O. Nathan

Excitation of collective optupole states in the Pd-Sm region

Abstract Gamma ray transitions following inelastic scattering of 14–20 MeV α-particles were observed from 30 even nuclei in the range 106≦ A ≦154. The angular correlations between backscattered α-particles and de-excitation γ-rays were measured in a number of cases. In addition to 2+ and 4+ collective quadrupole states we systematically excited collective 3− states at somewhat higher excitation energies. For the strongest octupole excitations the reduced electromagnetic transition probabilities B(E3) were derived from yield measurements at low bombarding energies. The B(E3) values were found to be higher than the single-particle estimate by factors ranging from ≈ 15 to ≈ 100. The energy systematics of the octupole vibrations are discussed qualitatively in terms of the shell model with residual interactions.

The (t, p) reaction with the even isotopes of Ca

Abstract The reactions 40, 42, 44, 46, 48 Ca(t, p) were investigated at 10 to 12 MeV bombarding energy with an overall energy resolution of 15–25 keV. The relative differential (t, p) cross sections for the strongest L = 0 transitions in the various isotopes were measured by means of a target composed of approximately equal amounts of the various even Ca isotopes. The systematic trends of the (t, p) angular distribution shapes were established for angular momentum transfers of 0, 2, 3 and 4 units of ħ. A number of 0 + , 2 + and 4 + assignments was made. A detailed comparison of the data from the one- and two-neutron capture reactions leading to 44 Ca is presented, and the systematics of the 0 + states in the Ca isotopes is discussed. Two distinct groups of 0 + states, both characterized by large (t, p) cross sections, were observed; one group comprises the 42, 44, 46, 48 Ca ground states and the second group consists of the following states: 5.85 MeV 42 Ca, 5.864 MeV 44 Ca, 5.595 and 5.628 MeV 46 Ca, 5.459 MeV 48 Ca and 50 Ca (ground state).

Coulomb excitation with 14–20 MeV α-particles: Double excitations and systematics of vibrational states in the rare earth region

Abstract An exploratory investigation of nuclei in the rare earth region has been performed by means of the Coulomb excitation process, using 14–20 MeV α -particle as projectiles and studying the deexcitation γ -rays. Rotational double excitations were systematically observed in deformed, even nuclei and evidence for double E2-E2 excitations was also found in some non-rotational, even nuclei. In single excitation a number of γ -ray were seen which have not been reported previously in Coulomb excitations, and approximative values for the corresponding partial, reduced E2 transition probabilities eB (E2) have been determined. Tentative level schemes are proposed which will explain the observations, and the nature of the excited states is discussed on the basis of the measured eB (E2) values. In particular, it is pointed out that our results, together with other data, may indicate the presence of γ -vibrations in Ho 165 and some other deformed nuclei with odd number of protons.

Proton pick-up from the even lead nuclei

Abstract Angular distributions of the Pb(t, α) reactions leading to states of 207Tl, 205Tl and 203Tl have been measured at an incident triton energy of 13.5 MeV using the Aldermaston tandem accelerator and multi-angle magnetic spectrograph. The states of 207Tl are probably single-proton hole states and were observed at excitations of 0 MeV (3 s 1 2 ) −1 ; 0.35 MeV , (2 d 3 2 ) −1 ; 1.34 MeV , (1 h 11 2 ) −1 ; 1.67 MeV , (2 d 5 2 ) −1 and 3.48 MeV possibly (1 g 7 2 ) −1 . For 205Tl sixteen excited states were observed up to an excitation of 2.74 MeV, and for 203Tl nine excited states were observed up to 1.69 MeV. The number of excited states observed in these two nuclei is in rough agreement with the prediction of the model of a single proton hole coupled to the states of the corresponding Pb cores. Some of the angular distributions for the three Tl isotopes have been analysed using distorted wave methods and spectroscopic factors were extracted. These factors for the four lowest states of 207Tl support the single-hole assignments and for the states of 205Tl and 203Tl are within the sum rule limits. The results are discussed on the basis of the above model.

Proton pick-up from the even calcium isotopes

Abstract The 42, 44, 46, 48Ca(t, α) proton pick-up reactions have been investigated at about 13 MeV incident energy, transition Q-values and α-particle angular distributions were measured for the stronger transitions. A common intensity scale was established by means of (t, α) reactions from a target consisting of known amounts of each of the even Ca isotopes. Assignments of l-values were made on the basis of the α-particle angular distributions. Relative spectroscopic factors were obtained by means of a DW analysis for the strongest 1 f 7 2 , 1 d 3 2 and 2 s 1 2 transitions. Some 1 f 7 2 transitions were observed for the targets of 40, 42, 44, 46Ca but not for 48Ca.

States of 208Pb from double triton stripping

Abstract The reaction 206 Pb(t, p) 208 Pb was investigated at an incident energy of 12 MeV, the protons being momentum analysed in a multi-angle magnetic spectrograph. A total of 56 excited states of 208 Pb was observed up to an excitation energy of 7.6 MeV. Strong excitations were found for the ground state, the 2.62 MeV 3 − state and the 3.20 MeV 5 − state, but the 3.71 MeV 5 − state was not observed. The different behaviour of these states in (d, p), (t, p) and inelastic scattering experiments is discussed. A state at 4.87 MeV in 208 Pb is assigned 0 + from the shape of the corresponding (t, p) angular distribution which has deep minima at 35° and about 75°. No other excited 0 + states of 208 Pb could be identified from the (t, p) data. It is demonstrated that the existence of two or three sharp minima, the positions of which depend smoothly on the mass number, is a characteristic feature of L = 0 (t, p) angular distributions over a wide range of nuclei. For L = 3 and L = 5 the Pb(t, p) angular distributions at 12 MeV bombarding energy have less characteristic shape than for L = 0.

Nuclear spectroscopy with 204Pb

Abstract The reactions 204 Pb(d, t), 204 Pb(d, p), 204 Pb(d, d′) and 204 Pb(t, p) were investigated at incident energies of 12–13 MeV, the reaction products being momentum analysed in a multi-angle, magnetic spectrograph. Seven excited states were observed in 203 Pb up to 2.8 MeV excitation energy; 27 excited states were observed in 205 Pb up to 4.1 MeV excitation energy; five excited states were identified in 204 Pb up to 2.7 MeV excitation energy, and four excited states were found in 206 Pb up to 3.8 MeV excitation energy. The measured angular distributions from the single transfer reactions (d, p) and (d, t) were compared with DWBA predictions, and spectroscopic factors were deduced for a number of levels. For the states of 203 Pb and 205 Pb near the Fermi surface and for the 204 Pb ground state the results are in general agreement with the pairing model. The data suggest that the four hole-two particle strength of 206 Pb is distributed over many close levels.

Of decay Eu152 and Eu152m

Abstract Using magnetic and scintillation spectrometers and coincidence techniques the radiations from pile-irradiated natural Europium have been studied. The energies of a number of beta- and gamma-rays and internal conversion lines were measured and isotopic assignments were made from the coincidence data. The internal conversion coefficients of a number of the transitions are determined from measurements of the relative intensities of gamma-rays and internal conversion lines. Decay schemes are proposed for the two isomers of Eu152 and plausible spin and parity assignments for some of the excited states of Sm152 and Gd152 are presented. The difference in level structure between these two nuclei is discussed in the light of the Bohr-Mottelson unified model and it is suggested that some of the high-lying excited states may possibly be interpreted as collective vibrations of the electric quadrupole and electric octupole type.

Coulomb excitation of lead and bismuth with 20 MeV α-particles

Abstract The γ-rays resultiing from Coulomb excitation of Pb 204 , Pb 206 , Pb 207 and Bi 209 have been measured in coincidence with the backwards scattered projectiles. The experiment was performed with α-particles accelerated to 20 MeV in a cyclotron. Reduced E2 transition probabilities have been obtained from the thick target γ-ray yields, and the errors whic may be involved in this procedure are discussed in some detail. For the single-particle transitions in Pb 207 and Bi 209 we have compared the observed E2 transition rates with the theoretical single-particle values calculate by Wahlborn for the case of a diffuse nuclear potential. The results indicate an effective E2 neutron charge of (0.85±0.20)· e in Pb 207 and an effective E2 proton charge ⪅2.6 e in Bi 209 . The results for Pb 204 and Pb 206 have been compared with the predictions of Kisslinger and Sorensen. The agreement is good if one uses an effective E2 neutron charge of 1.0 e in these two cases.

Possible vibrational levels in Dy160

Abstract The radiations of Tb 160 have been studied by means of magnetic and scintillation spectrometers and various coincidence techniques. A decay scheme has been proposed which includes the following excited states in Dy 160 : 87 keV (2+), 283 keV (4+), 964 keV (2+), 1047 keV (3+), 1262 keV (2−), and 1359 keV (3−). The level scheme is discussed in the light of the unified model and it is suggested that the states at 964 keV and 1047 keV may possibly belong to a rotational band associated with electric quadrupole vibrations (gamma vibrations) and that the states at 1262 keV and 1359 keV similarly may belong to a rotational band associated with electric octupole vibrations.