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Lifetimes of levels in two doubly-decoupled bands of ${}^{134}\mathrm{Pr}$ involving neutron intruder orbits have been measured using Doppler-shift techniques. The deduced transition quadrupole moments are consistent with total Routhian surface predictions for the suggested configurations of both bands. The negative-parity band with one neutron in the ${i}_{13/2}$ orbit has a much larger quadrupole deformation than the positive-parity band with a neutron in the ${(f}_{7/2}{/h}_{9/2})$ orbit, reflecting the strong polarizing effect of the $N=6$ intruder orbit on the nuclear shape.

Entrance channel effects in the fusion of heavy ions have been studied by using the 74Ge+74Ge reaction at 318 MeV. The population of the yrast superdeformed band in 144Gd shows an increase when compared with the results obtained in the more asymmetric 48Ti+100Mo reaction at 215 MeV. The relative yields of the different evaporation residues produced in the 74Ge+74Ge and in the 48Ti+100Mo reactions are very similar, with the exception of the 145,144Gd residual nuclei (3n and 4n decay channels) which are populated with a larger yield in the symmetric reaction. Statistical model calculations reproduce qualitatively such effect if a fission delay is explicitly taken into account. Effects related to fusion barrier fluctuations seem to be important in determining the spin distributions of the compound nucleus. The spectra of the high energy γ-rays emitted in the 74Ge+74Ge reaction have been measured as a function of the γ-ray multiplicity as well as in coincidence with selected evaporation residues. They are reproduced by standard statistical model calculations with GDR parameters taken from systematics, demonstrating that, in agreement with dynamical model prediction, the emission of γ-rays from the dinucleus formed in the earlier stage of the collision is unimportant.

Transitions linking the highly deformed (HD) bands to states of normal deformation in 137 Sm and 139 Gd have been identified in experiments performed at GASP. The spins deduced for the HD bands in these N = 75 isotones support the previously assigned νi 13 2 [660] 1 2 + configuration. The different decay-out patterns of the two otherwise similar HD bands are tentatively explained by the difference in pairing between the Z = 62 and Z = 64 proton systems.

Rotational structures in 132Nd have been investigated via the 104 Pd ( 32 S ,2p2n) reaction at 160 MeV. Four highly-deformed bands have been observed, out of which three have been linked to the normal-deformed states. Two of them are signature partners. A mixing at high spin is observed between levels of one highly-deformed band and the ground-state band allowing for an unambiguous assignment of the spins and parity of that band. The present data brings new evidence on the role of the N = 72 shell gap to the stabilization of the highly-deformed minimum in the A = 130 mass region and on the importance of the νi 13 2 intruder orbital in the structure of the highly-deformed bands.

The four-quasiparticle magnetic dipole band in {sup 128}Ba has been investigated with the {sup 96}Zr({sup 36}S,4n){sup 128}Ba reaction at the GASP spectrometer of the Laboratori Nazionali di Legnaro. Linking transitions to the previously known positive parity states have been observed for the first time in this mass region and new transitions on top of the band have been found. The experimental results are compared to previously made tilted axis cranking calculations. {copyright} {ital 1997} {ital The American Physical Society}

The high-spin structure of 137Nd has been studied through the 110Pd(30Si,3n) and the 123Sb(19F,5n) reactions at beam energies of 125 and 97 MeV, respectively. A very complex level scheme has been established up to spin 97 2 + and 23.9 MeV of excitation energy. Regular bands are observed at high-spin, consisting of either M1 and E2 crossover transitions, or of stretched M1 or E2 transitions. Calculations have been performed in the framework of the interacting boson-fermion model with broken pairs for the relatively strong ΔI = 1 regular structures observed above spins 27 2 − and 31 2 − , which are well described by the (νh 11 2 ) 3 and νh 11 2 ⊗(πh 11 2 ) 2 configurations, respectively.

High-spin states in 43Ca, 45Sc, and 45Ti were studied with the GASP multidetector array coupled with the Recoil Mass Spectrometer. The nuclei were excited in the 60 MeV 18O +30Si reaction. Lifetimes were extracted from the analysis of the Doppler-shift attenuation of γ-rays observed in the reversed 35Cl+12C reaction. The lifetimes, B(M1) and B(E2) values for 45Sc are presented. The measurements suggest significant deformation of the positive-parity intruder band in this nucleus. The band is predicted by the mean-field calculations to be the cross-shell particle-hole excitation associated with a strong quadrupole core-polarization. Spherical shell-model calculations reproduce observed excitation energies and transition rates in both spherical and deformed structures.

High-spin states in the doubly odd nucleus Br-76 have been investigated using the Mn-55(Si-30,2 alpha n) reaction at a beam energy of 130 MeV. Five bands have been established to high spin. The features of the level scheme, particularly the signature inversion and the band crossings in the yrast band as well as proton and neutron alignments in the negative-parity bands, are discussed in the framework of the cranked shell model. (C) 1997 Elsevier Science B.V.

The feeding mechanism of the superdeformed bands in ${}^{147}$Gd and ${}^{148}$Gd has been studied via the ${}^{124}$Sn + ${}^{29}$Si reaction at a beam energy of 157 MeV. Using the BGO inner ball of the GASP array, high-energy $\ensuremath{\gamma}$ rays have been detected in coincidence with discrete transitions deexciting normal-deformed (ND) and superdeformed (SD) states in the final product nuclei. The slope of the measured high-energy $\ensuremath{\gamma}$-ray spectra depends strongly on the number of emitted neutrons and is somewhat lower for spectra in coincidence with SD bands than for those in coincidence with ND structures. Both observations are qualitatively reproduced by statistical model Monte Carlo calculations, which point out the importance of angular momentum effects in the emission of energetic $\ensuremath{\gamma}$ rays. The present data exclude the enhanced population of SD bands when fed through high-energy $E1$ transitions.

The decay out of the yrast and excited highly deformed (HD) bands in ${}^{134}$Nd has been investigated via the ${}^{28}\mathrm{Si}{+}^{110}\mathrm{Pd}$ reaction at 130 MeV using the GASP array. Several deexcitation pathways have been established for both the yrast and excited HD bands. The resulting spins remove previous ambiguities in the assignment of the excited HD band and confirm the structure assigned to the yrast HD band. The decay out is understood in terms of mixing between the normal-deformed and HD states, which is triggered by the crossing between the $\ensuremath{\nu}{i}_{13/2}$ and $\ensuremath{\nu}{d}_{5/2}$ orbitals.

The giant dipole resonance (GDR) from the decay of excited 156Er nuclei, populated in the reaction 241 MeV 64Ni + 92Zr, has been studied employing a high-resolution 4π γ-ray spectrometer. High-energy γ-ray spectra have been measured in coincidence with both the spectrometer inner ball and the Ge detectors selecting discrete γ-transitions in the residual nuclei 155,154Er. The analysis of the high-energy γ-ray spectra shows that the GDR can be reproduced by a single-lorentzian fit using standard parameters for strength, energy and width, only when a fold k > 10 is required in the inner ball. On the contrary, with lower-fold conditions (k ≤ 10) unrealistic GDR parameters are obtained, mainly due to the presence of light target contaminants. The GDR width determined for k > 10 compares well with systematics and with predictions of adiabatic calculations. The line-shape analysis of the γ-ray spectrum associated with a single evaporation residue (154Er) yields GDR parameters similar to those obtained for the high-fold selected spectra, with the exception of a slightly larger width. No signature is therefore observed for a pre-equilibrium component in the decay of 156Er populated in a nearly symmetric reaction. Nevertheless, differences are evidenced in the comparison of the present spectrum from the 64Ni + 92Zr reaction with earlier results from the 12C + 144Sm asymmetric system.

High-spin structures in 136Nd have been investigated via the 110Pd(30Si,4n) reaction at 125 MeV using the GASP array. Several bands consisting of stretched quadrupole transitions were identified. Two of them reach spins comparable to those of the highly-deformed (HD) band in 136Nd, which is based on a neutron i 13 2 - h 9 2 f 7 2 configuration. Total routhian surface (TRS) calculations indicate that regular high-spin excitations in this γ-soft nucleus, can be also generated through successive pairs of h 11 2 protons and neutrons coupled to a stable small-deformation triaxial core. The previously reported γ-ray transitions of an excited HD band, identical to the yrast HD band, are not confirmed by our data.

The band structures of the doubly odd 134 Pr nucleus has been investigated via the 119 Sn( 19 F,4n) 134 Pr and 110 Pd( 28 Si,p3n) 134 Pr reactions at beam energies of 87 and 130 MeV, respectively. The three previously known rotational bands based on the π[541] 3 2 − (α=± 1 2 )⊗ν[514] 9 2 − and π[423] 5 2 + ⊗ν[514] 9 2 − configurations have been extended to higher spins. The difference of ≈2ħ in the experimental alignment of the bands based on the signature partners of the [541] 3 2 − h 11 2 proton orbital is discussed in terms of shape coexistence and coupling with the γ-phonon but no consistent interpretation can be found. A new band consisting of quadrupole transitions has also been identified and linked unambiguously to the low-lying levels of the yrast band. Total routhian surface and cranked shell model calculations suggest a (π h 11 2 ) 3 ⊗ν[530] 1 2 − configuration for this band. The experimental ratios of reduced transition probabilities B( M 1) B( E 2) of the various rotational structures are compared to the theoretical values obtained from a semiclassical model and from the two-particle plus triaxial-rotor model.

Lifetimes have been measured in 139Sm with the DSAM method, using the reaction 62Ni(81Br,p3n)139Sm at 350 MeV. In the negative-parity regular dipole band based on the 25 2 − state at 3325 keV values of 0.60(21), 0.40(14) and 0.25(8) ps were found for the 337, 409 and 473 keV transitions, respectively. The deduced B(M1) and B(E2) are in agreement with the predictions of the tilted axis cranking model, allowing a triaxial equilibrium shape for the assumed νh 11 2 ⊗ πh 11 2 2 configuration.

A dipole band with regular energy spacings has been identified in the nucleus137Nd built on aI=33/2 state atE x =5.60 MeV. The Doppler shift attenuation method analysis of a backed-target experiment allowed to extract the lifetimes of the band levels, which are of the order of 1 W. u., The resulting large B(M1) values, together with the high aligned angular momentum suggest a five-quasiparticle configuration (involving twoh11/2 protons and twoh11/2 neutrons).

High spin states have been observed for the first time in the odd-odd nucleus80Y, by using the24Mg(58Ni,pn) reaction at 180 MeV. Eight rotational bands have been established, indicating a nucleus with appreciable deformation.

A g-factor measurement in the superdeformed band of 133Nd has been performed by applying the transient field method in coincidence mode with the multidetector array GASP. The 133Nd nuclei were populated by the 104Pd(32S,2pn) reaction at a bombarding energy of 135 MeV. Polarized Gd has been used as ferromagnetic host. A mean g-factor of g = 0.31(8) has been determined at the I π = 41 2 + superdeformed state. The experimental value is compared with theoretical predictions and supports the assignment of the superdeformed band to the ν[660] 1 2 + Nilsson intruder orbital.

The nuclear structure of 145Gd has been investigated via the 114Cd(36S,5n) reaction. Three superdeformed bands have been discovered, consisting of 17, 16 and 10 transitions, respectively. The first excited superdeformed band shows two band crossings which are assigned to the subsequent alignment of an i 13 2 proton pair and a crossing of the i 13 2 and i 11 2 neutron orbitals, respectively. Such a double band crossing has been observed for the first time. The second excited superdeformed band is assigned as the signature partner of the previous band but shows no band crossing in the observed frequency range. The band crossing behaviour of the SD bands has been described theoretically.

The quadrupole interaction of high-spin isomers in 193Pb implanted into solid Hg cooled at a temperature T = 170 K has been investigated by the time-differential perturbed $\gamma$ -ray angular-distribution method. Spectroscopic quadrupole moment values of $\vert Q_{\rm s} \vert = 0.22(2)$ eb and 0.45(4) eb have been deduced for the 21/2- and 33/2 + three-neutron states, respectively. A much higher value $\vert Q_{\rm s} \vert = 2.84(26)$ eb has been determined for the 29/2- isomer, the band head of a magnetic rotational band.

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

The population of the highly-deformed band in 133 Nd has been studied using the reactions 32 S + 105 Pd and 60 Ni + 77 Se to form the compound nucleus 137 Sm at comparable excitation energy. Experimental results do not show any dependence on the entrance-channel mass asymmetry, in agreement with recent results for 135 Nd and at variance with those for the 147,148 Gd and 152 Dy nuclei. The experimental data on the entrance-channel dependence of the population of highly- and super-deformed bands in the mass regions A ˜130,150and190 are discussed in terms of dynamical effects which occur during the formation process of the compound nucleus as well as in the fission channel.

Transitions linking the highly deformed band to low deformation states have been unambiguously established in 133 Nd in the very first experiment performed with the GASP array. the highly deformed band becomes yrast at 29 2 + , where it mixes with the positive parity band built upon the [404] 7 2 Nilsson state. The experimentally deduced interaction amounts to 13 keV. The measurement of the spins in the highly deformed intruder band sheds some light upon the reported backbend anomaly in this mass region.

In-beam γ-rays in neutron-rich sdfp shell nuclei, produced in deep-inelastic collisions of 48Ca projectiles on 48Ca target nuclei, have been studied using Ge multidetector array EU-ROBALL III. New yrast states in heavy argon isotopes have been identified.

The mean life of the 12+ level at 4195 keV in146Sm has been measured with the Recoil Distance method. The reduced strength of the E3 decay 12+→9−, about 60 W.u., confirms the collectivedouble-octupole character of the 12+ level.

Two-phonon γ-vibrational states in166Er have been populated using Coulomb excitation. The Kπ=4+ component of the vibration appears to be fragmented over several states, whereas only one Kπ=0+ state is observed.

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.

New results on the high spin structure of the N=Z nuclei 48Cr and 52Fe are presented. Experiments were performed using the GASP array in coincidence with the 4π charged particle detector ISIS which allows a better selection of the reaction channel by γ-γ-particles and γ-γ-γ-particles coincidences.

High spin rotational bands in 162 Lu and 164 Lu have been studied through the 139 La( 28 Si,5n) and 139 La( 29(30) Si,4(5)n) reactions respectively. For both nuclei the yrast sequence which is associated with the πh 11/2 ⊗νi 13/2 configuration shows the signature inversion feature.

The ground state band of48Cr has been extended to high spins through the reaction24Mg(32S,2α). The assignment of the transitions was based onγ-γ-γ andγ-γ-particle(E, ΔE) - coincidences. The data confirm theoretical predictions based on fullfp spherical shell model calculations.

High-spin states in 196Pb have been populated using the reaction 170Er(30Si,4n). The previously observed shears bands in this nucleus have been extended and some of their transitions have been reordered. They now form regular bands with band crossings. One of the bands splits into two pathways at high spin.

Arguments in favor of the collective nature of the {ital E}3 transitions in {sup 144}Nd are discussed. In the authors{close_quote} opinion, the 12{sup +} level at 4354 keV remains a likely candidate for a double-octupole excitation. {copyright} {ital 1996 The American Physical Society.}

Gamma-ray studies of130Te+275 MeV64Ni reaction products have identified yrast states of129Te up to a 33 ns isomer at 2138 keV. Theβ−-decay of 17.7 min129Sb to levels in129Te is elucidated.

Two excited superdeformed bands have been found in196Pb using the GASPγ-ray spectrometer array. They are signature-partner bands with a small signature splitting developing at higher frequencies, similar to bands 2 and 3 in the isotone194Hg. The bands are probably built on an excited neutron configuration. They show an unusual incremental alignment of 1/2ħ with respect to the194Pb core.

The structure of the neutron deficient184Hg nucleus was investigated using the GASP γ-ray spectrometer.184Hg nucleus was populated through the156Gd(32S,4n) reaction at a beam energy of 163 MeV. Six bands were observed, four of them for the first time. The quadrupole deformations of the two stronger excited bands were measured using the Doppler shift attenuation method.

The previously unknown nucleus118Cs has been identified through γ-γ and γ-recoil coincidences using the GASP γ-spectrometer and Recoil Mass Spectrometer. The level scheme constructed on the base of triple γ coincidences shows a collective structure based on the π−1g9/2⊗νh11/2 configuration.

The magnetic hyperfine field for K, Ca, Ti in iron has been measured by means of time differential observation of the perturbed angular distribution of gamma rays emitted in the reactions37Cl(α,n)40K,39K(α, p)42Ca and42Ca(α, n)45Ti. The valuesHhf(0)=−66 (6)kG, −96(4) kG, −122(15) kG, respectively, were extrapolated at 0°K. In the case of calcium the presence of a satellite field was confirmed with a strength of −45(4)kG. In the case of potassium most of the implanted nuclei do not contribute to the Larmor precession.

The elastic scattering of protons by 46Ca has been measured at seven angles for Ep = 1.82−1.90 MeV. Thirteen resonances are observed and interpreted as components of the split analogue of the 47Ca first excited state. The resonance parameters are extracted and the proton width of the IAS is determined. The partial reduced widths are fitted to the Robson one-level formula and the pertinent parameters are deduced. In addition, γ-rays from the 46Ca(p, γ)47Sc reaction were detected; the decay scheme and Γγ are deduced. The summed M1 strength for the IAS is 1.0 W.u. Hindrance of the M1 decay is explained as resulting from the polarization due to the spin-isospin interaction, which is especially strong for the analogue-to-antianalogue transitions.

Optical properties of LPCVD amorphous silicon films deposited both from SiH4 and from Si2H6 are investigated at very low H contents. The optical energy gap varies with deposition temperature even if H concentration is constant. The non-homogeneous H profile seems not influence optical properties, which display features quite similar to those of GD samples.

Precessions of the first 2/sup +/ and 4/sup +/ states in /sup 22/Ne have been measured employing the transient field method. The g factor of the 4/sup +/ state has been deduced to be g = 0.55(14) using the known value of g(2/sup +/) as normalization. The obtained result agrees with the shell model prediction. The value of the transient magnetic field for Ne in Fe at vapprox.1.5v/sub 0/ points to a contribution of 1s vacancies to the transient magnetic field.

The precession of the lowest 3/2− and 5/2− states in107Ag and109Ag, recoiling in thin iron foils, have been measured employing the transient-field method. Theg-factors have been measured relative to that of the first 2+ state in106Pd and resulted to be $$\begin{gathered} g(\frac{3}{2}^ - ,{}^{107}Ag) = 0.70(9) g(\frac{5}{2}^ - ,{}^{107}Ag) = 0.45(6) \hfill \\ g(\frac{3}{2}^ - ,{}^{107}Ag) = 0.79(12) g(\frac{5}{2}^ - ,{}^{109}Ag) = 0.36(6) \hfill \\ \end{gathered} $$ (1) The values obtain have been compared with some theoretical predictions.

The 21+ level of138Ba has been Coulomb excited with a 105 MeV32S beam. The precession of the gamma ray angular distribution induced by the transient magnetic field when traversing a 2.14 mg/cm2 iron foil, has been measured to be 15.6(1.7) mr. A value of g(138Ba 21+)=0.72(11) was obtained assuming for the transient field strength the Chalk River calibration. The field parametrization has been checked using the first 2+ state in150Sm as probe. Theg value obtained is sensibly lower than predicted by large scale shell model calculations in a proton subspace. Theg-factor of the first 2+ state in148Sm has been remeasured yieldingg(148Sm 21+)=0.246(22).

Spin precessions of the28Si first 2+ state, caused by transient magnetic fields in thin Fe and Gd foils, were measured at a mean ion velocity of 7.5v0 (v0=c/137). Transient fields of 1.8 (3) kT and 1.1 (2) kT have been deduced for Fe and Gd, respectively. The observed field strengths are discussed in terms of the electron mean polarization in the SiK shell.

The angular precessions of the lowest (5/2)/sup +/ and (7/2)/sup +/ states in /sup 197/Au have been measured employing the transient field method. The /sup 197/Au nuclei, Coulomb-excited by a 180 MeV /sup 63/Cu beam, traversed the Gd foil with velocities between 5v/sub 0/ and 2v/sub 0/ (v/sub 0/ = c/137). We have obtained the values g((5/2)/sup +/) = 0.21(2) and g((7/2)/sup +/) = 0.15(2), which are consistent with the predictions of the particle-core weak-coupling model. The field has been calibrated with the Chalk River parametrization, which has been checked using the known g factors of the lowest 2/sup +/ states in /sup 184/W, /sup 186/W, /sup 194/Pt, and /sup 196/Pt as probes.

A multitarget reaction chamber and a gamma-ray detector system have been installed at the LNL for profile studies by means of nuclear reactions. In particular the system has been applied to hydrogen profiling via the 15 N(p, αγ) 12 C reaction. Several modifications to the 7 MV CN Van de Graaff of the LNL have been performed to allow 15 N beam acceleration.

The Doppler-shift attenuation method has been used to determine lower limits for the lifetimes of the first, second and third excited states in 47Ca. The limits obtained are 9, 17 and 2 ps, respectively. As a check, the known lifetime of the first excited state in 39Ca has been remeasured ( tau =230-30+40 fs).