arXiv subjects

J. H. Hamilton

Publications and source records attributed to J. H. Hamilton.

10 recordsLinked to original sources

arXiv2026

First observation of multi-phonon $\gamma$-vibrations in an odd-odd nuclear system

The identification of the first multi-phonon $\gamma$-vibrational bands in an odd-odd neutron-rich nucleus of the nuclear chart is presented. These high spin structures of hard to access $^{104}_{41}$Nb$_{63}$, produced in fission, were studied by combining a spectrometer with isotopic resolution coupled to a $\gamma$-ray tracking array and independently high-fold $\gamma$ coincidence measurements. Triaxial Projected Shell Model calculations for the high-spin states are in good agreement with the measured observables for the yrast, one-phonon and two-phonon $\gamma$ bands. The possibility of an oblate shape of an isomeric state and coexistence of triaxial and oblate configurations are investigated from the decay of the 141 keV isomer. The present work illustrates the robustness of vibration excitations in the presence of odd valence proton and neutron as well as the possibly coexisting shapes beyond the $N=60$ transitional region.

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arXiv2026

Level structure of light neutron-rich La isotopes beyond the N=82 shell closure

The high spin excited states of Lanthanum isotopes $^{140-143}$La, above the $N=82$ closed shell, have been populated in fission reactions. The prompt $\gamma$-ray transitions were measured using two complementary methods; a) in coincidence with the isotopically identified fragments produced in the fission of the $^{238}$U+$^{9}$Be system using the VAMOS++ and the AGATA spectrometers and b) high statistics three-fold $\gamma-\gamma-\gamma$ and four-fold $\gamma-\gamma-\gamma-\gamma$ coincidence data from the spontaneous fission of $^{252}$Cf using the Gammasphere. This work reports the first identification of a pair of parity doublet structures in $^{143}$La and the new high spin level structure in $^{140-142}$La from prompt $\gamma$-ray spectroscopy. The level structures are interpreted in terms of the systematics of neighbouring odd-$Z$ nuclei above $Z=50$ shell closure and large-scale shell model calculations. The present results indicate the presence of stable octupole deformation, in $^{143}$La. The excitation energy pattern and their comparison with neighbouring isotones, moving away from the N=82 closed shell, point towards a transition from single particle structures to an alternating parity rotational band structure in the La isotopic chain.

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arXiv2025

Shape evolution in neutron-rich odd-even $^{105-109}$Nb isotopes

Neutron-rich nuclei around $Z\sim40$ exhibit multiple shape transitions. This region shows one of the sharpest transitions in the nuclear chart, from a spherical vibrator at $N=58$ to a strongly deformed prolate shape at $N=60$, with largest deformations seen for $_{38}$Sr and $_{40}$Zr. Below $Z=36$, a spherical-to-oblate transition is predicted, while above $Z=42$ and $N\ge60$, the shape evolves from axial to triaxial. Even-$Z$ nuclei have been well studied, but odd-$Z$ isotopes such as Nb offer additional insights into these mechanisms. The Nb isotopes lie at the boundary between axially deformed Zr and triaxially deformed Mo nuclei. This work explores the structure of neutron-rich Nb nuclei up to $N=68$, aiming to understand shape evolution with isospin and the onset of triaxiality. Two complementary fission experiments were used: (i) $^{238}$U+$^9$Be at GANIL in inverse kinematics with AGATA, EXOGAM, and VAMOS++, allowing prompt and delayed $\gamma$-ray spectroscopy with isotopic identification; (ii) spontaneous fission of $^{252}$Cf with the Gammasphere array providing high-fold $\gamma$-coincidence data. The level scheme of $^{105}$Nb was significantly extended with two new negative-parity bands. A revised scheme is proposed for $^{107}$Nb, differing from previous results, and new structures are reported in $^{109}$Nb. The signature splitting analysis indicates triaxial deformation for positive-parity bands, while negative-parity bands show axial symmetry, similar to Zr. This reveals a shape coexistence in neutron-rich Nb nuclei.

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arXiv2021

Pseudo spin doublet bands and Gallagher Moszkowski doublet bands in $^{100}$Y

New transitions in neutron rich $^{100}$Y have been identified in a $^9$Be+$^{238}$U experiment with mass- and Z- gates to provide full fragment identification. These transitions and high spin levels of $^{100}$Y have been investigated by analyzing the high statistics $γ$-$γ$-$γ$ and $γ$-$γ$-$γ$-$γ$ coincidence data from the spontaneous fission of $^{252}$Cf at the Gammasphere detector array. Two new bands, 14 new levels and 23 new transitions have been identified. The $K^π=4^+$ new band decaying to an 1s isomeric state is assigned to be the high-$K$ Gallagher-Moszkowski (GM) partner of the known $K^π=1^+$ band, with the $π5/2[522] \otimes ν3/2[411]$ configuration. This 4$^+$ band is also proposed to be the pseudo spin partner of the new $K^π=5^+$ band with a 5$^{+}$ $π5/2[422] \otimes ν5/2[413]$ configuration, to form a $π5/2[422] \otimes ν[312$ $5/2,3/2]$ neutron pseudospin doublet. Constrained triaxial covariant density functional theory and quantal particle rotor model calculations have been applied to interpret the band structure and available electromagnetic transition probabilities and are found in good agreement with experimental values.

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arXiv2020

Anomalous Neutron Yields Confirmed for Ba-Mo and Newly Observed for Ce-Zr from Spontaneous Fission of $^{252}$Cf

We reinvestigated the neutron multiplicity yields of Ba-Mo, Ce-Zr, Te-Pd, and Nd-Sr from the spontaneous fission of $^{252}$Cf; by (i) using both $γ$-$γ$-$γ$-$γ$ and $γ$-$γ$-$γ$ coincidence data, (ii) using up to date level scheme structures, and (iii) cross-checking analogous energy transitions in multiple isotopes, we have achieved higher precision than previous analyses. Particular attention was given to the Ba-Mo pairs where our results clearly confirm that the Ba-Mo yield data have a second hot fission mode where 8, 9, 10, and now 11 neutron evaporation channels are observed. These are the first observations of the 11 neutron channel. These 8-11 neutron channels are observed for the first time in the Ce-Zr pairs, but are not observed in other fission pairs. The measured intensities of the second mode in Ba-Mo and Ce-Zr pairs are $\sim$1.5(4)$\%$ and $\sim$1.0(3)$\%$, respectively. These high neutron number evaporation modes can be an indication of hyperdeformation and/or octupole deformation in $^{143-145}$Ba and in $^{146,148}$Ce at scission to give rise to such high neutron multiplicities.

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arXiv2019

Deformed band structures in neutron-rich $^{152-158}$Pm isotopes

High spin band structures of neutron-rich $^{152-158}$Pm isotopes have been obtained from the measurement of prompt $γ$-rays of isotopically identified fragments produced in fission of $^{238}$U+$^{9}$Be and detected using the VAMOS++ magnetic spectrometer and EXOGAM segmented Clover array at GANIL and also from the high statistics $γ$-$γ$-$γ$ and $γ$-$γ$-$γ$-$γ$ data from the spontaneous fission of $^{252}$Cf using Gammasphere. The excited states in $^{157}$Pm and those above the isomers in even-A Pm isotopes $^{152,154,156,158}$Pm have been identified for the first time. The spectroscopic information on the rotational band structures in odd-A Pm isotopes has been extended considerably to higher spins and the possibility of the presence of reflection asymmetric shapes is explored. The configuration assignments are based on the results of Cranked Relativistic Hartree-Bogoliubov calculations. From the systematics of bands in odd-A Pm isotopes and weak population of opposite parity bands, octupole deformed shapes in neutron rich Pm isotopes beyond $N=90$ seem unlikely to be present.

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arXiv2015

Identification of new transitions and mass assignments of levels in $^{143-153}$Pr

The previously reported levels assigned to 151,152,153Pr have recently been called into question regarding their mass assignment. The above questioned level assignments are clarified by measuring g-transitions tagged with A and Z in an in-beam experiment in addition to the measurements from 252Cf spontaneous fission (SF) and establish new spectroscopic information from $N=84$ to $N=94$ in the Pr isotopic chain. The isotopic chain 143-153Pr has been studied from the spontaneous fission of 252Cf by using Gammasphere and also from the measurement of the prompt g-rays in coincidence with isotopically-identified fission fragments using VAMOS++ and EXOGAM at GANIL. The latter were produced using 238U beams on a 9Be target at energies around the Coulomb barrier. The g-g-g-g data from 252Cf (SF) and those from the GANIL in-beam A- and Z-gated spectra were combined to unambiguously assign the various transitions and levels in 151,152,153Pr and other isotopes. New transitions and bands in 145,147,148,149,150Pr were identified by using g-g-g and g-g-g-g coincidences and A and Z gated g-g spectra. The transitions and levels previously assigned to 151,153Pr have been confirmed by the (A,Z) gated spectra. The transitions previously assigned to 152Pr are now assigned to 151Pr on the basis of the (A,Z) gated spectra. Two new bands with 20 new transitions in 152Pr and one new band with 7 new transitions in 153Pr are identified from the g-g-g-g coincidence spectra and the (A,Z) gated spectrum. In addition, new g-rays are also reported in 143-146Pr. New levels of 145,147-153Pr have been established, reliable mass assignments of the levels in 151,152,153Pr have been reported and new transitions have been identified in 143-146Pr showing the new avenues that are opened by combining the two experimental approaches.

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arXiv2007

IBM-1 description of the fission products $^{108,110,112}$Ru

IBM-1} calculations for the fission products $^{108,110,112}$Ru have been carried out. The even-even isotopes of Ru can be described as transitional nuclei situated between the U(5) (spherical vibrator) and SO(6) ($γ$-unstable rotor) symmetries of the Interacting Boson Model. At first, a Hamiltonian with only one- and two-body terms has been used. Excitation energies and $B$(E2) ratios of gamma transitions have been calculated. A satisfactory agreement has been obtained, with the exception of the odd-even staggering in the quasi-$γ$ bands of $^{110,112}$Ru. The observed pattern is rather similar to the one for a rigid triaxial rotor. A calculation based on a Hamiltonian with three-body terms was able to remove this discrepancy. The relation between the IBM and the triaxial rotor model was also examined.

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arXiv2000

The Quasi-Molecular Stage of Ternary Fission

We developed a three-center phenomenological model,able to explain qualitatively the recently obtained experimental results concerning the quasimolecular stage of a light-particle accompanied fission process. It was derived from the liquid drop model under the assumption that the aligned configuration, with the emitted particle between the light and heavy fragment, is reached by increasing continuously the separation distance, while the radii of the heavy fragment and of the light particle are kept constant. In such a way,a new minimum of a short-lived molecular state appears in the deformation energy at a separation distance very close to the touching point. This minimum allows the existence of a short-lived quasi-molecular state, decaying into the three final fragments.The influence of the shell effects is discussed. The half-lives of some quasimolecular states which could be formed in the $^{10}$Be and $^{12}$C accompanied fission of $^{252}$Cf are roughly estimated to be the order of 1 ns, and 1 ms, respectively.

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arXiv1998

Neutronless $^{10}$be-Accompanied Ternary Fission of $^{252}$Cf}

A new type of decay corresponding to the neutronless $^{10}$Be-accompanied fragmentation of $^{252}$Cf is studied. We employ a cluster model similar to the model used for the description of cluster radioactivity. No preformation factors were considered. The ternary relative isotopic yields were calculated as the ratio of the penetrability of a given ternary fragmentation over the sum of penetrabilities of all possible ternary neutronless fragmentations. The corresponding barriers between the light and heavy fragment and between the $^{10}$Be cluster and the two heavier fragments were computed with the help of a double folding potential generated by M3Y-$NN$ effective interaction and realistic fragment ground state deformations. Also, we studied the influence of the fragment excitation energies on the yields, by including the level densities and the $β$-stretching of the fragments. The new phenomenon could be experimentally observed by the triple gamma coincidence technique between the fragments and $^{10}$Be.

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