M.C. Olesen

Coulomb excitation of vibrational states in deformed even nuclei

Abstract Low-lying states in deformed even rare-earth nuclei have been studied by Coulomb excitation with 43.5 MeV oxygen ions. Gamma rays from thin oxide targets (≈0.3 mg/cm 2 ) or thin metal targets (0.5–1.2 mg/cm 2 ) were observed in coincidence with back-scattered ions. The yields were normalized on the intensity of the scattered particles. Double groups of gamma rays ascribed to the 2 +′ → 0 + and the 2 +′ → 2 + transitions from K = 2 states were observed in Nd 150 (1.07 MeV), Sm 152 (1.09 MeV), Sm 154 (1.44 MeV), Gd 156 , Gd 158 , Gd 160 (1.02 MeV), Dy 160 , Dy 162 (0.89 MeV), Dy 164 (0.77 MeV), Er 164 (0.86 MeV), Er 166 , Er 168 , Er 170 (0.93 MeV) and Yb 176 (1.27 MeV), where the energies in the parentheses are given for 2 +′ states not observed earlier. Gamma rays ascribed to the 0 +″ → 2 + , 2 +″ → 0 + and 2 +″ → 2 + transitions from K = 0 states were observed in Nd 150 (0.69 MeV), Sm 152 , and Gd 154 (0.68 MeV), where the energies are for the 0 +″ states. Gamma rays in Sm 154 and Gd 156 suggest K = 0 states at 1.10 and 1.06 MeV, respectively. The B (E2 values determined from the yields range from 2 to 8 single-particle units, being roughly inversely proportional to the excitation energies for the levels. The theory of multiple Coulomb excitation for the different bands was in qualitative agreement with the experimental observations.

Inelastic scattering from even rare earth isotopes

Abstract The Coulomb excitation cross sections for the first excited state of 15 even-mass nuclei in the region of the rare earths have been determined from measurements on inelastically scattered protons and deuterons. From the cross sections, reduced E2-transition probabilities are obtained, in general in good agreement with those derived from the directly measured lifetimes of the nuclear states. The intrinsic quadrupole moments determined from the transition probabilities show, for each element, a regular variation with the mass number, but discontinuities occur when passing from one element to another. This behaviour appears to be correlated with the variation in the moment of inertia for the same nuclei. The individual intrinsic quadrupole moments of odd-mass nuclei in the same region often deviate from the moments of the neighbouring even isotopes, but on the average the quadrupole moments of odd-mass nuclei are almost the same as those for even nuclei.

Inelastic scattering from odd-mass rare earths

Abstract The reduced electric quadrupole transition probabilities and excitation energies of the accessible low lying states in Eu151, Eu153, Tb159, Ho165, Er167 and Tm169 have been measured by Coulomb excitation with protons or deuterons having an initial energy of about 4.5 MeV. The measurements were performed on the groups of inelastically scattered particles by means of a magnetic spectrograph, a method particularly suited for the determination of the absolute transition probability. The results are discussed in terms of the rotational model.

INELASTIC SCATTERING FROM HAFNIUM AND WOLFRAM ISOTOPES

Abstract The reduced electric quadrupole transition probabilities and the excitation energies of the accessible low lying states in the stable isotopes of Hf and W (except the rare isotope W180) have been measured by Coulomb excitation. The measurements were performed on inelastically scattered protons and deuterons recorded in a heavy particle spectrograph. The results are discussed in terms of the rotational model. The measured transition probabilities are compared with those derived from lifetime measurements.

ANGULAR DISTRIBUTIONS FOR INELASTIC DEUTERON SCATTERING FROM SAMARIUM.

Abstract The elastic and inelastic scattering of 12 MeV deuterons from targets of 148 Sm, 150 Sm, 152 Sm and 154 Sm has been investigated. Angular distributions for the elastic group and for the more prominent inelastic groups were measured by means of solid state counters. Supplementary information was obtained from high-resolution magnetic spectrograph data. The elastic angular distributions are smooth and without diffraction structure. The absolute cross section at back angles decreases with increasing mass number. This effect can probably be ascribed to differences in the inelastic excitations since the distributions for the sum of elastic and inelastic intensity are almost identical for all the nuclei. The shape of the angular distributions for the collective 2 + , 4 + and, when observed, for the 6 + levels, for each angular momentum is very similar in all the nuclei, although the character of the levels changes from vibrational to pure rotational. The same is true for the distributions of the strongly excited 3 - levels. It is thus indicated that the angular distributions give a simple determination of the multipolarity of the excitation, the tendency being a decrease in forward-backward ratio with increasing multipolarity.

Coulomb excitation of even Sm isotopes

Abstract Low-lying excited states in the 148 Sm, 150 Sm, 152 Sm and 154 Sm nuclei have been studied by means of Coulomb excitation with oxygen ions. Gamma rays from thin metallic targets were detected in coincidence with backscattered oxygen ions in NaI(Tl) crystals. In the case of 148 Sm and 150 Sm singles, gamma-ray spectra were also recorded by means of a Li-Ge detector. Gamma rays originating from the states at 0.551 MeV (2 + ), 1.162 MeV (3 − ), 1.181 MeV (4 + ) and 1.455 MeV (2 + ) were observed in the 148 Sm spectra and from the states at 0.334 MeV (2 + ), 0.741 MeV (0 +′ ), 0.774 MeV (4 + ), 1.046 MeV (2 +″ ), 1.072 MeV (3 − ) and 1.193 MeV (2 +′ ) in the 150 Sm spectra. The B (E2) values between several of the positive-parity states were derived from first- and second-order perturbation theory. The B (E2) values obtained for the 3- states were 0.37 ± 0.03 and 0.31 ± 0.03 e 2 × 10 −72 cm 6 for 148 Sm and 150 Sm, respectively. For the lowest octupoe bands in 152 Sm and 154 Sm, the B (E2) values were 0.14 ± 0.03 and 0.11 ± 0.03 e 2 × 10 −72 cm 6 , respectively.

Inelastic scattering from separated lutecium isotopes

Abstract Lutecium targets of high isotopic purity have been prepared in an electromagnetic isotope separator. In order to obtain thin deposits of the target material on fragile backings, a method has been developed where the ions after the separation are strongly retarded by an electrical potential on the collector. Targets prepared in this way have been used to study the Coulomb excitation of the rare odd isotope Lu 176 and of the abundant isotope Lu 175 by observation of inelastically scattered protons and deuterons in a magnetic spectrometer. The measured excitation energies and transition probabilities in Lu 176 are in good agreement with the predictions of the rotational model if the ground state spin of this isotope is 7.

Coulomb excitation cross sections of gadolinium isotopes from inelastic scattering measurements

The cross sections for Coulomb excitation and the energies of the accessible low-lying rotational states in the six most abundant isotopes of gadolinium have been determned from measurements on the corresponding groups of inelastically scattered protons and deuterons. The projectiles were accelerated in an electrostatic generator to energies around 4 Mev. Particles scattered from isotopically pure targets prepared in an isotope separator were observed at an angle of 145 deg with respect to the beam by means of a magnetic spectrometer of high resolution. The lifetimes for the first excited states in Gd/sup 154/ and Gd/sup 156/ derived from the measured cross sections are in good agreement with the reported directly measured lifetimes of these states. (auth)

Inelastic deuteron scattering from 148Sm, 150Sm, 152Sm and 154Sm

Abstract Targets of 148Sm, 150Sm, 152Sm and 154Sm have been bombarded with 12.1 MeV deuterons and the spectra of inelastic deuterons observed at 60°, 90°, 125° and 155° by means of a high resolution magnetic spectrograph. For the strongly populated levels the multipolarities of the excitations were determined from the slopes of the angular distributions which are characteristic functions of the multipolarity. The cross sections from the 2+ and 3− states were compared to the corresponding reduced transition probabilities B(Eλ) determined by Coulomb excitation with 15 or 16 MeV α-particles. On this basis, a normalization was obtained which allowed the extraction of reduced transition probabilities from the yields of inelastically scattered deuterons. The results are compared to previous studies and the nature of some of the states observed is discussed.

Inelastic scattering from Th232 and U238

Abstract The reduced electric quadrupole transition probabilities and excitation energies of the first excited states in Th232 and U238 have been determined from inelastic scattering measurements with protons and deuterons.