Citation for published version (APA): Tandel, S. K., Chowdhury, P., Kondev, F. G., Janssens, R. V. F., Khoo, T. L., Carpenter, M. P., Lauritsen, T., Lister, C. J., Seweryniak, D., Zhu, S., Deacon, A. N., Freeman, S. J., Hammond, N. J., Jones, G. D., Moore, E. F., & Smith, J. F. (2016). Configurations and decay hindrances of high-K states in 180 Hf. Physical Review C, 94, [064304]. https://doi.org/10.1103/PhysRevC.94.064304

Multi-quasiparticle high-K states, several of which are isomeric, were observed in Hf-180 with the Gammasphere array. Lifetimes in the ns-mu s range were determined using centroid-shift and decay measurements within a mu s coincidence time window. The configurations of high-K states involve two and four quasiparticles, with states up to K-pi = (18(-)) established. High-K excitations are found to be progressively more favored with increasing excitation energy. The K quantum number is quite robust up to the highest spins observed, as evidenced by the large values of the reduced hindrance for isomeric decays. Rotational bands built on three high-K states are identified, and the measured branching ratios in these sequences enable the assignment of underlying configurations. Multi-quasiparticle calculations using the Lipkin-Nogami approach for pairing, with blocking included, reproduce the observed high-K energies quite well.

Background: Obtaining reaction rates for nuclear astrophysics applications is often limited by the availability of radioactive beams. Indirect techniques to establish reaction rates often rely heavily on the properties of excited states inferred from mirror symmetry arguments. Mirror energy differences can depend sensitively on nuclear structure effects.Purpose: The present work sets out to establish a detailed comparison of mirror symmetry in the A = 23, T = 1/2 mirror nuclei Na-23 and Mg-23 both to high spin, and high excitation energy, including beyond the proton threshold. These data can be used to benchmark state-of-the-art shell-model calculations of these nuclei.Methods: Excited states in Na-23 and Mg-23 were populated using the C-12(C-12, p) and C-12(C-12,n) reactions at beam energies of 16 and 22 MeV, and their resulting gamma decay was measured with Gammasphere.Results: Level schemes for Na-23 and Mg-23 have been considerably extended; highly excited structures have been found in Na-23, as well as their counterparts in Mg-23 for previously known rotational structures in Na-23. Mirror symmetry has been investigated up to an excitation energy of 8 MeV and spin-parity of 13/2(+). Excited states in the region above the proton threshold have been studied in both nuclei.Conclusions: A detailed exploration of mirror symmetry has been performed which heavily constrains expectations as to how mirror energy differences should evolve for different structures. Agreement with shell-model calculations provides confidence in using such estimations where real data are absent.

High-spin states (I less than or similar to 50h) of the odd-odd nucleus Ta-170 have been investigated with the Sn-124(V-51, 5n) reaction. The resolving power of Gammasphere has allowed for the observation of eleven rotational bands ( eight of which are new) and over 430 transitions (similar to 350 of which are new) in this nucleus. Many interband transitions have been observed such that the relative spins and excitation energies of the 11 bands have been established. This is an unusual circumstance in an odd-odd study. Configurations have been assigned to most of these bands based upon features such as alignment properties, band crossings, B(M1)/B(E2) ratios, and the additivity of Routhians. A systematic study of the frequency at which normal signature ordering occurs in the pi h(9/2)nu i(13/2) band has been performed and it is found that its trend is opposite to that observed in the pi h(11/2)nu i(13/2) bands. A possible interpretation of these trends is discussed based on a proton-neutron interaction.

A measurement of the {Beta}-delayed {alpha} decay of {sup 16}N using a set of twin ionization chambers is described. Sources were made by implantation, using a {sup 16}N beam produced via the In-Flight Technique. The energies and emission angles of the {sup 12}C and {alpha} particles were measured in coincidence and very clean {alpha} spectra, down to energies of 450 keV, were obtained. The structure of the spectra from this experiment is in good agreement with results from previous measurements. An analysis of our data with the same input parameters as used in earlier studies gives S{sub E!}(300)=86{+-}22keVb for the E1 component of the S-factor. This value is in excellent agreement with the results obtained from various direct and indirect measurements. In addition, the influence of new measurements including the phase shift from Tischhauser et al on the value of S{sub E1} is discussed.

A measurement of the beta-delayed alpha decay of N-16 using a set of twin ionization chambers is described. Sources were made by implantation, using a N-16 beam produced via the In-Flight Technique. The energies and emission angles of the C-12 and alpha particles were measured in coincidence and very clean alpha spectra, down to energies of 450 keV, were obtained. The structure of the spectra from this experiment is in good agreement with results from previous measurements. An analysis of our data with the same input parameters as used in earlier studies gives S-E1(300) = 86 +/- 22 keVb for the E1 component of the S-factor. This value is in excellent agreement with results obtained from various direct and indirect measurements. In addition, the influence of new measurements including the phase shift data from Tischhauser et al. on the value of S-E1(300) is discussed.

The identification of single-particle states in heavy actinide nuclei by means of studying their decay schemes plays a seminal role in understanding the structure of the heaviest elements and testing the predictive power of modern theoretical models. The heaviest odd-mass nuclides available in sufficient quantity for detailed decay spectroscopic studies are 20-h Fm-255 (for neutrons) and 20-d Es-253 (for protons). Decay spectra of these isotopes, together with those for the odd-odd 276-d Es-254 nuclide, were measured using a variety of a-particle and gamma-ray spectroscopy techniques. Well-defined decay data are also essential pre-requisites for the detection and accurate characterization of fissile radionuclides. The parameters of greatest relevance include actinide half-lives, branching fractions, and a-particle and gamma-ray energies and emission probabilities. Their quantification to good accuracy provides the means of monitoring their presence, behavior and transport in nuclear facilities as well as any clandestine movement and usage. As a consequence of recommendations made at recent IAEA research coordination meetings on "Updated Decay Data Library for Actinides", measurements were under-taken to determine specific decay data of the more inadequately defined radionuclides.

We have studied the properties of the unbound isotope of helium He-7, using the H-2(Li-8,He-3)He-7 reaction. When combined with prior measurements of the H-2(He-6,p)He-7 reaction the data present a consistent picture for the low-lying excited states of He-7, specifically the negative parity sequence 3/2(-) (ground state) 1/2(-) (first-excited) and 5/2(-) (second-excited). The shapes but not the absolute magnitudes of the angular distributions are reproduced by ab-initio theory coupled with a DWBA reaction framework.

We have studied the properties of the unbound isotope of helium 7He, using the 2H(8Li,3He)7He reaction. When combined with prior measurements of the 2H(6He,p)7He reaction the data present a consistent picture for the low‐lying excited states of 7He, specifically the negative parity sequence 3/2− (ground state) 1/2− (first‐excited) and 5/2− (second‐excited). The shapes but not the absolute magnitudes of the angular distributions are reproduced by ab‐initio theory coupled with a DWBA reaction framework.

The 12C(α,γ)16O reaction is of great importance for the understanding the nuclear synthesis and explosion mechanism of the supernova. The cross section at the relevant stellar burning energies, around 300 keV, is dominated by the sub‐threshold resonances. The 16N β‐delayed α decay data provide the most sensitive constrain on this sub‐threshold resonance. Using twin‐ionization chambers, we have measured the α particles and 12C recoil nuclei in coincidence. The spectrum has been fitted together with the published 12C(α,γ)16O data and the elastic scattering phase shift data using R‐matrix. The SE1 factor at 300 keV has been determined as 73±21 keVb.

We report on a study of the structure of the unbound nucleus 7 He utilizing the proton-removal reaction 2 H( 8 Li, 3 He) 7 He. Combining the present results with those of our prior measurements of the neutron-adding reaction 2H( 6 He, p) 7 He, a consistent picture emerges for the low-lying excitations in 7 He. Specifically, the negative-parity sequence of resonances, in order of excitation energies, is consistent with 3/2 - , 1/2 - , and 5 /2 - . The stable-beam reactions 2 H( 7 Li, t) 6 Li and 2 H( 7 Li, 3 He) 6 He were also measured. The results are compared with the predictions of nuclear structure models, including those of ab initio quantum Monte Carlo calculations.

We report on a study of the structure of the unbound nucleus He-7 utilizing the proton-removal reaction H-2(Li-8,He-3)He-7. Combining the present results with those of our prior measurements of the neutron-adding reaction H-2(He-6,p)He-7, a consistent picture emerges for the low-lying excitations in He-7. Specifically, the negative-parity sequence of resonances, in order of excitation energies, is consistent with 3/2(-),1/2(-), and 5/2(-). The stable-beam reactions H-2(Li-7,t)Li-6 and H-2(Li-7,He-3)He-6 were also measured. The results are compared with the predictions of nuclear structure models, including those of ab initio quantum Monte Carlo calculations.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Xiaodong Tang, K. E. Rehm, I. Ahmad, C. R. Brune, A. Champagne, J. P. Greene, A. A. Hecht, D. Henderson, R. V. F. Janssens, C. L. Jiang, L. Jisonna, D. Kahl, E. F. Moore, M. Notani, R. C. Pardo, N. Patel, M. Paul, G. Savard, J. P. Schiffer, R. E. Segel, S. Sinha, B. Shumard, A. H. Wuosmaa; The SE1 factor of the 12C(α,γ)16O Reaction and the 16N β‐delayed α Decay. AIP Conf. Proc. 24 January 2008; 972 (1): 261–269. https://doi.org/10.1063/1.2870303 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

Gas catchers allow the transformation of radioactive recoils from various sources into a good optical quality low-energy radioactive beam that is then available for experiments at low-energy or for further acceleration. The CARIBU project uses such a large gas catcher to create beams of neutron-rich isotopes from a Californium source for post-acceleration through the ATLAS superconducting linac to open new research opportunities for nuclear structure physics and astrophysics. The RF gas catcher developed at Argonne has now demonstrated operation at the high intensity required for this application.

The C-12(alpha,gamma)O-16 reaction is of great importance for the understanding the nuclear synthesis and explosion mechanism of the supernova. The cross section at the relevant stellar burning energies, around 300 keV, is dominated by the sub-threshold resonances. The N-16 beta-delayed alpha decay data provide the most sensitive constrain on this sub-threshold resonance. Using twin-ionization chambers, we have measured the alpha particles and C-12 recoil nuclei in coincidence. The spectrum has been fitted together with the published C-12(alpha,gamma)O-16 data and the elastic scattering phase shift data using R-matrix. The S-E1 factor at 300 keV has been determined as 73 +/- 21 keVb.

With the Doppler Shift Attenuation Method, quadrupole transition moments Q(t) were determined for the two recently proposed triaxial strongly deformed (TSD) bands in Tm-163. The measured Q(t) values indicate that the deformation of these bands is larger than that of the yrast signature partners. However, the measured values are smaller than those predicted by theory. This observation appears to be valid for TSD bands in several nuclei of the region.

X. D. Tang,* K. E. Rehm, I. Ahmad, C. R. Brune, A. Champagne, J. P. Greene, A. A. Hecht, D. Henderson, R. V. F. Janssens, C. L. Jiang, L. Jisonna, D. Kahl, E. F. Moore, M. Notani, R. C. Pardo, N. Patel, M. Paul, G. Savard, J. P. Schiffer, R. E. Segel, S. Sinha, B. Shumard, and A. H. Wuosmaa Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA Ohio University, Athens, Ohio 45701, USA University of North Carolina, Chapel Hill, North Carolina 27599, USA University of Maryland, College Park, Maryland 20742, USA Northwestern University, Evanston, Illinois 60208, USA Michigan State University, East Lansing, Michigan 48824, USA Colorado School of Mines, Golden, Colorado 80401, USA Hebrew University, Jerusalem, Israel Western Michigan University, Kalamazoo, Michigan 49008, USA (Received 16 March 2007; published 3 August 2007)