Search

The 113Ru and 113Rh nuclei, produced in the spontaneous fission of 248Cm and in proton-induced fission of 238U , were studied by means of prompt gamma spectroscopy using the EUROGAM 2 array of Anti-Compton spectrometers and the IGISOL mass separator, respectively. For the 0.5s isomer, found in 113Ru in our recent study we propose the 7/2-[523] configuration. The present data indicate spin and parity 1/2+ for the ground state in 113Ru . This and some new data on the excited levels in 113Rh allows reinterpretation and a better understanding of the β- {} decay scheme of 113Ru . The properties of 113Ru were studied in the frame of the Core-Quasiparticle Coupling model, which has well reproduced the experimental data. [ABSTRACT FROM AUTHOR]

The 136I nucleus, populated in the spontaneous fission of 248Cm, was studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array. The observation in this work of the 42.6keV prompt-γ, M1 + E2 transition de-exciting the 7- level in 136I indicates that this level, interpreted as the $(\ensuremath \pi g_{7/2}^3 \nu f_{7/2})_{7^-}$ configuration, does not correspond to the T = 47s, β-decaying isomer in 136I. The isomer is placed 42.6keV below the 7- level. It has spin 6- and is interpreted as the $\ensuremath(\pi g_{7/2}^2 d_{5/2} \nu f_{7/2})_{6^-}$ configuration. This and other members of both multiplets can be reproduced properly only if one assumes that the π d 5/2 orbital in 136I is located 400keV lower than in 133Sb. Possible mechanisms causing this effect are discussed. [ABSTRACT FROM AUTHOR]

The111Ru nucleus, populated in the spontaneous fission of248Cm has been studied by means of prompt gamma spectroscopy using the EUROGAM2 array. Spin and parity assignments, based on angular correlations, linear polarization, and conversion coefficient measurements differ from those available in the literature. New bands are reported, which incorporate ? transitions seen previously but not placed in the scheme of111Ru or placed incorrectly. The bands are interpreted as neutron excitations into subshells originating predominantly from theh11/2,g7/2 ands1/2 spherical orbitals. Thes1/2 band, strongly mixed with thed3/2,d5/2 andg7/2 configurations, is observed for the first time in this region. [ABSTRACT FROM AUTHOR]

AT1/2 = 16(2)ns isomeric level, populated in the spontaneous fission of248Cm, has been found in101Zr at 941.8keV in a measurement of prompt ?-rays using the EUROGAM2 array. The level is interpreted as aK-isomer corresponding to the 9/2[404] neutron-hole excitation. The quadrupole moment,Q0 = 3.6(4)eb, deduced for the new band indicates a large deformation of ß2 = 0.38(4), which is produced by a specific shape-coexistence mechanism. This is another observation of the ?9/2[404] orbital in the massA~ 100 region, confirming the presence of the effect reported first in our previous work. The 9/2[404] neutron-hole excitation is also confirmed in the97Sr nucleus and the deformation ß2 = 0.44(2) is determined for this configuration. The properties of the 9/2[404] neutron orbital and its influence on the onset of deformation in theA~ 100 region are discussed. [ABSTRACT FROM AUTHOR]

Levels in115Pd and117Pd nuclei, populated in the spontaneous fission of248Cm were studied by means of prompt gamma spectroscopy using the EUROGAM2 array of Anti-Compton spectrometers. Negative-parity,I= 9/2 excitations were identified, which are associated with the long-lived isomers in these nuclei, reported previously as 11/2- excitations. The new data indicate spin and parity 3/2+ for ground states in115Pd and117Pd instead of 5/2+ proposed in previous works. This result implicates changes of spin assignments to other levels in both nuclei. [ABSTRACT FROM AUTHOR]

Lifetimes have been measured for dipole bands in 141Eu 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 can be interpreted as magnetic rotational bands. [ABSTRACT FROM AUTHOR]

For a level scheme investigation of 144Gd an experiment with the γ-spectrometer EUROBALL III has been carried out and lifetimes have been measured with the γ-spectrometer GASP using the Doppler-shift attenuation method. The high-spin states have been populated in these experiments by means of the 100Mo(48Ti,4n) reaction at 215 MeV and the 114Cd(36S,6n) reaction at E 182 MeV, respectively. The known quadrupole band has been modified and a new one has been established. Reduced E2 transition probabilities B (E2) were determined for seven members of these quadrupole bands. They show values between ≈ 60 and 130 W.u. and this considerable enhancement gives evidence for a significant nuclear deformation. A (πh11/2)2 ⊗ (vh11/2)-2 configuration may be assigned to one of the quadrupole bands according to total Routhian surface calculations. The spin dependence of the B(E2) values has been explained by IBM calculations involving high-spin quasiparticle excitations. [ABSTRACT FROM AUTHOR]

High-spin states in the odd-odd nucleus 172Lu have been populated in a 170Er(7Li,5n) reaction at 51 MeV and the emitted γ-radiation was detected with the GASP array. A new semidecoupled band with the proposed π1/2- [541] ® μ7/2+ [633] configuration has been established exhibiting a signature inversion. A systematic study of the signature inversion in odd-odd nuclei of the rare-earth region is presented. The variation of the inversion spin remains nearly constant for nuclei with the same N - Z, increases with N for an isotopic chain and decreases with Z for an isotonic chain. On the basis of the systematics a change of the spins by lℏ is proposed for the semidecoupled bands in 180Re, 182'184Ir and 184'186Au. [ABSTRACT FROM AUTHOR]

Excited levels in140Xe and142Xe nuclei, populated in the spontaneous fission of248Cm, were studied by means of prompt γ-ray spectroscopy, using EUROGAM2 array. We report the first observation of an octupole band in142Xe and extend the octupole band in140Xe. Level schemes of140Xe and142Xe obtained in this work show patterns characteristic of ocupole-vibrational bands. Properties of octupole bands in Xe isotopes indicate that octupole correlations in these nuclei are lower than in the corresponding Ba nuclei. The electric dipole moment of142Xe was found to be larger than in other Xe isotopes, contrary to theoretical predictions. This may be due to the special role of the N = 88 neutron number. [ABSTRACT FROM AUTHOR]

Excited states in the 134Sb nucleus, populated in the β--decay of 134Sn, have been studied at the mass separator OSIRIS. The 134Sn activity was produced via fast neutron-induced fission of 238U target. A main result was the discovery of a very low-lying first-excited state of 134Sb, at 13keV, which has led to a strong revision of the level scheme. The new results are compared with different theoretical calculations and with the known data for the analogous neutron and proton two-particle nucleus in the 208Pb region. On the basis of this comparison, the energy of the ( π g7/2ν f7/2)7- isomer is estimated to be about 250keV, some 100keV lower than previously reported. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The 137I nucleus, populated in the spontaneous fission of 248Cm has been studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array. Medium-spin yrast excitations in 137I were observed for the first time. The experimental level scheme is compared to the shell model calculation with modified Kuo-Herling interaction. The theoretical predictions differ significantly from the experimental results, indicating that the excitation pattern in 137I deviates significantly from the shell model scheme. [ABSTRACT FROM AUTHOR]

Neutron-rich, 88-94Kr nuclei, populated in spontaneous fission of 248Cm, have been studied with EUROGAM 2, by measuring prompt γ-rays. Many new excited states in even-even Kr isotopes have been identified. For the first time spins and parities were determined experimentally in these nuclei. Our results indicate that the quadrupole deformation of Kr isotopes will appear only above N = 58, as observed in Sr and Zr nuclei. The newly found 3- level at 1506.4 keV in 90Kr suggests the exsistence of a new region of increased octupole correlations, probably associated with the ν( d5/2 h11/2) pair of Δ l = Δ j = 3 orbitals. [ABSTRACT FROM AUTHOR]

Prompt γ radiation following spontaneous fission has been measured using the EUROGAM 2 array. Using these data and newly developed analysis techniques a number of subjects were studied, which are briefly discussed. One of these subjects, shape transition in A≈100 Sr and Zr nuclei is discussed in more detail. Quadrupole moments were determined for rotational bands in the N=58,59,60,62 and 64 Sr and Zr isotopes. Deformation parameters, which increase from β ≈ 0.1 at N=56 to β ≈ 0.4 at N=64, suggest that in strontium and zirconium isotopes shape change happens gradually between N=56 and N=62 and is probably due to an occupancy of three or more deformation-driving orbitals of h parentage. [ABSTRACT FROM AUTHOR]

High-spin states inOs have been populated by theW(He,4n)-reaction at 55MeV. The emitted γ-radiation was detected with the OSIRIS spectrometer. The yrast band, for which the nucleus has a prolate shape, was found to terminate at I =18. The γ-ray intensity is then distributed between several irregular sequences. Different to other cases of band termination, the minimum in the total routhian surface corresponding to a collective shape is calculated to disappear in this spin region, although the available spin of the valence nucleons is far from being exhausted. A different structure, which is dominated by non-collective states becomes yrast. [ABSTRACT FROM AUTHOR]

The proton capture cross sections for the reactionCu( p, γ)Zn leading to several resolved states in theZn nucleus have been measured for E =6.5-11.0 MeV. The excitation functions have been reproduced by the combined CN and DSD models. The extracted spectroscopic factors compared with those derived from the stripping reaction are found to show a distinct correlation. [ABSTRACT FROM AUTHOR]

The γ-decay and half life of the t=60(3) ns I=8 isomer inCd have been studied with a recoil catcher setup inside the multidetector π-array OSIRIS. Evaporation neutrons and charged particles from the reactionNi+Ti were measured in coincidence with delayed γ-rays. Six new γ-ray transitions with intensities of 1-10% of the main γ-ray cascade were found, two new states established and firm spin-parity assignments were made to all states below the isomer. The new states were identified as the 4 and 6 members of the proton πg multiplet. [ABSTRACT FROM AUTHOR]

The level scheme ofAu has been extended to high spins. Decoupled, strongly coupled as well as vibrational bands have been found indicating shape coexistence in this nucleus. [ABSTRACT FROM AUTHOR]

A non-yrast superdeformed band has been found inGd using thePd(Ar, 4n)Gd reaction. The nuclear assignment was made from the analysis of an experiment using a backed target. This band and the previously identified yrast SD band are probably not signature partners. [ABSTRACT FROM AUTHOR]

Highspin states ofIr were excited in theRe(α,6n) reaction and measured with the OSIRIS spectrometer. The first backbending in the πhx band was found at a rotational frequency of ħω=0.40 MeV. Blocking arguments suggest that this is due to the alignment of an h quasiproton pair. [ABSTRACT FROM AUTHOR]

Two-dimensional γ-ray energy correlations have been measured at high spins in0s with the TESSA2 spectrometer. The E − Ecorrelation matrix displays ridges characteristic of rotational bands with different energy separations of 96± and 72± keV for the energy regions of 660 to 840 keV and 975 to 1170 keV, respectively. The separation of these ridges remains constant in both energy regions. The dynamical moments of inertia are θ =83±3 and 111±5 ħ/MeV, respectively. The latter value suggests superdeformation in0s with an axis ratio c/a=1.76 (β ≅0.64) at high spins. [ABSTRACT FROM AUTHOR]