Search

The level scheme of 177Re has been extended extensively, with fragments of more than thirty bands, characterised by a given signature, observed. Alignments at low frequency in one-quasiparticle bands are interpreted as deformation effects and compared with the predictions of cranking calculations. The previously assigned one-quasiparticle π i 13 2 band is shown to be a mixture of three-quasiparticle and vibrational character. The non-observation of the one-quasiparticle π i 13 2 band is explained as being due to crossings of its s-band by competing bands. A number of high-K bands are also reported, including five- and seven-quasiparticle bands. Configuration assignments for these bands are aided by comparing experimental gκ values with “effective” gκ values, calculated with a semi-classical expression taking Coriolis mixing into account. The population of the yrast band was observed to oscillate with every four units of spin.

Deformations as function of spin, based on diabatic configurations, have been calculated for proton i132 and h92 bands in Re and Ir isotopes. Generally, constant deformations are predicted for the h92 bands while the i132 bands are predicted to increase in deformation until the alignment of i132 neutrons. The results are compared with recently measured Qt values. The alignment systematics are qualitatively explained in terms of the predicted deformations.

High-spin states in 171Re have been studied using the reaction 123Sb(52Cr, 4n)171Re. A back-bend in the i132 band of a Re nucleus has been fully delineated for the first time. A new back-bend has also been observed in the 52+[402] band and other bands have been extended to higher spin and added to the level scheme. Band crossings are interpreted using the CSM and three-band mixing calculations. These appear to show evidence for shape coexistence and configuration-dependent neutron pairing.

Negative-parity bands in the vicinity of {sup 156}Gd and {sup 160}Yb have been suggested as candidates for the rotation of tetrahedral nuclei. We report the observation of the odd and even-spin members of the lowest energy negative-parity bands in {sup 160}Yb and {sup 154}Gd. The properties of these bands are similar to the proposed tetrahedral band of {sup 156}Gd and its even-spin partner. Band-mixing calculations are performed and absolute and relative quadrupole moments deduced for {sup 160}Yb and {sup 154}Gd. The values are inconsistent with zero, as required for tetrahedral shape, and the bands are interpreted as octupole vibrational bands. The failure to observe the in-band E2 transitions of the bands at low spins can be understood using the measured B(E1) and B(E2) values.

Incomplete-fusion reactions have been used to study high-spin states in $^{171}\mathrm{Tm}$. Gamma rays and conversion electrons were measured using pulsed-beam conditions for enhanced isomer sensitivity. A ${K}^{\ensuremath{\pi}}=19/{2}^{+}$, three-quasiparticle isomer was identified, with a half-life of $1.7(2)$ \ensuremath{\mu}s. The faster than expected transition rates from the isomer can be understood as being due to a chance near-degeneracy, with mixing between the isomeric state and the ${I}^{\ensuremath{\pi}}=19/{2}^{+}$ member of the one-quasiparticle rotational band to which it decays. The implied mixing matrix element is $12(2)$ eV.

A candidate for chiral bands was found in Tl-198 for the first time in a mass region of oblate (or nonaxial with gamma >= 30 degrees) deformed nuclei. Two bands show very similar quasiparticle alignments, moments of inertia, and B(M1)/B(E2) ratios. They have a relative excitation energy of about 500 keV and different patterns of energy staggering. Calculations using the two-quasiparticle-plus-triaxial-rotor model with residual proton-neutron interaction included show that a triaxial deformation with gamma similar to 44 degrees agrees very well with all the experimental observations. Furthennore, considerable energy staggering for both partner bands was calculated for this pi h(9/2) circle times vi(13/2)(-1) configuration at gamma - 30 degrees, suggesting that chiral bands may have substantial energy staggering. (Less)

Decay schemes of the nuclei 171 Os, 172 Os and 173 Os were studied using the reactions 144 Sm( 30 Si,3n) 171 Os, 144 Sm( 31 P, p2n) 172 Os and 149 Sm( 28 Si, 4n) 173 Os. The 5 − 2 [523] and i 13 2 bands were identified in the odd nuclei. Low-spin properties of these bands are analyzed using the particle-rotor model, while band-crossing frequencies and alignments are examined with the aid of the cranked shell model. A low-frequency band crossing was found in the 5 − 2 [523] band of 173 Os. At higher frequencies, the measured B( M 1) B( E 2) transition rates and signature splittings in the 5 − 2 [523] bands of both nuclei are consistent with a neutron alignment. In the i 13 2 band of 173 Os, an upbend, in the unfavoured sequence, possibly due to the AD crossing, occurs at a lower frequency than a similar upbend, presumably from the BC crossing, in the favoured sequence. These crossings were also analyzed with phenomenological three-band-mixing calculations.

High-spin states have been identified in 174Os and 175Os using (HI, x>n) reactions and gamma-ray techniques. Rotational bands built on low-lying intrinsic states in 175Os have been observed for the first time. The intrinsic states are identified as a mixed i 13 2 neutron state (nominally 7 2 + [633] ) and the 1 2 − [521] and 5 2 − [512] Nilsson configurations. Differences in the alignment of the two signatures of the decoupled band built on the 1 2 − [521] state and the comparison between the signature splitting of routhians and if B(M1)/B(E2) values in the i 13 2 band suggest softness towards gamma deformation. Crossing transitions between the negative-parity bands at intermediate spin have been observed and the interaction strength derived from the branching ratios. A comparison of the properties of bands in 174Os and 175Os shows some expected similarities, but also surprising differences which point towards the need for a more comprehensive treatment in strong interaction cases. Depending on the choice of reference the alignment in the i l3 2 band might show degenerate BC and AD crossings at a relatively low frequency. This may be consistent with the alignment observed in the negative parity side bands in 174Os.

High-spin states in 181Ta have been studied via the 176Yb(11B,α2n) reaction at 52 MeV using the PEX array and at 57 MeV using the NORDBALL array, with α-particle detection. The previously known, Kπ=(7/2)+ ground state band and Kπ=(9/2)− band have been extended to spins (29/2)+ and (31/2)−, respectively. Two new one-quasiparticle bands, the Kπ=(5/2)+ band built on the known (5/2)+ isomer and a Kπ=((1/2)−) band have been observed. Two other rotational bands with three-quasiparticle structure, Kπ=(15/2)− and ((19/2)+ with π(7/2)[404]ν2(1/2)[510](9/2)[624] and π(9/2)[514]ν2(1/2)[510](9/2)[624] configurations, respectively, have been newly observed. The half-life of the Kπ=((19/2)+) bandhead which decays to the head of the (15/2)− band has been measured to be 140(36) ns. However, transitions from the ((19/2)+) state to the (15/2)− band have not been observed.

The neutron deficient nucleus 108Te was studied in the 54Fe(58Ni,2p2n) reaction. A detector system consisting of 4 Euroball cluster detectors, a charged-particle detector ball and a 16 element neutron multiplicity filter was used to detect the emitted particles and γ rays. A new, significantly extended level scheme was constructed on the basis of γγ-coincidence relations. Spin values for the states were determined from angular distribution ratios. The experimental results are discussed in terms of the shell model.

A search for isomeric states was performed in the nucleus Nd-140(60)80 using in-beam gamma-ray spectroscopy and the Te-126(O-18,4n) reaction. Prompt and delayed gamma-ray coincidences were measured with the AFRODITE spectrometer using the pulsed beam delivered by the Separated Sector Cyclotron of iThemba LABS. One new isomer was identified, with spin-parity I-pi=20(+) and lifetime T-1/2 >= 400 ns, at an excitation energy E-x=7430 keV. The lifetime of the 10(+) isomer at E-x=3619 keV was determined to be 32.9(1.8) ns, confirming the previously reported value. The configuration of the I-pi=20(+) isomer is assigned based on configuration-dependent cranked Nilsson-Strutinsky (CNS) calculations as a state pi(d(5/2)g(7/2))(10)(+-4)circle times nu(h(11/2)(-2))(10)(+), with the spin vectors of the six holes in the Gd-146(64)82 core fully aligned. (Less)

High-spin states in $^{185}\mathrm{Os}$ have been studied using the $^{176}\mathrm{Yb}(^{13}\mathrm{C},4n)$ reaction at a beam energy of $65\phantom{\rule{0.3em}{0ex}}\text{MeV}$. Previously known one-quasiparticle bands have been extended to higher spins. New high-$K$ bands based on three-quasiparticle excitation have been identified. Nilsson configurations are assigned based on the $g$ factors deduced from $M1∕E2$ branching ratios within the bands. In addition, a new isomer at $5007\phantom{\rule{0.3em}{0ex}}\text{keV}$ has been found with a half-life of $18(2)\phantom{\rule{0.5em}{0ex}}\text{ns}$. The hindrance in decays of the high-$K$ intrinsic states are discussed in terms of the $\ensuremath{\gamma}$ tunneling model where the low-$K$ and high-$K$ states interact through triaxial shape fluctuation.

The multipolarities of the main transitions deexciting yrast isomers in ${}^{190}\mathrm{Pb}$ have been measured using conversion electron spectroscopy with pulsed beams. The enhanced $E3$ character of the 407 keV transition from the ${11}^{\ensuremath{-}}$ isomer is confirmed and an independent value obtained for its lifetime. A new measurement of the properties of the 440 keV $E3$ decay from the corresponding ${11}^{\ensuremath{-}}$ state in ${}^{192}\mathrm{Pb},$ has resulted in the identification of a new branch and a significantly different lifetime from that reported previously. The abnormally large strength of the ${11}^{\ensuremath{-}}$ to ${8}^{+}$ transitions in both ${}^{190}\mathrm{Pb}$ and ${}^{192}\mathrm{Pb}$ match those known in some light polonium isotopes, an effect which is suggested to be linked to a change in structure of the orbitals in the ${8}^{+}$ configuration when oblate deformation is established; the lowest $\ensuremath{\Omega}{=7/2}^{\ensuremath{-}}$ proton Nilsson orbital changes from being predominantly of ${h}_{9/2}$ character at sphericity to a mixed ${f}_{7/2}{/h}_{9/2}$ parentage at oblate deformations, thus enabling an enhanced ${i}_{13/2}$ to ${f}_{7/2}$ octupole-coupled transition.

The conversion coefficients for several bandhead decays in Ta-180 have been measured using pulsed-beam techniques and the Yb-176(Li-7,3n)Ta-180 reaction. The spin and parity of the 520 keV Intrinsic state is established as 4(+) and several earlier assignments are confirmed. Two-quasiparticle configurations for the 520 and 592 keV states are discussed and following reanalysis of the band properties, a consistent interpretation is reached. The 520 keV 4(+) state is associated with the favored coupling of the nu 1/2(-)[521]x pi 9/2(-)[514] configuration while the 592 keV (5(+)) state is identified with the nu 1/2(-)[510]x pi 9/2(-)[514] configuration.

Two four-quasiparticle isomers, with ${K}^{\ensuremath{\pi}}{=12}^{+}$ and ${(14}^{+})$ and mean lives of 450(100) ns and $58(5)\ensuremath{\mu}\mathrm{s},$ have been identified in ${}^{176}\mathrm{Lu},$ at excitation energies of 1515 and 1588 keV, respectively. The ${12}^{+}$ isomer exhibits a large number of K-forbidden decay branches, populating the rotational sequences based on the ${K}^{\ensuremath{\pi}}{=7}^{\ensuremath{-}}$ ground state, two ${K}^{\ensuremath{\pi}}{=8}^{+}$ states, and a ${K}^{\ensuremath{\pi}}{=4}^{+}$ state from the $\ensuremath{\nu}{{7/2}^{\ensuremath{-}}[514]}\ensuremath{\bigotimes}\ensuremath{\pi}{{1/2}^{\ensuremath{-}}[541]}$ configuration. Most branches have decay rates that are consistent with normal K-hindrances except for the branch to the ${K}^{\ensuremath{\pi}}{=4}^{+}$ band. It has an anomalously low hindrance factor, which is attributed to two-state mixing due to a near-degeneracy between the ${12}^{+}$ isomer and the ${12}^{+}$ member of this band. The implied mixing matrix element has a value of only 5 eV, showing explicitly that very small mixing matrix elements may be responsible for anomalous K-hindered decays.

Time-correlated, particle-tagged $\ensuremath{\gamma}$ spectroscopy of the stable nucleus ${}^{179}\mathrm{Hf}$ was undertaken with incomplete fusion reactions initiated by beams of ${}^{9}\mathrm{Be}$ and ${}^{7}\mathrm{Li}$ incident on targets of ${}^{176}\mathrm{Yb}.$ Intrinsic and rotational states above the three-quasiparticle ${K}^{\ensuremath{\pi}}{=25/2}^{\ensuremath{-}}, {T}_{1/2}=25 \mathrm{day}$ isomer, ${}^{179}\mathrm{Hf}{}^{m2},$ are reported. The rotational band based on ${}^{179}\mathrm{Hf}{}^{m2}$ has ${g}_{K}\ensuremath{-}{g}_{R}$ values that are consistent with the previously suggested $\ensuremath{\nu}{9/2}^{+}\ensuremath{\bigotimes}{\ensuremath{\pi}}^{2}[{7/2}^{+}{,9/2}^{\ensuremath{-}}]$ configuration assignment. A value of ${g}_{R}=0.34(5)$ was derived for the collective g factor of ${}^{179}\mathrm{Hf}{}^{m2},$ which is considerably higher than that found for the ${9/2}^{+}$ ground state. The difference is consistent with a reduction of the proton pairing strength due to blocking in the ${K}^{\ensuremath{\pi}}{=25/2}^{\ensuremath{-}}\ensuremath{\nu}\ensuremath{\bigotimes}{\ensuremath{\pi}}^{2}$ configuration. A number of ${\ensuremath{\nu}}^{3}{\ensuremath{\pi}}^{2}$ five-quasiparticle configurations were identified, the highest of which is an yrast ${K}^{\ensuremath{\pi}}{=43/2}^{+}, {T}_{1/2}=15(5) \ensuremath{\mu}\mathrm{s}$ isomer. It decays to an yrast ${K}^{\ensuremath{\pi}}{=39/2}^{\ensuremath{-}}$ state, which in turn decays to a rotational band based on a ${K}^{\ensuremath{\pi}}{=33/2}^{\ensuremath{-}}$ state. The ${K}^{\ensuremath{\pi}}{=33/2}^{\ensuremath{-}}$ state decays to the rotational band associated with ${}^{179}\mathrm{Hf}{}^{m2}.$ Semiempirical calculations reproduce the excitation energies of the three- and five-quasiparticle states above ${}^{179}\mathrm{Hf}{}^{m2}$ to within $\ensuremath{\sim}200 \mathrm{keV}.$ The calculations predict that the lowest seven-quasiparticle state will arise from a ${\ensuremath{\nu}}^{5}{\ensuremath{\pi}}^{2}$ configuration with ${K}^{\ensuremath{\pi}}{=47/2}^{\ensuremath{-}},$ which is just beyond the maximum spin accessible with the reactions employed here.

In a search for exotic structures in odd-odd 164Lu, eight new, presumably triaxial, superdeformed bands were found. Two of the bands are connected to normal-deformed structures and the El strength of the connecting transitions appear to be enhanced over single particle expectations, possibly due to octupole correlations.

Several isomers in ${}^{188}\mathrm{Pb}$ have been identified using pulsed beams, the recoil-shadow technique, and the ${}^{164}\mathrm{Er}{(}^{28}\mathrm{Si}{,4n)}^{188}\mathrm{Pb}$ reaction. Two of the isomers feed the ${10}^{+}$ state of the yrast sequence and are suggested to be the ${11}^{\ensuremath{-}}$ and ${12}^{+}$ states from oblate and spherical configurations, respectively. The ${12}^{+}$ isomer is fed weakly by another isomer with a relatively long lifetime, but it has not been characterized. A fourth isomer with a lifetime of about $1.2 \ensuremath{\mu}\mathrm{s}$ leads via a complicated path to the ${8}^{+}$ and lower spin yrast states. It is a candidate for the ${K}^{\ensuremath{\pi}}{=8}^{\ensuremath{-}},$ two-quasineutron state which occurs systematically in $N=106$ prolate-deformed nuclei, supporting the assumption that the intruding collective well is prolate.

High-spin states up to the f7/2-shell band termination at J? = 15+ have been observed in the odd-odd N = Z = 23 nucleus V. A revised and significantly extended level scheme contains two distinct structures corresponding to spherical and prolate shapes. A band exhibiting rotational-like behaviour in the latter structure has excellent correspondence with the yrast sequence in Ti and is therefore assumed to be a T = 1 configuration. The difference between excited analogue states in the two nuclei is interpreted as a Coulomb effect and its variation with spin associated with np-pair alignment effects in V. Shell-model calculations have been performed and are in good quantitative agreement with experimental level energies. The competition between T = 1 and T = 0 structures is also reproduced. © 1999 Elsevier Science B.V. All rights reserved., Scientific Committee on Antarctic Research Engineering and Physical Sciences Research Council Komitet Badan Naukowych Natural Sciences and Engineering Research Council of Canada Engineering and Physical Sciences Research Council, The authors thank both Alfredo Poves and Alex Brown for permission to use results from their shell model codes and for helpful discussions. We also thank those responsible for all aspects of the PEX collaboration. This work was supported by the United Kingdom Engineering and Physical Sciences Research Council (EPSRC) from whom D. E. Appelbe was in receipt of an EPSRC studentship. A. Maj is grateful to the Polish State Committee for Scientific Research for partial financial support (KBN Grant No. 2 P03B 001 16). This work was also supported by the Danish Natural Science Research Council.

The decay scheme of the N=Z odd-odd nucleus, 62Ga has been deduced for the first time using the reactions 40Ca(24Mg,pn)62Ga and 40Ca(28Si,αpn)62Ga at beam energies of 65 MeV and 88 MeV respectively. Transitions from excited states in 62Ga were identified using the PEX apparatus at the Niels Bohr Institute Tandem Accelerator Laboratory. Gamma ray angular correlation data collected using the AYEBALL array at the Argonne National Laboratory are consistent with a cascade of stretched E2 transitions which decay from a spin 1+ bandhead via a pure magnetic dipole decay, directly linking a proposed T=0 structure with the T=1, Jπ=0+ ground state.

The low-lying levels in the odd-odd N = Z nucleus 62 Ga have been identified for the first time. These data reveal a cascade of stretched-E2 transitions based on a T =0, 1 + bandhead which decays directly to the T =1, 0 + ground state. The observed levels are interpreted in the context of theshell model, using as a basis, the pf 5/2 g 9/2 orbits with a 56 Ni core.

The DIAMANT light charged-particle detector will be coupled with the AFRODITE γ-ray spectrometer at iThemba LABS under a bilateral agreement between South Africa and Hungary. As a first step, the standalone 'Chessboard' section of DIAMANT has been integrated with AFRODITE in order to study incomplete fusion reactions instigated by beams of 13C ions incident on targets of 170Er and 176Yb. A fuller implementation of DIAMANT with AFRODITE will take place in due course.

Tilted-axis rotation, arising from Fermi-aligned configurations, has been observed for the first time to cause backbending in an odd-proton nucleus. In 181Re, two t-bands are found to be energetically favored relative to the usual rotation-aligned s-bands, presenting an alternative form of cold nuclear rotation. Interactions between the bands are weak, and unambiguous comparisons with tilted-axis-cranking calculations can be made.

The \ensuremath{\gamma} cascades feeding into low-K and high-K bands in ${}^{163}$Er are investigated analyzing variances and covariance of the spectrum fluctuations. From a large data set of 1${0}^{9}$ triple coincidences, \ensuremath{\gamma}-\ensuremath{\gamma} coincidence spectra gated by resolved low-lying rotational bands are analyzed. Low-K bands are found to be fed by a much larger effective number of cascades than high-K bands. The covariance between pairs of gated spectra shows that the cascades feeding low-K bands are different from those feeding the high-K bands. The persistence of the K-selection rules for the excited rotational bands within the angular momentum region $30\ensuremath{\Elzxh}\ensuremath{\le}I\ensuremath{\le}40\ensuremath{\Elzxh}$ is suggested as explanation.

A superdeformed (SD) band in 103Pd was studied using the reaction 76Ge(34S,α3n) at 148 MeV. Yields of γ-rays, γ-γ coincidences and γ-ray angular correlation measurements were obtained with the NordBall multi-detector system. The SD band is compared with similar bands in 104,105Pd. Calculations of spin diabatic surfaces have been performed and are used for assigning deformation parameters and quasiparticle configurations to the bands. Additional occupation of intruder orbitals from π or ν h 11 2 and the ν i 13 2 [660] 1 2 , in combination with band terminations of the normal deformed bands may explain the existence of the SD band in 103Pd.

A search for the γ decay of the Giant Dipole Resonance built on superdeformed (SD) nuclear configurations of 143Eu was made, using the reaction 110Pd(37Cl, 4n)143Eu at 165 MeV. Eight large BaF 2 scintillators and the NORDBALL array were used to measure high and low-energy γ-rays. The γ-spectrum gated by transitions populated by the SD states shows an excess yield at 7-10 MeV compared to the spectrum gated by transitions not populated by SD states. The comparison with statistical model predictions indicates that this excess most probably is due to γ-ray emission of the GDR built on superdeformed states.

High-spin states in 185Re have been studied using the 176Yb(13C,p3n) reaction at 65 MeV. Levels up to spin (37/2) h at Ex = 4.799 MeV have been identified. Among them two levels were observed with half-lives of 6 ± 2 ns and 123 ± 23 ns.

Several of the known rotational bands in 164Er are extended considerably (to around 35 h). In addition, a new coupled band is established and found to decay by an isomeric transition with t1/2 ≥ 170 nsec, to the 11t - state of the known Kπ =7− two-quasi-proton band. The new band is interpreted as a four-quasi-particle structure, with measured values of B(M1)/B(E2) consistent with the configuration [7t -] ⊗ ?i13/2[642 5/2+] ⊗ ?h9/2[523 5/2t -], i.e. [7t -]⊗ [AE,AF]. This is supported by the observation of a crossing which resembles the second i13/2 neutron crossing, BC, associated with the two-quasi-neutron band built on the configuration, [AE,AF]. The routhian of the new band is close to the sum of the individual routhians of [AE,AF] and [7−]. The cause of a small gain in energy of 130–272 keV is discussed.

Excited states in Sn-102 have been identified for the first time, in an in-beam gamma-ray spectroscopic experiment. Two gamma-ray transitions with energies 1472 and 497 keV following the decay of the seniority 6(+) isomer with t(1/2) = 1.0(5) mu s were unambiguously assigned to Sn-102. Due to the very low cross section of about 2 mu b for producing Sn-102 in the reaction Cr-50(Ni-58,1 alpha 2n), a highly selective detector setup utilizing NORDBALL ancillary detectors and a recoil catcher device was used. High gamma-ray detection efficiency was achieved with two EUROBALL Ge cluster detectors.

High spin states in Cd-104 have been investigated by means of heavy ion induced reactions using the Nordball detector array. The level scheme constructed from yy-coincidences is dominated by three ...

We report on new results for the decay of the superdeformed (SD) band in194Pb. No transitions linking the SD structure with the known level scheme of194Pb could be found, but the feeding intensities into the normal-deformed states are determined and limits on the one-step decay of the SD band are given.

h11/2 neutron and g9/2 proton alignments in 99,100Ru deduced from comparisons of experimental Routhians and aligned angular momenta to cranking model calculations. There is indication of band termination in100Ru.

Reduced hindrance factors of K-forbidden transitions are compiled for nuclei with A ~ 180 where γ-vibrational states are observed. Correlations between these reduced hindrance factors and a Coriolis forces, statistical level mixing and γ-softness have been studied. It is demonstrated that the K-forbidden transitions probabilities are related to γ-softness. The decay of the high-K bandheads has been studied by means of the two-state mixing, which would be induced by the γ-softness, with the use of a number of K-forbidden transitions compiled in the present work, where high-K bandheads are depopulated by both E2 and ΔI = 1 transitions. The validity of the two-state mixing scheme has been examined by using the proposed identity of the B(M1)/B(E2) ratios of transitions depopulating high-K bandheads and levels of low-K bands. A break down of the identity might indicate that other levels would mediate transitions between high- and low-K states.

The ground-state mass excess of 39 S has been determined from a measurement of the Q - value of the 40 Ar( 13 C, 14 O) 39 S reaction using a gas target. A value of −23.164±0.050 MeV was obtained in good agreement with the predictions of standard mass equations. In addition, a single excited state was observed at 1.469 ±0.025 MeV. The reaction mechanism of the ( 13 C, 140 O) reaction is discussed in terms of a two-step reaction model based on the second-order Born approximation. The degree of angular-momentum matching appears to be an important factor in determining the degree of participation of a possible reaction channel. Calculations indicate that in the case of the 40 Ar( 13 C, 14 O) 39 S reaction, the reaction is dominated by a single path because of poor matching in competing channels.

The mass excess of 35 Si has been determined as −14.427 ± 0.060 MeV from a measurement employing the 36 S( 13 C, 14 O) 35 Si reaction. No excited states of 35 Si were observed. The 34 S( 13 C, 14 O) 33 Si reaction was studied simultaneously, and previously unreported excited states in 33 Si were observed at 1.47, 2.00, 3.19, 4.13 and 5.48 MeV.

Yrast bands in 176Pt(N=98) and 178Pt have been identified. The level scheme of 176Pt changes from a quasi-vibrational pattern to that of a well deformed rotor, at very low spins, a behaviour similar to that attributed to shape coexistence in the light Hg isotopes. Analysis of The 176-188Pt yrast bands supports a shape coexistence interpretation, the excitation energy of the intruder state behaving as predicted by Wood, (1981).

The mass excesses of 33Si and 34Si have been measured using the 36S(11B, 14, 13N)33, 34Si; reactions. Values of −20.550 ± 0.030 MeV ( 33 Si) and −20.017 ± 0.025 MeV ( 34 Si) were obtained. In addition, an excited state of 34Si was observed at 5.33 ± 0.05 MeV, and excited levels of 33Si were observed at 1.06 ± 0.02 and 4.32 ± 0.03 MeV. These results are compared with recent shell-model calculations.

The mass of 25 Ne has been determined from the Q -value of the reaction 26 Mg( 13 C, 14 O) 25 Ne at a 13 C energy of 96 MeV. The 14 O ions were momentum-analysed using an Enge split-pole spectrometer and detected at the focal plane in a multi-element, gas-filled detector. The resulting mass excess for 25 Ne is −2.03±0.05 MeV. Excited states of 25 Ne were observed at energies of 1.74±0.03, 3.33±0.03, 4.07±0.03 and 6.28±0.05 MeV. The widths of the states at 1.74 and 3.33 MeV suggest that they may be unresolved doublets, the levels being separated by approximately 110 and 200 keV, respectively. A qualitative discussion of the possible reaction mechanisms and of the nuclear structure of the observed states is presented and a comparison made with recent shell-model calculations.

Observations have been made on twenty states in 57 Co via the 56 Fe( 7 Li, 6 He) 57 Co reaction at 38 MeV. J π values have been extracted for seventeen of these states using the J -dependence of the small-angle cross sections for this reaction. Full finite range DWBA predictions have been made for these states and the values of (2 J f + 1) C 2 S f obtained by least squares fitting. These spectroscopic values agree well with previous determinations from the ( 3 He, d) reaction where these exist. The analyses show an excess of 7 2 − strength and a deficiency of 3 2 − strength leading to the conclusion that there may be reduced occupancy of the f 7 2 proton orbitals in 56 Fe with the missing protons populating normally empty 2 p 3 2 orbitals.

The lifetime of the yrast 15 2 − state in 215 Ra was measured using pulsed beams and γ-ray and electron techniques. Transition multipolarities were established from measured conversion coefficients. The B (E3) of the 15 2 − → 9 2 + transition is found to be considerably larger than previously reported. A candidate for the corresponding transition in 217 Th was also observed. The E3 strength of the 15 2 − → 9 2 + transition in the N = 127 isotones is evaluated in the light of these and other recent results. Interpretation in the framework of particle-octupole vibration coupling requires a systematic lowering of the core 3 − vibration as proton pairs are added to 208 Pb.

The lifetime and branching ratio of the 19+ isomer in 210At have been measured. Its enhanced E3 decay and g-factor, and those of the related 39 2 − isomer in 211At are compared with the results of a semi-empirical shell model calculation which includes couplings to the 3− octupole vibration, resulting in mixed configurations. Lifetimes were also obtained for the 15− isomer in 210At, and the 29 2 + isomer in 209At.

Excited states in the neutron-deficient nucleus 170 Os were identified up to spin (24 + ) in the yrast band and to spin (23 − ) in the lowest negative-parity band. Deformation systematics implied by the 2 + state energies for the very light osmium isotopes are compared with theory. Band-crossing frequencies, alignments and alignment gains are compared with cranked shell-model calculations. Deformation changes are required to obtain detailed agreement. A three-band mixing approach is invoked to explain the low-spin yrast anomaly in 172 Os and to reproduce the yrast band in 170 Os. The excitation energy of the postulated “intruder” band in 170 Os and 172 Os is deduced.

The γ-decay of the Giant Dipole Resonance (GDR) built on excited nuclear states has been measured for the nucleus143Eu. The reaction110Pd(37Cl, 4n)143Eu at a beam energy of 165 MeV has been employed. This experiment aimed at searching the γ-decay of the GDR built on the superdeformed143Eu states, populated at high spins. High-energy γ-rays were detected in 8 large BaF2 scintillators in coincidence with discrete transitions measured with the NORDBALL array (in the configuration consisting of 17 HPGe detectors and a 2π multiplicity filter). The spectrum of high-energy γ-rays gated by low-energy transitions between states fed by the superdeformed states shows some excess of yield in the 7–10 MeV region with respect to that gated by transitions between states not populated by the superdeformed states. This excess should be due to the γ-decay of the the giant dipole oscillation along the superdeformed axis of the nucleus that is expected to have a frequency corresponding to ≈9–10 MeV (low-energy component of the GDR strength function). The measured excess, in spite of the large error bars, is found to be of the same order as predicted statistical model values.

High-spin states in 167Hf, populated in the 141Pr(30Si, p3n)167Hf reaction, have been studied using the nordball Ge detector array. Three rotational cascades have been observed for the first time and the previously-known level scheme has been extended to significantly higher spin. Band-crossing effects are discussed within the framework of Woods-Saxon cranking calculations and are found to be in good agreement.

The yrast and near-yrast energy levels of 206 Po have been investigated to over 9 MeV excitation and up to spins of 24. The measurements consisted of γγ-coincidence data, internal-conversion-electron spectra, time spectra of γ-rays relative to a pulsed beam, excitation functions and γ-ray angular distributions. Two new isomers, with lifetimes in the 1 ns range, were found. The observed level structure is compared with the predictions of empirical shell-model calculations in which 206 Po is regarded as a 208 Pb core with two valence protons and four valence neutron holes. The agreement is generally satisfactory for the observed odd-parity levels and for even parity levels with J > 12; those with J = 6−12 are better accounted for by weak coupling of two valence protons to a 204 Pb core in its 0 + 1 and 4 + 1 states.