The role of the shape driving neutron orbital in 108Cd

Abstract The nucleus 108Cd has been studied using a heavy-ion reaction and the NORDBALL multi-detector array. The yrast band has been extended to Ip = 24+, and nine quasi-rotational side bands have been identified. The n h 11 2 negative-parity orbital is found to play a dominant role both in the low-spin as well as in the high-spin structure of 108Cd. The first band crossing in the yrast band is caused by the h 11 2 neutrons. The 10+ state of the aligned n( h 11 2 ) 2 configuration decays strongly into a low-lying low-spin intruder-like positive-parity band. It is suggested that this intruder structure is dominated by a non-aligned n( h 11 2 ) 2 configuration. For the first time in this mas…

The distribution of the rotational transition strength in warm nuclei studied through γ-ray correlations

Abstract The study of damping of rotational motion applying te rotational plane mapping (RPM) method is presented and discussed. The aim of this technique is to extract the distribution of the rotational transition strength from an analysis of the shape of the “central valley” of two- and three-dimensional γ-ray spectra. The method is applied to a triple γ-coincidence data set of 162,163Tm nuclei formed in 37Cl+130Te reactions. The rotational transition strength is obtained as a function of rotational frequency for selected regions of entry states, and the width is found to be rather constant and approximately equal to 80 keV. This value is significantly smaller than the value predicted the…

Doubling of α-cluster statesin22Ne

Excitation functions for ${}^{18}\mathrm{O}+\ensuremath{\alpha}$ elastic scattering were measured by a method using inverse kinematics and a thick gas target. An analysis of the data corresponding to the excitation energy regions of 11.8--13.7 MeV and 19.0--22.0 MeV in ${}^{22}\mathrm{Ne}$ was carried out. A surprising splitting of ${1}^{\ensuremath{-}},$ ${3}^{\ensuremath{-}},$ ${7}^{\ensuremath{-}},$ and ${9}^{\ensuremath{-}}$ $\ensuremath{\alpha}$-cluster levels into doublets was found in ${}^{22}\mathrm{Ne}.$

Evidence for three microscopically different kinds ofE1 transition in lead-region nuclei

A survey of electric dipole transition rates, or B(E1) values, is done for lead-region nuclei with 82≦Z≦90 and 112≦N≦134. It is found that the major part of the E1 transitions are hindered by a factor of about 106–107 and these transitions are interpreted to proceed via admixtures of the collective 1− state. A second group, which is generally 10–100 times less hindered and is involving the πi13/2 orbital in the initial states, is suggested to proceed via the allowed πi11/2→πh9/2 admixtures in the wave functions. These two groups are compared to a third newly established category, the α-cluster or IBAp-boson mode, of the so-called vibron model.

Interaction strength and shape difference for the h9/2 and h11/2 configurations in163Tm

The strongly shape driving πh9/2[541]l/2− configuration with α=+1/2 exhibits some anomalous, and so far unexplained, features concerning the crossing frequency, ħωc, the aligned angular momentum, ix, and interaction strength, at the alignment of the first pair of i13/2 quasineutrons in several odd-Z rare earth-nuclei. The h9/2[541]1/2− and h11/2[523]7/2− bands have been studied in the stably deformed rare-earth nucleus163Tm to investigate these features. A difference in band crossing frequency of ∼ 80 keV between the two bands is found. Rotational bands built on these two configurations have been found to cross in the spin range I=25/2–29/2 ħ. Theγ-decay pattern between the two bands is est…

High-spin states in110Cd

Levels of110Cd have been investigated via the96Zr(18O,4n)110Cd reaction by employing the NORD-BALL array of 17 Compton- suppressed Ge detectors. The yrast band has been observed up to I=28 ħ and 14.2 MeV excitation energy with band crossing at ħωc=0.35 MeV. At least three side bands have been constructed. The negative parity bands experience band crossings at ħωc ≈ 0.45 MeV.

Crossing the dripline to11Nusing elastic resonance scattering

The level structure of the unbound nucleus N-11 has been studied by C-10+p elastic resonance scattering in inverse geometry with the LISE3 spectrometer at GANIL, using a C-10 beam with an energy of 9.0 MeV/ nucleon. An additional measurement was done at the A1200 spectrometer at MSU. The excitation function above the C-10+p threshold has been determined up to 5 MeV. A potential-model analysis revealed three resonance states at energies 1.27(-0.05)(+0.18) MeV (Gamma = 1.44 +/- 0.2 MeV), 2.01(-0.05)(+0.15) MeV (Gamma = 0.84 +/- 0.2 MeV), and 3.75 +/- 0.05 MeV (Gamma = 0.60 +/- 0.05 MeV) with the spin-parity assignments I-pi=1/2+,1/2,-,5/2+, respectively. Hence, N-11 is shown to have a ground …

In-beam γ -ray spectroscopy of low- and medium-spin levels in Po211

The structure of the low- and medium-spin levels of the $^{211}\mathrm{Po}$ nucleus have been studied with in-beam $\ensuremath{\gamma}$-ray spectroscopy with the $^{208}\mathrm{Pb}(\ensuremath{\alpha},n)^{211}\mathrm{Po}$ fusion-evaporation reaction. The level scheme was further extended with levels of the configurations $\ensuremath{\pi}{({h}_{9/2})}_{{2}^{+}\ensuremath{-}{4}^{+}}^{2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}$, $\ensuremath{\pi}{({h}_{9/2})}_{{8}^{+}}^{2}\ensuremath{\bigotimes}\ensuremath{\nu}{g}_{9/2}$, $\ensuremath{\pi}{({h}_{9/2})}_{{2}^{+}\ensuremath{-}{4}^{+}}^{2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{11/2}$, $\ensuremath{\pi}{({h}_{9/2})}_{{2}^{+}\ensurem…

Lifetimes of yrast states in 110Cd

Abstract Lifetimes or lifetime limits of 20 yrast levels in 110 Cd have been measured using the recoil-distance method and the NORDBALL array of Compton-suppressed Ge detectors. From the reduced transition probabilities competing rotational and vibrational behaviour of 110 Cd is revealed. Also non-collective states, associated with proton configurations, have been observed.

Evidence for Three Microscopically Different Kinds of E1 Transitions in Lead-Region Nuclei

One outstanding feature of the shell model in heavy nuclei is that within a main shell the single-particle transitions of electric dipole (E1) character are forbidden. This leads to the experimentally observed fact that the E1 transitions are usually hindered by a factor of about 10 with respect to the Weisskopf estimate. But since there is a dispersion of about two or three orders of magnitude among these hindrance factors, the isomeric E1 transitions have not been used to elucidate the mocroscopic properties of the involved states, as has been done for the E3 transitions of this nuclear region [1]. The E3 transitions often proceed via admixtures of the low-lying collective octupole state,…

Decay properties of very-high-spin states in transitional Er nuclei aroundA=154

Theγ ray continuum structures of the transitional Er isotopes withA∼154 are studied using the reaction74Ge(84Kr,xn)158−xEr atElab=340 MeV. The measurements include energy spectra, total energies, multiplicities, angular distributions and lifetimes using the DSAM method. The analysis of data confirms the previously observed two-bump structure of the continuum radiation. A meticulous subtraction of discrete contributions proves the persistence of the low-energy bump even at high spins, i.e.I>40ħ. The angular-distribution measurements assign predominant dipole structure to the bump atEγ=0.65 MeV, whereas the bump atEγ=1.3 MeV is of almost pure quadrupole character at high spins. The lifetime m…

Detailed spectroscopy of Bi195

An experiment focused on the study of shape coexistence and new high-spin structures in $^{195}\mathrm{Bi}$ has been performed. The nucleus is in a transitional region of the bismuth isotope chain. A large number of new states have been found, resulting in a significant extension of the previously known level scheme. Several new collective structures have been identified. A strongly coupled rotational band built upon the $13/{2}^{+}$ isomeric state was extended up to ${I}^{\ensuremath{\pi}}=(49/{2}^{+})$ and an energy of 5706 keV. The ${I}^{\ensuremath{\pi}}=31/{2}^{+}$ member of the $\ensuremath{\pi}{i}_{13/2}$ band was also found to feed a new long-lived isomeric state with an excitation …

On the decay of theJπ= 11/2−,T1/2= 38.9 h isomer in133Ba: search for the E5 transition and verification of the EC branch

International audience; This paper presents a search for the competing 11/2 − → 1/2 + E5 branch to the main 11/2 − → 3/2 + M4 transition from the T 1/2 = 39 h, J π = 11/2 − isomeric state in 133 Ba. An upper limit of 1.8 * 10 −5 could be established for the E5/M4 intensity ratio. In addition a long-standing controversy in the EC-decay of the same isomer was resolved: only one EC branch to the 11/2 + state in 133 Cs was observed. The shell-model structures of the involved states in 133 Ba and 133 Cs were studied with the microscopic quasiparticle-phonon model (MQPM). Good agreement with the decay rates B(λ) was obtained. In particular, the B(M4) value is well reproduced and further only one …

In-beam studies of203, 205Bi and shell-model features of odd-a bismuth isotopes

States in203, 205Bi are populated using the reaction203, 205Tl(3He,3n). Theπi13/2 single-proton states and all the members of thev(21+)⊗π h9/2 quintuplet are identified in both nuclei. The half-lives of the isomericJπ=21/2+ states in both isotopes are measured and found to be 90±7 ns and 100±6 ns, and from these values suggestions for the half-lives of the previously reportedJπ=25/2+ isomers are made. The structures of the multiplets of the formv(Pb)⊗π h9/2 are calculated in the framework of the shell model and it is shown that the main features can be derived from theπ−v−1 effective interaction. The wave functions of the 41+ and 40+ states in202, 204pb are deduced indirectly from the calcu…

Semiempirical calculations of shell model states in 212Rn

Properties of the 13/2+ isomeric decay in201Hg

The isomeric decay of theT1/2=94 us isomeric state in201Hg was studied in beam via the reaction198Pt(α, n). Gamma-ray and conversion-electron spectra were recorded. From the conversion coefficients, the multipolarities of the two depopulating transitions were determined to beM 2 + 10%E 3 andE 2, respectively. These assignments give the depopulating transitions to be 13/2+ → 9/2− and 9/2− → 5/2−, and these thus substantiate the previous suggestion that the isomeric state hasJπ=13/2+. For the 13/2+ → 9/2−M 2 transition a detailed study ofE 3 andM 4 admixed amplitudes was done. The microscopic properties of the 13/2+ and 9/2− states are discussed, and a comparison to the corresponding ones in1…

Half-life and configuration of the 1/2+ intruder state in203Bi

The decay properties of theJπ=1/2+,Eexc=1,098 keV state in203Bi were studied. The state was populated via the204Pb(p, 2n) reaction and the activity was studied with the ion guide isotope separator on-line system IGISOL. The half-life of the 1/2+ state was measured to beT1/2=303 ±5 ms. From this value the partial half-lives of the three depopulating branches 1/2+ →7/2− (E3), 1/2+→5/2− (E3 +M2) and 1/2+→9/2 g.s. − (M4) were deduced. Since all the transitions are configuration forbidden in first order, a detailed study of second-order shell-model configuration mixing could be performed.

Collectivity in ‘‘spherical’’Eu143,144nuclei

Long cascades of stretched E2 transitions have been observed in $^{143}\mathrm{Eu}$ and $^{144}\mathrm{Eu}$ nuclei which at low excitation exhibit spherical shape. Lifetime experiments demonstrate high collectivity values up to B(E2)\ensuremath{\approxeq}100 W.u. among these E2 cascades. The total Routhian surface calculations indicate many crossing rotational bands of the nucleus with triaxial shape at ${\mathrm{\ensuremath{\beta}}}_{2}$\ensuremath{\approxeq}0.25 and \ensuremath{\gamma}\ensuremath{\approxeq}30\ifmmode^\circ\else\textdegree\fi{}. The E2 cascades in $^{143}\mathrm{Eu}$ are proposed to represent the \ensuremath{\nu}${\mathit{h}}_{11/2}^{2}$\ensuremath{\pi}${\mathit{h}}_{11/2}…

Low-lying shears bands in very light odd—odd Bi isotopes

The concept of magnetic rotation in nuclei was introduced to explain the observed regular bands with enhanced M1 transitions and weak or absent E2 crossover transitions in nearly spherical nuclei around 198Pb [1]. These bands can be described by the coupling of high-j proton and neutron configurations to a total spin tilted at an angle of ~ 45° with respect to the symmetry axis. As the proton and neutron spins align with increasing excitation energy, a sequence of ΔI = 1 levels of fixed parity (“shears band”) is formed [2].

Low- and medium-spin states in theN=124 isotones208Po and209At

Excited levels in208Po and209At were populated in the reactions (p, 2n) and (3He, 3n), and208Po also in the EC-decay of the208At ground state, which was produced in the209Bi(3He, 4n) reaction. The experimental procedures comprised gamma-ray excitation functions,γ- γ coincidences, as well as gamma-ray angular distribution and conversionelectron measurements, both on- and off-line. The properties of about twenty-five levels in each nuclide were studied. In208Po the energy of the 8+→6+ transition could be determined to be 4.0±0.2keV and the 8+ state thus has an excitation energy of 1,528 keV. The effective quadrupole charge of theh 9/2 proton can be derived ase eff(τ h 9/2)=1.69(15)e. For the …

In-beam study of high-spin states in199,200,201Po and systematical features of Z=84 polonium isotopes

Excited states in199,200,201Po were populated in the reactions12C+194Pt and12C+195Pt. The subsequentγ-radiation was studied using conventional in-beam spectroscopic methods. States with spins up to (29/2), 18 and ≧35/2ħ, respectively, were populated in the three nuclides. Three isomeric states with the following half-lives were observed in200Po:T1/2(8+)=90(15) ns,T1/2(11−)=120(20) ns andT1/2(12+)=267(4) ns. The structure of the excited states was interpreted within the framework of the spherical shell model. The three isomers are suggested to be two-quasiparticle states with configurationsπ(h22)8J, π(h9i13/2)11- and v(i1 3/2−2)12+. A self-consistent Hartree-Fock calculation was performed to…

g-Factor of theT 1/2=35 ns isomeric state in154Er

The reaction32S+126Te has been used to determine theg-factor of theT 1/2=35 ns yrast isomeric state in154Er through the time-differential spin-rotation method. The experimental valueg=+0.017±0.003 agrees with an aligned two-neutron ν(i13/2,h9/2) main configuration and supports an 11− spin-parity assignment for the isomeric state. Unambiguous spin-parity assignment for upper energy yrast states can be deduced. The properties of the isomeric state are discussed.

High-spin bands in117,119I and118Xe

Excited states in117I,118Xe and119I were populated in the reactions106Pd+16O and108, 110Cd+12C. The groundstate band in118Xe was observed to its (18+) member and the 11/2− bands in117I and119I to their (35/2−) and (43/2−) members, respectively. The structure of the bands in the I isotopes is interpreted as aπ h11/2 proton coupled to an even-even band structure in Xe, and the band crossings observed in118Xe and119I are interpreted in the Cranked Shell Model framework asABn ofv h11/2.

Detailed spectroscopy of 195Bi

An experiment focused on the study of shape coexistence and new high-spin structures in 195 Bi has been performed. The nucleus is in a transitional region of the bismuth isotope chain. A large number of new states have been found, resulting in a significant extension of the previously known level scheme. Several new collective structures have been identified. A strongly coupled rotational band built upon the 13 / 2 + isomeric state was extended up to I π = ( 49 / 2 + ) and an energy of 5706 keV. The I π = 31 / 2 + member of the π i 13 / 2 band was also found to feed a new long-lived isomeric state with an excitation energy of 2616 keV and a spin and parity of I π = 29 / 2 + . The half-life …

In-Beam Study of213Rn,215Ra and217Ra: Strongly Enhanced E3 Transitions in Odd-A N= 127 Isotones

With the aim of searching for high-spin configurations involving the high-j neutron orbitals, excited states in 213Rn, 215Ra and 217Ra were populated in the bombardment of 208Pb with 13C ions. Gamma-ray singles, excitation functions and angular distributions, pulsed-beam-γ timing and γ-γ(t) coincidences were measured. Six isomeric levels were observed in 213Rn, three in 215Ra while none in 217Ra. The lowest-lying 15/2- states in all odd-A N = 127 isotones are de-excited by E3 transitions with a strength of about 23 W.u, suggesting that they are all coupled to the octupole phonon. In 217Ra no evidence for collective behavior is found despite its closeness to the actinide region. The low-lyin…

Study of a-cluster states of 22Mg from resonance scattering of a post-accelerated 18Ne radioactive ion beam

An experiment aimed at the study of the α-cluster structure of 22Mg was performed at the Louvain la Neuve RIB facility. Preliminary results from a first feasibility run will be presented.

In-beam γ-ray spectroscopy of low- and medium-spin levels in 211Po

The structure of the low- and medium-spin levels of the 211Po nucleus have been studied with in-beam γ-ray spectroscopy with the 208Pb(α,n)211Po fusion-evaporation reaction. The level scheme was further extended with levels of the configurations π(h9/2)22+−4+⊗νg9/2, π(h9/2)28+⊗νg9/2, π(h9/2)22+−4+⊗νi11/2, π(h9/2)22+−4+⊗νj15/2, π(h9/2f7/2)8+⊗νg9/2, and π(h9/2)20+⊗ν(g9/2)20+(s1/2)−1. The single-particle neutron states νd5/2 and νs1/2 were also identified. Furthermore, a number of states feeding the low-spin structures were added. peerReviewed

Doubling of α-cluster states in 22 Ne

Excitation functions for 18 O + α elastic scattering were measured by a method using inverse kinematics and a thick gas target. An analysis of the data corresponding to the excitation energy regions of 11.8–13.7 MeV and 19.0–22.0 MeV in 22 Ne was carried out. A surprising splitting of 1 − , 3 − , 7 − , and 9 − α -cluster levels into doublets was found in 22 Ne . peerReviewed

The g-factor of the J?=12+ isomeric state in188Hg

Using the reaction175Lu(19F, 6n) theg-factor of the188Hg isomeric state (Jπ=12+,T1/2=135 ns) has been measured with the TDPAD method. The experimental value g=−0.168(10) supports the interpretation of an almost pure (vi13/2)−2 configuration for this isomer.

Study of band crossings in 130Xe

Abstract Excited states in 130Xe were populated in the reaction 130 Te (α, 4 n ) , and the subsequent de-excitation was studied using in-beam γ-ray spectroscopic methods. High-spin states were observed to a possible spin of 19 kh at an excitation energy of 7 MeV. Band-crossings due to h 11 2 neutrons and protons were observed. The triaxial cranked shell model was applied in order to study the quasiparticle content of different bands. Excitation energies of two-quasiparticle states were calculated in the framework of the semiempirical shell model.