the decay of 16Be. A single-proton knockout reaction from a 53 MeV/u 17B beam was used to populate the ground state of 16Be. 16Be is bound with respect to the emission of one neutron and unbound to two-neutron emission. The dineutron character of the decay is evidenced by a small emission angle between the two neutrons. The two-neutron separation energy of 16Be was measured to be 1.35(10) MeV, in good agreement with shell model calculations, using standard interactions for this mass region.
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Sasano M, Perdikakis G, Zegers RGT, Austin SM, Bazin D, Brown BA, Caesar C, Cole AL, Deaven JM, Ferrante N, Guess CJ, Hitt GW, Meharchand R, Montes F, Palardy J, Prinke A, Riley LA, Sakai H, Scott M, Stolz A, Valdez L, Yako K. Gamow-Teller transition strengths from 56Ni. PHYSICAL REVIEW LETTERS 2011; 107:202501. [PMID: 22181727 DOI: 10.1103/physrevlett.107.202501] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Indexed: 05/31/2023]
Abstract
A new technique to measure (p,n) charge-exchange reactions in inverse kinematics at intermediate energies on unstable isotopes was successfully developed and used to study the (56)Ni(p,n) reaction at 110 MeV/u. Gamow-Teller transition strengths from (56)Ni leading to (56)Cu were obtained and compared with shell-model predictions in the pf shell using the KB3G and GXPF1A interactions. The calculations with the GXPF1A interaction reproduce the experimental strength distribution much better than the calculations that employed the KB3G interaction, indicating deficiencies in the spin-orbit and proton-neutron residual potentials for the latter. The results are important for improving the description of electron-capture rates on nuclei in the iron region, which are important for modeling the late evolution of core-collapse and thermonuclear supernovae.
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Ascher P, Audirac L, Adimi N, Blank B, Borcea C, Brown BA, Companis I, Delalee F, Demonchy CE, de Oliveira Santos F, Giovinazzo J, Grévy S, Grigorenko LV, Kurtukian-Nieto T, Leblanc S, Pedroza JL, Perrot L, Pibernat J, Serani L, Srivastava PC, Thomas JC. Direct observation of two protons in the decay of 54Zn. PHYSICAL REVIEW LETTERS 2011; 107:102502. [PMID: 21981498 DOI: 10.1103/physrevlett.107.102502] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2011] [Indexed: 05/31/2023]
Abstract
The two protons emitted in the decay of 54Zn have been individually observed for the first time in a time projection chamber. The total decay energy and the half-life measured in this work agree with the results obtained in a previous experiment. Angular and energy correlations between the two protons are determined and compared to theoretical distributions of a three-body model. Within the shell model framework, the relative decay probabilities show a strong contribution of the p2 configuration for the two-proton emission. After 45Fe, the present result on 54Zn constitutes only the second case of a direct observation of the ground state two-proton decay of a long-lived isotope.
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