g-factor of the first excited 4+ states in156Gd and158Gd

Relative g-factor of the first 2⁺ and 4⁺ states have been measured with the transient field technique in¹⁵⁶Gd and¹⁵⁸Gd. The precession of gamma rays depopulating the levels under study were observed, after passing through thin polarized gadolinium. The observed values agree with the predictions of the rotational model, i.c. g(4⁺)= g(2⁺), while contrasting the hypothesis that in¹⁵⁶Gd the g-factor of the 4⁺ is reduced with respect to the 2⁺, because of rotational alignment.     

Mössbauer-effect studies of excited states of 155Gd, 156Gd and 157Gd

Mössbauer-effect studies yield the following nuclear parameters: In ¹⁵⁵Gd, Q(86)/Q(0) = 0.087 ± 0.006, Q(105)/Q(0) = 1.00 ± 0.03. In ${}^{156}\text{Gd}\text{, g(89) = 0.386 ± 0.004,}{}^{156}\text{Q(89)/}{}^{155}\text{Q(0) = ?1.51 ± 0.02.}\text{In}{}^{157}\text{Gd}\text{, Q(64)/Q(0) = 1.80 ± 0.03}\text{and}\text{g(64) = ?0.185 ± 0.005}$. The value of g(89) is in very good agreement with the theoretical value.     

Mössbauer effect studies of excited states of 155Gd

Mössbauer effect studies of the 60.0, 86.5 and 105.3 keV transitions of ¹⁵⁵Gd, yield the following nuclear parameters: $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(60}\text{keV level}\text{) = 194 ± 15}\text{ps}$, $\text{g(87)}\text{g(0)}\text{= 1.235 ± 0.008}$, $\text{g(105)}\text{g(0)}\text{= 2.01 ± 0.05 or ?0.55 ± 0.05}$; $\text{Q(87)}\text{Q(0)}\text{= +0.087 ± 0.006}$ and $\text{Q(105)}\text{Q(0)}\text{= 1.00 ± 0.03}$ or $\text{Q(87)}\text{Q(0)}\text{= ?0.083 ± 0.008}$ and $\text{Q(105)}\text{Q(0)}\text{= = 1.16 ± 0.03}$. Theoretical considerations favour the first set of values of $\text{Q(87)}\text{Q(0)}$ and $\text{Q(105)}\text{Q(0)}$.     

Nuclear structure effects in the feeding of yrast states of Gd,Dy and Er nuclei

The population of the yrast and near-yrast levels in Gd, Dy and Er nuclei has been investigated experimentally in (heavy ion, xn) reactions through high-resolution γ-ray intensity measurements. A clear difference between non-rotor (N ? 86) and rotor nuclei (N > 86) is evident from the data. For the non-rotor nuclei we define the spin value I_sat below which the yrast population saturates. One finds that I_sat is independent of the bombarding energy when the latter becomes sufficiently high. We discuss the feeding pattern in relation to the single-particle structure of the yrast and near-yrast levels and in relation to the effect of shape changes, including the possibility of superdeformed shapes at high spin.     

First observation of yrastγ-rays in theN=78 nuclei142Gd and141Eu

Excitation function measurements with α-particles and HI-beams clearly attribute the yrast cascade previously proposed for¹⁴²Gd to the¹⁴¹Eu neighbouring nucleus. The so far unknown yrast transitions of¹⁴²Gd have been identified. Coincidence measurements establish the high-spin level schemes of the two nuclei up to 3.2 MeV.     

First observation of excited states in the neutron-rich nucleus 138Te

The very neutron-rich nucleus ¹³⁸Te produced in the spontaneous fission of ²⁴⁸Cm has been investigated using the EUROGAM II %-ray multidetector array. The excited states of ¹³⁸Te observed for the first time indicate that the region of ground state deformation beyond the doubly magic nucleus ¹³²Sn has yet not been reached.     

Development of magnetic rotation in light Gd nuclei; study of 142Gd

High-spin states in ¹⁴²Gd have been populated by means of the ⁹⁹Ru(⁴⁸Ti, 2p3n) reaction at 240 MeV and investigated with the γ-spectrometer EUROBALL III and the charged-particle detector array ISIS. The features of four dipole bands have been determined and compared with tilted-axis cranking model calculations indicating that they are magnetic rotational bands. A transition from regular to irregular bands has been found approaching N = 82 demonstrating that this is a general phenomenon in nuclei near a double-shell closure. Received: 9 December 2001 / Accepted: 9 January 2002     

Ground state bands in142Gd and140Sm

The ground state bands of theN=78 isotones¹⁴² Gd and¹⁴⁰Sm were observed up to the 8⁺ state by bombarding¹⁴⁴Sm and¹⁴²Nd withα-particles of energies between 80 and 130 MeV. Excitation functions,γ-γ coincidences, lifetimes and angular distributions were measured. The ground state band in¹⁴⁰Sm is partially fed by an isomeric state ofT _1/2?17ns. No such isomerism is observed for¹⁴²Gd. The level energies are very similar in both cases and agree well with the predictions of the VMI model.     

New yrast excited states of the N = 84 nucleus 142Ce observed in deep inelastic reactions

Excited states of ¹⁴²Ce, populated in deep inelastic reactions of ⁸²Se projectiles bombarding ¹³⁹La target, have been studied up to medium spins using in-beam γ spectroscopy techniques. Three new levels have been identified at 2625, 2995, 3834 keV, and assigned as 8⁺, 9^(-) and 11^(-), respectively. These new yrast states follow closely the level systematics of the even mass N = 84 isotones. Their strctures have been discussed with the help of empirical shell model calculations. Received: 2 November 2001 / Accepted: 15 January 2002     

Investigation of lifetimes in dipole bands of 142Gd

Lifetimes have been measured for dipole bands in ¹⁴²Gd using DSAM. The deduced B(M1) and B(E2) values as well as B(M1)/B(E2) ratios are compared with calculations in the framework of the TAC (Tilted Axis Cranking) and SPAC (Shears mechanism with Principal Axis Cranking) models. The dipole bands DB1 to DB4 can be interpreted as magnetic rotational bands.     

Investigation of lifetimes in quadrupole bands of 142Gd

For a level scheme investigation of ¹⁴²Gd an experiment with the γ -spectrometer EUROBALLIII has been carried out and lifetimes have been measured with EUROBALL IV using the Doppler-shift attenuation method. The high-spin states have been populated in these experiments by means of the ⁹⁹Ru(⁴⁸Ti, 2p3n) reaction at a beam energy of 240MeV and the ¹¹⁴Sn(³²S, 2p2n) reaction at 160MeV, respectively. Reduced E2 transition probabilities B(E2) were determined for 15 members of four quadrupole bands. For the interpretation of the positive-parity even-spin quadrupole bands, calculations in the cranked Nilsson-Strutinsky as well as interacting boson models have been performed. From the former calculations it was concluded that the high-spin states of the (+ , 0)₁ band in ¹⁴²Gd represent a triaxial nucleus rotating around the longest principal axis.     

Electromagnetic properties of high spin states in158Dy and164Dy

We present calculations of electromagnetic properties of¹⁵⁸Dy and¹⁶⁴Dy based on the solution of the self-consistent cranking model and approximate angular momentum projection technique developed earlier. The calculated values compare fairly well with the existing experimental data.     

Low-spin states in151Gd

The level structure of the 87-neutron nucleus¹⁵¹Gd has been investigated by studying the EC- andβ ⁺-decay of¹⁵¹Tb. Gamma-ray and conversion electron spectra as well as gamma-gamma coincidence spectra were measured by using semiconductor spectrometers and a high-capacity two-parameter recording system. The proposed decay scheme contains several new energy levels in¹⁵¹Gd, among them a 5^?/2 state at 427 keV. To explain the low-energy level structure, a small stable deformation is assumed for¹⁵¹Gd. Using a single-particle-plus-rotor model based on a generalized Woods-Saxon potential, complete mixing of the shells 1h _9/2, 2f _7/2 and separately 1i _13/2 is observed. By these mixings the correct level order and approximately correct excitation energies up to 1 MeV are reproduced.     

Yrast band spectroscopy of155Gd and157Dy

The yrast bands of¹⁵⁵Gd and¹⁵⁷Dy have been observed to high spins (I～25–40). The systematic properties of the N=91 isotones with particular reference to the second i_13/2 neutron and first h_11/2 proton alignments are discussed.     

The excited states of an intersubband exciton

The energy of intersubband collective spin-and charge-density excitations is calculated for a system of quasi-two-dimensional electrons at certain values of the angular-momentum component perpendicular to the plane of the electron free motion. The calculation is carried out within the Hartree-Fock approximation. It is shown that the excited states correspond to the electron transitions in the vicinity of the Fermi momentum. The dispersion of the collective excitations is considered.     

The first observation of electron spin polarization in the excited triplet states caused by the triplet-triplet annihilation

The spin polarization of excited triplet states caused by mutual annihilation of triplet states was detected by time-resolved electron paramagnetic resonance (EPR) of triplet excitons in two molecular crystals, anthracene-tetracyanobenzene and phenazine-tetracyanoquinodimenthane. The time profile of the two EPR lines of the triplet exciton spectrum have been studied in the time range up to 200 μs after a laser pulse. Besides the initial polarization of the lines, due to intersystem crossing, a long-lasting polarization process is detected which is attributed to the triplet-triplet annihilation. The investigation of the dependence of the phenomenon on the intensity of the light pulse and on the orientation of the crystals in the magnetic field is presented.     

The structure of83Sr excited states

The -decay of⁸³Y isomers (7.06 min and 2.85 min) have been studied by means of Ge (Li) detectors. The proposed level scheme of the⁸³Sr nucleus is based on the coincidence measurement and the analysis of energy sums. The intensity balance requirement leads to _T (35·5 keV)=3.2 which is consistent with M1 multipolarity of this transition. A probable structure of some of the excited states in the⁸³Sr nucleus is discussed in the framework of Alaga's model and Kuriyama's model.     

Superdeformed states in rotating152Dy

The recently observed gamma-spectrum of¹⁵²Dy at angular momenta 25>~I>~60 is interpreted in terms of a strongly deformed shape isomer. A pronounced minimum is found for these angular momenta in the sum of liquid-drop energy (including rotational part) and shell-correction (calculated in the Nilsson model) of¹⁵²Dy. The general criteria for stability of this minimum against rotation are discussed.