Projected Shell Model Description of Positive Parity Band of <Superscript>130</Superscript>Pr Nucleus

Theoretical investigation of positive parity yrast band of odd-odd ¹³⁰Pr nucleus is performed by applying the projected shell model. The present study is undertaken to investigate and verify the very recently observed side band in ¹³⁰Pr theoretically in terms of quasi-particle (qp) configuration. From the analysis of band diagram, the yrast as well as side band are found to arise from two-qp configuration πh _11/2???νh _11/2. The present calculations are viewed to have qualitatively reproduced the known experimental data for yrast states, transition energies, and B(M1) / B(E2) ratios of this nucleus. The recently observed positive parity side band is also reproduced by the present calculations. The energy states of the side band are predicted up to spin 25⁺, which is far above the known experimental spin of 18⁺ and this could serve as a motivational factor for future experiments. In addition, the reduced transition probability B(E2) for interband transitions has also been calculated for the first time in projected shell model, which would serve as an encouragement for other research groups in the future.     

High spin bands in120Xe

High spin states in¹²⁰Xe were populated in the reaction¹⁰⁶Cd(¹⁸O, 4n) at a bombarding. energy of 90 MeV and the subsequent de- excitation was studied using γ- ray spectroscopic methods. New levels and several. spin and parity. assignments were established. The yrast band was observed up to theK ^π=22⁺state with two band crossins athw _c=0.39MeV and 0.45Mev Negative parity levels and a new positive parity band were also identified.     

Positive parity low spin states of odd-mass tellurium isotopes

In this work, we analyse the positive parity of states of odd-mass nucleus within the framework of interacting boson fermion model. The result of an IBFM-1 multilevel calculation with the lg_9/2, 2d_5/2, 2d_3/2, 3s_1/2 and one level, 1h_11/2 with negative parity, single particle orbits is reported for the positive parity states of the odd mass nucleus ^123-125Te. Also, an IBM-1 calculation is presented for the low-lying states in the even-even ^124-126Te core nucleus. The energy levels and B (E2) transition probabilities were calculated and compared with the experimental data. It was found that the calculated positive parity low spin state energy spectra of the odd-mass ^123-125Te isotopes agree quite well with the experimental data.     

High spin states in102Ag

High spin states are populated in¹⁰²Ag using the reaction¹⁶O+⁸⁹Y with projectile energies in the energy range 60–80 MeV. Gamma multipolarities are inferred from DCO ratios and coincidence relationships are established among the gamma rays assigned to¹⁰²Ag. A comprehensive level scheme is constructed with four band systems, two of positive parity and the other two of negative parity. The present study extended spins upto 19^– in the main negative parity band. A new band is populated in the present work and is similar to the one observed in¹⁰⁶Ag.The authors wish to thank and record their appreciation to Dr. S.K. Parthasaradhi, VECC, Calcutta for preparing the target used in this experiment. The authors gratefully acknowledge useful discussions with Dr. Rakhesh Popli. The authors record their grateful thanks to Prof. A.P. Patro and Prof. G.K. Mehta, former and present directors of the Nuclear Science Centre, for their interest in this work, helpful discussions and providing excellent facilities. The authors also thank Dr. S.K. Datta of the Nuclear Science Centre for his continued interest and helpful discussions and accelerator staff of N.S.C. for their efficient services in delivering the beam. Grateful thanks are also due to the University Grants Commission for providing financial support.     

M1 and E2 band structures in the Sn-Xe-Ba region

In the present talk I will discuss some ‘rare’ aspects of the E2 band structures and the novel features concerning the dipole bands in this mass region. Reliable and accurate lifetimes have been measured using coincidence recoil distance method. The results of ^129,130Ba will be discussed. In contrast to the predictions of the tilted axis cranking model, the dipole bands in Sb-Xe-Ba nuclei can be nicely described as high-K prolate bands. New data from multi-detector arrays has established extended bands structure, their decay to low lying states have been established and the angular correlation supports the predominant, ΔI=1 character. Finally the sensitive measures, i.e. B(M1) rates of the tilted axis model are compared with the high-K formula based on 1-dim cranking model.     

Microscopic multichannel calculation of the molecular dipole degree of freedom in the18O nucleus

StrongB(E1) transitions have been recently observed between states in the¹⁸O nucleus which follow roughly the energy sequence of a dimolecular α+¹⁴C rotator. These findings have been interpreted by Gai et al. as evidence for a molecular dipole degree of freedom being present in the¹⁸O nucleus. However, this idea was contradicted by the results of a microscopic multichannel calculation performed by Descouvemont and Baye which was based on elastic α+¹⁴C and inelastic α+¹⁴C(2⁺) many-body cluster wave functions. We have improved this study by performing a microscopic multichannel calculation including additionally an+¹⁷O many-body fragmentation in order to enlarge our model space by those shell model components which dominate the structure of the (positive parity)¹⁸O ground state band. Like Descouvemont and Baye we find a positive parity α+¹⁴C molecular band in¹⁸O and, additionally, a rather strong collectivity in the lowest 1^?, 3^? and 5^? states in¹⁸O. However, since the internal structure is different within these states, the calculated states should not be interpreted as a negative parity α+¹⁴C molecular band. In this perspective, the microscopic multichannel calculations do not support the hypothesis of a molecular dipole degree of freedom being present in the¹⁸O nucleus.     

Investigation of lifetimes in the dipole band of 139Sm

Lifetimes have been measured for a dipole band in ¹³⁹Sm 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 band in ¹³⁹Sm can be considered as a magnetic rotational band with a prolate or triaxial nuclear deformation.     

102Ag: In-beam gamma-ray spectroscopy

Gamma-rays associated with the decay of states in the ¹⁰²Ag nucleus have been identified, sixty-four of them for the first time following the reaction ⁵⁰Cr(⁵⁶Fe, 3pn)¹⁰²Ag at a mean energy of 195 MeV. Identification was made using an array of nine escape-suppressed Ge detectors coupled to the Daresbury Recoil Separator. Excited states in ¹⁰²Ag were identified using recoil-gamma and γγ coincidences. From the intensity balance and the coincidence data, a new set of levels was identified which may be interpreted as reminiscent of “three-quasiparticle” bands in neighboring odd-mass nuclei and similar to a four-quasi-particle band observed in ¹⁰⁶Ag.     

Experimental consequences ofSU(3) symmetry in ans d g Boson Model

Energies of collective levels in¹⁷⁸Hf and²³⁴U are compared with predictions of theSU (3) limit of thesdg Interacting Boson Model. All known positive parity states of¹⁷⁸Hf below 1.8 MeV (with the exception of a 0⁺ band) have been satisfactorily reproduced. Most of the bands in²³⁴U are also described by the model. However, a few predicted states have no experimental counterpart. The introduction of theg-bosons strongly reduces the previously observed discrepancies between experimentalB(E2)'s in²³⁸U and thesd-IBM calculation.     

On the coexistence of oblate and prolate deformed bands in83Zr

Deformation parameters of the positive parity yrast band and negative parity bands in⁸³Zr are deduced from lifetimes andE2/M1 mixing ratios. Lifetimes of high spin states have been determined from recoil distance Doppler shift and Doppler shift attenuation measurements using the⁵⁴Fe(³²S,2pnγ) ⁸³Zr reaction. Ten lifetimes and five lifetimes limits were determined. The positive parity band, built on theg _9/2 K=5/2 orbital has an average deformation ¦β ₂¦=0.28(2), and shows a reduction ofE2 transition strengths in the observed backbend region at I^π≈21/2⁺. In contrast, theE2 strengths in the negative parity states show a steady increase up to I^π≈=15/2^?. These states are more strongly deformed than the positive parity states (¦β ₂¦=0.33(3)). TheE2/M1 mixing ratios show that the negative parity band hasK=3/2 and is prolate, and favour oblate deformation for the positive parity yrast band. In theK=1/2^? band theE2 strength of the 7/2^?→3/2^? transition yields a deformation ¦β ₂¦=0.26(5). The band structure is compared with calculations within the Hartree-Fock Bogoliubov cranking model.     

The low-energy dipole structure of <Superscript>232</Superscript>Th , <Superscript>236</Superscript>U and <Superscript>238</Superscript>U actinide nuclei

In this study, I^p = 1⁺\ensuremath I^{\pi} = 1^{+} and I^p = 1^-\ensuremath I^{\pi} = 1^{-} dipole mode excitations are systematically investigated within the rotational and translational + Galilean invariant quasiparticle random-phase approximation for ²³²Th , ²³⁶U , and ²³⁸U actinide nuclei. It is shown that the investigated nuclei reach a B(M1) strength structure, which corresponds to the scissors mode. The calculated mean excitation energies as well as the summed B(M1) value of the scissors mode excitations are consistent with the available experimental data. The results of calculations indicate large differences to the rare-earth nuclei as is the case for the experiment: a doubling of the observed dipole strengths and a shift of the energy centroid to the lower energies by about 800keV. The calculations indicate the presence of a few prominent negative-parity K^p = 1^-\ensuremath K^{\pi} = 1^{-} states in the 2.0-4.0MeV energy interval. The occurrence of the negative-parity dipole states with the rather high B(E1) value less than 4MeV shows the necessity of explicit parity measurements for the correct determination of the scissors mode strength in ²³²Th , ²³⁶U , and ²³⁸U isotopes.     

Low-spin states of odd-mass xenon isotopes

In this work, we analyse the positive parity of states of odd-mass nucleus within the framework of interacting boson-fermion model. The result of an IBFM-1 multilevel calculation with the 2d_5/2, 1g_7/2, 3s_1/2, 2d_3/2 and 1h_11/2, single particle orbits is reported for the positive parity states of the odd-mass nucleus ^125–129Xe. Also, an IBM-1 calculation is presented for the low-lying states in the even-even ^124–128Xe core nucleus. The energy levels and B(E2) transition probabilities were calculated and compared with the experimental data. It was found that the calculated positive parity low-spin state energy spectra of the odd-mass ^125–129Xe isotopes agree quite well with the experimental data.      

109Cd → 109Ag and 107Cd → 107Ag β decays

The energies, magnetic dipole and electric quadrupole moments, spectroscopic factors of the ground and excited states of ¹⁰⁹Ag and ¹⁰⁷Ag, the reduced probabilities of electromagnetic transitions between them, and the reduced probabilities of β transitions from the ground states of ¹⁰⁹Cd and ¹⁰⁷Cd to the excited states of ¹⁰⁹Ag and ¹⁰⁷Ag were calculated on the basis of the dynamic collective model. The vacuum fluctuations of quasiparticles and multiphonon (up to 10 phonons) states of the main band of the even-even core were taken into account. The calculation results show good agreement with the experimental data.     

Lifetimes in the ground-state band and the structure of 118Te

Lifetimes of excited states in ¹¹⁸Te have been measured using the Doppler Shift Attenuation (DSA) and Recoil Distance (RD) methods in the ¹⁰⁹Ag(¹³C, p3n) reaction at a beam energy of 54 MeV. Lifetime values of the ground-state band levels with spins I ^π = 2⁺-16⁺ have been obtained. The excitation energies and B(E2) values are interpreted in the framework of a version of IBFM ( IBM + 2qp) with the maximum boson number exceeding its standard value. A satisfactory agreement with experimental level scheme and B(E2) values for the ground-state band is achieved. Received: 7 June 2001 / Accepted: 7 February 2002     

High resolution measurements of the hyperfine structure of atomic Lanthanum for energetically low lying levels of odd parity

Doppler-reduced saturation absorption spectroscopy is applied to study the hyperfine structure of excited levels of Lanthanum. 16 transitions in the near infrared wavelength range are investigated. Precise values for the magnetic dipole hyperfine structure constants A as well as for the electric quadrupole hyperfine structure constants B of the isotope ¹³⁹La are determined for 14 levels of odd parity and nine levels of even parity. For levels of even parity a good agreement is found with values from previous measurements using sub-Doppler methods. For levels of odd parity previously determined values are improved and for two levels new values of the hyperfine structure constants are reported.     

Multiple Coulomb excitation of198Hg and200Hg

Multiple Coulomb excitation measurements on^{198, 200}Hg have been performed with 5MeV/amu²⁰⁸Pb projectiles andB(E2)-values are determined for transitions between states up to spin 8⁺. In¹⁹⁸Hg a reduction of theB(E2)-value for the yrast transition 8⁺→6⁺ by a factor of 3 as compared to the rigid rotor prediction is observed, which supports the earlier proposed idea that the ground state band is crossed between the 6⁺ and 8⁺ state by a weakly interactingvi ₁₃ ^2/2 rotation aligned band. In each of the two nuclei,¹⁹⁸Hg and²⁰⁰Hg, a state with a possibleI ^π=8⁺ assignment is observed, which is tentatively interpreted as the 8⁺ member of the ground state band.     

Boson description of nuclear collective motion

Nuclear system interacting via quadrupole and octupole particle-hole forces is studied by the boson expansion technique. Energy spectra of the negative parity yrast band and the ground state band are calculated and compared with experiment for¹⁰⁰Ru,¹¹²Cd,¹⁵⁰Sm and¹⁵⁰Gd. ExperimentalB(E1)/B(E2) ratios show strong hindrance for E1 transitions, and are used to deduce the static polarizability of E1 transitions.     

Magnetic layer thickness dependence of magnetization reversal in electrodeposited CoNi/Cu multilayer nanowires

The magnetization reversal of electrodeposited CoNi/Cu multilayer nanowires patterned in an array using a hole template has been investigated. The reversal mode is found to depend on the CoNi layer thickness t(CoNi); with increasing t(CoNi) a transition occurs from coherent rotation to a combination of coherent and incoherent rotation at around t(CoNi)=51 nm. The reversal mode has been identified using the magnetic hysteresis loops measured at room temperature for CoNi/Cu nanowires placed at various angles between the directions of the nanowire axis and external fields using a vibrating sample magnetometer. The nanowire samples have a diameter of ∼250 nm and constant Cu layer thickness of 4.2 nm with various t(CoNi) ranging from 6.8 nm to 7.5 μm. With increasing t(CoNi), the magnetic easy axis moves from the direction perpendicular to nanowires to that parallel to the nanowires at around t(CoNi)=51 nm, indicating a change in the magnetization reversal mode. The reversal mode for the nanowires with thin disk-shaped CoNi layers (t(CoNi)=6.8, 12 and 17 nm) is of a coherent rotation type, while that for long rod-shaped CoNi layers (t(CoNi)=150 nm, 1.0, 2.5 and 7.5 μm) can be consistently explained by a combination of coherent rotation and a curling mode. The effects of dipole–dipole interactions between nanowires and between adjacent magnetic layers in each nanowire on the reversal process have been discussed.     

Luminescent properties of red-emitting LiSr4B3O(9−3x/2)Nx:Eu2+ phosphor for white-LEDs

An Eu²⁺-activated oxynitride LiSr_(4?y)B₃O_(9?3x/2)N_x:yEu²⁺ red-emitting phosphor was synthesized by solid-state reactions. The synthesized phosphor crystallized in a cubic system with space group Ia–3d. The LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphors exhibited a broad red emission band with a peak at 610 nm and a full width at half maximum of 106 nm under 410 nm excitation, which is ascribed to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The optimal doped nitrogen concentration was observed to be x=0.75. The average decay times of two different emission centers were estimated to be 568 and 489 ns in the LiSr_3.99B₃O_8.25N_0.5:0.01Eu²⁺ phosphors, respectively. Concentration quenching of Eu²⁺ ions occurred at y=0.07, and the critical distance was determined as 17.86 Å. The non-radiative transitions via dipole–dipole interactions resulted in the concentration quenching of Eu²⁺-site emission centers in the LiSr₄B₃O₉ host. These results indicate LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphor is promising for application in white near-UV LEDs.     

Metal-insulator transition and variable-range hopping conductivity of n-CdSb in magnetic field

Resistivity, ρ, of a II-V group semiconductor n-CdSb doped with In is investigated in pulsed magnetic fields up to and at temperatures . The low-temperature resistivity ρ(T) increasing with T in the range of B<4 T is found to have an upturn around B∼4 T and strong activated behavior at further increase of B. These observations give evidence for magnetic-field-induced metal-insulator transition (MIT). In the insulating side of the MIT, Mott variable-range hopping (VRH) conductivity with two types of asymptotic behavior, ln ρ (T, B)∼T^−3/4B² and ln ρ (T, B)∼(B/T)^1/3, is established in low and high magnetic fields, respectively. The VRH conductivity is analyzed using a model of the near-edge electron energy spectrum established by investigations of the Hall effect. The VRH conductivity is shown to take place over the band tail states of one out of two impurity bands, which for T=0 and B=0 lie above the conduction band edge.