arXiv subjects

B. Herskind

Publications and source records attributed to B. Herskind.

14 recordsLinked to original sources

arXiv2017

Structure of the neutron mid-shell nuclei $^{111,113}_{\quad \ 47}$Ag$_{64,66}$

$^{111}$Ag and $^{113}$Ag were produced in induced fission reaction, where yrast and near-yrast states were populated. To interpret the new data the Interacting Boson-Fermion model was used. A good agreement with the experimental data is achieved, suggesting that the two Ag nuclei have a well developed collectivity, superimposed on $πg_{9/2}^{-3}$ excitations previously observed throughout the entire isotopic chain.

nucl-ex↗

arXiv2014

Co-existing structures in 105Ru

New positive-parity states, having a band-like structure, were observed in 105Ru. The nucleus was produced in induced fission reaction and the prompt gamma-rays, emitted from the fragments, were detected by the EUROBALL III multi-detector array. The partial scheme of excited 105Ru levels is analyzed within the Triaxial-Rotor-plus-Particle approach.

nucl-ex↗

arXiv2012

Observation of Positive-Parity Bands in $^{109}$Pd and $^{111}$Pd: Enhanced $γ$-Softness

The neutron-rich nuclei $^{109}$Pd and $^{111}$Pd were produced as fission fragments following the $^{30}$Si + $^{168}$Er reaction at 142 MeV. Using the identification based on the coincidences with the complementary fission fragments, the only positive-parity bands observed so far in $^{109}$Pd and $^{111}$Pd emerged from this work. A band, built on top of the 5/2$^+$ ground state exhibiting $ΔI$ = 1 energy-level staggering, was observed in each of these nuclei. Both nuclei of interest, $^{109}$Pd and $^{111}$Pd, are suggested to lie in the transitional region of Pd isotopes of maximum $γ$-softness. The ground states of both nuclei are predicted by TRS calculations to be extremely $γ$-soft with shallow triaxial minima. The first crossing in the new bands is proposed to be due to an alignment of $h^2_{11/2}$ neutrons.

nucl-ex↗

arXiv2008

Probing the order-to-chaos region in superdeformed 151Tb and 196Pb nuclei with continuum gamma-transitions

The gamma-decay associated with the warm rotation of the superdeformed (SD) nuclei 151Tb and 196Pb has been measured with the EUROBALL IV array. Several independent quantities provide a stringent test of the population and decay dynamics in the SD well. A Monte Carlo simulation of the gamma-decay based on microscopic calculations gives remarkable agreement with the data only assuming a large enhancement of the B(E1) strength at low excitation energy, which may be related to the evidence for octupole vibrations in both mass regions.

nucl-ex↗

arXiv2006

Strong Deformation Effects in Hot Rotating 46Ti

Exotic-deformation effects in 46Ti nucleus were investigated by analysing the high-energy gamma-ray and the alpha-particle energy spectra. One of the experiments was performed using the charged-particle multi-detector array ICARE together with a large volume (4"x4") BGO detector. The study focused on simultaneous measurement of light charged particles and gamma-rays in coincidence with the evaporation residues. The experimental data show a signature of very large deformations of the compound nucleus in the Jacobi transition region at the highest spins. These results are compared to data from previous experiments performed with the HECTOR array coupled to the EUROBALL array, where it was found that the GDR strength function is highly fragmented, strongly indicating a presence of nuclei with very large deformation.

nucl-ex↗

arXiv2004

GDR Feeding of the Highly-Deformed Band in 42Ca

The gamma-ray spectra from the decay of the GDR in the compound nucleus reaction 18O+28Si at bombarding energy of 105 MeV have been measured in an experiment using the EUROBALL IV and HECTOR arrays. The obtained experimental GDR strength function is highly fragmented, with a low energy (10 MeV) component, indicating a presence of a large deformation and Coriolis effects. In addition, the preferential feeding of the highly-deformed band in 42Ca by this GDR low energy component is observed.

nucl-ex↗

arXiv2004

Violation and persistence of the K-quantum number in warm rotating nuclei

The validity of the K-quantum number in rapidly rotating warm nuclei is investigated as a function of thermal excitation energy U and angular momentum I, for the rare-earth nucleus 163Er. The quantal eigenstates are described with a shell model which combines a cranked Nilsson mean-field and a residual two-body interaction, together with a term which takes into account the angular momentum carried by the K-quantum number in an approximate way. K-mixing is produced by the interplay of the Coriolis interaction and the residual interaction; it is weak in the region of the discrete rotational bands (U \lesim 1MeV), but it gradually increases until the limit of complete violation of the K-quantum number is approached around U \sim 2 - 2.5 MeV. The calculated matrix elements between bands having different K-quantum numbers decrease exponentially as a function of $ΔK$, in qualitative agreement with recent data.

nucl-th↗

arXiv2003

Evidence for the Jacobi shape transition in hot 46Ti

The gamma-rays from the decay of the GDR in 46Ti compound nucleus formed in the 18O+28Si reaction at bombarding energy 105 MeV have been measured in an experiment using a setup consisting of the combined EUROBALL IV, HECTOR and EUCLIDES arrays. A comparison of the extracted GDR lineshape data with the predictions of the thermal shape fluctuation model shows evidence for the Jacobi shape transition in hot 46Ti. In addition to the previously found broad structure in the GDR lineshape region at 18-27 MeV caused by large deformations, the presence of a low energy component (around 10 MeV), due to the Coriolis splitting in prolate well deformed shape, has been identified for the first time.

nucl-ex↗

arXiv2002

Rotational Damping and Compound Formation in Warm Rotating Nuclei

The rotational damping width Γ_{rot} and the compound damping width Γ_{comp} are two fundamental quantities that characterize rapidly rotating compound nuclei having finite thermal excitation energy. A two-component structure in the strength function of consecutive E2 transitions reflects the two widths, and it causes characteristic features in the double and triple gamma-ray spectra. We discuss a new method to extract experimentally values of Γ_{rot} and Γ_{comp}. The first preliminary result of this method is presented.

nucl-th↗

arXiv2001

Search for the Jacobi Instability in Rapidly Rotating 46Ti* Nuclei

The possible existence of Jacobi shape transition in hot 46Ti at high angular momenta was investigated with the Giant Dipole Resonance exclusive experiments. The GDR spectra and the angular distributions are consistent with predictions of the thermal shape fluctuation model indicating elongated nuclear shapes.

nucl-ex↗

arXiv2001

Gamma-ray strength functions in thermally excited rotating nuclei

A general discussion and illustration is given of strength functions for rotational transitions in two-dimensional E(gamma_1) x E(gamma_2) spectra. Especially, a narrow component should be proportional to the compound damping width, related to the mixing of basis rotational bands into compound bands with fragmented transition strength. Three E(gamma_1) x E(gamma_2) spectra are made by setting gates on triple coincidences, selecting cascades which feed into specific low-lying bands in the nucleus 168Hf. In each of the gated spectra, we find a ridge, carrying about 100 decay paths. This ridge is ascribed to rotational transitions in the excitation energy range of 1.0 to 1.5 MeV above the yrast line. The FWHM of the ridges are around 40 keV, about a factor of two smaller than calculated on the basis of mixed cranked mean field bands.

nucl-th↗

arXiv1999

Probing the width of compound states with rotational gamma rays

The intrinsic width of (multiparticle-multihole) compound states is an elusive quantity, of difficult direct access, as it is masked by damping mechanisms which control the collective response of nuclei. Through microscopic cranked shell model calculations, it is found that the strength function associated with two-dimensional gamma-coincidence spectra arising from rotational transitions between states lying at energies >1 MeV above the yrast line, exhibits a two-component structure controlled by the rotational (wide component) and compound (narrow component) damping width. This last component is found to be directly related to the width of the multiparticle-multihole autocorrelation function.

nucl-th↗

arXiv1992

Chaotic Behavior in Warm Deformed Nuclei Induced by Residual Two-Body Interactions

Band mixing calculations in rapidly rotating well-deformed nuclei are presented, investigating the properties of energy levels and rotational transitions as a function of excitation energy. Substantial fragmentation of E2 transitions is found for $E_x \gsim$ 800 keV above yrast, which represents the onset of rotational damping. Above $E_x \approx $ 2 MeV, energy levels and E2 strengths display fluctuations typical of quantum chaotic systems, which are determined by the high multipole components of the two-body residual interaction.

nucl-th↗

arXiv1992

Poisson and Porter-Thomas Fluctuations in off-Yrast Rotational Transitions

Fluctuations associated with stretched E2 transitions from high spin levels in nuclei around $^{168}$Yb are investigated by a cranked shell model extended to include residual two-body interactions. It is found that the gamma-ray energies behave like random variables and the energy spectra show the Poisson fluctuation, in the cranked mean field model without the residual interaction. With two-body residual interaction included, discrete transition pattern with unmixed rotational bands is still valid up to around 600 keV above yrast, in good agreement with experiments. At higher excitation energy, a gradual onset of rotational damping emerges. At 1.8 MeV above yrast, complete damping is observed with GOE type fluctuations for both energy levels and transition strengths(Porter-Thomas fluctuations).

nucl-th↗