Adopted spectroscopic information on 0 • i 0 • f pure E0 transitions has been deduced by critical... more Adopted spectroscopic information on 0 • i 0 • f pure E0 transitions has been deduced by critical evaluation of the available experimental data for all even-even nuclei ranging from 4 2 He 2 to 250 98 C f 152. Values of q 2 K´E 0 E2µ, the ratio of the K-conversion electron intensity of the 0 • i 0 • f , E0 transition to that of the 0 • i 2 • 1 , E2 transition, have been determined. This procedure, together with the most recent theoretical conversion coefficients for internal conversion and electron-positron pair creation, as well electronic factors, produced a large number of new X´E0 E2µ values, defined as the dimensionless ratio of the absolute B´E0µ and B´E2µ transition rates. The squared value of the monopole transition strength, ρ 2´E 0µ, has been deduced using the best available 0 •-level half-lives and branching ratios.
The level structure of 124 I (Z = 53, N = 71) has been studied via the 122 Sn(7 Li, 5n) 124 I rea... more The level structure of 124 I (Z = 53, N = 71) has been studied via the 122 Sn(7 Li, 5n) 124 I reaction with a beam energy of 54 MeV. Through in-beam and out-of-beam γ-ray spectroscopy, the sophisticated low-lying levels including isomeric states and numerous collective states have been established for the first time. A positive-parity collective band built on the 10 + state at 1297 keV is interpreted as being associated with the combination of a proton and a neutron in the same intruder h 11/2 orbital, namely the π h 11/2 νh 11/2 configuration. This band shows a typical quadrupole vibrational character. In contrast, the negative parity bands based on the π g 7/2 νh 11/2 configuration show a soft triaxial rotation. An isomeric 8 − state at 689 keV with a half-life of 14 ns can be explained as a K isomer due to a proton with an p = 9/2 in the g 9/2 orbital coupled to a neutron with an n = 7/2 in the h 11/2 orbital. The excited states based on this π g 9/2 νh 11/2 configuration show a coupled rotational structure. Another coupled rotational band built on the 6 + state at 714 keV is thought to be based on the π g 9/2 νd 3/2 configuration.
Background: Stellar carbon synthesis occurs exclusively via the 3α process, in which three α part... more Background: Stellar carbon synthesis occurs exclusively via the 3α process, in which three α particles fuse to form 12 C in the excited Hoyle state, followed by electromagnetic decay to the ground state. The Hoyle state is above the α threshold, and the rate of stellar carbon production depends on the radiative width of this state. The radiative width cannot be measured directly, and must instead be deduced by combining three separately measured quantities. One of these quantities is the E0 decay branching ratio of the Hoyle state, and the current 10% uncertainty on the radiative width stems mainly from the uncertainty on this ratio. The rate of the 3α process is an important input parameter in astrophysical calculations on stellar evolution, and a high precision is imperative to constrain the possible outcomes of astrophysical models. Purpose: To deduce a new, more precise value for the E0 decay branching ratio of the Hoyle state. Method: The E0 branching ratio was deduced from a series of pair conversion measurements of the E0 and E2 transitions depopulating the 0 + 2 Hoyle state and 2 + 1 state in 12 C, respectively. The excited states were populated by the 12 C(p, p) reaction at 10.5 MeV beam energy, and the pairs were detected with the electron-positron pair spectrometer, Super-e, at the Australian National University. The deduced branching ratio required knowledge of the proton population of the two states, as well as the alignment of the 2 + 1 state in the reaction. For this purpose, proton scattering and γ-ray angular distribution experiments were also performed. Results: An E0 branching ratio of Γ E0 π /Γ = 8.2(5) × 10 −6 was deduced in the current work, and an adopted value of Γ E0 π /Γ = 7.6(4) × 10 −6 is recommended based on a weighted average of previous literature values and the new result. Conclusions: The new recommended value for the E0 branching ratio is about 14% larger than the previous adopted value of Γ E0 π /Γ = 6.7(6) × 10 −6 , while the uncertainty has been reduced from 9% to 5%. The new result reduces the radiative width, and hence 3α reaction rate, by 11% relative to the adopted value, and the uncertainty to 6.1%. This reduction in width and increased precision is likely to constrain possible outcomes of astrophysical calculations.
Background: High-spin isomers at ≈9-MeV excitation energies have been reported in several N = 83 ... more Background: High-spin isomers at ≈9-MeV excitation energies have been reported in several N = 83 isotones near Z = 64. Spin and parity assignments of J π = 49/2 + remain tentative for a number of these states in the odd-A nuclei. Purpose: To study the decay of the (49/2 +) high-spin isomer in 145 Sm, make firm spin and parity assignments to the isomer and states populated in its decay, and investigate the structure of the nucleus. Methods: The 145 Sm isomer was populated in the 124 Sn(26 Mg,5n) reaction. Gamma-ray and conversion-electron data were collected using the Solenogam array. Results: A revised lifetime of t 1/2 = 3.52(16) µs was measured for the high-spin isomer. Several new states have been added to the level scheme, and a new state at 8815 keV is proposed as the isomer, based on decayproperty systematics, transition strengths, and spin and parity assignments. Firm spin and parity assignments have been made to states up to and including the isomer and the new level scheme is interpreted using shell-model calculations performed with the KShell program. Conclusions: The interpretation of the 49/2 + isomer as a deformed excitation of the core neutrons remains unchanged, although there has been a significant revision of the level scheme below the isomer, and hence significant reinterpretations of the lower-lying states.
Excited states in 174 Re have been populated in fusion-evaporation reactions at the Australian Na... more Excited states in 174 Re have been populated in fusion-evaporation reactions at the Australian National University, and γ-ray spectroscopy has been used to determine the level structure and to deduce the underlying nucleon configurations. The half-life of the bandhead of the K π = 8 − band has been measured to be 2.7(4) ns. A band built on an isomeric state of spin-parity (14 −) and a half-life of 53(5) ns has been observed here for the first time, and has been determined to have a four-quasiparticle structure. Contrasting reduced-hindrance values for its decay are discussed in terms of deformation and configuration changes, as indicated by configuration-constrained potential energy surface calculations.
The emergence of nuclear collectivity near doubly-magic 132Sn was explored along the stable, even... more The emergence of nuclear collectivity near doubly-magic 132Sn was explored along the stable, eveneven 124−130Te isotopes. Preliminary measurements of the B(E2; 41+ → 21+) transition strengths are reported from Coulomb excitation experiments primarily aimed at measuring the g factors of the 41+ states. Isotopically enriched Te targets were excited by 198-205 MeV 58Ni beams. A comparison of transition strengths obtained is made to large-scale shell-model calculations with successes and limitations discussed.
Excited states in 186 Re with spins up to J = 12 were investigated in two separate experiments us... more Excited states in 186 Re with spins up to J = 12 were investigated in two separate experiments using 186 W(d,2n) reactions at beam energies of 12.5 MeV and 14.5 MeV. Two-and threefold γ-ray coincidence data were collected using the CAESAR and CAGRA spectrometers, respectively, each composed of Compton-suppressed HPGe detectors. Analysis of the data revealed rotational bands built on several two-quasiparticle intrinsic states, including a long-lived K π = (8 +) isomer. Configuration assignments were supported by an analysis of in-band properties, such as |gK − gR| values. The excitation energies of the observed intrinsic states were compared with results from multiquasiparticle blocking calculations, based on the Lipkin-Nogami pairing approach, that included contributions from the residual proton-neutron interactions.
Using the 168 Er(10 B, 5n) reaction at a beam energy of 68 MeV, new data have been obtained for t... more Using the 168 Er(10 B, 5n) reaction at a beam energy of 68 MeV, new data have been obtained for the population and decay of a T 1/2 = 148 ns, K π = 21/2 − three-quasiparticle isomer at 1717 keV in 173 Ta. Revised decay energies and intensities have been determined, together with newly observed members of a rotational band associated with the isomer. By comparison with other isomers in the A ≈ 180 deformed region, the 173 Ta isomer properties help to specify the key degrees of freedom that determine K-forbidden transition rates. In particular, when all three quasiparticles are of the same nucleon type, there is a strong dependence of the E2 reduced hindrance factor on the isomer excitation energy.
Solenogam is a recoil spectrometer designed and constructed for use at the Australian National Un... more Solenogam is a recoil spectrometer designed and constructed for use at the Australian National University (ANU) Heavy-Ion Accelerator Facility (HIAF). The design enables the study of nuclear excitations populated by the decay of long-lived states such as isomers and radioactive ground states. Solenogam is comprised of high-sensitivity γ-ray and electron detector arrays coupled to a new 8-T solenoid. While the installation of the 8-T solenoid proceeds, off-line measurements have been made to characterise Solenogam's performance. Gamma-electron coincidences in the electron capture decay of 182 Re into 182 W were used to investigate conversion coefficients and γ-e − angular correlations. The measured conversion coefficients show good agreement with theoretical calculations and have been used to extract E0/E2 mixing ratios for a number of J → J transitions. The angular correlations measured by the array are in qualitative agreement with theoretical calculations. However, the magnitudes of the correlations are attenuated by approximately 40% for reasons unknown at present. These results are the first full use of the Solenogam system for γ-e − coincidence measurements and have proven that the system is capable of highly-sensitive internal conversion analysis of complex decays.
Excited states in 62 Ni were populated with a (p, p') reaction using the 14UD Pelletron accelerat... more Excited states in 62 Ni were populated with a (p, p') reaction using the 14UD Pelletron accelerator at the Australian National University. Electric monopole transition strengths, ρ 2 (E0), were measured through simultaneous detection of the internal conversion electrons and γ rays emitted from the de-excitation of populated states, using the Super-e spectrometer coupled with a germanium detector. The strength of the 0 + 2 to 0 + 1 transition has been measured to be 77 +23 −34 × 10 −3 and agrees with previously reported values. Upper limits have been placed on the 0 + 3 to 0 + 1 and 0 + 3 to 0 + 2 transitions. The measured ρ 2 (E0) value of the 2 + 2 to 2 + 1 transition in 62 Ni has been measured for the first time and found to be one of the largest ρ 2 (E0) values measured to date in nuclei heavier than Ca. The low-lying states of 62 Ni have previously been classified as one-and two-phonon vibrational states based on level energies. The measured electric quadrupole transition strengths are consistent with this interpretation. However as electric monopole transitions are forbidden between states which differ by one phonon number, the simple harmonic quadrupole vibrational picture is not sufficient to explain the large ρ 2 (E0) value for the 2 + 2 to 2 + 1 transition.
Spectroscopic information on the decay properties of high-K isomers in deformed and transitional ... more Spectroscopic information on the decay properties of high-K isomers in deformed and transitional nuclei has been evaluated and collated. Assigned multi-quasiparticle configurations are included. Factors that control the transitions strengths, such as various contributions to K mixing, are outlined. The systematics of K-forbidden transitions for different multipolarities are discussed for selected cases in terms of the hindrances, F W , and of the reduced hindrance factor per degree of K forbiddenness, f ν , where ν = |∆K − λ |, ∆K is the K-value difference between the initial and final state and λ is the transition multipole order. With the improved statistics for E1, M1 and E2 transitions, a factorization into the product of the underlying multipolarity-dependent transition strength and a ν-dependence, due to K forbiddenness (f 0), is possible. This suggests a weaker dependence on K forbiddenness than is commonly assumed.
Nuclear K-isomers play an important role in understanding the structure of deformed axially symme... more Nuclear K-isomers play an important role in understanding the structure of deformed axially symmetric nuclei. Examples are presented of recent studies in the rare-earth region (A∼180) using deep-inelastic and multinucleon transfer reactions, and in the trans-fermium region (A∼250) using fusion-evaporation reactions. A specific two-level mixing scenario is invoked to explain the unusual decay of the K π = 13 + isomer in 174 Lu. The identification of 2-and 4-quasiparticle isomers in 254 No is discussed and predictions of similar isomers in neighboring No and Rf nuclei are presented.
The level scheme of 212 Rn has been extended to spins of ∼ 38h and excitation energies of about 1... more The level scheme of 212 Rn has been extended to spins of ∼ 38h and excitation energies of about 13 MeV using the 204 Hg(13 C, 5n) 212 Rn reaction and γ-ray spectroscopy. Time correlated techniques have been used to obtain sensitivity to weak transitions and channel selectivity. The excitation energy of the 22 + core-excited isomer has been established at 6174 keV. Two isomers with τ = 25(2) ns and τ = 12(2) ns are identified at 12211 and 12548 keV, respectively. These are the highest-spin nuclear isomers now known, and are attributed to configurations involving triple neutron core-excitations coupled to the aligned valence protons. Semi-empirical shell-model calculations can account for most states observed, but with significant energy discrepancies for some configurations.
The evaluated spectroscopic data are presented for 12 known nuclides of mass 84 (Ga, Ge, As, Se, ... more The evaluated spectroscopic data are presented for 12 known nuclides of mass 84 (Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo). Except for the stable nuclides 84Sr and 84Kr, extensive new data are available for all the other nuclides since the 1997 evaluation by J.K. Tuli (1997Tu02) of A = 84 nuclides. Many precise Penning-trap mass
Excited states in 181 Ta have been identified using time-correlated ␥-ray spectroscopy and partic... more Excited states in 181 Ta have been identified using time-correlated ␥-ray spectroscopy and particle-␥ techniques following the incomplete fusion reaction 176 Yb(11 B,␣2n) 181 Ta. As well as observing the rotational band based on the 11 ns isomer at 482 keV from the 5/2 ϩ ͓402͔ proton configuration, which is found to be essentially identical to that associated with its 7/2 ϩ ͓404͔ pseudospin partner, several multi-quasiparticle isomers are observed including a 33 s state, of probable spin and parity 21/2 Ϫ , at 1483 keV. Experimental states are compared with multi-quasiparticle calculations. ͓S0556-2813͑98͒02909-4͔
Conversion electrons from 208 Bi have been measured using singles and coincidence techniques with... more Conversion electrons from 208 Bi have been measured using singles and coincidence techniques with the 208 Pb(p, n) 208 Bi reaction at 9 MeV. The new information on multipolarities and spins complements that available from recent γ-γ-coincidence studies with the same reaction [Boutachkov et al., Nucl. Phys. A768, 22 (2006)]. The results on electromagnetic decays taken together with information on spectroscopic factors from earlier single-particle transfer reaction measurements represent an extensive data set on the properties of the one-proton one-neutron-hole states below 3 MeV, a spectrum which is virtually complete. Comparison of the experimental observables, namely, energies, spectroscopic factors, and γ-branching ratios, with those calculated within the shell model allows extraction of the matrix elements of the shell model residual interaction. More than 100 diagonal and nondiagonal elements can be determined in this way, through a least squares fit to the experimental data. This adjustment of the interaction significantly affects the calculated properties of the γ-ray transitions. Nevertheless, the matrix elements thus obtained are remarkably similar to those of a realistic interaction calculated from free-nucleon scattering. Characteristic features of the interaction are discussed.
The g factors of the 9 − and 11 − yrast states in 194 Pb and 196 Pb have been measured using the ... more The g factors of the 9 − and 11 − yrast states in 194 Pb and 196 Pb have been measured using the time-dependent perturbed angular distribution (TDPAD) technique. An analysis of the systematics of the properties of these states in the light Pb isotopes is presented. The results confirm the dominance of the ͑2f 5/2 −1 1i 13/2 −1 ͒ configuration in the 9 − isomer. The values for the 11 − isomers are consistent with the ͑3s 1/2 −2 1h 9/2 1i 13/2 ͒ configuration, but they are smaller than those in the Po isotones. The effects of core excitation and particle-vibration coupling are considered, but these do not lead to a detailed agreement between theory and experiment. A Nilsson approach, however, gives good agreement, providing support for a proposed oblate deformation.
Adopted spectroscopic information on 0 • i 0 • f pure E0 transitions has been deduced by critical... more Adopted spectroscopic information on 0 • i 0 • f pure E0 transitions has been deduced by critical evaluation of the available experimental data for all even-even nuclei ranging from 4 2 He 2 to 250 98 C f 152. Values of q 2 K´E 0 E2µ, the ratio of the K-conversion electron intensity of the 0 • i 0 • f , E0 transition to that of the 0 • i 2 • 1 , E2 transition, have been determined. This procedure, together with the most recent theoretical conversion coefficients for internal conversion and electron-positron pair creation, as well electronic factors, produced a large number of new X´E0 E2µ values, defined as the dimensionless ratio of the absolute B´E0µ and B´E2µ transition rates. The squared value of the monopole transition strength, ρ 2´E 0µ, has been deduced using the best available 0 •-level half-lives and branching ratios.
The level structure of 124 I (Z = 53, N = 71) has been studied via the 122 Sn(7 Li, 5n) 124 I rea... more The level structure of 124 I (Z = 53, N = 71) has been studied via the 122 Sn(7 Li, 5n) 124 I reaction with a beam energy of 54 MeV. Through in-beam and out-of-beam γ-ray spectroscopy, the sophisticated low-lying levels including isomeric states and numerous collective states have been established for the first time. A positive-parity collective band built on the 10 + state at 1297 keV is interpreted as being associated with the combination of a proton and a neutron in the same intruder h 11/2 orbital, namely the π h 11/2 νh 11/2 configuration. This band shows a typical quadrupole vibrational character. In contrast, the negative parity bands based on the π g 7/2 νh 11/2 configuration show a soft triaxial rotation. An isomeric 8 − state at 689 keV with a half-life of 14 ns can be explained as a K isomer due to a proton with an p = 9/2 in the g 9/2 orbital coupled to a neutron with an n = 7/2 in the h 11/2 orbital. The excited states based on this π g 9/2 νh 11/2 configuration show a coupled rotational structure. Another coupled rotational band built on the 6 + state at 714 keV is thought to be based on the π g 9/2 νd 3/2 configuration.
Background: Stellar carbon synthesis occurs exclusively via the 3α process, in which three α part... more Background: Stellar carbon synthesis occurs exclusively via the 3α process, in which three α particles fuse to form 12 C in the excited Hoyle state, followed by electromagnetic decay to the ground state. The Hoyle state is above the α threshold, and the rate of stellar carbon production depends on the radiative width of this state. The radiative width cannot be measured directly, and must instead be deduced by combining three separately measured quantities. One of these quantities is the E0 decay branching ratio of the Hoyle state, and the current 10% uncertainty on the radiative width stems mainly from the uncertainty on this ratio. The rate of the 3α process is an important input parameter in astrophysical calculations on stellar evolution, and a high precision is imperative to constrain the possible outcomes of astrophysical models. Purpose: To deduce a new, more precise value for the E0 decay branching ratio of the Hoyle state. Method: The E0 branching ratio was deduced from a series of pair conversion measurements of the E0 and E2 transitions depopulating the 0 + 2 Hoyle state and 2 + 1 state in 12 C, respectively. The excited states were populated by the 12 C(p, p) reaction at 10.5 MeV beam energy, and the pairs were detected with the electron-positron pair spectrometer, Super-e, at the Australian National University. The deduced branching ratio required knowledge of the proton population of the two states, as well as the alignment of the 2 + 1 state in the reaction. For this purpose, proton scattering and γ-ray angular distribution experiments were also performed. Results: An E0 branching ratio of Γ E0 π /Γ = 8.2(5) × 10 −6 was deduced in the current work, and an adopted value of Γ E0 π /Γ = 7.6(4) × 10 −6 is recommended based on a weighted average of previous literature values and the new result. Conclusions: The new recommended value for the E0 branching ratio is about 14% larger than the previous adopted value of Γ E0 π /Γ = 6.7(6) × 10 −6 , while the uncertainty has been reduced from 9% to 5%. The new result reduces the radiative width, and hence 3α reaction rate, by 11% relative to the adopted value, and the uncertainty to 6.1%. This reduction in width and increased precision is likely to constrain possible outcomes of astrophysical calculations.
Background: High-spin isomers at ≈9-MeV excitation energies have been reported in several N = 83 ... more Background: High-spin isomers at ≈9-MeV excitation energies have been reported in several N = 83 isotones near Z = 64. Spin and parity assignments of J π = 49/2 + remain tentative for a number of these states in the odd-A nuclei. Purpose: To study the decay of the (49/2 +) high-spin isomer in 145 Sm, make firm spin and parity assignments to the isomer and states populated in its decay, and investigate the structure of the nucleus. Methods: The 145 Sm isomer was populated in the 124 Sn(26 Mg,5n) reaction. Gamma-ray and conversion-electron data were collected using the Solenogam array. Results: A revised lifetime of t 1/2 = 3.52(16) µs was measured for the high-spin isomer. Several new states have been added to the level scheme, and a new state at 8815 keV is proposed as the isomer, based on decayproperty systematics, transition strengths, and spin and parity assignments. Firm spin and parity assignments have been made to states up to and including the isomer and the new level scheme is interpreted using shell-model calculations performed with the KShell program. Conclusions: The interpretation of the 49/2 + isomer as a deformed excitation of the core neutrons remains unchanged, although there has been a significant revision of the level scheme below the isomer, and hence significant reinterpretations of the lower-lying states.
Excited states in 174 Re have been populated in fusion-evaporation reactions at the Australian Na... more Excited states in 174 Re have been populated in fusion-evaporation reactions at the Australian National University, and γ-ray spectroscopy has been used to determine the level structure and to deduce the underlying nucleon configurations. The half-life of the bandhead of the K π = 8 − band has been measured to be 2.7(4) ns. A band built on an isomeric state of spin-parity (14 −) and a half-life of 53(5) ns has been observed here for the first time, and has been determined to have a four-quasiparticle structure. Contrasting reduced-hindrance values for its decay are discussed in terms of deformation and configuration changes, as indicated by configuration-constrained potential energy surface calculations.
The emergence of nuclear collectivity near doubly-magic 132Sn was explored along the stable, even... more The emergence of nuclear collectivity near doubly-magic 132Sn was explored along the stable, eveneven 124−130Te isotopes. Preliminary measurements of the B(E2; 41+ → 21+) transition strengths are reported from Coulomb excitation experiments primarily aimed at measuring the g factors of the 41+ states. Isotopically enriched Te targets were excited by 198-205 MeV 58Ni beams. A comparison of transition strengths obtained is made to large-scale shell-model calculations with successes and limitations discussed.
Excited states in 186 Re with spins up to J = 12 were investigated in two separate experiments us... more Excited states in 186 Re with spins up to J = 12 were investigated in two separate experiments using 186 W(d,2n) reactions at beam energies of 12.5 MeV and 14.5 MeV. Two-and threefold γ-ray coincidence data were collected using the CAESAR and CAGRA spectrometers, respectively, each composed of Compton-suppressed HPGe detectors. Analysis of the data revealed rotational bands built on several two-quasiparticle intrinsic states, including a long-lived K π = (8 +) isomer. Configuration assignments were supported by an analysis of in-band properties, such as |gK − gR| values. The excitation energies of the observed intrinsic states were compared with results from multiquasiparticle blocking calculations, based on the Lipkin-Nogami pairing approach, that included contributions from the residual proton-neutron interactions.
Using the 168 Er(10 B, 5n) reaction at a beam energy of 68 MeV, new data have been obtained for t... more Using the 168 Er(10 B, 5n) reaction at a beam energy of 68 MeV, new data have been obtained for the population and decay of a T 1/2 = 148 ns, K π = 21/2 − three-quasiparticle isomer at 1717 keV in 173 Ta. Revised decay energies and intensities have been determined, together with newly observed members of a rotational band associated with the isomer. By comparison with other isomers in the A ≈ 180 deformed region, the 173 Ta isomer properties help to specify the key degrees of freedom that determine K-forbidden transition rates. In particular, when all three quasiparticles are of the same nucleon type, there is a strong dependence of the E2 reduced hindrance factor on the isomer excitation energy.
Solenogam is a recoil spectrometer designed and constructed for use at the Australian National Un... more Solenogam is a recoil spectrometer designed and constructed for use at the Australian National University (ANU) Heavy-Ion Accelerator Facility (HIAF). The design enables the study of nuclear excitations populated by the decay of long-lived states such as isomers and radioactive ground states. Solenogam is comprised of high-sensitivity γ-ray and electron detector arrays coupled to a new 8-T solenoid. While the installation of the 8-T solenoid proceeds, off-line measurements have been made to characterise Solenogam's performance. Gamma-electron coincidences in the electron capture decay of 182 Re into 182 W were used to investigate conversion coefficients and γ-e − angular correlations. The measured conversion coefficients show good agreement with theoretical calculations and have been used to extract E0/E2 mixing ratios for a number of J → J transitions. The angular correlations measured by the array are in qualitative agreement with theoretical calculations. However, the magnitudes of the correlations are attenuated by approximately 40% for reasons unknown at present. These results are the first full use of the Solenogam system for γ-e − coincidence measurements and have proven that the system is capable of highly-sensitive internal conversion analysis of complex decays.
Excited states in 62 Ni were populated with a (p, p') reaction using the 14UD Pelletron accelerat... more Excited states in 62 Ni were populated with a (p, p') reaction using the 14UD Pelletron accelerator at the Australian National University. Electric monopole transition strengths, ρ 2 (E0), were measured through simultaneous detection of the internal conversion electrons and γ rays emitted from the de-excitation of populated states, using the Super-e spectrometer coupled with a germanium detector. The strength of the 0 + 2 to 0 + 1 transition has been measured to be 77 +23 −34 × 10 −3 and agrees with previously reported values. Upper limits have been placed on the 0 + 3 to 0 + 1 and 0 + 3 to 0 + 2 transitions. The measured ρ 2 (E0) value of the 2 + 2 to 2 + 1 transition in 62 Ni has been measured for the first time and found to be one of the largest ρ 2 (E0) values measured to date in nuclei heavier than Ca. The low-lying states of 62 Ni have previously been classified as one-and two-phonon vibrational states based on level energies. The measured electric quadrupole transition strengths are consistent with this interpretation. However as electric monopole transitions are forbidden between states which differ by one phonon number, the simple harmonic quadrupole vibrational picture is not sufficient to explain the large ρ 2 (E0) value for the 2 + 2 to 2 + 1 transition.
Spectroscopic information on the decay properties of high-K isomers in deformed and transitional ... more Spectroscopic information on the decay properties of high-K isomers in deformed and transitional nuclei has been evaluated and collated. Assigned multi-quasiparticle configurations are included. Factors that control the transitions strengths, such as various contributions to K mixing, are outlined. The systematics of K-forbidden transitions for different multipolarities are discussed for selected cases in terms of the hindrances, F W , and of the reduced hindrance factor per degree of K forbiddenness, f ν , where ν = |∆K − λ |, ∆K is the K-value difference between the initial and final state and λ is the transition multipole order. With the improved statistics for E1, M1 and E2 transitions, a factorization into the product of the underlying multipolarity-dependent transition strength and a ν-dependence, due to K forbiddenness (f 0), is possible. This suggests a weaker dependence on K forbiddenness than is commonly assumed.
Nuclear K-isomers play an important role in understanding the structure of deformed axially symme... more Nuclear K-isomers play an important role in understanding the structure of deformed axially symmetric nuclei. Examples are presented of recent studies in the rare-earth region (A∼180) using deep-inelastic and multinucleon transfer reactions, and in the trans-fermium region (A∼250) using fusion-evaporation reactions. A specific two-level mixing scenario is invoked to explain the unusual decay of the K π = 13 + isomer in 174 Lu. The identification of 2-and 4-quasiparticle isomers in 254 No is discussed and predictions of similar isomers in neighboring No and Rf nuclei are presented.
The level scheme of 212 Rn has been extended to spins of ∼ 38h and excitation energies of about 1... more The level scheme of 212 Rn has been extended to spins of ∼ 38h and excitation energies of about 13 MeV using the 204 Hg(13 C, 5n) 212 Rn reaction and γ-ray spectroscopy. Time correlated techniques have been used to obtain sensitivity to weak transitions and channel selectivity. The excitation energy of the 22 + core-excited isomer has been established at 6174 keV. Two isomers with τ = 25(2) ns and τ = 12(2) ns are identified at 12211 and 12548 keV, respectively. These are the highest-spin nuclear isomers now known, and are attributed to configurations involving triple neutron core-excitations coupled to the aligned valence protons. Semi-empirical shell-model calculations can account for most states observed, but with significant energy discrepancies for some configurations.
The evaluated spectroscopic data are presented for 12 known nuclides of mass 84 (Ga, Ge, As, Se, ... more The evaluated spectroscopic data are presented for 12 known nuclides of mass 84 (Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo). Except for the stable nuclides 84Sr and 84Kr, extensive new data are available for all the other nuclides since the 1997 evaluation by J.K. Tuli (1997Tu02) of A = 84 nuclides. Many precise Penning-trap mass
Excited states in 181 Ta have been identified using time-correlated ␥-ray spectroscopy and partic... more Excited states in 181 Ta have been identified using time-correlated ␥-ray spectroscopy and particle-␥ techniques following the incomplete fusion reaction 176 Yb(11 B,␣2n) 181 Ta. As well as observing the rotational band based on the 11 ns isomer at 482 keV from the 5/2 ϩ ͓402͔ proton configuration, which is found to be essentially identical to that associated with its 7/2 ϩ ͓404͔ pseudospin partner, several multi-quasiparticle isomers are observed including a 33 s state, of probable spin and parity 21/2 Ϫ , at 1483 keV. Experimental states are compared with multi-quasiparticle calculations. ͓S0556-2813͑98͒02909-4͔
Conversion electrons from 208 Bi have been measured using singles and coincidence techniques with... more Conversion electrons from 208 Bi have been measured using singles and coincidence techniques with the 208 Pb(p, n) 208 Bi reaction at 9 MeV. The new information on multipolarities and spins complements that available from recent γ-γ-coincidence studies with the same reaction [Boutachkov et al., Nucl. Phys. A768, 22 (2006)]. The results on electromagnetic decays taken together with information on spectroscopic factors from earlier single-particle transfer reaction measurements represent an extensive data set on the properties of the one-proton one-neutron-hole states below 3 MeV, a spectrum which is virtually complete. Comparison of the experimental observables, namely, energies, spectroscopic factors, and γ-branching ratios, with those calculated within the shell model allows extraction of the matrix elements of the shell model residual interaction. More than 100 diagonal and nondiagonal elements can be determined in this way, through a least squares fit to the experimental data. This adjustment of the interaction significantly affects the calculated properties of the γ-ray transitions. Nevertheless, the matrix elements thus obtained are remarkably similar to those of a realistic interaction calculated from free-nucleon scattering. Characteristic features of the interaction are discussed.
The g factors of the 9 − and 11 − yrast states in 194 Pb and 196 Pb have been measured using the ... more The g factors of the 9 − and 11 − yrast states in 194 Pb and 196 Pb have been measured using the time-dependent perturbed angular distribution (TDPAD) technique. An analysis of the systematics of the properties of these states in the light Pb isotopes is presented. The results confirm the dominance of the ͑2f 5/2 −1 1i 13/2 −1 ͒ configuration in the 9 − isomer. The values for the 11 − isomers are consistent with the ͑3s 1/2 −2 1h 9/2 1i 13/2 ͒ configuration, but they are smaller than those in the Po isotones. The effects of core excitation and particle-vibration coupling are considered, but these do not lead to a detailed agreement between theory and experiment. A Nilsson approach, however, gives good agreement, providing support for a proposed oblate deformation.
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Papers by Tibor Kibedi