Levels of146Ce studied through the decay of high-spin isomer of146La

The decay of 10.0 s high-spin isomer of¹⁴⁶La to levels of¹⁴⁶Ce has been studied using the on-line isotope separator KUR-ISOL. Gamma-ray singles,γ -γ coincidence and conversion-electron spectra have been measured. A level scheme containing 90 levels and 206γ-ray transitions has been constructed for¹⁴⁶Ce, populated in the decay of the high-spin isomer of¹⁴⁶La. Among these, 39 levels are reported for the first time. Spins and parities for some levels are proposed on the basis ofγ-decay mode, logft values and conversion-electron measurements. The band structure of the low-lying levels in¹⁴⁶Ce is discussed.     

Tentative level diagram of146Pm below 1.1 MeV

The level scheme of the doubly odd nucleus¹⁴⁶Pm was investigated by means of in-beam spectroscopy. The¹⁴⁶Nd(p, n) reaction in the 3.5–8 MeV proton energy interval on enriched targets has been used to populate the exited states of¹⁴⁶Pm. High resolutionγ-ray spectra using Ge(Li) and hyperpure Ge detectors and conversion electrons with a mini-orange spectrometer were measured. Withγ-exitation functions andnγ-coincidences usingnγ-discriminated NE231 neutron detectors transitions in¹⁴⁶Pm were identified,γγ-coincidences gave information aboutγ-cascades. With these data a level scheme of 38 levels below 1.1 MeV exitation energy has been deduced including 73 transitions. For 12 transitions experimental conversion coefficients have been evaluated, which agree with the expected values forM1/E2-transitions.     

The decay scheme of the 3-s Isomer of100Nb and the properties of levels in100Mo

Theβ ^? decay of the longer-lived isomer in¹⁰⁰Nb has been studied at the fission-product separator JOSEF. Measurements ofγ-ray singles spectra, ofγ-γ coincidences and ofγ-γ angular correlations have been performed. A value oft _1/2=2.99(11)s has been determined for the isomer which probably hasI ^π=4⁺ or 5⁺. A scheme of the levels of¹⁰⁰Mo which are populated in the decay of this isomer has been established. Information on the spins of several states of¹⁰⁰Mo has been obtained. Thus,I=0 levels have been identified at 1,505, 2,038 and 2,087 keV. The mixing ratios have been determined for the 2₂ ⁺→2₁ ⁺ and 2₃ ⁺→2₁ ⁺ transitions. The results provide evidence for a vibrational structure of¹⁰⁰Mo with separate bands based on the ground state and on the first excited 0⁺ level.     

β + ratio andβ-delayedγ-decay of146Eu

The positron decay of¹⁴⁶Eu was investigated, firstly to derive for the allowed transition to the 2046 keV state in¹⁴⁶Sm the electron capture to positron decay ratio. The experimental valueEC/β ⁺=43.7(42) is found to be in agreement within the respective error intervals with the ones calculated from the formalism of allowed decay using the recentQ-values of¹⁴⁶Eu. Further on, theγ-decay properties of¹⁴⁶Eu have been reinvestigated with emphasis on implied modifications of the hitherto accepted decay scheme: 42 new levels and 33 newγ-transitions were placed in the revised level scheme, 12 of the previously reported levels were deleted. The level distribution of¹⁴⁶Sm is discussed within a statistical model. The indication for a non-statisticalβ-strength function is observed.     

The decay of the 560 ns Isomer at 8.6 MeV in 64 147 Gd83

In (α,xn) and (¹²C, 5n) in-beamγ-ray experiments with pulsed beams the decay of the 560 ns high-spin isomer in¹⁴⁷Gd has been investigated. Extensive coincidence measurements identified in the isomeric decay more than eightyγ-rays which almost all were placed in the level scheme. Of crucial importance for establishing the highly complex decay was the comparison of data from the different reactions and the identification of transitions which bypass the 27 ns isomer at 3.58 MeV. Our data determine the excitation of the 560 ns isomer as 8.588 MeV and suggest 47/2 as its most probable spin.     

Lifetimes of a dipole cascade in 192Hg

The β-spectrum of the 3^?-2⁺ transition in the decay of¹⁴⁶Pm has been investigated with a 4π-Si(Li)-semiconductor spectrometer in a β-γ-coincidence experiment for the first time. The shape factor has been determined: C(W)=1?0.394W}-0.275/W+0.044 W². The spin and parity of the ground state of¹⁴⁶Pm can be determined to be 3^?. The shape of this non-allowed spectrum indicates the existence of the “cancellation” or “selection rule” effect.     

Particle-hole multiplets in146Gd from in-beam studies of non-yrast levels

Non-yrast levels of¹⁴⁶Gd have been investigated by in-beamγ-ray and conversion electron spectroscopy following the¹⁴⁴Sm(α, 2n) reaction at 25.7 MeV, an energy which was determined to provide optimum population of levels above the yrast line. The detailed¹⁴⁶Gd level scheme includes twenty-one newly identified levels, many of which can be characterized in terms of specific proton particle-hole configurations. Several twoparticle-twohole states involving the 3^? phonon have also been identified.     

The decay of uranium shape isomers investigated by photonuclear reactions

The half-life of the ²³⁸U shape isomer and its yield ratio in a (γ, γ') reaction have been measured by pulsed beam techniques at a bremsstrahlung endpoint energy of 12 MeV. From the results $\text{(T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 146 ± 22}\text{ns}\text{, Y}{}_{\mathrm{<mtext>iso</mtext>}}\text{/Y}{}_{\mathrm{<mtext>pr</mtext>}}\text{= (6.6 ± 1.0) × 10}{}^{\mathrm{?6}}\text{)}$ the isomeric fission cross section has been deduced. Combining this information with the results of a previous ²³⁸U(γ, xnγ) study, an upper limit for the branching ratio Γ_γ/Γ_f|II < 13 for the decay of ^238mU can be obtained. The decay properties of the ²³⁶U and ²³⁸U shape isomers are discussed.     

Beta-Gamma-Winkelkorrelation bei146Pm

A measurement of theβ-γ directional correlationω(W, Θ) of the 3^?(β)2⁺(γ)0⁺ decay of¹⁴⁶Pm is described. Spin and parity of the ground state of¹⁴⁶Pm are found to be 3^?. A set of matrix elementsY=0.94;x=0.20;u=0.20;z=1, which is chosen to fit the experimental results for ω(W, Θ) and which is in agreement with the CVC theory, indicates aK-selection rule effect for the 0,795 MeV beta transition of¹⁴⁶Pm.     

Gamma deexcitation of the 180m Ta isomer

Vibrational states built on the K ^π = 9^? isomer and on the ground state (K ^π = 1⁺) in ¹⁸⁰Ta are calculated within the quasiparticle-phonon nuclear model using the ¹⁷⁸Hf nucleus as a core. A procedure for calculating the rates of K-allowed γ-ray transitions from vibrational states built on the isomer to those built on the ground state is presented. The probabilities of two-step processes consisting of a dipole excitation of the isomer and successive E1 and E2 transitions from them to vibrational states built on the ground state of the ¹⁸⁰Ta nucleus are calculated. Two-step transitions from the isomer to vibrational states below 2.7 MeV and to the vibrational states built on the ground state appear to be very weak. There are many E1 transitions from the vibrational states built on the isomer to the vibrational states built on the ground state. They are weak and cannot be responsible for the strong deexcitation of ^180m Ta in the relevant (γ, γ′) reaction. A decisive role is played by collective E2 transitions from dipole excitations in several excitation energy intervals ranging between 2.7 and 4.0 MeV. These highly intense K-allowed two-step γ-ray transitions can be responsible for the strong deexcitation of the ^180m Ta state in the (γ, γ′) reactions.     

A 45 ns 8+ isomer in the doubly odd150Eu nucleus

In the doubly odd ₆₃ ¹⁵⁰ Eu⁸⁷ nucleus a 45 ns 8⁺ isomer at 589 keV excitation has been identified through (p, 3n) in beamγ ande ^? measurements. The low lying negative parity levels populated in its decay show great similarity to analogous states in the lighter odd-odd Eu neighbours suggesting a spherical shape for¹⁵⁰Eu. A spherical shape is also proposed for the isomer which is assigned as (πh _11/2 vf ₇ ^2/?3 )8⁺ state analogous to the 9⁺ isomers known in¹⁴⁸Eu and¹⁴⁶Eu. The spin change is attributed to the crossing of the half-filledf _7/2 neutron shell atN=86.     

Structure of the doubly odd nucleus 180Ta: Description of 23 bands

The structure of the doubly-odd nucleus ¹⁸⁰Ta has been studied by γ–γ coincidence measurements with a DC beam at 52 and 57 MeV and time-correlated γ–γ coincidence measurements with a pulsed beam at 55 MeV via the ¹⁷⁶Yb(¹¹B, α3n)¹⁸⁰Ta reaction. In all measurements, γ-rays were detected in coincidence with charged particles. In the time-correlated γ–γ coincidence measurements with a pulsed ¹¹B beam, three rotational bands and one octupole vibrational band have been identified above the I^π=15⁻ T_1/2=30 μs isomer. The configuration of three bands built on 8⁺ states has been discussed by means of three-band mixing calculations. BCS calculations with blocking have been used in support of configuration assignment of four- and six-quasiparticle structures. Totally, 19 rotational bands, one β-, one γ- and two octupole-vibrational bands, plus one intrinsic state have been identified with two-, four- and six-quasiparticle configurations. The K values of these bands range from 0 to 19. The K-forbidden transition rates are discussed on the basis of mixing between states with widely different K-values. The BBCS calculations predict a K^π=22⁻ isomer not identified experimentally in this nor in previous works.A search for specific intermediate states which could explain the transformation from K^π=9⁻ to 1⁺ during the astrophysical s- and r- processes was negative.     

Beta delayed proton emission from the 14s 21/2+ spin gap isomer in95Pd

The residual activities of the projectile-target system⁴⁰Ca→⁵⁸Ni have been investigated with gamma and proton multi spectrum analyses,γγ andpγ coincidences. Aβ decaying high-spin isomer in⁹⁵Pd withJ ^π=(21/2⁺), a half-life of 14±1 s and an excitation energy of about 2 MeV has been identified. It has been found that⁹⁵Pd ^m is aβ delayed proton precursor. The totalβ branching to proton emitting states has been determined to be (0.74±0.19)·10^?2. It has been observed that the final state in⁹⁴Ru, populated after proton emission, is dominantly the 8⁺ state. A decay scheme of⁹⁵Pd ^m has been derived.     

Subshell closure effects on the collectivity of 36 88 Kr52 and the beta decay of88Br to levels in88Kr

The level structure of⁸⁸Kr has been investigated by measurements on chemically separated bromine samples. A total of 146γ-rays have been assigned to the decay of⁸⁸Br, and a level scheme with 58 levels is proposed. The collectivity of⁸⁸Kr has been investigated within the framework of the Interacting Boson Approximation (IBA-2 model). Comparison of our detailedγ-ray data and calculations have led to the establishment of a protonhole boson desciption rather than protonparticle nature. This supports recent works establishingZ=40 as a major subshell closure.     

Low-lying excited states of106Ag studied with the103Rh (α,nγ)106Ag and104Pd (α,pnγ)106Ag Reactions

The level scheme of¹⁰⁶Ag has been studied using the¹⁰³Rh(α,nγ)¹⁰⁶Ag and¹⁰⁴Pd(α,pnγ)¹⁰⁶Ag Reactions. The experimental information is taken fromγ-ray coincidence data using Ge(Li)-Ge(Li) and HPGe-planar Ge(Li) configurations andγ-ray angular distributions. With these measurements 126 γ rays have been assigned to¹⁰⁶Ag with 116 deexciting 78 states below 2.26 MeV in excitation. The location of the 8.4-day 6⁺ isomer is established at 89.63±0.09 keV. Many of the low-lying states are interpreted in terms of a slightly deformed rotor model.     

Levels in154Eu populated by thermal neutron capture

The level scheme of¹⁵⁴Eu has been investigated by means of thermal neutron captureγ-rays and conversion electrons. The high energyγ-ray spectrum from thermal neutron capture in enriched¹⁵³Eu has been studied in the energy range of 5700 to 6500 keV. Low energyγ radiation has been observed with Ge(Li) and Si(Li) detectors from 5 to 300 keV and conversion electrons have been measured from 15 to 300 keV. Low energy (n, γγ) coincidences and half lives of transitions have been measured. The data, combined with three very recent studies of the 8^? isomer decay in¹⁵⁴Eu has led to the construction of a level scheme with 12 excited levels. Nuclear Reaction¹⁵³Eu(n, γ),E _n =thermal, measuredE _γ ,I _γ ,E _ce ,I _ce ,γγ-coincidence, halflives,¹⁵⁴Eu deduced levels.     

Theg-factor of the 8+ isomer of142Eu

Theg-factor of the 8⁺ isomer of¹⁴²Eu with mean lifeτ=9 ns, has been measured by the time-differential perturbedγ ray angular distribution (TDPAD) method. The 8⁺ isomer was populated with the reaction¹¹⁴Cd(³²S,p3n)¹⁴²Eu at 155 MeV. The obtained valueg(8⁺)=0.51(3) agrees with shell model calculations using effective single-particle moments taken from neighbouring nuclei. A main configurationπh_11/2?(vh _11/2)^?1 has been confirmed for the 8⁺ isomer.     

On theβ − decay of the 2s isomer in98Y and the existence of an intruder band in98Zr

The γ radiation from the ß^? decay of the high-spin isomer in⁹⁸Y has been studied at the separator JOSEF. A main goal was to get insight into the spins of levels in⁹⁸Zr which have been interpreted as members of an intruder band based on the 0₂ ⁺ state at 854 keV. The measuredγ-γ angular-correlations lead to the assignment of spins of 4 and 3 ? to the 2491 and 1844 keV levels, respectively, and contradict their interpretation as the 6⁺ and 4⁺ states of the proposed band. For the 2.0s isomer of⁹⁸Y, the ß{?}-decay properties suggest I=5 with a major configuration [πg_9/2,νs_1/2(g² _7/2)₀].     

Yields and cross sections of the 241Am(γ, n)240mfAm and 243Am(γ, n)242mf-Am reactions in the E1 giant resonance region

The ratio of delayed to prompt fission yields has been measured for ²⁴¹Am and ²⁴³Am samples irradiated by a bremsstrahlung photon pulsed beam over the energy range E_γmax = 10–80 MeV. The relative probabilities of ^240mfAm and ^242mfAm isomer production and the cross sections of the ²⁴¹Am(γ, n)^240mfAm and ^243Am(γ, n)^242mfAm reactions were deduced from the yields measured in the E1 giant resonance region.