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Carpenter, M. P.

Publications and source records attributed to Carpenter, M. P..

72 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Ground-state and decay properties of neutron-rich 106 Nb

The ground-state properties of neutron-rich 106 Nb and its β decay into 106 Mo have been studied using the CARIBU radioactive-ion-beam facility at Argonne National Laboratory. Niobium-106 ions were extracted from a 252 Cf fission source and mass separated before being delivered as low-energy beams to the Canadian Penning Trap, as well as the X-Array and SATURN β-decay-spectroscopy station. The measured 106 Nb ground-state mass excess of –66202.0(13) keV is consistent with a recent measurement but has three times better precision; this work also rules out the existence of a second long-lived, β-decaying state in 106 Nb above 5 keV in excitation energy. The decay half-life of 106 Nb was measured to be 1.097(21) s, which is 8% longer than the adopted value. Here, the level scheme of the decay progeny, 106 Mo, has been expanded up to ≈ 4 MeV. The distribution of decay strength and considerable population of excited states in 106 Mo of J ≥ 3 emphasizes the need to revise the adopted J π = 1 – ground-state spin-parity assignment of 106 Nb; it is more likely to be J ≥ 3.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Nanosecond isomers and the evolution of collectivity in stable, even- A Hg isotopes

Isomeric states and associated collective structures have been studied up to high spin in 198,200,202 Hg using multinucleon transfer reactions and the Gammasphere array. A coupled rotational band, with possible four-quasiparticle character, is established in 198 Hg. Sequences built on two-quasiparticle, positive- and negative-parity levels are assigned to 202 Hg. New isomers in 202 Hg with I π = (7 – ) and (9 – ), and T 1/2 = 10.4(4) ns and 1.4(3) ns, respectively, have been identified. A half-life of 1.0(3) ns is established for the I π = 12 + state in 200 Hg. B(E2) values deduced from isomeric transitions in Hg isotopes indicate that, while collectivity near the ground state gradually diminishes from N = 112 to N = 124, it is found to increase for the 12 + and 9 – states up to N = 118, followed by a reduction for higher neutron numbers. Calculations using the ultimate cranker code provide insight into the variation of deformation with spin and allow for an understanding of observed band crossings. As a result, the evolution of collectivity with spin, and along the isotopic chain, is described.

190 ≤ A ≤ 219↗
DOE OSTI2021

Highly deformed band structures due to core excitations in 123 Xe

High-spin states in 123 Xe were populated in the 80 Se( 48 Ca, 5n) 123 Xe reaction at a beam energy of 207 MeV. γ-ray coincidence events were recorded with the Gammasphere spectrometer. Four new high-spin bands have been discovered in this nucleus. The bands are compared with those calculated within the framework of cranked Nilsson-Strutinsky and cranked Nilsson-Strutinsky-Bogoliubov models. Furthermore, it is concluded that the configurations of the bands involve two-proton excitations across the Z = 50 as well as excitation of neutrons across the N = 82 shell gaps resulting in a large deformation, ε 2 ≈ 0.30 and γ ≈ 5°.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Quadrupole and octupole collectivity in 143 Ba

The neutron-rich barium nuclei have been the subject of intense interest due to the enhanced octupole correlations they are predicted to exhibit. The observation of enhanced octupole collectivity in 144,146 Ba as measured in sub-barrier Coulomb excitation, consistent with static octupole deformation, has further heightened this interest. In the present work, these studies are extended to the neighboring odd-mass 143 Ba to investigate the interplay between single-particle and collective octupole degrees of freedom. A new measurement of the first 9/2 – -state lifetime is also presented. Reflection-Asymmetric Triaxial Particle Rotor Model calculations indicate that the negative-parity bands in 143 Ba can be understood as a decoupled structure of νh 9/2 parentage, while the positiveparity bands are built on a decoupled octupole phonon. Here, no evidence for E3 excitation is observed in this work, but an upper limit is placed on the E3 matrix element to the lowest octupole band.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

19 Ne level structure for explosive nucleosynthesis

Ne 19 is an important isotope in nuclear astrophysics due to its role in both the F 18 ( p , α ) O 15 and O 15 ( α , γ ) Ne 19 reactions in novae and Type I x-ray bursts, respectively. The energy levels of Ne 19 near the α and proton thresholds ( S α = 3529 keV, S p = 6410 keV) correspond to resonances in both of these reactions. Previous measurements to study the structure of Ne 19 have focused on both regions in an effort to constrain these reaction rates. Discrepancies in the energies, spins, and parities for levels in Ne 19 from previous measurements contribute to the reaction-rate uncertainties. Gamma rays from the depopulation of excited states in Ne 19 were measured to reduce the level-energy uncertainties and inconsistencies in previous spin-parity assignments.The F 19 ( He 3 , t ) Ne 19 reaction was used to elucidate the structure of Ne 19 levels up to E x = 6.9 MeV. The reaction products were measured using Gammasphere ORRUBA: Dual Detectors for Experimental Structure Studies—a coupling of the Oak Ridge Rutgers University Barrel Array and Gammasphere at Argonne National Laboratory. Tritons produced in the reaction were measured in coincidence with γ rays from the deexcitation of Ne 19 energy levels. Previously unobserved transitions allowed for discrepancies in the resonance properties relevant to these two reactions to be resolved. In total, 41 transitions from 21 energy levels were measured in Ne 19 , with 21 of those transitions being previously unobserved. Of particular importance, transitions from two 3 / 2 + states with energies of 6423(3) and 6441(3) keV, crucial for accurate estimations of the F 18 ( p , α ) O 15 reaction rate, were found. Energies and spin-parities of important energy levels near the proton and α thresholds were measured and some of the discrepancies in previous measurements were resolved. Overall, measurement of the two near-threshold 3 / 2 + states reduced the calculated upper limit of the F 18 ( p , α ) O 15 reaction rate by factors of 1.5–17 in the nova temperature range.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Spectroscopy of 30 P and the abundance of 29 Si in presolar grains

The astrophysical 29 Si(p,γ) reaction is expected to play a key role in determining the final 29 Si yields ejected in nova explosions. Such yields are used to accurately identify the stellar origins of meteoritic stardust and recently, distinctive silicon isotopic ratios have been extracted from a number of presolar grains. Here, the light-ion 28 Si( 3 He,p) fusion-evaporation reaction was used to populate low-spin proton-unbound excited states in the nucleus 30 P that govern the rate of the astrophysical 29 Si(p,γ) reaction. In particular, γ decays were observed from resonances up to E r = 500keV, and key resonances at 217 and 315 keV have now been identified as 2 + and 2¯ levels, respectively. Here, the present paper provides the first estimate of the 217-keV resonance strength and indicates that the strength of the 315-keV resonance, which dominates the rate of the 29 Si(p,γ) reaction over the entire peak temperature range of oxygen-neon novae, is higher than previously expected. As such, the abundance of 29 Si ejected during nova explosions is likely to be less than that predicted by the most recent theoretical models.

20 ≤ A ≤ 38↗
DOE OSTI2020

State-of-the-art γ-ray assay of 86 Y for medical imaging

An emerging direction in nuclear medicine is the coupling of a therapeutic isotope with an imaging isotope to form a so-called theranostic pair, which allows one to quantitatively track and image the delivery of the therapeutic isotope. 90 Y is used in several therapy applications and a convenient candidate imaging partner is the positron emitter 86 Y. A 27.6 MBq source of 86 Y was produced at the University of Wisconsin and assayed with the Gammasphere array at Argonne National Laboratory. Over 200 γ-ray transitions were identified, more than double that which was previously known. In conclusion, the positron emission probability inferred from the present level scheme leads to 27.9(12)%, an important (≈14%) reduction with respect to the previously recommended value.

59 ≤ A ≤ 89↗
DOE OSTI2020

Metastable states from multinucleon excitations in 202 Tl and 203 Pb

The excited level structures of 202 Tl and 203 Pb, above the 7 + and 29/2 – isomers, respectively, have been studied. An isomer with I π = 20 + and T 1/2 = 215(10) μs has been established in 202 Tl, and the level scheme extended from I = 10 to 20ℏ with the placement of fifteen new transitions. In 203 Pb, the I π = 37/2 + state is established to be metastable, with T 1/2 = 2.5(3) ns. Levels in both nuclei arise from intrinsic excitations, with likely particle-hole character for the higher-lying states in 203 Pb. The 20 + isomer in 202 Tl is most likely associated with a $πh$ $^{–1}_{11/2}$ Ⓧ ν($i$ $^{–2}_{13/2}$, $f$ $^{–1}_{5/2}$) configuration, while the 37/2 + state in 203 Pb results from the excitation of five neutrons. Furthermore, calculations, using both an empirical approach and the oxbash code, have been performed to aid in the description of the excited level structure.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Onset of high-spin rotational bands in the $N = Z$ nucleus 62 Ga

The fusion-evaporation reaction 28 Si + 40 Ca at 122 MeV beam energy was used to populate high-spin states in the odd-odd $N = Z$ nucleus 62 Ga. With the combination of the Gammasphere spectrometer and the Microball CsI(Tl) charged-particle detector array the decay scheme of 62 Ga was extended beyond 10 MeV excitation energy. The onset of band structures was observed. These high-spin rotational states are interpreted and classified by means of cranked Nilsson-Strutinsky calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Search for Nova Presolar Grains: $γ$-Ray Spectroscopy of 34 Ar and its Relevance for the Astrophysical 33 Cl($p,γ$) Reaction

The discovery of presolar grains in primitive meteorites has launched a new era of research in the study of stellar nucleosynthesis. However, the accurate classification of presolar grains as being of specific stellar origins is particularly challenging. Recently, it has been suggested that sulfur isotopic abundances may hold the key to definitively identifying presolar grains with being of nova origins and, in this regard, the astrophysical Cl 33 ( p , γ ) Ar 34 reaction is expected to play a decisive role. As such, we have performed a detailed γ -ray spectroscopy study of Ar 34 . Excitation energies have been measured with high precision and spin-parity assignments for resonant states, located above the proton threshold in Ar 34 , have been made for the first time. Uncertainties in the Cl 33 ( p , γ ) reaction have been dramatically reduced and the results indicate that a newly identified ℓ = 0 resonance at E r = 396.9 ( 13 ) keV dominates the entire rate for T = 0.25 – 0.40 GK . Furthermore, nova hydrodynamic simulations based on the present work indicate an ejected S 32 / S 33 abundance ratio distinctive from type-II supernovae and potentially compatible with recent measurements of a presolar grain.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

First candidates for $γ$ vibrational bands built on the [ 505 ] 11 / 2 - neutron orbital in odd- A Dy isotopes

In this work, rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the Gd 155 ( α , 2 n ) Dy 157 and Nd 148 ( C 12 , 5 n ) Dy 155 reactions at 25 and 65 MeV, respectively. We report high- K bands, which are conjectured to be the first candidates of a K π = 2 + γ vibrational band, built on the [ 505 ] 11 / 2 - neutron orbital, in both odd- A Dy 155 , 157 isotopes. The coupling of the first excited K = 0 + states or the so-called β vibrational bands at 661 and 676 keV in Dy 154 and Dy 156 to the [ 505 ] 11 / 2 - orbital, to produce a K π = 11 / 2 - band, was not observed in both Dy 155 and Dy 157 , respectively. The implication of these findings on the interpretation of the first excited 0 + states in the core nuclei Dy 154 and Dy 156 are also discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

High- K , two-quasiparticle states in Gd 160

Excited states in Gd 160 were populated via β decay from the low- and high-spin isomers in Eu 160 . The high-spin, K π = 5 - state feeds several two-quasiparticle levels, as well as a sequence associated with a γ vibration and a K π = 4 + , hexadecapole vibrational structure. The decay scheme was significantly improved with the observation of new transitions and states when compared with the two competing level schemes from over four decades ago. Configuration assignments for some of the multiquasiparticle levels have been suggested, based upon decay properties, systematics from neighboring nuclei, and comparisons with theoretical calculations. Finally, in addition, 15 new low-spin states and approximately 60 new transitions were observed resulting from the decay of the low-spin Eu 160 isomer.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Multinucleon transfer in the interaction of 977 MeV and 1143 MeV Hg 204 with Pb 208

A previous study of symmetric collisions of massive nuclei has shown that current models of multinucleon transfer (MNT) reactions do not adequately describe the transfer product yields. To gain further insight into this problem, we have measured the yields of MNT products in the interaction of 977 (E/A = 4.79 MeV) and 1143 MeV (E/A = 5.60 MeV) 204 Hg with 208 Pb. We find that the yield of multinucleon transfer products are similar in these two reactions and are substantially lower than those observed in the reaction of 1257 MeV (E/A = 6.16 MeV) 204 Hg+ 198 Pt. We compare our measurements with the predictions of the GRAZING-F, dinuclear systems (DNS), and improved quantum molecular dynamics (ImQMD) models. We report that for the observed isotopes of the elements Au, Hg, Tl, Pb, and Bi, the measured values of the MNT cross sections are orders of magnitude larger than the predicted values. Furthermore, the various models predict the formation of nuclides near the N = 126 shell, which are not observed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Evolution of collective and noncollective structures in 123 Xe

An experiment involving a heavy-ion-induced fusion-evaporation reaction was carried out where high-spin states of 123 Xe were populated in the 80 Se( 48 Ca,5n) 123 Xe reaction at 207 MeV beam energy. Gamma-ray coincidence events were recorded with the Gammasphere Ge detector array. The previously known level scheme was confirmed and enhanced with the addition of five new band structures and several interband transitions. Furthermore, cranked Nilsson-Strutinsky (CNS) calculations were performed and compared with the experimental results in order to assign configurations to the bands.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Longitudinal Wobbling Motion in Au 187

The rare phenomenon of nuclear wobbling motion has been investigated in the nucleus 187Au. A longitudinal wobbling-bands pair has been identified and clearly distinguished from the associated signature-partner band on the basis of angular distribution measurements. Theoretical calculations in the framework of the particle rotor model are found to agree well with the experimental observations. This is the first experimental evidence for longitudinal wobbling bands where the expected signature partner band has also been identified, and establishes this exotic collective mode as a general phenomenon over the nuclear chart.

150 ≤ A ≤ 189↗