Μs Isomer Research Articles

High spin states inSm143

The high spin states of $^{143}\mathrm{Sm}$ have been studied by in-beam \ensuremath{\gamma}-spectroscopy following the reaction $^{130}\mathrm{Te}$($^{20}\mathrm{Ne}$,$7n$)$^{143}\mathrm{Sm}$ at ${E}_{\mathrm{lab}}=137$ MeV, using a Clover detector array. More than 50 new gamma transitions have been placed above the previously known ${J}^{\ensuremath{\pi}}=23/{2}^{\ensuremath{-}}$, 30 ms isomer at 2795 keV. The level scheme of $^{143}\mathrm{Sm}$ has been extended up to 12 MeV and spin-parity assignments have been made to most of the newly proposed level. Theoretical calculation with the relativistic mean field approach using blocked BCS method, has been performed. A sequence of levels connected by $M1$ transitions have been observed at an excitation energy \ensuremath{\sim}8.6 MeV. The sequence appears to be a magnetic rotational band from systematics.

Prediction and possible observation of an oblate shape isomer in 190W

Energy-surface calculations for nuclides in the neutron-rich 19074W116 region show consistently that the collective rotation of a deformed oblate shape is an energetically favoured mode, especially for angular momenta I>12ℏ. By comparing the calculations with existing experimental data, it is concluded that the reported t1/2∼1 ms isomer in 190W may be an oblate shape isomer.

Structure of odd–odd 136La at high spin

The high spin states in the N = 79 odd–odd 136La nucleus have been investigated by in-beam γ-spectroscopic techniques following the 130Te( 11B, 5 n) 136La reaction at E = 52 MeV using an array, consisting of eight Compton-suppressed clover germanium detectors. Thirty nine new γ rays have been assigned to 136La on the basis of γ ray singles and γγ-coincidence data. The level scheme of 136La has been extended above the known 115 ms isomer upto an excitation energy of 4.6 MeV and spin 18 ℏ. Thirty one new levels have been proposed and spin-parity assignments for most of the newly proposed levels have been made on the basis of the deduced asymmetry ratios and polarisation information for the de-exciting transitions. The observed positive parity yrast band has been compared with the theoretical calculation, done within the framework of particle rotor coupling model (PRM) where the two odd quasi-particles are coupled to an axially symmetric core. The level structure has been discussed in the light of the known systematics of the neighbouring N = 79 isotonic nuclei.

The $\pi h_{11/2}^{-1}\nu i_{13/2}^{-2}$ three-hole isomeric state and octupole core excitation in the 205 Tl nucleus

New high-spin states were identified in the 205Tl isotope produced in deep-inelastic heavy-ion reactions. The expected 29/2 + yrast state and 35/2- isomeric state with 235 ns half-life were located above the 2.6 μs isomer known from previous studies. Above this isomer a 7092 keV level was interpreted as a 41/2 + state arising from the coupling of the octupole vibration of the 208Pb core with the three-hole structure of the 35/2- isomer.

G-factors of isomeric states in the neutron-rich nuclei

We report the results from the first experiment to measure gyromagnetic factors of μs isomers in neutron-rich nuclei produced by intermediate-energy projectile-fragmentation reactions. The Time Dependent Perturbed Angular Distribution (TDPAD) method was applied in combination with the heavy-ion-gamma correlation technique. The nuclides in the vicinity of 68 Ni were produced and spin-oriented following the fragmentation of a 76 Ge, 61.4 MeV/u beam at GANIL. The results obtained, |g|(69m Cu) = 0.225(25) and |g|(67m Ni) = 0.125(6) provide another indication of the importance of proton excitation across the Z = 28 shell gap for the description of these states.

A new μs isomer in 136Sb produced in the projectile fission of 238U

The neutron-rich isotope 136Sb has been produced following the relativistic projectile fission of 238U in an experiment performed at the Fragment Separator at GSI, Darmstadt. Delayed γ-ray spectroscopy of the fission products has been performed after isotope separation. A new isomeric state in 136Sb has been populated, and its lifetime measured as T1/2 = 565(50) ns. Realistic and empirical shell-model calculations have been performed and are compared to the experimental observables.

Measurement of a strong atomic hyperfine field allowing the determination of nuclear g-factors in (sub)nanosecond states

An extension of the time-integrated atomic decoupling technique to measure g-factors of (sub)nanosecond isomers and/or the magnetic hyperfine field induced by highly excited atomic electrons on nuclei recoiling into vacuum is discussed. A high average field B hf =1080 −175 +270 T and an average atomic spin J=2.7(2) is deduced using the known magnetic moment of a 4.05(7) μs isomer in 69Ge. Such high magnetic fields allow g-factor measurements of (sub)nanosecond states. Ab initio calculations show that the combination of a high average magnetic hyperfine field and a high average atomic spin is only possible if a considerable fraction of the ions is in a metastable excited state.

Recoil-isomer tagging near the mass 140 proton drip line

This contribution discusses the recoil-isomer tagging technique and its application to study isomeric states near the mass 140 proton drip line. The recoiling nuclei from a fusion-evapn. reaction were implanted into a silicon detector at the focal plane of a gas-filled separator, where prompt and delayed g-ray transitions were correlated across isomeric states. New states were established upon a known 15 ms isomer in 142Tb and the feeding and decay of a new 0.5(2)ms isomeric state was established in 144Ho. This measurement represents the first observation of excited states in 144Ho. [on SciFinder (R)]

On the nature of the 17 μs isomer of the 133Sb valence nucleus

The decay of the 17 μs isomer of 133Sb was re-investigated experimentally. It was produced by thermal neutron induced fission of 241Pu. Its detection is based on time correlation between fission fragments selected by the LOHENGRIN spectrometer at ILL (Grenoble), and the γ-rays, and conversion electrons from the isomer. The interpretation of the level scheme is based on shell model calculations, where empirical two-body matrix elements were employed. The good agreement between theory and experiment suggests that the isomer is the 21/2+ member of the 2p-1h πg7/2ν(f7/2h11/2−1) configuration.

On the nature of the 17 μs isomer of the

On the nature of the 17 μs isomer of the

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.

A new isomer in 125La

Levels in 125La have been studied via β+/EC decay of on-line mass-separated 125Ce using the HIGISOL technique. A new (390 ± 40) ms isomer is definitely attributed to 125La by conversion electron measurements of the 107 keV E3 isomeric transition.

High spin states in doubly-odd142Pm

The high spin states in the N=81 odd-odd ${}^{142}\mathrm{Pm}$ have been investigated by in-beam \ensuremath{\gamma}-spectroscopy following the reaction ${}^{133}\mathrm{Cs}{(}^{13}\mathrm{C}{,4n)}^{142}\mathrm{Pm}$ at E=63 MeV and using a gamma detector array. Thirty new $\ensuremath{\gamma}$ rays have been assigned to ${}^{142}\mathrm{Pm}$ on the basis of the $\ensuremath{\gamma}$-ray singles and $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidence data. The level scheme of ${}^{142}\mathrm{Pm}$ has been extended considerably above the known 2 ms isomer at 883.0 keV and spin-parity assignments for several levels have been made. The proposed level structure is discussed in the light of available data for the neighboring odd-odd isotones.

High spin states above the α-decaying isomer in 211Po

Prompt and delayed γ-rays in nuclei of the 208Pb region produced in 450 MeV 76Ge +208Pb collisions have been studied at GASP. Yrast states above the α-decaying isomer in 211Po have been located including a 0.25 μs 31/2− isomer at 2135 keV and a 2 μs isomer at 4874 keV.

C4898d50: The Two-Proton-Hole Spectrum inS50100n50

Excited states in 98Cd, two proton holes from 100Sn, were identified and studied for the first time, using in-beam spectroscopy with highly selective ancillary detectors. The structure of the (πg9/2)−2 two-proton-hole spectrum below a T1/2=0.48(16)μs isomer is deduced and compared to shell-model predictions. A tentative Iπ=(8+) assignment, as suggested by systematics, yields a strongly reduced B(E2,8+→6+)=0.44(−10+20)W.u., corresponding to an effective proton charge of eπ=0.85(−10+20)e, which is at variance with existing theoretical predictions.Received 18 December 1996DOI:https://doi.org/10.1103/PhysRevLett.79.2415©1997 American Physical Society

A new method for isomer lifetime measurement

We report on the application of a new multi-parameter data acquisition system to lifetime measurement of isomers in nuclear cascades. Decay curves obtained with the new system are largely free of distortion that are often present in results obtained by conventional methods. Minimal electronics are required and data acquisition times are much shorter with the new method, especially for isomers with longer lifetimes. Virtues of this method are demonstrated by studying the decay of the 9 μs isomer of 67Zn at 93-keV excitation energy.

Spin-lattice relaxation of Ra in Tl and g factor of the 213Ram, tau =2.1 ms isomer.

The nuclear spin-lattice relaxation of Ra in Tl is found to be mainly due to the magnetic dipole interaction of the nuclear spins with the conduction electrons in the Tl metal. The influence of magnetic spin-lattice relaxation on an initially oriented system of nuclear spins has been calculated as a function of the lattice temperature. Measurements of the time-integrated anisotropy as a function of the temperature permit to extract the Korringa constant for $^{213}\mathrm{Ra}^{\mathit{m}}$Tl and $^{214}\mathrm{Ra}^{\mathit{m}}$Tl. The Korringa relation has been used to derive the Knight shift K(RaTl) and to obtain the g factor for the $^{213}\mathrm{Ra}$ isomer.

A new sequence of high-spin states built on the 17/2+ isomer in 85Kr

High-spin states in 85Kr have been studied via in-beam spectroscopy by bombarding a 82Se target with 32 MeV 7Li ions. Since 85Kr is only formed with a small relative cross section proton-γ—γ coincidence techniques have been applied to enhance the γ rays of 85Kr, even with respect to those of 86Kr, in the measurements. A new sequence of high-spin states with excitation energies up to 4.8 MeV and tentative spins up to (23/2) has been established on top of the 17/2+ Μs isomer. A tentative assignment of the configuration vg 9 2/−1 π(g9/2 p 3 2/−1 or f 5 2/−1 ) to the new levels is proposed.

Identification of the rare neutron-rich isotope 117Rh.

In this paper we wish to report on the first observation of the beta decay of the very neutron-rich nucleus $^{117}\mathrm{Rh}$. It was produced via 23 MeV proton induced fission of $^{238}\mathrm{U}$ using the ion guide set-up of the LISOL separator. A beta half-life of 0.44\ifmmode\pm\else\textpm\fi{}0.04 s was measured for this nucleus from the decay of the beta-coincident K x rays of Pd. The half-lives of neutron-rich Rh isotopes are compared with the newest model calculations. Three gamma rays of 34.6, 131.7, and 481.6 keV were found to be associated with the decay of $^{117}\mathrm{Rh}$. Its proposed beta decay scheme and the decay of the recently discovered 19 ms isomer in $^{117}\mathrm{Pd}$ imply spin and parity of 11/${2}^{\mathrm{\ensuremath{-}}}$ for the isomer fed directly in fission.

A 35 ?s isomer in the exoticN=83 Nucleus154Lu

Measurements of γ-rays from mass analyzed nuclear recoils produced in the102Pd +54Fe reaction at 245MeV have allowed us to characterize the decay of a 35 μs isomer in154Lu. The rates of E2 transitions de-exciting isomeric levels in proton-rich N=82, 83 isotones are discussed.