Nuclear Data Sheets for A = 232

Browne, E.

doi:10.1016/j.nds.2006.09.001

Cited by 55 publications

(40 citation statements)

References 223 publications

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“…This is shown in Fig. 1 for the four actinide nuclei 222 Ra [1,23], 228 Th [1,24], 232 U [1,25], and 236 Pu [1,26] modeled as 208 Pb + 14 C, 20 O, 24 Ne, and 28 Mg, respectively, where we plot the radial wave functions u L (R) obtained from a numerical solution of the Schrödinger equation for the potential V (R) described above and the L values of 0, 4, 8, 12, 16, and 20. The main differences between the radial wave functions for a given nucleus occur close to the origin and are due to the node number differences.…”

Section: Cluster Modelmentioning

confidence: 89%

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Generation of excitedKbands in heavy nuclei

2011

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It is known that coupling an intrinsic excitation of integer spin and positive parity I + to a rotor having a degenerate set of states L π = 0 + , 2 + , 4 + , . . . , generates a series of K bands. A given value of I + gives rise to several bands labeled by K + = 0 + , 1 + , 2 + , . . . , I + , that is, a total of (I + 1) such bands, in the spectrum of the combined system. We discuss how a binary cluster model of an excited core orbited by a spinless cluster can approximate these conditions. A crucial point is that the radial wave functions of relative motion are very similar for low L, and their radial coupling integrals even more so, such that the wave functions play the model role of a common intrinsic state for the lowest excited states of the system. If the core has a 0 + ground state and a low-lying 2 + excited state, then lifting the degeneracy leads to a ground state K + = 0 + band and low-lying excited K + = 0 + , 1 + , and 2 + bands. Although these are all seen in light nuclei, the K + = 1 + band is conspicuous by its apparent absence in heavy nuclei, and we urge experimental groups to reexamine their data for signs of it.

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Section: Cluster Modelmentioning

confidence: 89%

“…(24), (25), and (26) tell us that all states with J |K| have the same energy E K . The different |K| I thus each correspond to a K band generated by coupling the excitation I of the even-even core to the cluster-core relative rotational motion.…”

Section: Generating the K Bandsmentioning

confidence: 99%

Generation of excitedKbands in heavy nuclei

2011

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“…The empirically inferred values of the first and second barrier heights EA and EB [37], as well as the measured energy of the fission isomer EII [66], are marked.…”

Section: Fig 2 (Color Online) Potential Energy Curves Formentioning

confidence: 99%

Third minima in thorium and uranium isotopes in a self-consistent theory

2013

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Background: Well-developed third minima, corresponding to strongly elongated and reflection-asymmetric shapes associated with dimolecular configurations, have been predicted in some non-self-consistent models to impact fission pathways of thorium and uranium isotopes. These predictions have guided the interpretation of resonances seen experimentally. On the other hand, self-consistent calculations consistently predict very shallow potential energy surfaces in the third minimum region.Purpose: We investigate the interpretation of third-minimum configurations in terms of dimolecular (cluster) states. We study the isentropic potential energy surfaces of selected even-even thorium and uranium isotopes at several excitation energies. In order to understand the driving effects behind the presence of third minima, we study the interplay between pairing and shell effects. Methods:We use the finite-temperature superfluid nuclear density functional theory. We consider two Skyrme energy density functionals: a traditional functional SkM * and a recent functional UNEDF1 optimized for fission studies.Results: We predict very shallow or no third minima in the potential energy surfaces of 232 Th and 232 U. In the lighter Th and U isotopes with N = 136 and 138, the third minima are better developed. We show that the reflection-asymmetric configurations around the third minimum can be associated with dimolecular states involving the spherical doubly-magic 132 Sn and a lighter deformed Zr or Mo fragment. The potential energy surfaces for 228,232 Th and 232 U at several excitation energies are presented. We also study isotopic chains to demonstrate the evolution of the depth of the third minimum with neutron number. Conclusions:We show that the neutron shell effect that governs the existence of the dimolecular states around the third minimum is consistent with the spherical-to-deformed shape transition in the Zr and Mo isotopes around N = 58. We demonstrate that the depth of the third minimum is sensitive to the excitation energy of the nucleus. In particular, the thermal reduction of pairing, and related enhancement of shell effects, at small excitation energies help to develop deeper third minima. At large excitation energies, shell effects are washed out and third minima disappear altogether.

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“…Even though low-spin hyperdeformation has already proved to be a general feature of uranium [8][9][10] and thorium isotopes [11], no HD state has been found in protactinium isotopes so far. In particular, the level scheme of the odd-odd 232 Pa is completely unknown in the 1 st minimum of the potential barrier, only the ground-state properties are known at present (I π gs =2 − ) [12]. The fine structure of the fission resonances of 232 Pa has been studied so far only via the (n, f ) reaction [13] with high resolution, but the results showed no convincing evidence on the existence of HD states.…”

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confidence: 99%

Transmission resonance spectroscopy in the third minimum of232Pa

et al. 2012

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The fission probability of 232 Pa was measured as a function of the excitation energy in order to search for hyperdeformed (HD) transmission resonances using the (d, pf ) transfer reaction on a radioactive 231 Pa target. The experiment was performed at the Tandem accelerator of the MaierLeibnitz Laboratory (MLL) at Garching using the 231 Pa(d, pf ) reaction at a bombarding energy of E d =12 MeV and with an energy resolution of ∆E=5.5 keV. Two groups of transmission resonances have been observed at excitation energies of E * =5.7 and 5.9 MeV. The fine structure of the resonance group at E * =5.7 MeV could be interpreted as overlapping rotational bands with a rotational parameter characteristic to a HD nuclear shape (h 2 /2Θ=2.10±0.15 keV). The fission barrier parameters of 232 Pa have been determined by fitting TALYS 1.2 nuclear reaction code calculations to the overall structure of the fission probability. From the average level spacing of the J=4 states, the excitation energy of the ground state of the 3 rd minimum has been deduced to be EIII=5.05MeV.PACS numbers: 21.10. Re; 24.30.Gd; 25.85.Ge; 27.90.+b The observation of discrete γ transitions between hyperdeformed (HD) nuclear states represents one of the last frontiers of high-spin physics. Although a large community with 4π γ arrays was searching for HD states in very long experiments, no discrete HD γ transition was found in the mass region of A ≈100-130 [1-5]. On the other hand, the existence of low-spin hyperdeformation in the third minimum of the fission barrier is established both experimentally and theoretically in the actinide region [6,7]. Observing transmission resonances as a function of the excitation energy caused by resonant tunneling through excited states in the third minimum of the potential barrier can specify the excitation energies of the HD states. Moreover, the observed states could be ordered into rotational bands and the moments of inertia of these bands can characterize the underlying nuclear shape, proving that these states have indeed a HD configuration.Regarding hyperdeformation, the double-odd nucleus 232 Pa is of great interest. Even though low-spin hyperdeformation has already proved to be a general feature of uranium [8-10] and thorium isotopes [11], no HD state has been found in protactinium isotopes so far. In particular, the level scheme of the odd-odd 232 Pa is completely unknown in the 1 st minimum of the potential barrier, only the ground-state properties are known at present (I π gs =2 − ) [12]. The fine structure of the fission resonances of 232 Pa has been studied so far only via the (n, f ) reaction [13] with high resolution, but the results showed no convincing evidence on the existence of HD states. A possible reason was the rather limited momentum transfer of the (n, f ) reaction at that low neutron energy (E n ≈100 keV), which did not allow for the population of rotational bands. In contrast, the (d, p) reaction can transfer considerable angular momentum, thus full sequences of rotational states with higher sp...

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Nuclear Data Sheets for A = 232

Cited by 55 publications

References 223 publications

Generation of excitedKbands in heavy nuclei

Generation of excitedKbands in heavy nuclei

Third minima in thorium and uranium isotopes in a self-consistent theory

Transmission resonance spectroscopy in the third minimum of232Pa

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