Proton-neutron excitations in the high-spin states of 95Tc

The high-spin states of ⁹⁵Tc have been studied in the reaction ⁹³Nb(α, 2n)⁹⁵Tc using inbeam spectroscopy of both γ-rays and conversion electrons. A new sequence of negative-parity states extending up to angular momentum $\text{I =}\text{29}\text{2}$ was found to exist within an excitation energy interval of 4.1 MeV. The positive-parity states are in remarkable agreement with the predictions of a simplified shell-model approach on the basis of coupled excitations of $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ proton and $\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}{}^{\mathrm{?}}$ as well as $\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ neutron configurations. A similar analysis for the negative-parity states shows qualitative agreement with the experimental results.     

Proton spectroscopy of 96Tc from the (3He,d) reaction

Energy levels of the even-mass odd nucleus ⁹⁶Tc have been populated with the ⁹⁵Mo(³He, d)⁹⁶Tc reaction at a bombarding energy of 33.6 MeV and with 28 keV resolution (FWHM). Thirty levels were observed below 2.10 MeV excitation. Comparison of experimental angular distributions with DWBA calculations allowed l-value assignments and the extraction of spectroscopic factors for most levels. Over eighty-five percent of the observed spectroscopic strength is located in the lowlying $\text{π1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{-}\text{v}\text{2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ configuration multiplet. A simple residual interaction shell model calculation reproduces the observed low-lying positive parity multiplet relatively well although the experimental spectrum indicates much configuration mixing is present.     

High-spin states in 92Tc

High-spin states in ⁹²Tc have been studied using the 33 MeV ⁹²Mo(³He, p2nγ)⁹²Tc reaction. Levels up to J = (13) are identified. The results are compared with various shell-model calculations.     

Isomeric γ-ray transitions in 98Tc

Delayed γ-rays from ⁹⁸Tc have been observed following pulsed proton beam bombardment of an enriched ⁹⁸Mo target. The energies of the delayed γ-rays are 43.5 ± 0.5 keV and 21.8 ± 0.1 keV. Also seen are delayed Tc X-rays. These radiations all have the same half-life which has been measured to be 14.6 ± 0.7 μs. The 21.8 keV γ-ray is identified as the first excited state to ground state transition. An estimate of the internal conversion coefficients of the 21.8 and 43 keV decays suggests that both transitions are M1.     

Multipolarities of γ-rays from 92, 94Nb and 94,95,96,97,98Tc

^{92, 94}Nb and ^{94, 96, 98}Tc have been produced by the (p, n) reaction at proton energies on and near the $\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ isobaric analog resonance. ^95,97Tc have been produced by the (p, γ) reaction below the (p, n) threshold. Internal conversion electrons due to the decay of their excited states were detected on-line with a mini-orange spectrometer which is optimized for the energy range 50 to 500 keV. Gamma rays from these nuclei were detected with a thin Ge(Li) detector. Isomeric-delayed internal conversion electrons and γ-rays were observed, using a nanosecond-pulsed beam. The internal conversion coefficients for 55 transitions in these nuclei have been determined and their multipolarities deduced. The multipolarity of the transitions in these nuclei is predominantly M1. Negative parities have been assigned through use of the $\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ isobaric analog resonance enhancements of the population of negative-parity final states. The systematic behavior of the 2^?, 3^? doublet and of the $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{?}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ multiplet in these nuclei is discussed.     

Average resonance spectroscopy in 93, 95, 97Tc

The (p, γ) reactions on the ⁹²Mo, ⁹⁴Mo and ⁹⁶Mo isotopes were studied in the energy range E_p = 2.4–3.0 MeV using a Ge(Li) detector incorporated into a three-crystal pair spectrometer and a Ge(Li) detector in coincidence with a NaI(Tl) detector. A three-crystal pair spectrometer was utilized to determine the average yield of γ-rays leading directly to the low-lying states in each of the three residual nuclei. These average yields were examined for a possible correlation between the intensity of high-energy γ-ray transitions and the J^π of the final state. The data indicate that such a correlation exists. A two-dimensional coincidence experiment determined the decay scheme of the low-lying excited states in ⁹³Tc ⁹⁵Tc and ⁹⁷Tc. The J^π assignments inferred from these experiments are consistent with those for the states in ⁹³Tc, ⁹⁵Tc and ⁹⁷Tc which have previously been obtained. For those states which were previously unassigned, the results of this experiment are as follows (all energies are in keV): . The state at 2429 keV in ⁹³Tc has not been reported previously.     

High-spin states of 39K and 42Ca

High-spin states of ³⁹K and ⁴²Ca have been investigated with the ²⁸Si(¹⁶O, αpγ)³⁹K and ²⁸Si(¹⁶O, 2pγ)⁴²Ca reactions at a beam energy of 45 MeV. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization measurements were performed with a Ge(Li)-NaI(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. High-spin states of ³⁹K at E_x = 7.14,7.78and8.03 and of ⁴²Ca at E_x = 7.75MeV are established. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{=}\text{11}\text{2}{}^{\mathrm{?}}\text{,}\text{13}\text{2}{}^{\mathrm{?}}\text{,}\text{15}\text{2}{}^{\mathrm{+}}\text{,}\text{15}\text{2}{}^{\mathrm{?}}\text{,}\text{17}\text{2}{}^{\mathrm{+}}\text{and}\text{19}\text{2}{}^{\mathrm{?}}$ to the ³⁹K levels at E_x = 5.35, 5.72, 6.48, 7.14, 7.78 and 8.03 MeV and of 6^?, 7^?, 8^?, 9^? and(8, 10)^? to the ⁴²Ca levels at E_x = 5.49, 6.15, 6.41, 6.55 and 7.37 MeV, respectively, have been obtained. Further spin-parity restrictions, lifetime limits, excitation energies, branching ratios and multipole mixing ratios are reported. Discrepancies with previous J^π assignments are discussed in detail.     

High-spin states in 107Sn and 107In isotopes

The isotopes ¹⁰⁷Sn and ¹⁰⁷In were produced through the ¹⁰⁶Cd(³He, 2n)¹⁰⁷Sn and ¹⁰⁶Cd(³He, pn)¹⁰⁷In reactions. They were studied by means of γ-spectroscopy, excitation functions, γγ coincidences and angular distributions of γ-rays. A level scheme is proposed for the newly discovered ¹⁰⁷Sn, and new states belonging to ¹⁰⁷In are given. Microscopic calculations have been performed in a three-quasiparticle approximation for a large number of tin isotopes in order to get a wide view of the systematic evolution of the various states.     

Neutron hole states in 138La and 140Pr

Protons accelerated to 30 MeV were used to investigate low-lying states in the odd-odd nuclei ¹³⁸La and ¹⁴⁰Pr with (p, d) reactions. The elastic scattering of 30 MeV protons and 23 MeV deuterons was also studied to determine optical potentials. Experimental angular distributions are compared with distorted-wave Born approximation calculations to extract spin, parity, and spectroscopic factors for levels up to 432 keV of excitation in ¹⁴⁰Pr and 530 keV in ¹³⁸La. Comparisons with the simple shell-model predictions and extended shell-model calculations are presented. The ¹⁴⁰Pr levels appear experimentally to have an almost pure particle-hole structure whereas the ¹³⁸La levels exhibit substantial mixing.     

High spin rotational states in 154Dy, 164Er And 162Yb

High spin rotational states in ¹⁵⁴Dy, ¹⁶⁴Er and ¹⁶²Yb have been investigated with (α, 4nγ) and (α, 6nγ) reactions. The ground state rotational bands have been identified up to spin 14 for ¹⁵⁴Dy and ¹⁶²Yb and spin 16 for ¹⁶⁴Er. Anomalous behaviour of the moment of inertia has been observed in ¹⁶⁴Er.     

High-spin states in 58Ni

High-spin states of ⁵⁸Ni were investigated via the study of in-beam γ-ray induced by the compound reaction ⁴⁸Ti(¹²C, 2n)⁵⁸Ni between 26 and 48 MeV. The energies and decay modes of these levels were determined from the analysis of γ-γ coincidence measurements at 35 MeV. The most intense lines in the ⁵⁸Ni γ-ray spectrum correspond to a cascade to the ground state, through levels at 1.454, 2.459, 3.619 and 4.381 MeV, also fed in other reactions, and by two previously unknown levels at 5.125 and 5.662 MeV; the spin assignments based on the present study are (apart from the ground state) 2, 4, 4, 5, 6 and 7 respectively for these levels. The first three were already known and the last three are new. The mixing ratios for the transitions between these levels are also determined. We observe also the same cascade in the reaction ⁵⁶Fe(α, 2n)⁵⁸Ni at an incident energy 18–24 MeV. Comparisons with other reactions, previous studies and recent shell-model calculations are presented.     

High-spin states in 38K

High-spin states in ³⁸K are investigated with the ²⁴Mg(¹⁶O, pnγ)³⁸K reaction at $\text{E(}{}^{16}\text{O}\text{) = 36–44}\text{MeV}$. A recently developed Compton-suppression spectrometer with 120 msr solid angle and a pulsed beam are employed to study their γ-decay. For the E4 transition from the isomeric level at E_x = 3458 keV to the ground state a branching ratio of (0.15 ± 0.02)% is found. On the basis of angular distribution and polarization measurements, in which the delayed feeding component is eliminated, spin-parity assignments are obtained of J^π(2646 keV) = (2, 4)^?, J^π(3420 keV) = (4, 6)^? and J^π(3458 keV) = (5, 7)⁺. Prompt-delayed and prompt γγ coincidence experiments are performed to locate high-spin levels above the isomer. Hitherto unobserved levels of high spin are found at E_x = 5254, 7397, 8693, 8747 and 10980 keV and assignments of J^π = (9⁺), (10^?), (12^?), (11^?) and (13^?) respectively, are suggested by weak-coupling considerations. The experimental results are compared with a large-scale shell-model calculation performed in a configuration space with a ²⁸Si core and ten active particles distributed over the ($\text{2}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{, 1}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{, 1}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{, 2}\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{)}$ shells. The high-spin states appear to have a rather simple shell-model structure.     

High-spin states in 208Rn

The yrast decay scheme of ²⁰⁸Rn has been investigated up to spin $\text{≈ 20}\text{h}\text{?}$ and an excitation energy of ≈ 6 MeV. Several different γ-ray spectroscopic techniques were used to determine the properties of excited states and transitions in the nucleus. Significant changes to the previously established level scheme are proposed, based on the existence of an unobserved 3.1 keV transition. Simple empirical shell-model calculations of level energies aided in the assignment of shell-model configurations to excited states and the decay scheme is discussed in terms of these configurations. The energy level systematics for the even radon isotopes, from A = 206 to 212 are discussed, as are core polarization effects in the even radon isotopes (A = 204 to 210) and polonium isotopes (A = 202–208).     

Excited states in 216Ra

Excited states in ²¹⁶Ra have been studied using in-beam spectroscopic techniques. The reactions used were ²⁰⁸Pb(¹²C, 4n)²¹⁶Ra and ²⁰⁸Pb(¹³C, 5n)²¹⁶Ra at 80 and 95 MeV, respectively. The level scheme of ²¹⁶Ra was extended up to the (28^?) state at 6266 keV. Two new isomers, whose mean lives are 8.7 ± 0.6 ns and 9.7 ± 0.9 ns, were found to be the 19^? state at 3763 keV and the (25^?) state at 5170 keV. Levels up to the (25 ^?) state in ²¹⁶Ra are interpreted as arising from the weak coupling of two neutrons to the excited states in ²¹⁴Ra.     

Lifetimes of some excited states in 64Ni, 66Zn and 68Zn

Mean lives and excitation energies of the lowest levels in⁶⁴Ni,⁶⁶Zn and⁶⁸Zn were measured with the aid of the (α, α′γ) and (α, pγ) reactions. The γ-rays were detected in coincidence with the outgoing particles. The following mean lives were determined from DSA measurements: 400 ± 150 fs for the level at E_x = 1.35 MeV in ⁶⁴Ni; 270 ± 100, 210 ± 110, 330 ± 200, 80 ± 70 fs for the levels at E_x = 1.87, 2.45, 2.83, 2.94 MeV in ⁶⁶Zn, and 1300 ± 300, > 160, 600 ± 200 fs for the levels at E_x = 1.08, 1.89 and 2.76 MeV in ⁶⁸Zn, respectively.     

High-spin states in 90Nb

The high-spin states in ⁹⁰Nb have been studied by in-beam γ-ray spectroscopy using the 35 MeV ⁸⁹Y(α, 3nγ)⁹⁰Nb and 33 MeV ⁹⁰Zr(³He, p2nγ)⁹⁰Nb reactions. A new isomeric state with half-life 0.44±0.02 σs and J^π = 11^? has been located in this nucleus. The level scheme derived from these measurements is compared with shell-model calculations.     

Analogue states in 61Cu

Resonances in the reaction ⁶⁰Ni(p, γ)⁶¹Cu have been studied in the energy region E_p ≈ 1550–1950 keV. Decay schemes and branching ratios are presented for 12 resonances and the resonance strength has been determined for most of these. Gamma-ray angular distribution measurements on two resonances yield the following spin assignments $\text{(E}{}_{\mathrm{<mtext>p</mtext>}}\text{(}\text{keV}\text{; J): (1668;}\text{5}\text{2}\text{), (1850;}\text{3}\text{2}\text{,}\text{5}\text{2}\text{)}$. Several of the resonances studied are identified as fragments of the analogue states of the ground and first two excited states in ⁶¹Ni. M1 transitions strengths to the corresponding antianalogue candidates have been measured.     

High-spin states in 59Ni

High-spin states in ⁵⁹Ni have been investigated via the study of in-beam γ-rays following the reactions ⁵⁰Cr(¹²C, 2pn)⁵⁹Ni (26–58 MeV) and ⁵⁶Fe(α, n)⁵⁹Ni (10, 15, 22.5 MeV). The spins of previously known levels have been confirmed or determined for the first time, in particular for those at $\text{3376.8}\text{keV}\text{(J =}\text{11}\text{2}\text{)}\text{and}\text{4141.3}\text{keV}\text{(J =}\text{13}\text{2}\text{or}\text{15}\text{2}\text{)}$. New states have been established and their spin determined, at $\text{1739.2}\text{keV}\text{(J =}\text{9}\text{2}\text{), 2349.2}\text{keV}\text{(J =}\text{11}\text{2}\text{), 2535.5}\text{keV}\text{(J =}\text{13}\text{2}\text{), 4455.4}\text{keV}\text{(J =}\text{13}\text{2}\text{), 4947.5}\text{keV}\text{(J =}\text{15}\text{2}\text{)}\text{and}\text{5251.7}\text{keV}\text{(J =}\text{13}\text{2}\text{or}\text{15}\text{2}\text{)}$. The resulting ⁵⁹Ni decay scheme is discussed in the framework of nuclear models.     

High-spin states in 218Ra

Yrast states in ²¹⁸Ra up to spin and parity I^π = 17^? were identifíed by means of the ²⁰⁸Pb(¹³C, 3n) reaction and standard γ-ray spectroscopic techniques. The level scheme is characterized by two bands of opposite parity with nearly constant level spacing. A cascade of strong E1 interband transitions connects both bands.The results are discussed within the systematics of the even Ra isotopes. The negative-parity band which is observed from the I^π = 5^? to the I^π = 17^? state, is interpreted as an octupole vibrational band. The level scheme can be well reproduced in the vibrational limit of the interacting boson approximation (IBA1) which fails, however, to explain the strong E1 feeding of the negative-parity band from the ground-state band     

High-spin states in 222Th

Levels to spin 16⁺ in the ground band and 17^? in the octupole band in ²²²Th have been identified using the reaction ²⁰⁸Pb(¹⁸O, 4n)²²²Th at 93 MeV. To suppress intense γ-ray background from fission a residue detector was built and operated in coincidence with the Ge(Li) and NaI(Tl) detectors. The apparent moment of inertia in the ground-state rotational band rises very rapidly with increasing spin, however, no indications of backbending were observed. The octupole band at low spin has an aligned angular momentum $\text{J ≈ 3}\text{h}\text{?}$ relative to the ground-state band. Strong cross-band E1 transitions competed with collective E2 transitions within each band. Analysis showed that the ratios $\text{B(}\text{E}\text{1)}\text{B(}\text{E}\text{2)}$ were within experimental uncertainty independent of both the spin and parity of the parent state.The average γ-ray multiplicity per cascade was measured for ²²²Th. The results were in reasonable agreement with the computer code ORNL-ALICE.