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.     

Structure of 74Ge from the 72Ge(t,p) reaction

The reaction ⁷²Ge(t, p)⁷⁴Ge has been investigated with a 15 MeV triton beam. Fifty energy levels of ⁷⁴Ge were identified up to about 4.9 MeV excitation, eighteen of which were previously unreported. Angular distributions were measured and compared with DWBA calculations. Two low-lying states at 1.913 and 2.164 MeV have been assigned as J^π = 0⁺, corresponding to the 0₃⁺ and 0₄⁺ states in ⁷⁴Ge. The 4₂⁺ state has been located at 2.674 MeV, and the 2₄⁺ at 2.836 MeV. Many additional spin and parity assignments have been made. The ⁷⁴Ge nucleus shows a considerably different structure of 0⁺ states compared with the neighboring ⁷⁶Ge and ⁷⁸Ge nuclei, perhaps further evidence for the shape transition suggested recently for the Ge isotopes.     

Shape coexistence in the odd-odd 186Au nucleus

Low-spin states of ¹⁸⁶Au have been studied from the β⁺/EC decay of ¹⁸⁶Hg using the ISOCELE facility. Precise conversion-electron measurements were performed with a semicircular magnetic spectrograph. The ¹⁸⁶Au level scheme has been established with spin and parity assignments deduced from transition multipolarities and log $\text{?t}$ values. It shows two separate groups of levels which could be interpreted as due to shape coexistence: prolate deformation for the first low-lying states, and oblate deformation for the 251.5 keV (2^?) and 363.6 keV (1 ⁺) states.     

The width of the 5.11 MeV state in 10B and isovector parity mixing

We review estimates for effects of parity mixing on the α-capture of vector polarized ⁶Li to the 5.16 MeV, 2⁺, T = 1 state in ¹⁰B. The cross section depends on the ⁶Li polarization direction because of isovector parity mixing with the 5.11 MeV, 2^?, T = 0 state. The effect is enhanced due to isospin conservation. The α-width of the 5.11 MeV state, an important parameter for calculating the enhancement, has been measured to be 0.98 ± 0.07 keV. The consequences of parity mixing are reevaluated using best available values for the relevant parameters.     

On the nature of the superband in156Dy

Superbands, responsible for the backbending in¹⁵⁶Dy and other N=90 and N=88 nuclei, are proposed to be alignedn(i_13/2)² bands, whereas it is argued that the recently discovered positive parity band in¹⁵⁶Dy withI ^π= (2⁺) up to 10⁺ members does not constitute the low spin extension of the superband.     

A partial wave analysis of the (3π)0 system from the charge exchange reaction π+n→π+π−πop AT 4 GeV/c

From a partial wave analysis of the (3π)^o state in the charge exchange reaction π⁺n→π⁺π^?π^op, we observe strong unnatural parity as well as natural parity production. The observed strong unnatural parity states are identified with well-established resonances. The unnatural parity production is consistent with Reggeized Deck model predictions, with the exception of the I = 1, JP = 1⁺ state. Here there is no evidence for A₁ production at ～1.1 GeV, but the data could support resonance production at higher masses.     

Low-spin states of153Gd observed in the decay of153Tb

Level structure of the 89-neutron nucleus¹⁵³Gd has been investigated by studying theEC-decay of isotope-separated¹⁵³Tb sources with several semiconductor detectors. In addition to singles gamma and electron spectra,γ-γ ande ^?-γ coincidences were investigated by using Ge(Li) and Si(Li) spectrometers and a high-capacity two-parameter recording system. In all, 191γ-rays are assigned to the decay of the 2.4d¹⁵³Tb. The proposed level scheme of¹⁵³Gd containing most of the observed transitions shows a very high density of low-spin states (45 states below 1.5MeV). Spin and/or parity assignments based mainly on coincidence data and measured transition multipolarities are proposed for a majority of these states. Nilsson model classifications of some levels are discussed. On the basis of logf t values the spin and parity of the ground state of¹⁵³Tb are suggested to be 3/2⁺ or 5/2⁺.     

The 2+-2+ transition of 879 keV in160Dy investigated by electron-gamma directional correlation

e-γ directional correlation measurements of 2⁺(879 keV)2⁺(87 keV)0⁺ cascade in¹⁶⁰Dy have been made and the magnitude of electric monopole to quadrapole mixing ratio for 879 keV transition was found to beq _k =?0.03(10) for λ=0 (λ-according to Hager-Saltzer definition).     

Electroexcitation of high spin states in 208Pb

The formfactors for the electroexcitation of the collective states of ²⁰⁸Pb have been calculated within the Model of Separable Residual Interaction (MSI); the results for the even parity states up to J^π = 10⁺ agree nicely with recent measurements. It turns out, that the energies of the lowest collective states of positive parity follow rather closely a J(J + 1) law.     

Directional correlations of gamma cascades in153Gd

TheEC-decay of¹⁵³Tb to the levels of¹⁵³Gd has been studied in singles and coincidence mode using high resolution x-ray andγ-ray Ge(Li) detectors. The results, in general, are in agreement with the recent findings of Tuurnalaet al. showing a very high density of low-spin states in¹⁵³Gd. The results of theγγ directional correlation experiment using two Ge(Li) detectors together with the I.C.C. data have been used in assigning the spin and parity of 5/2^?, 5/2^?, 3/2^?, 3/2⁺, 5/2⁺, 3/2⁺ and 3/2⁺ to the 41.6, 109.8, 129.1, 212.0, 303.5, 945.6 and 1102.0 keV states respectively. Multipolarity assignments to majority of theγ-transitions have been made from the I.C.C. data obtained through the knowledge of ourγ-ray intensities and the published conversion-electron intensities. From the multipole characters of theγ-transitions, parity assignments have been made to seven states in¹⁵³Gd. Our results have been discussed and compared with that of Tuurnalaet al.     

Exotic clustering in 232,234,236,238U

We account for the energies and electromagnetic E2 transitions of the J^π = 0⁺, 2⁺, 4⁺ … ground state bands of ^{232,234,236,238}U, using a model in which these bands are treated in terms of a ²⁴Ne cluster orbiting the appropriate Pb core. The cluster-core potential parameters used are identical to those employed in a previous study of ^222,224,226Ra. In addition to the simultaneous fitting of energies and B(E2) strengths, we also obtain good agreement with the measured half-life for the ²⁴Ne decay of the 0⁺ ground state of ²³²U and ²³⁴U as well as with the measured B(E4 ↑; 0⁺ → 4⁺) transition strengths in ^234,236U. We find that a small parity dependence of the cluster-core potential is required in order to give a good account of the energies of the J^π = 1⁻, 3⁻, 5⁻,… states of the lowest negative parity band of ^{232,234,236,238}U, and of the B(E3 ↑; 0⁺ → 3⁻) strengths in ^234,236,238U.     

States in95Mo and99Mo populated in the (3He, α) reaction

The (³He,α) reaction on⁹⁶Mo and¹⁰⁰Mo targets has been studied at a bombarding energy of 18 MeV. Thel _n transfer assignments have been made on the basis of angular distribution patterns and on an analysis of the ratios of the experimental and theoretical cross-sections of (³He,α) and (d, t) reactions data leading to the same final states. New states are observed in⁹⁵Mo at 3373 keV (9/2⁺); spin and parity assignments are made to levels in⁹⁹Mo at 1621 keV 7/2⁺ (9/2⁺), 1778 keV (5/2^?) and 2078 keV (11/2^?).     

A limit parity admixtures in the atomic 2s → 1s transitions

From a measurement of the intensity of the atomic 2s→1s transition in Tm (Z = 69) a limit of F² < 10^?8 was derived for the square of the parity admixing amplitude in the 2s state, not inconsistent with predictions of neutral current models.     

Angular distribution measurements of gamma-rays from the22Ne(p, γ)23Na reaction

Angular distribution measurements of gamma-rays from the²²Ne(p, γ)²³Na reaction on theE _p =897, 1006, 1091 and 1278 keV resonances have been made. Spin and parity assignments for several bound states are presented together with multipole mixing ratios for transitions from resonance and bound states. The level at 6617 keV (7/2⁺) is proposed to be a member of the rotational band based on the Nilsson orbit 5(K ^π=5/2⁺).     

Multipolarity determination fromL x-ray spectra in the decays of227Th,243Am,and249Cf

A new method to determine the multipolarity of a converted γ-transition from itsL x-ray spectrum has been extended by a coincidence technique and applied in the complex decays of²²⁷Th,²⁴³Am, and²⁴⁹Cf. TheL x-ray spectra of four low energy transitions have been measured in coincidence with cascading high energy γ-rays and theirM1-E2 mixing ratios obtained by comparison with calculatedL x-ray line intensities. The following results were obtained: for the 3/2⁺→l/2⁺ ground-state transition in²²³Ra, an admixture of (74±12)%E2, for the 7/2⁺→5/2⁺ ground-state transition in²³⁹Np, less than 30%E2, for the 9/2⁺→7/2⁺ ground-state transition in²⁴⁵Cm, (63±10)%E2, and for the 11/2^?→ 9/2^? transition in the third rotational band in²⁴⁵Cm, (32±10)%E2.     

High spin states in97Rh

High spin states in⁹⁷Rh were excited via the⁹⁶Ru (α,2np) reaction at 45 MeV. As a main finding we have observed a positive parity band, built on the 9/2⁺ ground state, which depopulated levels at 3,550.7 (25/2⁺), 3,259.1 (23/2⁺), 2,895.1 (23/2⁺), 1,961.3 (19/2⁺), 1,553.1 (17/2⁺) and 857.1 (13/2⁺). Also we have excited levels at 3,055.8 (21/2), 2,225.4 (17/2) and 1,463.5 (15/2), which most likely are negative parity states.     

Decay of three-particle high spin states in85Y

High spin states in⁸⁵Y have been excited in the reaction⁷²Ge(¹⁶O,p2n) at 48–60 MeV beam energy. From measurements ofnγ andγγ coincidences, excitation functions and angular distributions, the high spin spectrum of⁸⁵Y has been established up to 5.4 MeV excitation energy and spinI≦29/2. Lifetimes or limits of lifetimes have been determined for 14 levels via the recoil distance and Doppler shift attenuation method. Theg _9/2 decoupled proton band is found to backbend atI ^π=17/2⁺ as also seen in the reduction of the 17/2⁺→13/2⁺ and 21/2⁺→17/2⁺ E2 transition strengths. The lowest (3qp) positive parity band has predominantly aν ² g _9/2×πg _9/2 structure. The observed negative parity yrast states in the spin range 15/2^?≦I≦29/2^? are most probably of (g _9/2)² ×(f _5/2,p _1/2) (3qp) nature as suggested by a comparison of the⁸⁴Sr and⁸⁵Y level structures and electromagnetic transition strengths.     

Structure of 14C from 12C(t,p)

The reaction ¹²C(t, p)¹⁴C has been investigated with an 18 MeV triton beam. Twenty energy levels of ¹⁴C were identified up to 13 MeV excitation. Angular distributions were measured and compared with DWBA calculations. A previously unreported 0⁺ level at 9.75 MeV was observed; it undoubtedly corresponds to the second predominantly sd shell 0⁺ state in ¹⁴C. Additional spin and parity assignments have been made in the present work: 9.81 MeV, (1^?); 10.43 MeV, 2⁺; 10.50 MeV, (3^?); 10.74 MeV, 4⁺; 11.40 MeV, 1^?; 11.67 MeV, (1^?); 11.73 MeV, (5^?); 12.58 MeV, (2⁺, 3^?); 12.87 MeV. 2⁺, 3^?; and 12.96 MeV, (1^?); none of which had a definite spin and parity assignment previously. Our results confirm the previous information on the level structure of ¹⁴C below 8.5 MeV. The cross section for the unnatural parity state at 7.34 MeV, J^π = 2^?, is well reproduced by a two-step reaction calculation. The results are compared with the predictions of a weak coupling model.     

Spin assignment of the 8.555 MeV state in28Si

Angular correlations between the gamma rays following the decay of the 8.555 MeV state in²⁸Si, known to have natural parity, were measured. The spin assignment of this state, found in this experiment, isJ ^π=6⁺. Energy sequence of the lowestJ ^π=2⁺, 4⁺ and 6⁺ states in²⁸Si compares well with the energy sequence of the ground state rotational bands in²⁰Ne and²⁴Mg.     

Yrast levels of 220Ra populated in the 208Pb(14C, 2n) reaction

Yrast states in the nucleus ²²⁰Ra were studied by means of the ²⁰⁸Pb(¹⁴C, 2n) reaction at 61 and 64 MeV. A staggering sequence of levels of positive and negative parity has been observed up to spin and parity I^π = 16⁺ (18 ⁺) and from I^π = 5^? to I^π = 17^?, respectively. These states are connected by strong E1 transitions competing with the stretched E2 transitions, the $\text{B(}\text{E}\text{1)}\text{B(}\text{E}\text{2)}$ ratio being ~ 10 ^?6 fm^?2. The ratio of the excitation energy of the 4⁺ state to that of the 2⁺ state is close to the vibrational limit. The moment of inertia associated with the negative-parity yrast states is slightly increasing with the rotational frequency ω. It is considerably higher than that of the positive-parity states at lower spins, the difference decreasing monotonically with increasing ω. The data are discussed with reference to the octupole vibrational picture as well as to the results of recent models predicting reflection-asymmetric shapes in the Ra-Th region.