Pavel Petkov - Academia.edu (original) (raw)

Papers by Pavel Petkov

EPJ Web of Conferences, 2014

To investigate the interplay between collective and single particle degrees of freedom in odd nuc... more To investigate the interplay between collective and single particle degrees of freedom in odd nuclei, Recoil distance Doppler-shift and Doppler-shift attenuation lifetime measurements were carried out for levels in 155 Dy in coincidence detection of gamma-rays. 26 lifetimes were determined using the Differential decay curve method. Particle plus triaxial rotor model (PTRM) calculations were performed to compare the experimental level scheme and transition strengths with theoretical ones in order to get information on the quadrupole deformation (ǫ,γ) of the bands. As a result, different quadrupole deformations for the one-quasineutron bands at low and medium spins are deduced.

Physics Letters B, 2014

A simultaneous lifetime and relative g-factor measurement of the 2 + 1 levels in 138,142 Ce was p... more A simultaneous lifetime and relative g-factor measurement of the 2 + 1 levels in 138,142 Ce was performed using the Time Dependent Recoil Into Vacuum (TDRIV) technique. The excitation mechanism was Coulomb excitation in inverse kinematics, and the experimental setup included the Yale plunger device and the Gammasphere array. The latter was used to extract angular distributions for the 2 + 1 → 0 + γ-ray transitions at various target-to-stopper distances. A g(2 + 1) factor of 0.26(8) for 138 Ce was obtained relative to the literature value of g(2 + 1) = 0.21(5) in 142 Ce. In addition, high-precision values of the B(E2; 2 + 1 → 0 +) strengths were obtained. The new data support a proposed subshell closure for the π g 7/2 orbital at Z = 58.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2015

In this article a method for lifetime measurements in the sub-picosecond regime via the Doppler-s... more In this article a method for lifetime measurements in the sub-picosecond regime via the Doppler-shift attenuation method (DSAM) following the inelastic proton scattering reaction is presented. In a pioneering experiment we extracted the lifetimes of 30 excited low-spin states of 96 Ru, taking advantage of the coincident detection of scattered protons and de-exciting γ-rays as well as the large number of particle and γ-ray detectors provided by the SONIC@HORUS setup at the University of Cologne. The large amount of new experimental data shows that this technique is suited for the measurement of lifetimes of excited low-spin states, especially for isotopes with a low isotopic abundance, where (n, n γ) or-in case of investigating dipole excitations-(γ, γ) experiments are not feasible due to the lack of sufficient isotopically enriched target material.

Physical Review C, 2014

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

EPJ Web of Conferences, 2015

Background: Excitations with mixed proton-neutron symmetry have been previously observed in the N... more Background: Excitations with mixed proton-neutron symmetry have been previously observed in the N = 52 isotones. Besides the well-established quadrupole mixed-symmetry states (MSS), octupole and hexadecapole MSS have been recently proposed for the nuclei 92 Zr and 94 Mo. Purpose: The heaviest stable N = 52 isotone 96 Ru was investigated to study the evolution of octupole and hexadecapole MSS with increasing proton number. Methods: Two inelastic proton-scattering experiments on 96 Ru were performed to extract branching ratios, multipole mixing ratios, and level lifetimes. From the combined data, absolute transition strengths were calculated. Results: Strong M1 transitions between the lowest-lying 3 − and 4 + states were observed, providing evidence for a one-phonon mixed-symmetry character of the 3 (−) 2 and 4 + 2 states. Conclusions: sdg-IBM-2 calculations were performed for 96 Ru. The results are in excellent agreement with the experimental data, pointing out a one-phonon hexadecapole mixed-symmetry character of the 4 + 2 state. The 3 − 1 ||M1||3 (−) 2 matrix element is found to scale with the 2 + s ||M1||2 + ms matrix element.

EPJ Web of Conferences, 2014

Excited states in 102 Rh were populated in the fusion-evaporation reaction 94 Zr(11 B, 3n) 102 Rh... more Excited states in 102 Rh were populated in the fusion-evaporation reaction 94 Zr(11 B, 3n) 102 Rh at a beam energy of 36 MeV, using the INGA spectrometer at IUAC, New Delhi. The angular correlations and the electromagnetic character of some of the γ-ray transitions observed in 102 Rh were investigated in detail. A new candidate for a chiral twin band was identified in 102 Rh for the first time.

Nuclear Physics A, 2008

Lifetimes of prolate intruder states in 186 Pb and 188 Pb and oblate intruder states in 194 Po ha... more Lifetimes of prolate intruder states in 186 Pb and 188 Pb and oblate intruder states in 194 Po have been determined through recoil distance Doppler-shift lifetime measurements. Deformation parameters of |β 2 | = 0.29(5) and |β 2 | = 0.17(3) have been

Physical Review Letters, 2011

The transition rates for the 2 + 1 states in 62,64,66 Fe were studied using the Recoil Distance D... more The transition rates for the 2 + 1 states in 62,64,66 Fe were studied using the Recoil Distance Doppler-Shift technique applied to projectile Coulomb excitation reactions. The deduced E2 strengths illustrate the enhanced collectivity of the neutron-rich Fe isotopes up to N = 40. The results are interpreted using the generalized concept of valence proton symmetry which describes the evolution of nuclear structure around N = 40 as governed by the number of valence protons with respect to Z ≈ 30. The trend of collectivity suggested by the experimental data is described by state-of-the-art shell calculations with a new effective interaction developed for the f pgd valence space.

Physical Review Letters, 2006

Exited states in 134 Pr were populated in the fusion-evaporation reaction 119 Sn 19 F; 4n 134 Pr.... more Exited states in 134 Pr were populated in the fusion-evaporation reaction 119 Sn 19 F; 4n 134 Pr. Recoil distance Doppler-shift and Doppler-shift attenuation measurements using the Euroball spectrometer, in conjunction with the inner Bismuth Germanate ball and the Cologne plunger, were performed at beam energies of 87 MeV and 83 MeV, respectively. Reduced transition probabilities in 134 Pr are compared to the predictions of the two quasiparticle triaxial rotor and interacting boson fermion-fermion models. The experimental results do not support the presence of static chirality in 134 Pr underlying the importance of shape fluctuations. Only within a dynamical context the presence of intrinsic chirality in 134 Pr can be supported.

Physical Review C, 2007

Lifetimes of exited states in 134 Pr were measured by means of the recoil distance Doppler-shift ... more Lifetimes of exited states in 134 Pr were measured by means of the recoil distance Doppler-shift and Doppler-shift attenuation techniques. The branching ratios and the electric or magnetic character of the transitions were also investigated. The experiments were performed at IReS, Strasbourg, using the EUROBALL IV spectrometer, in conjunction with the inner bismuth germanate ball and the Cologne coincidence plunger apparatus. Exited states in 134 Pr were populated in the fusion-evaporation reaction 119 Sn(19 F, 4n) 134 Pr. The possible chiral interpretation of twin bands was investigated in the two-quasiparticle triaxial rotor and interacting boson-fermion-fermion models. The analysis of the wave functions has shown that the possibility for the angular momenta of the proton, neutron, and core to find themselves in the favorable, almost orthogonal geometry, is present but is far from being dominant. The structure is characterized by large β and γ fluctuations. The existence of doublets of bands in 134 Pr can be attributed to weak chirality dominated by shape fluctuations.

Physical Review C, 2013

Lifetimes of excited states of 157 Dy were measured by recoil distance Doppler-shift (RDDS) and D... more Lifetimes of excited states of 157 Dy were measured by recoil distance Doppler-shift (RDDS) and Doppler-shift attenuation (DSAM) methods. The γ-ray coincidence data were analyzed by the differential decay curve method. The level scheme and the newly deduced transition strengths were simultaneously described in the framework of the particle plus triaxial rotor model (PTRM) and the rigid-rotor model.

Physical Review C, 2004

Lifetime measurements in 154 Gd were performed by means of the recoil distance Doppler-shift meth... more Lifetime measurements in 154 Gd were performed by means of the recoil distance Doppler-shift method. Excited states of 154 Gd were populated via Coulomb excitation with a 32 S beam at 110 MeV delivered by the FN tandem accelerator of the University of Cologne. The determined transition probabilities as well as the low-spin level scheme of 154 Gd demonstrate a good agreement with the predictions of the critical point symmetry X(5). Comparison of specific experimental observables for the N = 90 rare earth isotones with the calculations of the X(5) model clearly show that 154 Gd is one of the good examples of the realization of the X(5) dynamical symmetry. In addition, the experimental data are compared to fits in the framework of the IBA and the general collective model.

Physical Review C, 2005

The mean lifetimes of the 25/2 + , 21/2 + , and 17/2 + states in the highly deformed (HD) band of... more The mean lifetimes of the 25/2 + , 21/2 + , and 17/2 + states in the highly deformed (HD) band of 133 Nd, excited via the reaction 104 Pd(32 S,2pn) 133 Nd, have been measured using a recoil distance Doppler-shift method. The decay out of the HD band occurs as a result of an admixture of normally deformed (ND) components into the HD states' wave function. The consistency in the mixing amplitude was assessed from the measured lifetimes, branching ratios, and quadrupole moments of the HD and the ND bands. This analysis unequivocally confirms the earlier approach to explain the decay-out mechanism.

Physical Review C, 2013

Centrifugal stretching in the deformed rare-earth nucleus 170 Hf is investigated using high-preci... more Centrifugal stretching in the deformed rare-earth nucleus 170 Hf is investigated using high-precision lifetime measurements, performed with the New Yale Plunger Device at Wright Nuclear Structure Laboratory, Yale University. Excited states were populated in the fusion-evaporation reaction 124 Sn(50 Ti,4n) 170 Hf at a beam energy of 195 MeV. Recoil distance doppler shift data were recorded for the ground state band through the J = 16 + level. The measured B(E2) values and transition quadrupole moments improve on existing data and show increasing β deformation in the ground state band of 170 Hf. The results are compared to descriptions by a rigid rotor and by the confined β-soft rotor model.

Physical Review C, 2002

Lifetime measurements in the mirror nuclei 47 Cr and 47 V were performed by means of the Doppler-... more Lifetime measurements in the mirror nuclei 47 Cr and 47 V were performed by means of the Doppler-shift attenuation method using the multidetector array EUROBALL, in conjunction with the ancillary detectors ISIS and the Neutron Wall. The determined transition strengths in the yrast cascades are well described by full pf shell model calculations.

Nuclear Physics A, 2007

Nanosecond lifetime measurements were performed in 196 Au by means of the pulsed-beam technique. ... more Nanosecond lifetime measurements were performed in 196 Au by means of the pulsed-beam technique. Using the centroid-shift method, one new lifetime has been determined and three known have been remeasured. The data for the transition probabilities are compared to the predictions of the extended supersymmetry for 196 Au. The comparison reveals a partial agreement, which can be considered as a success for the theory describing the complicated structure of the odd-odd nucleus.

Journal of Physics: Conference Series, 2012

Lifetimes of excited states in 155 Dy were measured by means of the Recoil Distance Dopplershift ... more Lifetimes of excited states in 155 Dy were measured by means of the Recoil Distance Dopplershift technique in the coincidence mode. The experiment was performed at the Laboratori Nazionali di Legnaro with the GASP array and the Cologne plunger using the reaction 124 Sn(36 S,5n) 155 Dy at a beam energy of 155 MeV. The Differential decay-curve method was applied for the lifetime determination. The measured transition probabilities in 155 Dy and the energy spectrum are compared to the predictions of the Particle plus rotor model. The comparison indicates slightly different quadrupole deformations characterizing the low-lying one-quasineutron bands which may point to a shape coexistence.

Journal of Physics: Conference Series, 2012

Low-spin excited states of 140 Nd have been studied via the 140 Ce(3 He,3n) 140 Nd reaction. The ... more Low-spin excited states of 140 Nd have been studied via the 140 Ce(3 He,3n) 140 Nd reaction. The data show that one of the candidates for the one-phonon mixed-symmetry state (MSS) of 140 Nd, namely, the 2 + 3 state at 2140 keV with an effective lifetime of 220(90) fs, exhibits a fast M1 decay to the 2 + 1 state. Thus, this state can be considered, at least, as a fragment of the one-phonon MSS of 140 Nd. This is the first example where mixed symmetry character is tentatively assigned to a state of an unstable nucleus from the mass A ≈ 140 region based on the data on absolute M1 transition rates. However, the data are not conclusive on whether this decay exhausts the total M1 strength or whether the one-phonon MSS of 140 Nd is fragmented.

Journal of Physics: Conference Series, 2011

The properties of exotic neutron-rich nuclei between the proton shell closures Z = 20 and Z = 28 ... more The properties of exotic neutron-rich nuclei between the proton shell closures Z = 20 and Z = 28 are of particular interest for the understanding of the shell structure for large neutron excess. Effects related to the energy gap between the neutron f p and 1g9/2 shells lead to a strong variation of collectivity for nuclei around N = 40. Whereas 68 Ni was found to have doubly magic properties, this was not observed in neighbouring nuclei. Recent shell model calculations for the neutron rich iron isotopes clearly reveal the difficulty to describe nuclei in this mass region and resulted in large deviations of the predicted collectivity depending on the valence space. However, no experimental data on the transition strength existed for the very exotic nucleus 66 Fe at N = 40. Here we present the newest results on absolute transition strengths of the lowest excited states in 62,64,66 Fe measured model independently using the recoil distance Doppler-shift (RDDS) method. The experiments were performed at NSCL at Michigan State University with the Cologne/NSCL plunger device using Coulomb excitation in inverse kinematics at energies of 80 MeV/u. Our results yield a much higher collectivity for 64,66 Fe than expected and allow tests of new calculations.

EPJ Web of Conferences, 2014

To investigate the interplay between collective and single particle degrees of freedom in odd nuc... more To investigate the interplay between collective and single particle degrees of freedom in odd nuclei, Recoil distance Doppler-shift and Doppler-shift attenuation lifetime measurements were carried out for levels in 155 Dy in coincidence detection of gamma-rays. 26 lifetimes were determined using the Differential decay curve method. Particle plus triaxial rotor model (PTRM) calculations were performed to compare the experimental level scheme and transition strengths with theoretical ones in order to get information on the quadrupole deformation (ǫ,γ) of the bands. As a result, different quadrupole deformations for the one-quasineutron bands at low and medium spins are deduced.

Physics Letters B, 2014

A simultaneous lifetime and relative g-factor measurement of the 2 + 1 levels in 138,142 Ce was p... more A simultaneous lifetime and relative g-factor measurement of the 2 + 1 levels in 138,142 Ce was performed using the Time Dependent Recoil Into Vacuum (TDRIV) technique. The excitation mechanism was Coulomb excitation in inverse kinematics, and the experimental setup included the Yale plunger device and the Gammasphere array. The latter was used to extract angular distributions for the 2 + 1 → 0 + γ-ray transitions at various target-to-stopper distances. A g(2 + 1) factor of 0.26(8) for 138 Ce was obtained relative to the literature value of g(2 + 1) = 0.21(5) in 142 Ce. In addition, high-precision values of the B(E2; 2 + 1 → 0 +) strengths were obtained. The new data support a proposed subshell closure for the π g 7/2 orbital at Z = 58.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2015

In this article a method for lifetime measurements in the sub-picosecond regime via the Doppler-s... more In this article a method for lifetime measurements in the sub-picosecond regime via the Doppler-shift attenuation method (DSAM) following the inelastic proton scattering reaction is presented. In a pioneering experiment we extracted the lifetimes of 30 excited low-spin states of 96 Ru, taking advantage of the coincident detection of scattered protons and de-exciting γ-rays as well as the large number of particle and γ-ray detectors provided by the SONIC@HORUS setup at the University of Cologne. The large amount of new experimental data shows that this technique is suited for the measurement of lifetimes of excited low-spin states, especially for isotopes with a low isotopic abundance, where (n, n γ) or-in case of investigating dipole excitations-(γ, γ) experiments are not feasible due to the lack of sufficient isotopically enriched target material.

Physical Review C, 2014

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

EPJ Web of Conferences, 2015

Background: Excitations with mixed proton-neutron symmetry have been previously observed in the N... more Background: Excitations with mixed proton-neutron symmetry have been previously observed in the N = 52 isotones. Besides the well-established quadrupole mixed-symmetry states (MSS), octupole and hexadecapole MSS have been recently proposed for the nuclei 92 Zr and 94 Mo. Purpose: The heaviest stable N = 52 isotone 96 Ru was investigated to study the evolution of octupole and hexadecapole MSS with increasing proton number. Methods: Two inelastic proton-scattering experiments on 96 Ru were performed to extract branching ratios, multipole mixing ratios, and level lifetimes. From the combined data, absolute transition strengths were calculated. Results: Strong M1 transitions between the lowest-lying 3 − and 4 + states were observed, providing evidence for a one-phonon mixed-symmetry character of the 3 (−) 2 and 4 + 2 states. Conclusions: sdg-IBM-2 calculations were performed for 96 Ru. The results are in excellent agreement with the experimental data, pointing out a one-phonon hexadecapole mixed-symmetry character of the 4 + 2 state. The 3 − 1 ||M1||3 (−) 2 matrix element is found to scale with the 2 + s ||M1||2 + ms matrix element.

EPJ Web of Conferences, 2014

Excited states in 102 Rh were populated in the fusion-evaporation reaction 94 Zr(11 B, 3n) 102 Rh... more Excited states in 102 Rh were populated in the fusion-evaporation reaction 94 Zr(11 B, 3n) 102 Rh at a beam energy of 36 MeV, using the INGA spectrometer at IUAC, New Delhi. The angular correlations and the electromagnetic character of some of the γ-ray transitions observed in 102 Rh were investigated in detail. A new candidate for a chiral twin band was identified in 102 Rh for the first time.

Nuclear Physics A, 2008

Lifetimes of prolate intruder states in 186 Pb and 188 Pb and oblate intruder states in 194 Po ha... more Lifetimes of prolate intruder states in 186 Pb and 188 Pb and oblate intruder states in 194 Po have been determined through recoil distance Doppler-shift lifetime measurements. Deformation parameters of |β 2 | = 0.29(5) and |β 2 | = 0.17(3) have been

Physical Review Letters, 2011

The transition rates for the 2 + 1 states in 62,64,66 Fe were studied using the Recoil Distance D... more The transition rates for the 2 + 1 states in 62,64,66 Fe were studied using the Recoil Distance Doppler-Shift technique applied to projectile Coulomb excitation reactions. The deduced E2 strengths illustrate the enhanced collectivity of the neutron-rich Fe isotopes up to N = 40. The results are interpreted using the generalized concept of valence proton symmetry which describes the evolution of nuclear structure around N = 40 as governed by the number of valence protons with respect to Z ≈ 30. The trend of collectivity suggested by the experimental data is described by state-of-the-art shell calculations with a new effective interaction developed for the f pgd valence space.

Physical Review Letters, 2006

Exited states in 134 Pr were populated in the fusion-evaporation reaction 119 Sn 19 F; 4n 134 Pr.... more Exited states in 134 Pr were populated in the fusion-evaporation reaction 119 Sn 19 F; 4n 134 Pr. Recoil distance Doppler-shift and Doppler-shift attenuation measurements using the Euroball spectrometer, in conjunction with the inner Bismuth Germanate ball and the Cologne plunger, were performed at beam energies of 87 MeV and 83 MeV, respectively. Reduced transition probabilities in 134 Pr are compared to the predictions of the two quasiparticle triaxial rotor and interacting boson fermion-fermion models. The experimental results do not support the presence of static chirality in 134 Pr underlying the importance of shape fluctuations. Only within a dynamical context the presence of intrinsic chirality in 134 Pr can be supported.

Physical Review C, 2007

Lifetimes of exited states in 134 Pr were measured by means of the recoil distance Doppler-shift ... more Lifetimes of exited states in 134 Pr were measured by means of the recoil distance Doppler-shift and Doppler-shift attenuation techniques. The branching ratios and the electric or magnetic character of the transitions were also investigated. The experiments were performed at IReS, Strasbourg, using the EUROBALL IV spectrometer, in conjunction with the inner bismuth germanate ball and the Cologne coincidence plunger apparatus. Exited states in 134 Pr were populated in the fusion-evaporation reaction 119 Sn(19 F, 4n) 134 Pr. The possible chiral interpretation of twin bands was investigated in the two-quasiparticle triaxial rotor and interacting boson-fermion-fermion models. The analysis of the wave functions has shown that the possibility for the angular momenta of the proton, neutron, and core to find themselves in the favorable, almost orthogonal geometry, is present but is far from being dominant. The structure is characterized by large β and γ fluctuations. The existence of doublets of bands in 134 Pr can be attributed to weak chirality dominated by shape fluctuations.

Physical Review C, 2013

Lifetimes of excited states of 157 Dy were measured by recoil distance Doppler-shift (RDDS) and D... more Lifetimes of excited states of 157 Dy were measured by recoil distance Doppler-shift (RDDS) and Doppler-shift attenuation (DSAM) methods. The γ-ray coincidence data were analyzed by the differential decay curve method. The level scheme and the newly deduced transition strengths were simultaneously described in the framework of the particle plus triaxial rotor model (PTRM) and the rigid-rotor model.

Physical Review C, 2004

Lifetime measurements in 154 Gd were performed by means of the recoil distance Doppler-shift meth... more Lifetime measurements in 154 Gd were performed by means of the recoil distance Doppler-shift method. Excited states of 154 Gd were populated via Coulomb excitation with a 32 S beam at 110 MeV delivered by the FN tandem accelerator of the University of Cologne. The determined transition probabilities as well as the low-spin level scheme of 154 Gd demonstrate a good agreement with the predictions of the critical point symmetry X(5). Comparison of specific experimental observables for the N = 90 rare earth isotones with the calculations of the X(5) model clearly show that 154 Gd is one of the good examples of the realization of the X(5) dynamical symmetry. In addition, the experimental data are compared to fits in the framework of the IBA and the general collective model.

Physical Review C, 2005

The mean lifetimes of the 25/2 + , 21/2 + , and 17/2 + states in the highly deformed (HD) band of... more The mean lifetimes of the 25/2 + , 21/2 + , and 17/2 + states in the highly deformed (HD) band of 133 Nd, excited via the reaction 104 Pd(32 S,2pn) 133 Nd, have been measured using a recoil distance Doppler-shift method. The decay out of the HD band occurs as a result of an admixture of normally deformed (ND) components into the HD states' wave function. The consistency in the mixing amplitude was assessed from the measured lifetimes, branching ratios, and quadrupole moments of the HD and the ND bands. This analysis unequivocally confirms the earlier approach to explain the decay-out mechanism.

Physical Review C, 2013

Centrifugal stretching in the deformed rare-earth nucleus 170 Hf is investigated using high-preci... more Centrifugal stretching in the deformed rare-earth nucleus 170 Hf is investigated using high-precision lifetime measurements, performed with the New Yale Plunger Device at Wright Nuclear Structure Laboratory, Yale University. Excited states were populated in the fusion-evaporation reaction 124 Sn(50 Ti,4n) 170 Hf at a beam energy of 195 MeV. Recoil distance doppler shift data were recorded for the ground state band through the J = 16 + level. The measured B(E2) values and transition quadrupole moments improve on existing data and show increasing β deformation in the ground state band of 170 Hf. The results are compared to descriptions by a rigid rotor and by the confined β-soft rotor model.

Physical Review C, 2002

Lifetime measurements in the mirror nuclei 47 Cr and 47 V were performed by means of the Doppler-... more Lifetime measurements in the mirror nuclei 47 Cr and 47 V were performed by means of the Doppler-shift attenuation method using the multidetector array EUROBALL, in conjunction with the ancillary detectors ISIS and the Neutron Wall. The determined transition strengths in the yrast cascades are well described by full pf shell model calculations.

Nuclear Physics A, 2007

Nanosecond lifetime measurements were performed in 196 Au by means of the pulsed-beam technique. ... more Nanosecond lifetime measurements were performed in 196 Au by means of the pulsed-beam technique. Using the centroid-shift method, one new lifetime has been determined and three known have been remeasured. The data for the transition probabilities are compared to the predictions of the extended supersymmetry for 196 Au. The comparison reveals a partial agreement, which can be considered as a success for the theory describing the complicated structure of the odd-odd nucleus.

Journal of Physics: Conference Series, 2012

Lifetimes of excited states in 155 Dy were measured by means of the Recoil Distance Dopplershift ... more Lifetimes of excited states in 155 Dy were measured by means of the Recoil Distance Dopplershift technique in the coincidence mode. The experiment was performed at the Laboratori Nazionali di Legnaro with the GASP array and the Cologne plunger using the reaction 124 Sn(36 S,5n) 155 Dy at a beam energy of 155 MeV. The Differential decay-curve method was applied for the lifetime determination. The measured transition probabilities in 155 Dy and the energy spectrum are compared to the predictions of the Particle plus rotor model. The comparison indicates slightly different quadrupole deformations characterizing the low-lying one-quasineutron bands which may point to a shape coexistence.

Journal of Physics: Conference Series, 2012

Low-spin excited states of 140 Nd have been studied via the 140 Ce(3 He,3n) 140 Nd reaction. The ... more Low-spin excited states of 140 Nd have been studied via the 140 Ce(3 He,3n) 140 Nd reaction. The data show that one of the candidates for the one-phonon mixed-symmetry state (MSS) of 140 Nd, namely, the 2 + 3 state at 2140 keV with an effective lifetime of 220(90) fs, exhibits a fast M1 decay to the 2 + 1 state. Thus, this state can be considered, at least, as a fragment of the one-phonon MSS of 140 Nd. This is the first example where mixed symmetry character is tentatively assigned to a state of an unstable nucleus from the mass A ≈ 140 region based on the data on absolute M1 transition rates. However, the data are not conclusive on whether this decay exhausts the total M1 strength or whether the one-phonon MSS of 140 Nd is fragmented.

Journal of Physics: Conference Series, 2011

The properties of exotic neutron-rich nuclei between the proton shell closures Z = 20 and Z = 28 ... more The properties of exotic neutron-rich nuclei between the proton shell closures Z = 20 and Z = 28 are of particular interest for the understanding of the shell structure for large neutron excess. Effects related to the energy gap between the neutron f p and 1g9/2 shells lead to a strong variation of collectivity for nuclei around N = 40. Whereas 68 Ni was found to have doubly magic properties, this was not observed in neighbouring nuclei. Recent shell model calculations for the neutron rich iron isotopes clearly reveal the difficulty to describe nuclei in this mass region and resulted in large deviations of the predicted collectivity depending on the valence space. However, no experimental data on the transition strength existed for the very exotic nucleus 66 Fe at N = 40. Here we present the newest results on absolute transition strengths of the lowest excited states in 62,64,66 Fe measured model independently using the recoil distance Doppler-shift (RDDS) method. The experiments were performed at NSCL at Michigan State University with the Cologne/NSCL plunger device using Coulomb excitation in inverse kinematics at energies of 80 MeV/u. Our results yield a much higher collectivity for 64,66 Fe than expected and allow tests of new calculations.