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Abstract:: Lifetimes of excited states in 118Te have been measured using the Doppler Shift Attenuation (DSA) and Recoil Distance (RD) methods in the 109Ag(13C, p3n) reaction at a beam energy of 54 MeV. Lifetime values of the ground-state band levels with spins I π = 2+-16+ have been obtained. The excitation energies and B(E2) values are interpreted in the framework of a version of IBFM ( IBM + 2qp) with the maximum boson number exceeding its standard value. A satisfactory agreement with experimental level scheme and B(E2) values for the ground-state band is achieved.

Lifetimes in four negative-parity bands of 119I were measured using DSAM and RDM. 119I nuclei were produced in the 109Ag(13C,3n) reaction, γγcoincidences were collected using the NORDBALL array. RDDSA — a new method of RDM analysis — is described. This method allowed for the self-calibration of stopping power. From 31 measured lifetimes, 39 values of B(E2) were established. Calculations in the frame of the Core Quasi Particle Coupling (CQPC) model were focused on the problem of susceptibility of the nucleus to γ-deformation. It was established that nonaxial quadrupole deformation of 119I plays on important role. The Wilets–Jean model of a γ-soft nucleus describes the 119I nucleus in a more consistent way then the Davydov–Filippov model of a γ-rigid nucleus.

Abstract:: Prompt and delayed γ-rays have been observed from very neutron deficient 192–195Po nuclei by using the recoil-decay tagging (RDT) and recoil gating techniques. The yrast levels up to the (10+) state in the 192Po were identified for the first time. Comprehensive data for 194Po rendered it possible to extend the yrast line and to observe several positive and negative parity non-yrast states. In the odd-mass isotopes 193Po and 195Po, favoured and unfavoured states on top of the 13/2+ state have been identified. The results are discussed within the simple vibrator and rotor pictures as well as in the framework of coexisting spherical and deformed-intruder structures.

Connections between the superdeformed and normaldeformed states in 143Eu have been established by measuring energy sums of two consecutive γ-ray transitions in the linking cascade. Six decay paths have been observed connecting discrete states in the two potential wells. The absolute excitation energy and the most likely spin of a superdeformed band have been determined directly for the first time.

Excited states in 154,156,158,160Gd have been populated through the multiple coulomb excitation process by 32S, 48Ti, 58Ni ions. The ground band, γ-band and octupole Kπ= 0−band were extended to Iπ= 16+, (12+), and (11−) state respectively in 160Gd. The octupole Kπ= 1−band was extended to Iπ= 9−state in 158Gd. Excitation cross sections of individual levels relative to that of the Iπ= 4+state in the ground band in each nucleus were compared with the simulation by the computer code GOSIA within the framework of the pure rotational model. From these comparisons the matrix elements for both intra-band and inter-band transitions were deduced.

A superdeformed (SD) band in 103Pd was studied using the reaction 76Ge(34S,α3n) at 148 MeV. Yields of γ-rays, γ-γ coincidences and γ-ray angular correlation measurements were obtained with the NordBall multi-detector system. The SD band is compared with similar bands in 104,105Pd. Calculations of spin diabatic surfaces have been performed and are used for assigning deformation parameters and quasiparticle configurations to the bands. Additional occupation of intruder orbitals from π or ν h112and the νi132[660]12, in combination with band terminations of the normal deformed bands may explain the existence of the SD band in 103Pd.

The NORDBALL detector array has been used in a γ-ray spectroscopic study of neutron deficient nuclei close to 100Sn. A beam of 270 MeV 58Ni ions was used to bombard a target of 54Fe. Reaction channel separation was achieved with a 4π charged particle Si-ball together with a 1π neutron detector wall. Altogether 29 final nuclei were identified and excited states were observed for the first time in 8 of them. The weakest identified channel was 100Cd which represented 4.10−3% of the observed total yield. Level schemes of 102In, 104In and 108Sb constructed from γ-γ-particle-coincidence and γ-γ-angular correlation analyses are presented. The observed structures are discussed in the framework of the nuclear shell-model. In 108Sb also a deformed, strongly coupled, level sequence is observed. This deformed structure is interpreted as built on a πg −192⊗νvh112configuration in agreement with TRS calculations.

High-lying and high spin states of nuclei around N,Z=40 have studied using the (58Ni + 28Si) and (58Ni + 32S) reactions and NORDBALL Ge-Array equipped with a Silicon Ball for light charged particle detection. Simultaneously complementary experiment have been carried out using in-beam and β decay measurements to establish lifetimes and spin-party values of low-lying and ground states at Kyushu University. Some of results are reported.

An in-beam?-ray study performed with the114Cd(30Si,p 3n) reaction has established the structure of theN=79 nucleus140Pm. States up toI=(20)h and 5.5 MeV excitation energy have been recognized above the 5.95 m isomeric state which we identify, from the GT decay to140Nd, as the 8- member of the (pd52/-1vh112/-1) multiplet, changing the present 7- assignment. The low energy part of the level scheme is discussed in terms of the coupling of the valence holes in respect to theZ=64,N=82 shell closure. A new 8+ isomeric state witht1/2=1-0.5+1 ns has been observed, having most likely a (ph11/2vh11/2-1)8 configuration.

Microsecond isomers in the exotic proton-richN=82, 83 nuclei153Yb,153Lu,154Lu and154Hf have been identified by?-ray spectroscopy following mass analysis of102Pd+245 MeV54Fe reaction products using the Daresbury Recoil Separator. The decays of the isomers, interpreted asph112/n andph112/n vf7/2 states, are characterized. The reduced E2 transition rates indicate that half-filling of theph11/2 subshell occurs just belowZ=71, and results for theN=83 odd-odd isotones are also consistent with this finding.

The level structure of194Au has been studied by observing prompt and delayed?-rays following194Pt(p,n) and195Pt(p,2n) reactions. The conversion electron and?-ray spectra from the decay of the 0.42s (10-) and 0.60s (5+) isomers at 476 keV and 107.4 keV, respectively, have been measured using the He-jet method. The half-lives of the 6+ (278.2 keV, 1.1±0.4 ns), 7+ (224.6 keV, 2.6±0.2 ns) and 8+ (406.8 keV, 2.9±0.4 ns) members of thepd3/2-vi13/2 multiplet have been obtained from the time distributions between cyclotron beam pulses and?-rays depopulating these levels. A calculation made assuming a pure two-particle configuration for the multiplet predicts very well theB(E2) values for the transitions between the levels of this multiplet but the calculatedB(M1) values are not in agreement with experimental results.

A spectroscopic study of 108Sb has been carried out as a part of a larger experiment where in total twenty-nine different residual nuclei were identified. This study gives the first information on excited levels in this nucleus. A low-lying two-quasi-particle multiplet together with some of the higher lying levels are discussed within the framework of the nuclear shell model. A rotational, strongly coupled, band is identified as, most likely, being built on the deformed πg92−1⊗ νh112configuration in accordance with total routhian surface calculations. Tentative spins and parities are presented as well as B(M1)B(E2)ratios for some of the transitions in the strongly coupled band.

Yrast- and above-yrast states in149Tb were investigated in (a, 6n) and (7Li, 2n) in-beam?-ray experiments. The yrast?-ray cascade strongly populates three-valenceparticle states involving theh11/2 proton and thef7/2,h9/2, or;i13/2 neutron orbitals, as well as the high-spin levels formed by the couplings of the three149Tb valence particles, to the low-lying146Gd octupole phonon and to higher-lying proton particle-hole core excitations. The data give the (ph11/2vi13/2)12- attraction free of octupole contributions as -631 keV. The shell model with empirical two-particle- and particle-phonon residual interactions gives an excellent quantitative description of the149Tb energy levels. It is noted that the observed highspin members of theph11/2vh9/2vf7/2 configuration closely resemble the lowest symmetric and mixed-symmetry representations of theS3 permutation group.

The strongly shape driving ph9/2[541]l/2- configuration with a=+1/2 exhibits some anomalous, and so far unexplained, features concerning the crossing frequency, h?c, 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 h. The?-decay pattern between the two bands is established in the crossing region and analysed in terms of a moderate shape difference between them. A theoretical estimate of the size of the interaction strength between the two bands is presented and compared to the experimental value. The observed band structure in163Tm is very similar to that of167Lu which has 2 protons and 2 neutrons in addition. This observation is discussed in relation to the similarity of the yrast bands of the two even-even “core” nuclei162Er and166Yb, for which the?-transition energies are identical within ~0.2 keV below the vi13/2 crossing.

In-beam?-ray and conversion electron measurements with (a, xn) reactions have established the145Sm highspin states up toIp=25/2+ at 3.5 MeV excitation. A shell model analysis using empirical two- and one-body energies from neighbouring nuclei classifies the low-lying odd-parity levels as 3-quasiparticle states formed by the144Sm two-proton-hole excitations and thef7/2 valence neutron. The higher-lying positive-parity states involve particle-hole core excitations with one proton inh11/2.

Through (a, 4n) and (t, 3n) reactions the high-spin states in the two-neutron nucleus148Gd were populated up toIp=21- at 7.2 MeV, including numerous states above the yrast line. The148Gd energy spectrum is interpreted in terms of the spherical shell model. Identification of the (?f7/2i1 3/2)10- state gives the ?i13/2 single particle energy free of octupole admixtures as 2.1(1) MeV. Eight high-spin states between 1.2 and 3.7 MeV were identified as the couplings of the two valence-particles to the146Gd octupole phonon, and three above-lying levels are assigned as double-octupole excitations including a 12+ state which decays by anE3-E3 stretched cascade. All these octupole levels can be quantitatively predicted from the one-particle x phonon spectrum of147Gd. The high-spin states above 3 MeV are four-quasiparticle excitations ofp+1p-1?2 andp2?2 type and their energies are in good accord with shell model estimates.

Levels of135Pr populated in the (p,2n) reaction were studied using methods of in-beam?-ray and conversion electron spectroscopy. Many low-lying positive-parity states give evidence of a deformation ofß=0.15–0.20. The same conclusion is evident from band structures built on these positive-parity states and on theh11/2 negative-parity state. The triaxial rotor-plus-particle model reproduces quite well band structures withß=0.20 and?= 21°.

Firm spin-parity assignments for the high-spin states up to 3.5 MeV in the one-proton nucleus147Tb were obtained from144Sm(6Li, 3n) in-beam?-ray and conversion electron measurements. The energies of these two-particle one-hole excitations were calculated from the shell model with empirical nucleon-nucleon interaction energies. The calculated energy splittings agree well with experiment, whereas the theoretical excitation energies disagree by ?1 MeV if recently measured ground state masses are used.

From in-beamγ-ray measurements we have established the high-spin states in146Eu up to 3.5 MeV excitation andIπ=(15+). The highest levels observed are formed by alignment of four nucleons, involving excitation of the144Sm core. Negative-parity states at about 2 MeV are classified asπh11/2νf7/2 × 3− octupole excitations. Quantitative analyses for the octupole multiplet members and for theν=4 states based on empirical data from neighbouring nuclei are presented.

Levels of theN=83 nucleus147Gd have been investigated by methods of in-beam?-ray and conversion electron spectroscopy using the147Sm(3He, 3n) and144Sm(a, n) reactions. Sixteen new low- and medium-spin levels have been observed in147Gd. We have located six members of thevf7/2×3- particle-octupole septuplet and several neutron single-particle states in147Gd. The levels of147Gd are discussed on the basis of the spherical shell model.

From (p, xn) in-beam?-ray and electron measurements aT1/2=235(14) ns isomer at 720 keV was identified in63148Eu85 and the levels populated in its decay have been characterized. The results determineIp=9+ for the isomeric state, and we assign it as the (ph11/2j0-2? f72/3)9+ shell model state, analogous to the configuration of the 235 µs isomer in63146Eu83.

Multiple coincidence rates have been measured using a detector system consisting of a Ge(Li) spectrometer and eight NaI(Tl) or eight liquid scintillators. Reactions induced bya-particles with energies of 51–55 MeV and 118 MeV12C ions are studied. The data are analysed to give the first and second central moments of the distribution of the number of?-rays feeding individual levels in the final nuclei. When these numbers are compared to spin distributions calculated with the statistical model code GROGI the relative importance of dipole and quadrupole deexcitation modes can be ascertained. In particular, in the122Te(a, 4n)122Xe reaction the?-decay prior to the entry into the ground band is well described as a statistical process proceeding to 50% by dipole and 50% by quadrupole radiation. In the166Er(a,4n)166Yb and192Os(a,4n)192Pt reactions the relative amount of quadrupole radiation is larger and it seems that the dipole and quadrupole decay takes place via separate cascades. In the164Dy(12C, 7-8n) reactions the average multiplicity is independent of spin, suggesting that the nucleus forgets the spin of the entry state before the process enters into the ground band. In the176Yb(12C, 8n)180Os reaction, finally, the nucleus definitely retains memory of the entry state during the decay. In this last case the multiplicity measurement is combined with a?-ray singles measurement to give an average excitation energy prior to thea-decay and the average moment of inertia characterising the decay of the high-spin states.

The high spin level structure of the three-neutron nucleus149Gd has been investigated by in-beam?-ray and electron spectroscopy with (a, xn) reactions. The observed levels are characterized as members of the shell model multiplets?f72/3,?h9/2f72/2,?f72/3×3-,?h9/2f72/2×3-, and tentatively?f72/3×(3-)2. The energies of the?f72/3 states agree only moderately with those calculated using empirical two-nucleon interactions taken from148Gd, which indicates the importance of long range contributions already atN=85.

Angular distribution measurements of gamma-rays from the22Ne(p, γ)23Na reaction on theEp=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(Kπ=5/2+).

The level scheme of144Pr has been studied from the decay of144Ce. The intensities and energies of gamma rays have been determined with a X-ray Ge(Li) detector. TheK-shell internal conversion coefficients for γ-rays have been measured with theKX-ray/γ-ray ratio method using NaI(Tl)—X-ray Ge(Li) coincidence techniques.

The gamma decays of 1922Ne(p, γ)23Na resonances in the range ofEp=400−1300 keV have been investigated by means of a 38 cm3Ge(Li) detector. Branching ratios of the resonances and bound states were determined. Gamma-ray energy measurements yield the energies of 19 bound states and the value of 8794.0±1.5 keV forQ. The existence of the 3913 keV doublet state was studied through the (p, γ) reaction. No evidence for such a doublet was found.

The gamma decay of the low-lying energy levels (Ex<4MeV) in25Al has been studied through the24Mg(p, γ)25Al reaction using seven resonances in the proton energy rangeEp+200−1700 keV. Ge(Li) detectors and isotopically separated targets have been used. Energies and branching ratios of several excited states have been measured. TheQ-value of the reaction was determined to be 2271.3±0.8 keV. Lifetimes, investigated by the Doppler-shift attenuation method and γ-ray angular distributions have been determined using theEp+823, 1201, 1490 and 1660 keV resonances of the24Mg(p, γ)25Al reaction.

A rotational band with 15 transitions has been observed in142Eu in an experiment with the GASP Ge detector array by the110Pd(37Cl,5n) reaction. The average energy spacing between the neighbouring transitions is 60 keV, which is similar to the energy spacings in the superdeformed bands in the mass 140 region. The band has a constant dynamic moment of inertia as suggested by Cranked Shell Model calculations.

Excited states of108Te were populated in the54Fe +58Ni (270 MeV) reaction using the NORDBALL detector array equipped with charged-particle and neutron detector systems for reaction channel separation. Gamma rays belonging to the neutron deficient nucleus108Te were identified for the first time. On the basis of ??-coincidence and angular correlation relations a level scheme was constructed with tentative spin and parity assignments. The structure of the nucleus is discussed in the framework of systematics of heavier Te nuclei.

Through an in-beam study of the69153Tm84 nucleus we have identified the ph112/5/2?f72/2 and ph112/5?f7/2h9/2 7-valence particle configurations up to their fully aligned spins of 47/2- and 51/2-. Shell model calculations predict that in the ph112/5?f7/2h9/2 configuration, contrary to the p112/5?f72/2 case, the h11/2 proton seniority does not increase regularly with spin. This seniority inversion is verified by the data.

In an in-beam study of67151Ho84 we have established its high-spin states up to 10 MeV and have suggested spin assignments up to (49/2) at 6.2 MeV. The main decay-cascade proceeds through the yrast states of the ph311/2?f27/2 and ph311/2?f7/2h9/2 5-particle configurations, which are predicted with good accuracy in parameter-free shell-model calculations. States with one proton in d3/2, or involving ?i13/2 or ?f7/2×3- excitations were also identified.

h11/2 neutron and g9/2 proton alignments in99,100Ru deduced from comparisons of experimental Routhians and aligned angular momenta to cranking model calculations. There is indication of band termination in100Ru.

Neutron deficient nuclei close to100Snhave been investigated in-beam by γ-ray spectroscopic methods using the NORDBALL detector array. A beam of 270 MeV58Niwas used to bombard a target of54Fe.Reaction channel separation was achieved with a 4π charged particle multidetector setup together with a 1π neutron detector wall placed in the forward direction. Excited states of102Inwere identified for the first time. The level scheme constructed from γ-γ-particle-coincidence and γ-γ-angular correlation analysis is presented. The structure of102In is discussed and compared to neighboring nuclei in the framework of the nuclear shell-model.

We report on new results for the decay of the superdeformed (SD) band in194Pb. No transitions linking the SD structure with the known level scheme of194Pb could be found, but the feeding intensities into the normal-deformed states are determined and limits on the one-step decay of the SD band are given.

High spin states in104Cd have been investigated by means of heavy ion induced reactions using the Nordball detector array. The level scheme constructed from ??-coincidences is dominated by three band structures. The positive parity band shows no rotational like energy spacing. It is thus understood mostly in terms of quasiparticle excitations with vd5/2, vg7/2 andpg9/2 configurations. The collective properties of the negative parity bands are more pronounced. These bands are most likely due to v(h11/2,d5/2) and v(h11/2,g7/2) structures.

A 53.3 keV E2 transition de-exciting the 60 ns isomer in152Dy has been identified in γγ-coincidence measurements, which locates that isomer at Ex=5088 keV. The half life of the 11− level at 3161 keV was measured to be T1/2=4.3±0.9 ns.

Through (p,2n) in-beam ? and e- measurements the excitation of the 235 µs 9+ isomer in146Eu has been determined to be 666.3 keV. High spin members of the pd52/-1 ?f7/2 and pg72/-1 ?f7/2 particle hole multiplets populated in the isomeric decay were located.

Three yrast isomers in151Dy, at 6.03 MeV (I=49/2, T/=15(3) ns), 4.90 MeV (41/2-, 5.5(1.0) ns), and at 2.96 MeV(27/2-, 1.3(6) ns) have been located through152Gd(a,5n) and136Ce(18O, 3n) measurements. Shell model configurations are suggested for them.

Adedicated γ-ray measurement with mass-separated 147Dy activity gave the direct β-feeding intensities to the 147Tb πs1=2and πh11=2single proton states in decay of the 147Dyνs-11=2andνh-111=2activities.With these results the absolute transition rates for the three Gamow-Teller decay modes of 147Dy can be deduced.