Search

The light krypton isotopes were studied in a series of Coulomb excitation experiments using radioactive beams at GANIL. The static quadrupole moments found in these experiments give firm experimental evidence for the shape coexistence scenario that is based on theoretical calculations and on the systematics of low-lying excited 0+ states. The experimental results are interpreted within a phenomenological two-band mixing model. Configuration mixing calculations based on triaxial Hartree-Fock-Bogolyubov calculations with the Gogny D1S effective interaction have been performed and compared to experimental data.

Angular distributions of the 7Li + 18O elastic and inelastic scattering were measured at the energy E lab (18O) = 114 MeV (32 MeV c.m.) in inverse kinematics. This technique allowed both small and large angle data to be collected simultaneously. The data were analyzed within the optical model and coupled-reaction-channels method to determine the potential parameters of 7Li + 18O scattering and reaction channels dominating the scattering. 18O inelastic scattering deformation parameters were obtained. The present data show that the 7Li + 18O system has a much stronger absorption when compared to previously measured 7Li + 16O data. The derived optical model parameters clearly show the scattering difference between two systems.

Lifetime measurements were made for the $\ensuremath{\nu}{h}_{11/2}$ band in $^{101}\mathrm{Pd}$, which had been interpreted as a possible antimagnetic rotation band based on the comparison of $I\ensuremath{-}\ensuremath{\omega}$ behavior with the calculation of a semiclassical particle-rotor model in our previous study. Doppler broadened line shapes were analyzed for the decaying $\ensuremath{\gamma}$ rays in the band following the reaction $^{68}\mathrm{Zn}(^{37}\mathrm{Cl},\phantom{\rule{0.16em}{0ex}}\text{1p3n})^{101}\mathrm{Pd}$. The semiclassical particle-rotor model was modified to reproduce both the $I\ensuremath{-}\ensuremath{\omega}$ plot and the $B(E2)$ behavior simultaneously for the antimagnetic rotation bands in Pd and Cd nuclei, for which $B(E2)$ values had been measured so far. Reasonable agreements between the experiment and the calculation were obtained. It is concluded that the lower part of the $\ensuremath{\nu}{h}_{11/2}$ band in $^{101}\mathrm{Pd}$ can be interpreted as an antimagnetic rotor.

Coulomb excitation experiments were performed with 96 Mo , 98 Mo and 100 Mo isotopes using both beam and target excitation. As a result, quadrupole deformation parameters were deduced for two lowest-lying (ground and excited) 0+ states. Surprising shape changes of these states were observed.

The magnitudes and signs of twenty eight E2 and three M1 matrix elements involving 17 low-lying excited states in 104Ru have been measured by Coulomb excitation using 208Pb, 136Xe and 58Ni ions. The completeness of the set of E2 matrix elements is sufficient to extract, directly from the data, the expectation values of the intrinsic-frame E2 moments that provide considerable insight into the underlying collectivity. The measured E2 properties strongly correlate with macroscopic quadrupole collective degrees of freedom. Detailed comparison of the experimental results and theoretical microscopic calculations within the general quadrupole collective Bohr Hamiltonian are presented. Very good agreement of calculations and experiment is achieved without any parameters fitted to the 104Ru experimental data. Results of phenomenological γ-unstable and γ-rigid models are also given.

Coulomb excitation experiment of 100 Mo has recently been performed using 40 Ar beam from the Warsaw Cyclotron. Three lowest 2+ states, two 4+ and one 0+ excited states have been observed. It is a continuation of the systematic study of 96 Mo and 98 Mo nuclei having low lying 0+ excited state, with energy very close to the first 2+ state.

Angular distributions of the 12C( 11B, 15N) 8Be reaction were measured at the energy Elab(11B) = 49 MeV for the transitions to the ground and 2.94 MeV (2+) excited state of 8Be and to the ground and 5.270 MeV (5/2+) + 5.299 MeV (1/2+), 6.324 MeV (3/2-), 7.155 MeV (5/2+) + 7.301 MeV (3/2+), 7.567 MeV (7/2+) excited states of 15N. The data were analyzed by the coupled-reaction-channel method. The elastic, inelastic scattering and one- and two-step transfers were included in the coupling scheme. The data of the 12C( 11B, 8Be) 15N reaction at Ecm = 9.4-17.8 MeV known from the literature, were also included in the analysis. The mechanism of the 12C( 11B, 15N) 8Be reaction and the optical-model potential parameters for the 15N + 8Be channel were deduced. The energy dependence of the optical-model parameters for the 15N + 8Be channel was obtained.

We report experimental attempts to determine the sign of the electric dipole moment (relative to the electric octupole moment) in the octupole deformed nucleus 226 Ra. Sensitivity to this quantity is observed in the measured yields of γ-ray transitions following very low energy Coulomb excitation.

Coulomb excitation experiment was carried out with a 68Zn beam bombarding a nat Pb target. Two E2 matrix elements and the quadrupole moment of the 21+ state were newly derived with the least-squares search code GOSIA. The potential energy surface (PES) was calculated with the Nilsson–Strutinsky model, showing two shallow minima: the first minimum does not contain the 1g9/2 orbit below the Fermi surface, while the second minimum does. The ground state band and the intruder band seem to be constructed on the first and the second minimum, respectively. As for the ground state band, the asymmetric rotor model and the IBM in O(6) limit reproduced the experimental values rather well. The shallow PES may suggest instability of the shape. The ground state band structure may be explained assuming a soft triaxial deformation.

A Coulomb excitation experiment was carried out with a 66Zn beam bombarding a ${}^{\rm nat}$ Pb target. Four E2 matrix elements and the quadrupole moment of the 21 + state were derived with the least-squares search code GOSIA. According to the B(E2) values, the ground band can be interpreted as a quasirotational band. It was found that the 21 + level has a positive quadrupole moment, which may be interpreted as a soft triaxial deformation.

Angular distributions of the 9 Be( 11 B, 10 B) 10 Be reaction were measured at E lab ( 11 B)=45 MeV for the transitions to the ground and excited states of the 10 B and 10 Be nuclei. The data were analyzed within the coupled-reaction-channels (CRC) method. One- and two-step transfers were studied. The optical potential parameters for the 10 Be+ 10 B interaction were deduced. We also analyze the 9 Be+ 10 B elastic scattering data at energies E cm =8.42–47.37 MeV known from the literature in order to study isotopic effect for the 9 Be+ 10 B, 9 Be+ 11 B and 10 Be+ 10 B channels. The energy dependence of the 9 Be+ 10 B and 10 Be+ 10 B OM potential parameters was deduced.

The level structure of 231 Pa was investigated by Coulomb excitation using 148 MeV 32 S and 255, 260 and 261 MeV 58 Ni projectiles and the NORDBALL detector array. The 1/2[530] ground-state rotational band was excited up to spin 39/2 − . The 3/2[651] band, established up to spin 37/2 + , was observed to be populated apart from direct Coulomb excitation by the de-excitation of the 1/2[530] band. The 1/2[400] band could be followed up to spin 23/2 + . Weak excitation of the bands 5/2[642], 5/2[512], 3/2[532] and 3/2[521] was seen up to spins 11/2 + , 15/2 − , 9/2 − and 9/2 − , respectively. Matrix elements were extracted from the γ -ray yields with the help of the semi-classical Coulomb-excitation least-squares search code GOSIA. The level scheme and transition intensities were analyzed in the framework of the quasiparticle-plus-phonon model including Coriolis-coupling (QPMC).

Electromagnetic properties of the low-lying states in a 70Ge nucleus were studied through the multiple Coulomb excitation of a 70Ge beam with a natPb target. Relative γ-ray intensities were measured as a function of emission angle relative to the scattered projectile. Sixteen E2 matrix elements, including diagonal ones, for 6 low-lying states have been determined using the least-squares search code GOSIA. The expectation values 〈Q 2〉 of 01 + and 02 + states in 70Ge are compared with those in 72, 74, 76Ge. Simple mixing calculations indicate that the 02 + states in 70Ge and 72Se can be treated as deformed intruder states. It is shown that the deformed intruder becomes the ground state in 74Kr. These interpretations of the 02 + states in this region are compared with the potential-energy surface calculations by the Nilsson-Strutinsky model, which allow to interpret the experimental results in a qualitative way from the theoretical point of view.

Angular distributions of the 9Be+11B elastic and inelastic scattering were measured at Elab(11B)=45 MeV in a large angular range for the transitions to the ground and excited states of the 11B and 9Be nuclei. The data were analyzed within the coupled-reaction-channels (CRC) method. We have also included the data of the 11B+9Be elastic scattering at Ecm≈9–22 MeV known from the literature. The mechanisms of the 9Be+11B anomalous large angle scattering (ALAS) were studied both for the elastic and inelastic channels including the 9Be and 11B reorientations and transfer reactions. The optical potential parameters for the 9Be+11B elastic scattering and the 11B and 9Be deformation parameters were deduced.

Collective structures in 180 Ta built on the meta-stable K π =9 − high-spin isomer were investigated using two types of Coulomb excitation experiments. In-beam studies identify γ -vibrational bands with typical bandhead E2 excitation strengths of 6 Weisskopf units (W.u.). Coulomb activation of the 180 Ta ground state was measured with 36 S and 64 Ni projectiles using thin targets. The excitation functions and the 180 Ta recoil angular distributions favor a K π =7 + octupole vibration at E x =1155(40) keV as intermediate state in the population of the ground state.

The nucleus 98 Mo was multiply Coulomb excited using 20 Ne, 84 Kr and 136 Xe beams. Eighteen E2 and M1 reduced matrix elements connecting 7 low-lying levels have been determined using the least-squares code GOSIA. The results are compared with the predictions of an extended version of the IBM1 model. The quadrupole sum rules approach was used to determine the shape parameters in two 0 + (ground and first excited) states. The rotational invariants 〈Q 2 〉 and 〈 cos 3δ〉 obtained show the shape coexistence in 98 Mo nucleus: the triaxial ground state and the prolate first excited state.

A 84 Kr beam was Coulomb-excited on a 98 Mo target and a nat Ta target. Six reduced matrix elements for 5 low-lying states were derived from the analysis using the least-squares code GOSIA. The quadrupole moment of the 21+ was newly obtained. The measured quadrupole moment and the B(E2) values are consistent with large-scale shell-model calculations which give a systematic description of N=50 isotones.

A multiple Coulomb excitation experiment on a 76Ge beam was performed using a natPb target. The relative excitation probabilities were measured as a function of the projectile scattering-angle. 15 E2 matrix elements, including diagonal ones, for seven low-lying states were determined using the least-squares search code GOSIA. The expectation values of centroid for the magnitude of the intrinsic frame E2 properties Q2 show that the ground state is weakly deformed, while the shape of the 02+ level is almost spherical. The 22+ state is found to be a band head of the γ vibrational band and the 42+ state is a member of this band.

74Ge beam was Coulomb-excited on a natPb target. Ten E2 matrix elements including diagonal matrix elements for 5 low-lying states have been determined using the least-squares search code GOSIA. The expectation values of the rotational invariants 〈Q 2〉 and 〈cos3δ〉 show the small and triaxial deformation of the two lowest members of the ground-state band , while the 02 + and 22 + states are found to be almost spherical.

The nuclear capture of antiprotons from atomic states is studied. New measurements of level shifts and widths of deuterium are analysed and compared with similar results obtained in heavy nuclei. Some properties of antiproton nucleus interactions are outlined, a comparison of cold and total capture modes is done.

Two different methods were employed by the collaboration PS209 at LEAR (CERN) to investigate the nucleon density at the outer nuclear periphery. The first one was the comparison of the yield of (N − 1) nuclei and (Z − 1) nuclei produced by antiproton annihilation on a nucleus with mass number A (here N and Z denote the neutron and proton number of the nucleus, respectively); the second one is the measurement of widths and shifts of the last observable transitions in antiprotonic atoms. Earlier studies of (A−1) production were extended by measurements of short-lived isotopes (lifetimes down to a few seconds). More than thirty widths and twenty shifts were extracted from the antiprotonic x-ray data. The results fit nicely into the systematics established recently by C.J. Batty, E. Friedman, and A. Gal [Nucl. Phys. A592, 487 (1995)]. Pronounced isotope effects were found for some of the investigated elements.

The research of the surface and the near-surface region of Cz-Si wafers irradiated with fast oxygen and neon ions of energy 4 MeV/u and dose 10 14 particles/cm 2 is presented. In our study several methods based on the Bragg case of X-ray diffraction using Ag K« 1 , as well as reflection high-energy electron diffraction and Nomarsky optical microscopy were used. It was • shown that implantation with fast neon ions causes larger disturbances of silicon crystal structure than irradiation with oxygen ions.

The study of the polarization direction correlation method (PDCO) for γ quanta emitted from the nuclear states oriented in fusion-evaporation reactions is discussed with emphasis on making unique multipolarity assignments. The method is applied to the data coming from a typical experiment performed with the EUROGAM II array, where polarization-sensitive CLOVER detectors were used. The accuracy obtained in the experiment for the studied transitions was high enough to exclude, using the PDCO method, most of the ambiguities which occur if the assignments are made on the basis of angular correlation measurements alone.

Multiple Coulomb excitation with heavy-ion beams offers an unique opportunity to study model-independently the collective properties of the nuclear structure. Existing detector systems and data analysis methods allow not only to measure complete sets of parameters describing the electromagnetic properties of the nuclei-electric and magnetic multipole matrix elements-but also by using sum rules to translate these results to the shape evolution of the charge distributions independently for each level. The technique of Coulomb excitation can also be used to answer specific questions, as illustrated in this paper.

The nucleon density at the nuclear periphery has been investigated with two different methods. The first one is the measurement of the energy shift and the width of antiprotonic X-ray lines. Besides various other nuclides the X-rays from the isotopes 172Yb and 176Yb have been measured very extensively. From these data the absorption widths of six antiprotonic levels and the shifts of the lowest visible transitions could be determined. The comparison of the experimental intensities of the transitions with results from calculations of the antiprotonic cascade showed a good agreement. The second method is the determination of the yield of the annihilation products from the reaction of the antiprotons with nuclei. From this the neutron-to-proton density ratio at a distance of about 3 fm outside the half-density radius can be determined. This method was extended to short-lived residual nuclei with a half-life down to 5 s. The experiment confirmed the previously found negative correlation between the size of the neutron skin and the binding energy of the last neutron. The results have been compared with calculations. For many nuclei a good agreement was found between experiment and calculation, however for some nuclei measured and calculated values are at variance.

The antiprotonic x-ray cascade in ${}^{172}\mathrm{Yb}$ and ${}^{176}\mathrm{Yb}$ was studied and the widths and shifts of the levels which are affected by the strong interaction were deduced. A large number of transitions up to $\ensuremath{\Delta}n=5$ could be observed. This opened the possibility to determine for the first time also the widths of noncircular orbits. In ${}^{172}\mathrm{Yb}$ and ${}^{176}\mathrm{Yb}$ four level shifts and seven level widths were measured in each case. The widths are slightly increasing from ${}^{172}\mathrm{Yb}$ to ${}^{176}\mathrm{Yb}$ whereas the shifts stay roughly constant. The experimental intensities of the transitions are compared with results from calculations of the antiproton cascade. Using a Fermi distribution for the nucleon densities the neutron diffuseness parameter was deduced to be for ${}^{172}\mathrm{Yb} (0.58\ifmmode\pm\else\textpm\fi{}0.04) \mathrm{fm}$ larger than the proton diffuseness parameter. For ${}^{176}\mathrm{Yb}$ this value is $(0.71\ifmmode\pm\else\textpm\fi{}0.04) \mathrm{fm}.$

The near-surface layers of dislocation free silicon crystals implanted with 4 MeV/u oxygen and neon ions were investigated. The following methods: X-ray diffraction and reflectometry, reflection high-energy electron diffraction and Nomarski optical microscopy were used. The fine structural changes induced by irradiation were observed. For silicon crystal implanted with neon ions the increase of the lattice parameter and a disturbance of crystal structure were detected, whereas for silicon crystal bombarded with oxygen ions postimplantation defects on the surface were observed. For both cases the increase in the surface roughness was shown.

The role of quadrupole and octupole collectivity in the shape-transitional nucleus 148 Nd has been studied by Coulomb excitation using beams of 58 Ni and 92 Mo, and a beam of 148 Nd (using a 208 Pb target). The extracted E1, E2 and E3 matrix elements involving states up to 12 + ·in the ground band and 13 − in the negative-parity band are presented, and compared to calculations that assume a vibrational and rotational octupole nature for the negative-parity band. The positive-parity ground-band states are well described in terms of a prolate deformed shape with Q 20 ≈ 400 e fm 2 ( β 2 rms ≈ +0.18). The present results suggest a vibrational octupole nature for the low-spin negative-parity states, with an intrinsic moment Q 30 ≈ 1500 e fm 3 ( β 3 rms ≈ 0.12). The E2 and E3 matrix elements connecting these bands to the β- and γ-vibrational bands (and within these bands) are also presented, and compared to calculations incorporating the coupling between the rotational and vibrational modes. These calculations describe reasonably well the E2 matrix elements involving the gamma band, but do not reproduce the measured E2 matrix elements for the beta band, implying a complicated intrinsic structure for the beta band. The strong enhancement of the measured E3 matrix elements connecting the negative-parity band to the beta band could be indicative of a significant component of the two-phonon octupole vibration in the wavefunction of the so-called beta band.

E2 collective properties for the low-lying states in 186,188,190,192 Os and 194 Pt have been investigated experimentally by means of Coulomb excitation using 3.3–4.8 MeV/nucleon 40 Ca, 58 Ni, 136 Xe and 208 Pb beams. The deexcitation γ rays following Coulomb excitation were detected in coincidence with the scattered particles. Levels with excitation energies up to 3–4 MeV of the ground-state, γ and 4 + collective bands as well as excited 0 + states were populated in each nucleus studied. A semiclassical Coulomb-excitation least-squares search code GOSIA was used to extract E2 matrix elements from the measured γ-ray yields. For each nucleus studied, a unique and almost complete set of E2 matrix elements for the low-lying states has been determined, which includes both the magnitudes and signs of the transitional and diagonal matrix elements. The completeness of the set of measured E2 matrix elements makes it possible to determine the intrinsic quadrupole deformation for the low-lying states in these nuclei via a model-independent method. The results indicate clearly that the E2 properties for the low-lying states in these nuclei are correlated well using only the quadrupole collective degrees of freedom. The extracted E2 matrix elements are compared with the prediction of various collective models such as the asymmetric rigid rotor model, the γ-soft model of Leander, and the IBA-2 model. These particular models do not reproduce the data satisfactorily, however the general trends of the data are consistent with the descriptions of γ-soft type collective models through a prolate to oblate shape-transition region. That the enhanced B (E2) values between the I ,quasi- K π = 4,4 + state and members of the I ,quasi- K π = 2,2 + band are well reproduced by the γ-soft model is consistent with the interpretation of the I ,quasi- K π = 4,4 + state being a two-phonon γ-vibration excitation.

Coulomb fission of 238U has been studied in the interaction of a 24.3 MeV/nucleon U beam with a Au target. A novel experimental approach is followed, aiming at distinguishing fission of Coulomb origin from nuclear fission. The Z distribution of the fragments is studied for both fission processes.

Vibrational bands in 226Ra were studied by Coulomb excitation and by the 226Ra(d,pnγ) reaction. The first-excited K π = 0+ and 1− bands with known band heads at 825 and 1049 keV, respectively, were extended up to the 8+ and 7− levels. A new 2+ level at 1110 keV and the known 2+ level at 1156 keV were observed following Coulomb excitation and interpreted as γ vibration and possible member of a second-exited K π = 0+ band, respectively. The E1 and E2 branching ratios from these vibrational bands to the ground and first-excited 0− band are explained within the rotational model including band mixings. No evidence was found for a 0+ level at 650 keV proposed earlier.

The Coulomb excitation experiment to study electromagnetic properties of the heaviest stable Mo isotope, ${}^{100}$Mo, was performed using a 76 MeV ${}^{32}$S beam from the Warsaw cyclotron U-200P. Magnitudes and relative signs of 26 $E1$, $E2$, $E3$, and $M1$ matrix elements coupling nine low-lying states in ${}^{100}$Mo were determined using the least-squares code gosia. Diagonal matrix elements (related to the spectroscopic quadrupole moments) of the 2${}_{1}^{+}$, 2${}_{2}^{+}$, and 2${}_{3}^{+}$ states as well as the 4${}_{1}^{+}$ state were extracted. The resulting set of reduced $E2$ matrix elements was complete and precise enough to obtain, using the quadrupole sum rules approach, quadrupole deformation parameters of ${}^{100}$Mo in its two lowest 0${}^{+}$ states: ground and excited. The overall deformation of the 0${}_{1}^{+}$ and 0${}_{2}^{+}$ states in ${}^{100}$Mo is of similar magnitude, in both cases larger compared to what was found for the neighboring isotopes ${}^{96}$Mo and ${}^{98}$Mo. At the same time, the asymetry parameters obtained for both states strongly differ, indicating a triaxial shape of the ${}^{100}$Mo nucleus in the ground state and a prolate shape in the excited 0${}^{+}$ state. Low-energy quadrupole excitations of the ${}^{100}$Mo nucleus were studied in the frame of the general quadrupole collective Bohr Hamiltonian model (GBH). The potential energy and inertial functions were calculated using the adiabatic time-dependent Hartree-Fock-Bogoliubov (ATDHFB) method starting from two possible variants of the Skyrme effective interaction: SIII and Sly4. The overall quadrupole deformation parameters resulting from the GBH calculations with the SLy4 variant of the Skyrme interaction are slightly closer to the experimentally obtained values than those obtained using SIII.

The collective structure of the even-even nuclei 76,80,82 Se has been studied using Coulomb excitation with 16 O, 48 Ti and 208 Pb ions. About 20 E2 matrix elements were determined in each isotope. The measured matrix elements are compared with the predictions of simple geometric and algebraic collective models. The E2 properties and energy level spectra of the 76,80,82 Se nuclei exhibit features characteristic of anharmonic vibrational collective motion. Although the simplest collective vibrational models exhibit the general features of the data, they do not reproduce the fine details. The influence of a number of physical effects on the data was investigated. These include Coulomb-nuclear interference, mutual excitation and the effect due to the semiclassical approximation of the Coulomb-excitation formalism.

The nuclei 106 Pd and 108 Pd have been Coulomb excited using beams of 16 O, 58 Ni and 208 Pb. The data determined 25 and 31 E2 matrix elements in 106 Pd and 108 Pd, respectively. The experimental data are qualitatively in agreement with the spherical-harmonic quadrupole vibrational model, but quantitatively there are large discrepancies, even for the states generally accepted to be the two-phonon vibrational states. A sum-rule method was applied to the data, the result of which implies that the vibrational quadrupole strengths of the 0 + and 4 + two-phonon states are fragmented and shared between several E2 matrix elements. The E2 matrix elements imply appreciable quadrupole triaxiality with a γ-centroid of about 20°. A systematic comparison is made with neighbouring Pd-isotopes and with 114 Cd.

High-spin states of ${}^{101}$Pd were studied through in-beam $\ensuremath{\gamma}$-ray spectroscopy by using the reaction ${}^{68}$Zn(${}^{37}$Cl, $1p3n$). The band based on the ${h}_{11/2}$ neutron orbital was extended up to (${\frac{51}{2}}^{\ensuremath{-}}$), and the band based on the ${d}_{5/2}$ neutron orbital was revised. Various transitions decaying to these bands were observed, and consequently several side bands were established. Electric dipole transitions from the $\ensuremath{\nu}{h}_{11/2}$ band to the $\ensuremath{\nu}{d}_{5/2}$ band were also observed. The structure of the $\ensuremath{\nu}{h}_{11/2}$ band is discussed from the viewpoint of antimagnetic rotation based on a semiclassical particle-rotor model by taking neutron alignments into account. The possible existence of octupole correlations is also discussed on the basis of $B(E1)/B(E2)$ ratios for the decays of the $\ensuremath{\nu}{h}_{11/2}$ band.

The characteristics of the low-lying levels in the doubly even Ge isotopes are studied by means of multiple Coulomb excitation experiments. The 〈Q2〉 values of two 0+ states in the Ge isotopes have shown the presence of the coexcistence of a spherical and deformed structures. The mixing between the regular and intruder structures is derived in a simple two states mixing model. The crossing of the two 0+ might take place; the intruder state might become the ground state in 70Ge.

E3 matrix elements have been determined for transitions between states up to ${\mathit{I}}^{\mathrm{\ensuremath{\pi}}}$=${13}^{\mathrm{\ensuremath{-}}}$ in $^{148}\mathrm{Nd}$, providing direct evidence for strong octupole collectivity in a rotational band. These values, as well as the corresponding E1 and E2 matrix elements, were obtained from Coulomb excitation data using $^{58}\mathrm{Ni}$ and $^{92}\mathrm{Mo}$ ions, projectile excitation using a $^{208}\mathrm{Pb}$ target, and from recoil distance lifetime measurements. The results are consistent with collective model predictions for $^{148}\mathrm{Nd}$ assuming intrinsic quadrupole and octupole moments of ${\mathit{Q}}_{20}$\ensuremath{\approxeq}400 e ${\mathrm{fm}}^{2}$ and ${\mathit{Q}}_{30}$\ensuremath{\approxeq}1500 e ${\mathrm{fm}}^{3}$. The E3 strength coupling the negative-parity states to the \ensuremath{\beta} band is found to be appreciable.

Radioactive targets of 226 Ra were Coulomb excited by 4 He projectiles (particle spectroscopy), and 16 O, 32 S and 208 Pb projectiles (particle-γ coincidences). The K = 0± rotational bands could be followed up to spin 18 + and 17 − , respectively. All experiments were simultaneously analyzed in terms of E1, E2, E3 and E4 matrix elements coupling the positive- and negative-parity rotational states. The systematics of level energies, as well as dipole, quadrupole and octupole matrix elements are discussed in the framework of models assuming stable octupole deformation.

The richness of information pertaining to El, E2, E3 and M1 interaction deduced from Coulomb excitation experiments is illustrated. E2 and particularly M1 transition probabilities in 128 Xe are presented. Large set of E3 and E1 additionally to E2 transition probabilities in 226 Ra are shown.

Quadrupole collectivity in 182,184 W has been studied by Coulomb excitation with 58 Ni and 136 Xe projectiles. The yields of the de-excitation γ-rays, measured in coincidence with the scattered ions, were used to determine a fairly complete set of electromagnetic matrix elements for the low-lying states. A separate experiment measured lifetimes for five and eight states respectively in 182 W and 184 W by the recoil distance method following Coulomb excitation with a 245 MeV 58 Ni projectile. These lifetime measurements are in good agreement with the results for the Coulomb excitation yield measurements. The correlations of the extracted E2 matrix elements are examined using the Cline-Flaum sum-rule technique and discussed in the framework of the various collective models. These correlations are well described with quadrupole shape degrees of freedom. Strong mixing between the β- and γ-vibration degrees of freedom, claimed in the pairing-plus-quadrupole model of Kumar and Baranger, is not supported by the present results.

Cross sections for the quasielastic channels have been measured at energies slightly above the Coulomb barrier using 58 Ni and 112,116 Sn projectiles on targets of 117,118 Sn and 161,162,163,164 Dy. The deexcitation γ-rays were detected in a 4π NaI array (the Spin Spectrometer of Oak Ridge National Laboratory) in kinematic coincidence with both target-like and projectile-like particles; thus providing a measure of the total energy and multiplicity of the entry state. The reaction channels were identified by characteristic γ-deexcitation transitions measured with Ge detectors substituted for array elements in the Spin Spectrometer. The angular distribution for inelastic scattering is well described by both semiclassical and quantal calculations. Two general features for few-neutron transfer channels are observed; (i) the dependence of the total cross section on the ground-state Q -value, (ii) the “coldness” of the reaction mechanism indicated by the measured entry states. For one-neutron transfer the distorted-wave Born approximation seems to give a correct overall qualitative description of the reaction mechanism for spherical nuclei, and reproduces the cross sections within a factor of two. The ground-to-ground two-neutron transfer probability for the reaction between Sn isotopes was deduced and found to be strongly enhanced ( F ≈ 760), which is consistent with the expectation of strong pairing correlations. Two-neutron transfer to the ground-state band in Dy was partially resolved from transfer to other intrinsic states by using the Spin Spectrometer. The oscillating radial dependence of the probability for populating the ground-state band was found to be related to the nuclear deformation. This leads to an explanation of the “slope anomaly” where the measured radial dependence of the total two-neutron transfer probability has too flat a slope compared to the prediction based on a simple binding energy argument. The probability for two-neutron transfer to the ground-state band is found to be similar to the probability for ground-to-ground transfer in the Sn+Sn system, suggesting a comparable strength for pairing correlations in the two systems.

The Spin Spectrometer was used to separate Dy ground-band and two-quasiparticle populations in one- and two-neutron transfer reactions with Sn and Ni projectiles. Transfer probabilities {ital P}{sub 1{ital n},2{ital n}} and two-neutron enhancement factors {ital F}=={ital P}{sub 2{ital n}}/{ital P}{sub 1{ital n}}{sup 2} were determined as a function of scattering angle. For the two-quasiparticle bands {ital F}{congruent}7--20, but for the ground band {ital F}{congruent}30--500, indicating large pairing effects in two-particle transfer to the ground band. The data also indicate larger enhancement factors in Sn than in Ni collisions.

Analytical approximation of the Voigt function has been derived. The Voigtian lineshape is reproduced without numerical integration or recourse to special functions. The formula derived contains also the Gaussian lineshape as a limiting case, thus allowing for pattern recognition if the appropriate lineshape is not a priori known.

The nucleus 72Ge has been Coulomb excited using 16O, 58Ni and 208Pb. Seventeen E2 matrix elements coupling the low-lying states have been determined. Based on these data, an interpretation of the structure of 72Ge has been proposed that includes an “intruder” 0+ state perturbing what the present work shows to be a triaxial quadrupole-deformed collective rotational structure.

The x-ray cascade from antiprotonic atoms was studied for $^{208}\mathrm{Pb}$ and $^{209}\mathrm{Bi}$. Widths and shifts of the levels due to the strong interaction were determined. Using modern antiproton-nucleus optical potentials, the neutron densities in the nuclear periphery were deduced. Assuming two-parameter Fermi distributions (2pF) describing the proton and neutron densities, the neutron rms radii were deduced for both nuclei. The difference of neutron and proton rms radii $\ensuremath{\Delta}{r}_{\mathit{np}}$ equal to $0.16\ifmmode\pm\else\textpm\fi{}(0.02){}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}(0.04){}_{\mathrm{syst}}$ fm for $^{208}\mathrm{Pb}$ and $0.14\ifmmode\pm\else\textpm\fi{}(0.04){}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}(0.04){}_{\mathrm{syst}}$ fm for $^{209}\mathrm{Bi}$ were determined, and the assigned systematic errors are discussed. The $\ensuremath{\Delta}{r}_{\mathit{np}}$ values and the deduced shapes of the neutron distributions are compared with mean field model calculations.

GANIL E344aS; Shape coexistence in the light krypton isotopes was studied in two low-energy Coulomb excitation experiments using radioactive $^{74}$Kr and $^{76}$Kr beams from the SPIRAL facility at GANIL. The ground-state bands in both isotopes were populated up to the $8^+$ state via multi-step Coulomb excitation, and several non-yrast states were observed. Large sets of matrix elements were extracted for both nuclei from the observed $\\gamma$-ray yields. Diagonal matrix elements were determined by utilizing the reorientation effect. In both isotopes the spectroscopic quadrupole moments for the ground-state bands and the bands based on excited $0_2^+$ states are found to have opposite signs. The experimental data are interpreted within a phenomenological two-band mixing model and model-independent quadrupole invariants are deduced for the relevant $0^+$ states using the complete sets of matrix elements and the formalism of quadrupole sum rules. Configuration mixing calculations based on triaxial Hartree-Fock-Bogolyubov calculations with the Gogny D1S effective interaction have been performed and are compared both with the experimental results and with recent calculations using the Skyrme SLy6 effective interaction and the full generator-coordinate method restricted to axial shapes.

Using a method whereby molecular and atomic ions are independently selected, an isobarically pure beam of Se-70 ions was postaccelerated to an energy of 206 MeV using REX-ISOLDE. Coulomb-excitation yields for states in the beam and target nuclei were deduced by recording deexcitation gamma rays in the highly segmented MINIBALL gamma-ray spectrometer in coincidence with scattered particles in a silicon detector. At these energies, the Coulomb-excitation yield for the first 2(+) state is expected to be strongly sensitive to the sign of the spectroscopic quadrupole moment through the nuclear reorientation effect. Experimental evidence is presented here for a prolate shape for the first 2(+) state in Se-70, reopening the question over whether there are, as reported earlier, deformed oblate shapes near to the ground state in the light selenium isotopes.

The E1 transition from the 3/2− state to the ground state of 229Pa was identified in the (p,tγ) reaction. Its energy is found to be 11.6(3) keV. This leads to a value of Qg.s.=−4133(2) keV and to a mass defect of 229Pa of 29894(3) keV. It is concluded that the ground-state configuration of 229Pa is 3/2[651].