High-spin states in {sup 171}Ta were populated in the {sup 124}Sn({sup 51}V,4n) reaction at 228 M... more High-spin states in {sup 171}Ta were populated in the {sup 124}Sn({sup 51}V,4n) reaction at 228 MeV to search for evidence of stable triaxial deformation. Identification of a wobbling sequence based on the previously known {pi}i{sub 13/2} structure would provide a unique signature for this rarely observed shape. No such sequence was identified in these data, which suggests that the island of triaxial strongly deformed bands may be smaller than once thought. However, over 200 new transitions and two new bands were placed in the level scheme and the sequence based on the {pi}i{sub 13/2} orbital could be observed up to spin and parity I{sup {pi}}=(101/2{sup +}). The relative excitations of all the sequences were determined and the ground state of {sup 171}Ta was found to have 5/2{sup +} quantum numbers, contrary to previous reports. All of the previously known structures were extended to much higher spin and their high-frequency band crossings are interpreted within the framework of th...
It is demonstrated that combination of the (n,n'-r) reaction and the Doppler Shift Attenuation Me... more It is demonstrated that combination of the (n,n'-r) reaction and the Doppler Shift Attenuation Method is ah extremely useful tool to identify various kinds of low energy collective excitations. Evidences for double octupole and quadrupole-octupole modes ate presented in 9SZr and 144Sm nuctei. Newly' measured transition rates of the 2 + rraxedsymnaetry states in the la4Ba 0(6) nucleus are reported.
Elastic and inelastic neutron differential cross sections are measured at the University of Kentu... more Elastic and inelastic neutron differential cross sections are measured at the University of Kentucky Accelerator Laboratory (www.pa.uky.edu/accelerator/) at incident energies in the fast neutron region. The laboratorys facilities and instrumentation will be described and our measurement and analysis procedures outlined. Many corrections are required for neutron scattering experiments and the analysis utilizes information from many other cross section data sets and model calculations. Exploring and understanding the limitations of the foundational information and procedures are important for controlling the accuracy of the cross section results. We are examining the limitations in neutron detection efficiency, the normalization of (n,n γ) cross sections, background reduction, spectrum stripping techniques, and attenuation and multiple scattering corrections. The resulting differential cross sections provide information on the compound elastic and coupled channels reaction mechanisms important for advanced reactor designs. Figure 6. Elastic angular distribution 12 C(n,n) at 2.05 MeV. Present results are compared with the ENDF/B-VII.1 compilation [4] and those of Refs. [5, 6].
The exotic wobbling mode (which is direct experimental confirmation of asymmetric nuclear shapes)... more The exotic wobbling mode (which is direct experimental confirmation of asymmetric nuclear shapes) has now been observed in ^163,165,167Lu and ^167Ta. Particle-rotor model calculations have successfully described the transition strength ratios between the wobbling band and the pii13/2 sequence upon which it is based [1]. However, assumptions made in this model suggest that the wobbling band should increase in energy (with respect to the pii13/2 band) with spin. This is in direct contrast to what is systematically observed in experiments. Using a different set of assumptions within the particle-rotor model, the transition strength ratios can be reproduced while also predicting correctly the reduction in the energy splitting between the bands with increasing spin.[4pt] [1] I. Hamamoto and G.B. Hagemann, Phys. Rev. C 67, 014319 (2003).
Excited levels in the even-even isotopes ^120-130Te have been investigated to 3.3 MeV using gamma... more Excited levels in the even-even isotopes ^120-130Te have been investigated to 3.3 MeV using gamma-ray spectroscopy following inelastic neutron scattering. Level characterisitics including spins, multipole-mixing and branching ratios, and lifetimes in the fs to ps regime have been deduced from gamma-ray angular distributions, excitation functions, and Doppler-shift measurements, as well as gamma-gamma coincidence measurements. This consistent sent of measurements has enabled us to examine multi-phonon excitations across the isotopic chain. In particular, the quintet of negative-parity states (1^--5^- ) arising from the coupling of the lowest quadrupole- and octupole-phonon exitations have been examined and candidates have been identified. Results from these investigations across the Te isotopic chain will be presented.
On attaining eV energy resolution in an ionization energy shift at ˜ 60 keV
The K-line energy of high atomic number atoms depends to some degree on the atom's ionization... more The K-line energy of high atomic number atoms depends to some degree on the atom's ionization stage, hence a high-resolution measurement of the K-line energy could, under the right circumstances, become a way to diagnose the plasma's ionization. Recently, we could measure a blue-shift close to ˜10 eV in the Kα2 line of iridium ionized in the Plasma-Filled Rod Pinch. with a technique based on the line's transmission through a filter with a near-coincident K-edge. The presentation disxusses the measurements and analyses done to improve the systematic energy resolution to below 3 eV, with additional measurements and analysis of the K-ege filter with radiation from cold iridium excited with a PIXE source.
Decay Characteristics of ^122Te Levels Below 3.3 MeV Excitation
Excited levels of ^122Te have been investigated using the (n,n^'gamma) reaction. Gamma-ray ex... more Excited levels of ^122Te have been investigated using the (n,n^'gamma) reaction. Gamma-ray excitation functions for incident neutron energies between 1.92 and 3.35 MeV were measured in 100 keV steps at the University of Kentucky Van de Graaff Laboratory using a 97% isotopically enriched ^122Te sample. Gamma-ray angular distributions and Doppler shifts at E_n=2.8 and 3.3 MeV were also measured, as
^124Te Spectroscopic Studies Using (n,n^'gammagamma) Coincidence Techniques
Transitions between ^124Te excited levels up to 3.1 MeV excitation were examined using inelastic-... more Transitions between ^124Te excited levels up to 3.1 MeV excitation were examined using inelastic-neutron scattering techniques at the University of Kentucky CN Van de Graaff facility. Gamma-gamma coincidences were measured using the 4-element HpGe KEGS array. Combined with angular distributions and lifetimes measured using the Doppler-shift attenuation method, these data are used to evaluate the mixing of intruder-state and normal
Decay Properties and Lifetimes of States in ^124Te from (n,n^'gamma) Reaction Studies
The excited levels of ^124Te have been studied using the (n,n^'gamma) reaction at the Univers... more The excited levels of ^124Te have been studied using the (n,n^'gamma) reaction at the University of Kentucky CN Van de Graaff Laboratory. Gamma-ray excitation functions, angular distributions, and Doppler shifts were measured for transitions from levels up to 3.3 MeV excitation in ^124Te; multipole-mixing ratios, branching ratios and electromagnetic transition rates were deduced. These results are compared with theoretical predictions
Quadrupole-Octapole Coupled State Candidates in ^122Te
The University of Kentucky Van de Graaff Laboratory has been host to a variety of (n,n'gamma)... more The University of Kentucky Van de Graaff Laboratory has been host to a variety of (n,n'gamma) experiments to investigate the low-lying excited levels of the 122Te nucleus. Gamma-gamma coincidence measurements were made at an approximate incident neutron energy of 3.5 MeV, gamma-ray angular distributions were measured at En=2.8 and 3.3 MeV, and excitation functions were measured for En from 1.92
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1991
A simple external-beam ion milliprobe system was designed and constructed as part of an undergrad... more A simple external-beam ion milliprobe system was designed and constructed as part of an undergraduate honors research project. The system includes an adjustable object slit, a compact electrostatic quadrupole triplet lens, a lens positioner, and a shielded tip with a thin Kapton window through which the beam exits the accelerator vacuum and enters a sample enclosure with interlocked doors. Auxiliary equipment includes a four-segment lens-entrance collimator with a beam-current monitor that facilitates steering the beam and an interlock system that intercepts the beam when any of the doors to the sample enclosure are opened. Details of the design and construction of the system will be presented and its performance will be described.
Although the existence of asymmetric (or triaxial) shaped nuclei has been predicted for decades, ... more Although the existence of asymmetric (or triaxial) shaped nuclei has been predicted for decades, acquiring experimental proof of this shape has been quite challenging. A triaxial nucleus should produce a collective wobbling mode when it is given significant angular momentum. Indeed, evidence of this phenomenon has been observed in a few odd-A Lu nuclei. A neutron shell gap is often
The General Collective Model and its Application to Even-Even Tellurium Nuclei
The level schemes of the Tellurium nuclei are being developed with in beam gamma-ray spectroscopy... more The level schemes of the Tellurium nuclei are being developed with in beam gamma-ray spectroscopy using the CN Van de Graaff at the University of Kentucky Nuclear Structure Laboratory. Excitation functions, gamma-gamma coincidences, and angular distributions are measured following the (n,n'g) reaction on isotopically enriched targets. Spectroscopic information such as spins and parities, branching and mixing ratios, and transition rates
Measurements of neutron elastic and inelastic scattering from 23 Na have been performed for sixte... more Measurements of neutron elastic and inelastic scattering from 23 Na have been performed for sixteen incident neutron energies above 1.5 MeV with the 7-MV University of Kentucky Accelerator using the 3 H(p,n) reaction as the neutron source. These measurements were complemented by γ-ray excitation functions using the (n,n'γ) reaction. The time-of-flight technique is employed for background reduction in both neutron and γray measurements and for determining the energy of the scattered neutrons. Cross section determinations support fuel cycle and structural materials research and development. Previous reaction model evaluations [1] relied primarily on total cross sections and four (n,n0) and (n,n1) angular distributions in the En = 5 to 9 MeV range. The inclusion of more inelastic channels at lower neutron energies provides additional information on direct couplings between elastic and inelastic scattering as a function of angular momentum transfer. Reaction model calculations examining direct collective and statistical properties were performed.
The level structure of 120 Te has been examined utilizing gamma-ray spectroscopy following the (␣... more The level structure of 120 Te has been examined utilizing gamma-ray spectroscopy following the (␣,2n␥) reaction and 120 I decay. Excitation functions, ␥-␥ coincidences, and angular distributions were measured. Spectroscopic information, e.g., spins, branching ratios, and multipole-mixing ratios, was obtained for many new levels below 4.5 MeV in excitation energy. The level scheme was examined from the viewpoint of an anharmonic vibrator model, the general collective model, the particle-core coupling model, and interactingboson-model-based intruder models. Particular aspects of the level sequence can be reproduced by each of these models, but the agreement with transition rate data is modest. The B(E2) transition rate ratios are most consistent with the simple U͑5͒ pattern. The higher-spin intruder states are identified in 120 Te by comparison to the known band structures and decay patterns of the Nϭ66 and Nϭ68 tin and cadmium nuclei. The intruder signature vanishes below spin-8, where there is strong mixing between states.
The phenomenon of wobbling can only occur for a nuclear shape with stable triaxial deformation. T... more The phenomenon of wobbling can only occur for a nuclear shape with stable triaxial deformation. To date, only a few examples of this exotic collective mode have been observed in lutetium and tantalum isotopes. A search for a wobbling sequence was performed in 171 Re to determine if this feature can be observed in Z > 73 nuclei. No evidence was found for wobbling; however, an interaction between the πi 13/2 sequence and another positive-parity band may give an indication on why wobbling may not occur in this nucleus. The level scheme for 171 Re was significantly extended and interpretations for the decay sequences are proposed within the context of the cranked shell model.
High-spin states in 171 Ta were populated in the 124 Sn(51 V,4n) reaction at 228 MeV to search fo... more High-spin states in 171 Ta were populated in the 124 Sn(51 V,4n) reaction at 228 MeV to search for evidence of stable triaxial deformation. Identification of a wobbling sequence based on the previously known πi 13/2 structure would provide a unique signature for this rarely observed shape. No such sequence was identified in these data, which suggests that the island of triaxial strongly deformed bands may be smaller than once thought. However, over 200 new transitions and two new bands were placed in the level scheme and the sequence based on the πi 13/2 orbital could be observed up to spin and parity I π = (101/2 +). The relative excitations of all the sequences were determined and the ground state of 171 Ta was found to have 5/2 + quantum numbers, contrary to previous reports. All of the previously known structures were extended to much higher spin and their high-frequency band crossings are interpreted within the framework of the cranked shell model.
... the first time, so their relative excitation energies have been determined. A systematic comp... more ... the first time, so their relative excitation energies have been determined. A systematic comparison of the experimental bandhead energies is made with the predictions of Nazarewicz, Riley, and Garrett [14] for the Ta nuclei. II. ...
High-spin states in the odd-odd nucleus 168 Ta have been populated in the 120 Sn(51 V,3n) reactio... more High-spin states in the odd-odd nucleus 168 Ta have been populated in the 120 Sn(51 V,3n) reaction. Two multi-quasiparticle structures have been extended significantly from spin ∼ 20h to above 40h. As a result, the first rotational alignment has been fully delineated and a second band crossing has been observed for the first time in this nucleus. Configurations for these strongly-coupled rotational bands are proposed based on signature splitting, B(M 1)/B(E2) ratio information, and observed rotation-alignment behavior. Properties of the observed bands in 168 Ta are compared to related structures in the neighboring odd-Z, odd-N , and odd-odd nuclei and are discussed within the framework of the cranked shell model.
We study the sensitivity of the neutron skin thickness, S, in a 208 Pb nucleus to the addition of... more We study the sensitivity of the neutron skin thickness, S, in a 208 Pb nucleus to the addition of nucleon-sigma-rho coupling corrections to a selection (PK1, NL3, S271, Z271) of interactions in relativistic mean field model. The PK1 and NL3 effective interactions lead to a minimum value of S = 0.16 fm in comparison with the original value of S = 0.28 fm. The S271 and Z271 effective interactions yield even smaller values of S = 0.11 fm, which are similar to those for nonrelativistic mean field models. A precise measurement of the neutron radius, and therefore S, in 208 Pb will place an important constraint on both relativistic and nonrelativistic mean field models. We also study the correlation between the radius of a 1.4 solar-mass neutron star and S.
High-spin states in {sup 171}Ta were populated in the {sup 124}Sn({sup 51}V,4n) reaction at 228 M... more High-spin states in {sup 171}Ta were populated in the {sup 124}Sn({sup 51}V,4n) reaction at 228 MeV to search for evidence of stable triaxial deformation. Identification of a wobbling sequence based on the previously known {pi}i{sub 13/2} structure would provide a unique signature for this rarely observed shape. No such sequence was identified in these data, which suggests that the island of triaxial strongly deformed bands may be smaller than once thought. However, over 200 new transitions and two new bands were placed in the level scheme and the sequence based on the {pi}i{sub 13/2} orbital could be observed up to spin and parity I{sup {pi}}=(101/2{sup +}). The relative excitations of all the sequences were determined and the ground state of {sup 171}Ta was found to have 5/2{sup +} quantum numbers, contrary to previous reports. All of the previously known structures were extended to much higher spin and their high-frequency band crossings are interpreted within the framework of th...
It is demonstrated that combination of the (n,n'-r) reaction and the Doppler Shift Attenuation Me... more It is demonstrated that combination of the (n,n'-r) reaction and the Doppler Shift Attenuation Method is ah extremely useful tool to identify various kinds of low energy collective excitations. Evidences for double octupole and quadrupole-octupole modes ate presented in 9SZr and 144Sm nuctei. Newly' measured transition rates of the 2 + rraxedsymnaetry states in the la4Ba 0(6) nucleus are reported.
Elastic and inelastic neutron differential cross sections are measured at the University of Kentu... more Elastic and inelastic neutron differential cross sections are measured at the University of Kentucky Accelerator Laboratory (www.pa.uky.edu/accelerator/) at incident energies in the fast neutron region. The laboratorys facilities and instrumentation will be described and our measurement and analysis procedures outlined. Many corrections are required for neutron scattering experiments and the analysis utilizes information from many other cross section data sets and model calculations. Exploring and understanding the limitations of the foundational information and procedures are important for controlling the accuracy of the cross section results. We are examining the limitations in neutron detection efficiency, the normalization of (n,n γ) cross sections, background reduction, spectrum stripping techniques, and attenuation and multiple scattering corrections. The resulting differential cross sections provide information on the compound elastic and coupled channels reaction mechanisms important for advanced reactor designs. Figure 6. Elastic angular distribution 12 C(n,n) at 2.05 MeV. Present results are compared with the ENDF/B-VII.1 compilation [4] and those of Refs. [5, 6].
The exotic wobbling mode (which is direct experimental confirmation of asymmetric nuclear shapes)... more The exotic wobbling mode (which is direct experimental confirmation of asymmetric nuclear shapes) has now been observed in ^163,165,167Lu and ^167Ta. Particle-rotor model calculations have successfully described the transition strength ratios between the wobbling band and the pii13/2 sequence upon which it is based [1]. However, assumptions made in this model suggest that the wobbling band should increase in energy (with respect to the pii13/2 band) with spin. This is in direct contrast to what is systematically observed in experiments. Using a different set of assumptions within the particle-rotor model, the transition strength ratios can be reproduced while also predicting correctly the reduction in the energy splitting between the bands with increasing spin.[4pt] [1] I. Hamamoto and G.B. Hagemann, Phys. Rev. C 67, 014319 (2003).
Excited levels in the even-even isotopes ^120-130Te have been investigated to 3.3 MeV using gamma... more Excited levels in the even-even isotopes ^120-130Te have been investigated to 3.3 MeV using gamma-ray spectroscopy following inelastic neutron scattering. Level characterisitics including spins, multipole-mixing and branching ratios, and lifetimes in the fs to ps regime have been deduced from gamma-ray angular distributions, excitation functions, and Doppler-shift measurements, as well as gamma-gamma coincidence measurements. This consistent sent of measurements has enabled us to examine multi-phonon excitations across the isotopic chain. In particular, the quintet of negative-parity states (1^--5^- ) arising from the coupling of the lowest quadrupole- and octupole-phonon exitations have been examined and candidates have been identified. Results from these investigations across the Te isotopic chain will be presented.
On attaining eV energy resolution in an ionization energy shift at ˜ 60 keV
The K-line energy of high atomic number atoms depends to some degree on the atom's ionization... more The K-line energy of high atomic number atoms depends to some degree on the atom's ionization stage, hence a high-resolution measurement of the K-line energy could, under the right circumstances, become a way to diagnose the plasma's ionization. Recently, we could measure a blue-shift close to ˜10 eV in the Kα2 line of iridium ionized in the Plasma-Filled Rod Pinch. with a technique based on the line's transmission through a filter with a near-coincident K-edge. The presentation disxusses the measurements and analyses done to improve the systematic energy resolution to below 3 eV, with additional measurements and analysis of the K-ege filter with radiation from cold iridium excited with a PIXE source.
Decay Characteristics of ^122Te Levels Below 3.3 MeV Excitation
Excited levels of ^122Te have been investigated using the (n,n^'gamma) reaction. Gamma-ray ex... more Excited levels of ^122Te have been investigated using the (n,n^'gamma) reaction. Gamma-ray excitation functions for incident neutron energies between 1.92 and 3.35 MeV were measured in 100 keV steps at the University of Kentucky Van de Graaff Laboratory using a 97% isotopically enriched ^122Te sample. Gamma-ray angular distributions and Doppler shifts at E_n=2.8 and 3.3 MeV were also measured, as
^124Te Spectroscopic Studies Using (n,n^'gammagamma) Coincidence Techniques
Transitions between ^124Te excited levels up to 3.1 MeV excitation were examined using inelastic-... more Transitions between ^124Te excited levels up to 3.1 MeV excitation were examined using inelastic-neutron scattering techniques at the University of Kentucky CN Van de Graaff facility. Gamma-gamma coincidences were measured using the 4-element HpGe KEGS array. Combined with angular distributions and lifetimes measured using the Doppler-shift attenuation method, these data are used to evaluate the mixing of intruder-state and normal
Decay Properties and Lifetimes of States in ^124Te from (n,n^'gamma) Reaction Studies
The excited levels of ^124Te have been studied using the (n,n^'gamma) reaction at the Univers... more The excited levels of ^124Te have been studied using the (n,n^'gamma) reaction at the University of Kentucky CN Van de Graaff Laboratory. Gamma-ray excitation functions, angular distributions, and Doppler shifts were measured for transitions from levels up to 3.3 MeV excitation in ^124Te; multipole-mixing ratios, branching ratios and electromagnetic transition rates were deduced. These results are compared with theoretical predictions
Quadrupole-Octapole Coupled State Candidates in ^122Te
The University of Kentucky Van de Graaff Laboratory has been host to a variety of (n,n'gamma)... more The University of Kentucky Van de Graaff Laboratory has been host to a variety of (n,n'gamma) experiments to investigate the low-lying excited levels of the 122Te nucleus. Gamma-gamma coincidence measurements were made at an approximate incident neutron energy of 3.5 MeV, gamma-ray angular distributions were measured at En=2.8 and 3.3 MeV, and excitation functions were measured for En from 1.92
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1991
A simple external-beam ion milliprobe system was designed and constructed as part of an undergrad... more A simple external-beam ion milliprobe system was designed and constructed as part of an undergraduate honors research project. The system includes an adjustable object slit, a compact electrostatic quadrupole triplet lens, a lens positioner, and a shielded tip with a thin Kapton window through which the beam exits the accelerator vacuum and enters a sample enclosure with interlocked doors. Auxiliary equipment includes a four-segment lens-entrance collimator with a beam-current monitor that facilitates steering the beam and an interlock system that intercepts the beam when any of the doors to the sample enclosure are opened. Details of the design and construction of the system will be presented and its performance will be described.
Although the existence of asymmetric (or triaxial) shaped nuclei has been predicted for decades, ... more Although the existence of asymmetric (or triaxial) shaped nuclei has been predicted for decades, acquiring experimental proof of this shape has been quite challenging. A triaxial nucleus should produce a collective wobbling mode when it is given significant angular momentum. Indeed, evidence of this phenomenon has been observed in a few odd-A Lu nuclei. A neutron shell gap is often
The General Collective Model and its Application to Even-Even Tellurium Nuclei
The level schemes of the Tellurium nuclei are being developed with in beam gamma-ray spectroscopy... more The level schemes of the Tellurium nuclei are being developed with in beam gamma-ray spectroscopy using the CN Van de Graaff at the University of Kentucky Nuclear Structure Laboratory. Excitation functions, gamma-gamma coincidences, and angular distributions are measured following the (n,n'g) reaction on isotopically enriched targets. Spectroscopic information such as spins and parities, branching and mixing ratios, and transition rates
Measurements of neutron elastic and inelastic scattering from 23 Na have been performed for sixte... more Measurements of neutron elastic and inelastic scattering from 23 Na have been performed for sixteen incident neutron energies above 1.5 MeV with the 7-MV University of Kentucky Accelerator using the 3 H(p,n) reaction as the neutron source. These measurements were complemented by γ-ray excitation functions using the (n,n'γ) reaction. The time-of-flight technique is employed for background reduction in both neutron and γray measurements and for determining the energy of the scattered neutrons. Cross section determinations support fuel cycle and structural materials research and development. Previous reaction model evaluations [1] relied primarily on total cross sections and four (n,n0) and (n,n1) angular distributions in the En = 5 to 9 MeV range. The inclusion of more inelastic channels at lower neutron energies provides additional information on direct couplings between elastic and inelastic scattering as a function of angular momentum transfer. Reaction model calculations examining direct collective and statistical properties were performed.
The level structure of 120 Te has been examined utilizing gamma-ray spectroscopy following the (␣... more The level structure of 120 Te has been examined utilizing gamma-ray spectroscopy following the (␣,2n␥) reaction and 120 I decay. Excitation functions, ␥-␥ coincidences, and angular distributions were measured. Spectroscopic information, e.g., spins, branching ratios, and multipole-mixing ratios, was obtained for many new levels below 4.5 MeV in excitation energy. The level scheme was examined from the viewpoint of an anharmonic vibrator model, the general collective model, the particle-core coupling model, and interactingboson-model-based intruder models. Particular aspects of the level sequence can be reproduced by each of these models, but the agreement with transition rate data is modest. The B(E2) transition rate ratios are most consistent with the simple U͑5͒ pattern. The higher-spin intruder states are identified in 120 Te by comparison to the known band structures and decay patterns of the Nϭ66 and Nϭ68 tin and cadmium nuclei. The intruder signature vanishes below spin-8, where there is strong mixing between states.
The phenomenon of wobbling can only occur for a nuclear shape with stable triaxial deformation. T... more The phenomenon of wobbling can only occur for a nuclear shape with stable triaxial deformation. To date, only a few examples of this exotic collective mode have been observed in lutetium and tantalum isotopes. A search for a wobbling sequence was performed in 171 Re to determine if this feature can be observed in Z > 73 nuclei. No evidence was found for wobbling; however, an interaction between the πi 13/2 sequence and another positive-parity band may give an indication on why wobbling may not occur in this nucleus. The level scheme for 171 Re was significantly extended and interpretations for the decay sequences are proposed within the context of the cranked shell model.
High-spin states in 171 Ta were populated in the 124 Sn(51 V,4n) reaction at 228 MeV to search fo... more High-spin states in 171 Ta were populated in the 124 Sn(51 V,4n) reaction at 228 MeV to search for evidence of stable triaxial deformation. Identification of a wobbling sequence based on the previously known πi 13/2 structure would provide a unique signature for this rarely observed shape. No such sequence was identified in these data, which suggests that the island of triaxial strongly deformed bands may be smaller than once thought. However, over 200 new transitions and two new bands were placed in the level scheme and the sequence based on the πi 13/2 orbital could be observed up to spin and parity I π = (101/2 +). The relative excitations of all the sequences were determined and the ground state of 171 Ta was found to have 5/2 + quantum numbers, contrary to previous reports. All of the previously known structures were extended to much higher spin and their high-frequency band crossings are interpreted within the framework of the cranked shell model.
... the first time, so their relative excitation energies have been determined. A systematic comp... more ... the first time, so their relative excitation energies have been determined. A systematic comparison of the experimental bandhead energies is made with the predictions of Nazarewicz, Riley, and Garrett [14] for the Ta nuclei. II. ...
High-spin states in the odd-odd nucleus 168 Ta have been populated in the 120 Sn(51 V,3n) reactio... more High-spin states in the odd-odd nucleus 168 Ta have been populated in the 120 Sn(51 V,3n) reaction. Two multi-quasiparticle structures have been extended significantly from spin ∼ 20h to above 40h. As a result, the first rotational alignment has been fully delineated and a second band crossing has been observed for the first time in this nucleus. Configurations for these strongly-coupled rotational bands are proposed based on signature splitting, B(M 1)/B(E2) ratio information, and observed rotation-alignment behavior. Properties of the observed bands in 168 Ta are compared to related structures in the neighboring odd-Z, odd-N , and odd-odd nuclei and are discussed within the framework of the cranked shell model.
We study the sensitivity of the neutron skin thickness, S, in a 208 Pb nucleus to the addition of... more We study the sensitivity of the neutron skin thickness, S, in a 208 Pb nucleus to the addition of nucleon-sigma-rho coupling corrections to a selection (PK1, NL3, S271, Z271) of interactions in relativistic mean field model. The PK1 and NL3 effective interactions lead to a minimum value of S = 0.16 fm in comparison with the original value of S = 0.28 fm. The S271 and Z271 effective interactions yield even smaller values of S = 0.11 fm, which are similar to those for nonrelativistic mean field models. A precise measurement of the neutron radius, and therefore S, in 208 Pb will place an important constraint on both relativistic and nonrelativistic mean field models. We also study the correlation between the radius of a 1.4 solar-mass neutron star and S.
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Papers by Jeff Vanhoy