Gamma decay of the giant dipole resonance and feeding of superdeformed states in 143Eu

The γ decay of the giant dipole resonance (GDR) built on excited nuclear states has been measured in coincidence with the low-energy γ discrete transitions for the nucleus ¹⁴³Eu. The reaction used was ¹¹⁰Pd(³⁷Cl, 4n)¹⁴³Eu at a beam energy of 165 MeV. The EUROBALL spectrometer (for the measurement of discrete γ transitions) coupled with the HECTOR array (for high-energy γ-ray detection) has been used. The high-energy γ-ray spectrum in coincidence with superdeformed (SD) discrete transitions of ¹⁴³Eu shows an “excess” between 9–12 MeV if compared with the one associated to cascades which do not pass through the SD configurations. Such an “excess” is in the energy region where one expects the low-energy component of the GDR strength function built on a SD state. The measured intensity can be reproduced by the statistical model assuming that the superdeformation survives only few MeV above the yrast line. A similar and consistent scenario has also been obtained by comparing the high-energy γ-ray spectra of ¹⁴³Eu in coincidence with its spherical (which is fed by the SD configuration) and its triaxial configuration (which is bypassed by the decay of the SD states).     

Experimental evidence for tunneling in the decay of superdeformed states

A systematic study of the depopulation of superdeformed rotational bands in neutron-deficient nuclei has been performed. We observed a correlation between the rotational frequency at which the decay out of the superdeformed bands takes place and the difference between the transition quadrupole moments of states in the superdeformed bands and high-lying states with normal deformation. The observation may constitute direct experimental evidence that the commonly adopted tunneling picture for the decay of superdeformed states is valid.Received: 25 September 2003, Revised: 20 July 2004, Published online: 17 August 2004PACS: 21.10.Ky Electromagnetic moments - 21.60.Ev Collective modelsK. Lagergren: Present address: Department of Physics, Florida State University, Tallahassee, FL-32306, USA     

Favoured superdeformed states in 89Tc

A superdeformed band consisting of a cascade of ten γ-ray transitions has been identified and assigned to the nucleus ⁸⁹Tc, close to the proton dripline. The quadrupole moment of the band (Q _t= 6.7^+3.0 _−2.3 eb, as measured by the Residual Doppler Shift Method) as well as a large dynamic moment of inertia point to a highly elongated shape. With a relative population of approximately 15% of the γ-ray flux in the ⁸⁹Tc exit channel, the band is among the most intense superdeformed bands observed to date. Received: 6 July 1999     

Gamma-ray investigation of different silver isotope decay

The investigation of different silver isotope decay gamma-rays fromA=102 toA=113 was made using two Ge(Li) detectors with resolution 3·7–6 keV. The results obtained and data from other papers were analyzed to correct and to complete the decay schemes of these nuclei. The radioactivity having a half-time of 3 min. is considered as a new isotope of⁹⁷Ag. Three new states were added to the level scheme of¹⁰²Ag in agreement with the results of the -gamma and gamma-gamma coincidences. Two gamma-ray transitions were added to the scheme of excited levels of¹⁰³Pd. About 60 transitions were found in the decay of the two known isomers of¹⁰⁴Ag. Most of them are located in the decay scheme of the 19 excited levels of the¹⁰⁴Pd isotope. Positive parity was assigned to all of them.The¹¹²Ag and¹¹³Ag gamma-ray spectra were first obtained with the aid of a Ge(Li) spectrometer. The observed transitions were placed in a decay scheme containing 16 levels in the case of¹¹²Cd and 5 levels in the case of¹¹³Cd.The properties of the low excited even-even isotope states of Ru, Pd and Cd are discussed and compared.The authors are deeply indebted to M. K. Nikitin for participation in the chemical separation of a series of samples and to L. F. Protasova for help in the measurements. One of the authors (E.P.G.) expresses his sincere thanks to Prof. V. Petrílka for kindly providing him with excellent conditions for research in Prague.     

Observation of superdeformed states in 88Mo

High-spin states in ⁸⁸Mo were studied using the Gammasphere germanium detector array in conjunction with the Microball CsI(Tl) charged-particle detector system. Three γ-ray cascades with dynamic moments of inertia showing similar characteristics to superdeformed rotational bands observed in the neighbouring A= 80 region have been identified and assigned to the nucleus ⁸⁸Mo. The quadrupole moment of the strongest band, deduced by the Residual Doppler Shift Method, corresponds to a quadrupole deformation of β₂≈ 0.6. This confirms the superdeformed nature of this band. The experimental data are interpreted in the framework of total routhian surface calculations. All three bands are assigned to two-quasi-particle proton configurations at superdeformed shape. Received: 20 May 1999 / Revised version: 25 August 1999     

Lifetime measurements and decay of superdeformed bands in Hg isotopes

The lifetimes of states in Superdeformed (SD) bands in ^192,194Hg have been measured using the Doppler shift attenuation method. Intrinsic quadrupole moments have been extracted for band 1 of ¹⁹²Hg and for bands 1, 2, and 3 of ¹⁹⁴Hg. It was found that the quadrupole moments for the “identical” SD bands in these nuclei are the same. In the same experiment, one-step transitions linking SD states to yrast and near yrast states for bands 1 and 3 of ¹⁹⁴Hg have been identified. From this observation, excitation energies, spins and probable parities have been assigned to SD states in these bands.     

Gamma-ray spectrum from gravitino dark matter decay

Gravitinos are very promising candidates for the cold dark matter of the Universe. Interestingly, to achieve a sufficiently long gravitino lifetime, R parity conservation is not required, thus preventing any dangerous cosmological influence of the next-to-lightest supersymmetric particle. When R parity is violated, gravitinos decay into photons and other particles with a lifetime much longer than the age of the Universe, producing a diffuse gamma-ray flux with a characteristic spectrum that could be measured in future experiments, such as GLAST or AMS-02. In this Letter we compute the energy spectrum of photons from gravitino decay and discuss its main qualitative features.     

Conversion-electron spectroscopy in the decay of superdeformed 135Nd

We have investigated the structure of the superdeformed band in ¹³⁵Nd using conversion-electron spectroscopy. The transitions within the superdeformed band show conversion coefficients which are consistent with an E2 multipolarity. From the conversion coefficients of transitions linking this band with known low-lying states its positive parity was established. Hence, a direct determination of the parity of a high-spin superdeformed band could be performed for the first time.     

The decay of208Tl. Gamma-ray measurement

The gamma rays following the decay of²⁰⁸Tl have been studied using a separated²⁰⁸Tl-source and a Ge(Li)-detector. A decay scheme is proposed, with levels in²⁰⁸Pb at 3,920, 4,126 and 4,180 keV in addition to previously well-established levels. No support was found forΒ-branching to levels above 4.2 MeV.     

The role of high-N orbits in superdeformed states

It is investigated how particles in high-N shells affect the moment of inertia,

⁽²⁾, and the quadrupole moment, Q₀, of superdeformed high-spin states. The different behaviour of

⁽²⁾ versus the rotational frequency observed for superdeformed states in ¹⁵²Dy and ¹⁴⁹Gd is explained in terms of different occupations of a few high-N orbits. Predictions for

⁽²⁾ and Q₀ for the neighbouring nucleus ¹⁴⁸Eu are presented.     

Determining the energy barrier for decay out of superdeformed bands

An asymptotically exact quantum mechanical calculation of the matrix elements for tunneling through an asymmetric barrier is combined with the two-state statistical model for decay out of superdeformed bands to determine the energy barrier (as a function of spin) separating the superdeformed and normal-deformed wells for several nuclei in the 190 and 150 mass regions. The spin-dependence of the barrier leading to sudden decay out is shown to be consistent with the decrease of a centrifugal barrier with decreasing angular momentum. Values of the barrier frequency in the two mass regions are predicted.     

On the decay of the superdeformed band in194Pb

We report on new results for the decay of the superdeformed (SD) band in¹⁹⁴Pb. No transitions linking the SD structure with the known level scheme of¹⁹⁴Pb could be found, but the feeding intensities into the normal-deformed states are determined and limits on the one-step decay of the SD band are given.     

Gamma-ray transitions in Bi following the decay of Po

The decay of 5.7 h ²⁰⁷Po to levels in ²⁰⁷Bi has been studied using a Ge(Li) detector. Combining the relative gamma-ray intensities with previously established conversion electron intensities, K-conversion coefficients are determined. The multipolarities of 29 transitions are deduced from a comparison with theoretical conversion coefficients, thus establishing the following spins and parities for the excited levels:

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. A comparison with a recent shell-model calculation shows good agreement for all negative parity levels.     

Gamma-ray branching ratios in the decay of 49Cr

The European Physical Journal A - 7Be(p, $\gamma$ )8B has an important role in nuclear astrophysics, having a direct impact on both the high energy component of solar neutrinos and the 7Li...     

Transition quadrupole moments of superdeformed states in194Pb

Lifetimes of superdeformed states in¹⁹⁴Pb were measured by the Doppler-shift attenuation method. Quadrupole moments around 20 eb, that are constant over the observed frequency range, are derived. The results rule out large centrifugal stretching effects.