Band head spin assignment of superdeformed bands in 86Zr

Two parameter expressions for rotational spectra viz. variable moment of inertia (VMI), ab formula and three parameter Harris ω² expansion are used to assign the band head spins (I₀) of four rotational superdeformed bands in ⁸⁶Zr. The least-squares fitting method is employed to obtain the band head spins of these four bands in the A~80 mass region. Model parameters are extracted by fitting of intraband γ-ray energies, so as to obtain a minimum root-mean-square (rms) deviation between the calculated and the observed transition energies. The calculated transition energies are found to depend sensitively on the assigned spins. Whenever an accurate band head spin is assigned, the calculated transition energies are in agreement with the experimental transition energies. The dynamic moment of inertia is also extracted and its variation with rotational frequency is investigated. Since a better agreement of band head spin with experimental results is found using the VMI model, it is a more powerful tool than the ab formula and Harris ω² expansion.     

A superdeformed band in131Ce

A rotational band of 16γ-rays has been found in¹³¹Ce with a high moment of inertia indicating a deformation ε₂～0.38 and extending to spin ～40?. Its intensity is ～～5% of the total in¹³¹Ce, confirming a difference in the intensity systematics for superdeformed states in Ce nuclei compared with Nd.     

Indpeendent Yields of Iodine and Tellurium Isotopes in Fission of 232 Thorium with 30.5 MeV Alpha Particles

Iodine and tellurium isotopes produced in the fission of ²³²Th with 30.5 MeV alpha particles were separated using a method of sublimation in an air stream and the independent yields of ¹³⁰I, ¹³¹I, ^132m,gI, ¹³³I ¹³⁴I, ^134m,gTe, ^133mTe and ¹³⁴Te (cumulative) were determined by means of high resolution Ge(Li) γ-ray spectrometry. A Gaussian fit to the experimental data was used to obtain the width parameter σ_z and the most probable charge Z_p of the nuclear charge distribution in the isobaric chains 130 – 131. The most probable masses for fission fragments with Z = 52 and Z = 53 were also deduced from the measured fission yields.     

Band head spin assignment of superdeformed bands in Hg isotopes through power index formula

The power index formula has been used to obtain the band head spin(I_0) of all the superdeformed(SD) bands in Hg isotopes. A least squares fitting approach is used. The root mean square deviations between the determined and the observed transition energies are calculated by extracting the model parameters using the power index formula. Whenever definite spins are available, the determined and the observed transition energies are in accordance with each other. The computed values of dynamic moment of inertia J~((2)) obtained by using the power index formula and its deviation with the rotational frequency is also studied. Excellent agreement is shown between the calculated and the experimental results for J~((2)) versus the rotational frequency. Hence, the power index formula works very well for all the SD bands in Hg isotopes expect for ~(195)Hg(2, 3, 4).     

Band head spin assignment of Tl isotopes of superdeformed rotational bands

The Variable Moment of Inertia (VMI) model is proposed for the assignment of band head spin of super deformed (SD) rotational bands, which in turn is helpful in the spin prediction of SD bands. The moment of inertia and stiffness parameter (C), were calculated by fitting the proposed transition energies. The calculated transition energies are highly dependent on the prescribed spins. The calculated and observed transition energies agree well when an accurate band head spin (I ₀) is assigned. The results are in good agreement with other theoretical results reported in literature. In this paper, we have reported the band head spin value 16 rotational band of super deformed Tl isotopes.     

Lifetime measurements of the high spin yrast states in 128Ce

Lifetime measurements of the high spin states in the yrast band of ¹²⁸Ce were performed using the Doppler shift attenuation method in connection with the reaction ¹⁰⁰Ru(³²S, 2p2n) ¹²⁸Ce at incident energy of 141 MeV. In the vicinity of the band crossing, the previously reported anomalously high B(E2) value was not observed. The gross behavior of the normalized transition strength is approximate to symmetric rotor. It is confirmed that the trend of increase in collectivity with decreasing neutron number, which was indicated in the previous studies on ^{130, 132, 134}Ce, continues in ¹²⁸Ce. The value of quadrupole deformation parameter β₂ deduced from the measured lifetimes is in good agreement with the theoretical calculation using a cranking model based on a non-axially deformed Woods-Saxon potential.     

Identification of band structures in the 137La nucleus

High-spin states of ¹³⁷La have been investigated with the reaction ¹³⁰Te(¹¹B, 4n) at a beam energy of 50MeV. The level scheme of ¹³⁷La has been expanded with spin up to 33/2ℏ. Several new bands have been found in this nucleus. A band crossing in the band based on the 17/2^- level has been observed at a rotational frequency of ℏω ∼ 0.48MeV. From systematic comparison, this band crossing probably originates from the alignment of protons. One of the bands with strong M1 transitions is proposed as a collective oblate band ( γ ∼ -60^°).     

Non-yrast states of 132Ce polutated in β-decay

Non-yrast low spin states of the nucleus ¹³²Ce were studied by means of γ-spectroscopy following the β-decay of the ground and medium spin isomeric states of ¹³²Pr. The activity was produced with the reaction ¹¹⁷Sn(¹⁹F,4n) ¹³²Pr at the Cologne FN TANDEM accelerator. The γγ coincidences and singles spectra were measured with the OSIRIS cube spectrometer. The β-decay of ¹³²Pr populates states with spins up to 6ħ and excitation energies up to 4.4 MeV in ¹³²Ce. Besides ground and quasi-gamma bands, an excited band based on the 0₂⁺ state and many other low-lying states were observed. The γγ angular correlations were analyzed to assign spins and parities to the excited states, and to determine the multipolarities of the γ-transitions. We found dominant E2 transitions in the quasi-gamma band and from the quasi-gamma band to the ground band. The experimental data are compared with calculations using the Interacting Boson Model (IBM). Good agreement is reached in the vicinity of the O(6) limit.     

High-spin yrast states in Ce

Yrast states up to spin 18 have been identified in ¹³²Ce. The energies and spins of the levels suggest the existence of two fairly well-behaved collective bands. The results are compared with those obtained in the rare-earth deformed region.     

Simple model calculations of spin and quantized aligment for the A ∼ 60–90 superdeformed mass region

We have used a simple model based on the rotational energy formula E(I, K) to study the structure of the superdeformed (SD) mass region 60–90. The higher order inertial parameters A and B of such model were determined by using the Marquardt method of nonlinear least-squares routines to fit the proposed transition energies with their observed values. A good agreement between the calculated and corresponding experimental transition energies of the SD bands is obtained which supports our proposed model. In addition, the frequency dependence of the dynamic, θ⁽²⁾, and static, θ⁽¹⁾, moments of inertia is used to determine the lowest spin (I_f) and the K-value of the considered SD bands; namely, ⁵⁸Ni(b1), ⁵⁸Cu, ⁵⁹Cu(b1), ⁶¹Zn, ⁶²Zn, ⁶⁵Zn, ⁶⁸Zn, ⁸⁴Zr, ⁸⁶Zr(b1), ⁸⁸Mo(b1, b2, b3) and ⁸⁹Tc. As a result of the identity exist among some of the considered SD bands, we have studied the incremental alignment and also the angular momentum alignment.     

Evidence for the particle-plus-rotor model in133La

The beta decay of the 5.4-hour isomer of¹³³Ce to levels in¹³³La has been studied using mass separated sources; a portion of the¹³³La level scheme is presented. These experimental results are compared with calculations using an asymmetric particle-plus-rotor model. The good agreement between experiment and theory confirms the applicability of the particle-plus-rotor model with prolate deformation to the light lanthanum nuclei.     

Superfluid-to-normal phase transition in superdeformed bands

A semiclassically exact solution for the second inertial parameter B is found for the superfluid and normal phases. An interpolation between these limiting values shows that B changes sign in the transition region at the spin I _c that is critical for the rotational spectrum. A superfluid-to-normal transition reveals itself in a specific variation of B versus the spin I. Experimental data show the existence of a transition for superdeformed bands in the A～80, 130, and 150 mass regions and for some bands characterized by a normal deformation. A transition to the normal phase explains the extreme regularity of superdeformed bands.     

Half-life measurement of 133mCe with $ \gamma$ -spectrometry

In this paper we describe our experiment determining the half-life of ^133mCe . An activation-based nuclear-reaction cross-section measurement has been carried out for the ¹³⁰Ba(a \alpha, n)^133mCe reaction, in order to improve our knowledge of the astrophysical p-process. For the analysis of such a measurement, the precise knowledge of the decay half-life of the reaction product is desired. In the case of ^133mCe the literature half-life value has only been known with a high relative uncertainty. A measurement utilizing g \gamma -spectrometry has been carried out to refine the half-life of ^133mCe . As a result, the new recommended half-life is t _1/2 = (5.326±0.011) h. This value has been found to be consistent with the previous literature value, while its uncertainty has been reduced by more than a factor of 30.     

Observation of superdeformed bands in194Hg

Two rotational bands, with energy spacings characteristic of superdeformed shapes, have been observed following bombardment of¹⁵⁰Nd with⁴⁸Ca. The more intensively populated band consists of 18 transitions and is assigned to¹⁹⁴Hg. The depopulation of this band occurs around spin 10. The second band, consisting of at least 16 transitions, was populated less strongly and is tentatively assigned to¹⁹⁴Hg also. The lowest level in this band is assigned spin 8. The energy differences between transitions for both bands decrease from ～40 keV at low rotational frequencies to ～30 keV at the highest observed frequencies. The moments of inertia of the bands are similar to those of the two previously observed superdeformed bands in^191,192Hg. The similarities and differences of the four known bands in the mercury region are discussed.     

Structure of <Emphasis Type="Italic">A</Emphasis>∼130 nuclei in La-Ce region

The variety of shapes and structures, observed in light rare earth A ∼ 130 nuclei, have been discussed in view of different angular momentum coupling schemes and their interplay that comes into effect at high spin. The N = 79 and 80 isotopes in La-Ce region, produced via fusion evaporation reaction, have been studied using the Indian National Gamma Array (INGA) consisting of 18 clover HPGe detectors. Two nearly degenerate ΔI = 1 bands have been observed at high spin of ¹³⁷Ce and a triaxial deformation of γ = ±30° has been assigned to the bands, from the total Routhian surface (TRS) calculations. The high-spin candidates of the yrast band of ¹³⁸Ce show signature splitting both in energy and B(M1)/B(E2) values. The bandcrossing due to the alignment of a pair of h _11/2 proton particles has been conjectured at ℏω ∼ 0.3 MeV, from the single-particle Routhians obtained from TRS calculations. Lifetime measurements by Doppler shift attenuation method (DSAM) has been carried out and from the estimated reduced transition probability B(M1), the ΔI = 1 band in ¹³⁸Ce has been characterized as a magnetic rotation (MR) band. The rise in the values of B(M1), for the higher spin candidates of the band, has been conjectured as the reopening of a different shear at the top of the Band B1. The characteristic of the MR bands in A ∼ 130 region has been discussed in the light of a phenomenological calculation and compared to the MR bands in other mass regions.     

Magnetic rotation — past,present and future

Magnetic-dipole rotational (MR) bands were discovered about 15 years ago without any theoretical prediction in contrast to the super-deformed (SD) bands which were predicted long ago. First identification of a quasirotational structure as MR band occurred around 1992 although Kr isotopes probably have the first set of data having the signatures of MR bands as shown by us. Our first compilation of MR bands listed 120 MR bands in 56 nuclides which have now grown to more than 180 bands in 80 nuclides. We have observed new MR bands in the A = 130 mass region in ¹³⁷Pr, ¹³⁹Nd and ¹³⁵Ba nuclei. This led to the observation of the smallest MR bands in ¹³⁷Pr, multiple minima in the γ deformation in ¹³⁵Ba, coexistence of band structure based on these minima and band crossing of MR bands in A = 130 region. Some of these results have been reviewed in this paper along with theoretical calculations. There are still a number of questions related to MR bands which have not been fully resolved. The role of neutrons/protons in magnetic rotation still needs to be delineated. Do the MR bands follow the I(I + 1) behaviour? Are these structures as regular as normal rotational bands? How important is the existence of deformation for MR bands? We address some of these questions in this paper.     

Präzisions-Massenbestimmungen mit dem elektrischen Massenfilter

The construction of an electric quadrupole spectrometer for precision mass determinations in the regionA>130 is described. The hyperbola-shaped electrodes are formed by sets of wires. A method is discussed which reduces the measurement of a mass ratio to a measurement of the ratio of two resistors. In contrast to the conventional ‘peak matching’ technique, in this method the intensity ratio of both members of a dublett occurs as an additional parameter and has to be measured. For testing, measurements were done on Xe-isotopes. The mass ratios obtained are:¹³²Xe/¹³¹Xe=1.007 632 1 ±5,¹³⁴Xe/¹³²Xe=1.015 730. The intensity ratio of¹³²Xe/¹³¹Xe is 0.7872±0.0020. These values are in good agreement with the most accurate measurements of Nier's laboratory.     

Statistical binary decay of35Cl+24Mg at ≈ 8 MeV/nucleon

High spin rotational bands in ¹⁶² Lu and ¹⁶⁴ Lu have been studied through the ¹³⁹ La( ²⁸ Si,5n) and ¹³⁹ La( ²⁹⁽³⁰⁾ Si,4(5)n) reactions respectively. For both nuclei the yrast sequence which is associated with the πh _11/2 ?νi _13/2 configuration shows the signature inversion feature.     

Measurement of transition quadrupole moments of high-spin states in the N=74 isotones Pr, Ce and La

The Doppler-Shift Attenuation Method has been used to extract transition quadrupole moments of high-spin bands in the N=74 isotones ¹³³Pr, ¹³²Ce and ¹³¹La, produced in the ³⁷Cl + ¹⁰⁰Mo reaction. The results appear to be configuration dependent and, for ¹³³Pr and ¹³²Ce, the involvement of Ω=1/2 νh_9/2 and νf_7/2 intruder orbitals appears to enhance the collectivity at high spin (I>25 ).     

Identification of Bandhead Spin and Identical Bands for Odd-A Nuclei in $A\sim190$ Superdeformed Mass Region

The dynamical moment of inertia is estimated with its even-power expansion of the rotational frequency and in accordance we determine the intermediate spins of the superdeformed (SD) rotational bands. Using Marquardt method of nonlinear least-squares routines, we determine the expansion coefficients by fitting the proposed dynamical moment of inertia with its recent experimental data of the SD nuclei in the A=190 mass region. The comparison between our theoretical and available experimental data for the dynamic moment of inertia and spin shows good agreements. Also, we have calculated the static moment of inertia at three alternative values of spin. The value of spin at which the two moments of inertia are nearly equals is to be regarded as a bandhead spin of the corresponding band. These studies are carried out for eighteen bands of odd-A nuclei of the superdeformed region 190, namely ¹⁸⁹Hg(b1), ¹⁹¹Hg(b1, b2, b3, b4), ¹⁹³Hg(b2, b3, b5), ¹⁹⁵Hg(b1, b2, b3, b4), ¹⁹³Tl(b1, b2, b3, b5), ¹⁸⁹Tl(b1), and ¹⁹⁷Bi(b1). We also notice the occurrence of identical SD bands with near identical transition energies among the considered SD bands.