Electromagnetic transitions in the ground-state rotational band of159Tb

The ground-state band of¹⁵⁹Tb has been Coulomb excited up to spin 23/2 by 151-MeV⁴⁰Ar ions. The lifetimes of the 9/2 to 23/2 levels have been determined by combining results obtained with the RD and DSA methods, theE2/M1 mixing ratios for ΔI=1 transitions have been measured using angular correlation techniques and the branching ratios for the levels up to spin 17/2 have been determined. The energies of the levels and the reducedM1 andE2 transition probabilities for their decay have been compared with the predictions of the rotational model, without and with ΔK=1 admixtures. No satisfactory agreement could be achieved for all available experimental data simultaneously.     

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.     

Yrast states in the doubly-odd nucleus100Tc

High spin states up toJ=14 and excitation energy up toE ^*=3076 keV have been observed in the odd-odd nucleus¹⁰⁰Tc with the reaction⁹⁶Zr(⁷Li, 3n), at bombarding energies between 21 and 31 MeV, by in-beam γ spectroscopy and conversion-electron measurements. A ΔJ=1 negative parity band similar to that observed in theN=57 isotone¹⁰²Rh, and based on the 8^?, 708 keV state has been identified. The observed band can be interpreted in terms of collective core excitations based on a two-quasiparticle state of(πg_9/2 ? νh_11/2) configuration. Comparison with IBFM-2 calculations have been performed.     

On the level scheme of the159Tm nucleus

Level in¹⁵⁹Tm have been excited in the¹⁵⁰Sm(¹⁴N,5n reaction. The yrast band 7/2^?[523] observed up to spin 45/2^? is built on a isomeric state at 166 keV (T _1/2=37±5ns). Connections between the 7/2^?[523] and 7/2⁺ [404] bands fix the band-head energies.     

The spin of the 2,198 keV level in74Ge and multipole mixing ratios of gamma transitions in the decay of74As

Directional-correlation measurements of several cascades in the⁷⁴As decay have been made with a NaI — Ge(Li) detectors system. In the⁷⁴Ge the following cascades were measured: 608–596 keV, 994–1,204 keV, 994-(608)-596 keV and 887-596 keV. The corresponding results give a unique spin assignment of 2 for the 2,198 keV level and determine theE2/M 1 mixing ratios ofδ(608)=3.4±0.4 andδ(994)=?(2.8 ± 0.2). In the⁷⁴Se it was measured the 635-635 keV cascade. The result obtained assigned the spin of the 1,270 keV level as 2 and fixed the E2/M1 mixing ratio of δ(635)=?(2.6 ± 0.2). Also aγ-intensity study has been made to determine the branching ratios of the transitions that deexcite the 1,270 keV level in⁷⁴Se. From these data aI(635)/I(1,270)=12.5 ± 5.0 is obtained.     

Lifetime measurements in166Er

The lifetimes of five states in the ground band, from spin 6⁺ up to spin 14⁺, and of all even states in the gamma band up to spin 12⁺, have been measured in¹⁶⁶Er using the recoil distance method. The reduced electric quadrupole transition probabilities have been determined from the measured lifetimes using previously measured branching ratios, and the mixing between the ground band and theγ-band has been studied. The transitional electric quadrupole moments for the ground band and theγ-band have been deduced and are discussed.     

Niederenergetische Gammalinien vom Neutroneneinfang in Lu 175 und Lu 176

The low energy gamma-rays from neutron-capture in Lu 175 and Lu 176 have been investigated by means of the bent crystal-spectrometer at the DR-3-reactor at Risø. From the transitions in Lu 177 3 rotational bands have been determined. The levels of the (404)K=7/2⁺ groundstate rotational band are: 121,62 keV (I=9/2), 268,79keV (I=11/2), 440,66 keV (I=13/2), 636,22 keV (I=15/2), 854,34 keV (I=17/2). The level-sequence of the (514)K=9/2^?-band is: 150,39 keV (I=9/2), 288,99 keV (I=11/2), 451,49 keV (I=13/2), 637,05 keV (I=15/2) and 844,88 keV (I=17/2). At 457,92 keV is the basis for the (402)K=5/2⁺-band the higher levels of which are 552,05 keV (I=7/2), 671,89 keV (I=9/2), 816,63 keV (I=11/2), 985,23 keV (I=13/2), 1176,73keV (I=15/2) and probably 1389,5 keV (I=17/2). The energies of the levels apart from the 1389 keV-level have an accuracy of 7×10^?5. The energy differences between the 3 bands agree very well with the values expected from the Bohr-Mottelson-formulaE=A·I(I+1)+B·I ²(I+1)². The calculated branching-ratios within the 3 bands are in fairly good agreement with the experimental values. Theg _K -factors have been determined for 2 bands: It was found that for the (514)-bandg _K =1,16±0,04 and for the (402)-bandg _K =1,33±0,07.     

Recoil distance lifetime measurements in82Kr

The lifetimes τ=124±12, 6 _?2 ⁺⁴ and 380±100 ps of theE _x (I ^π )=3.46(8⁺), 2.92(6⁺) and 3.04(6^?) MeV states, respectively, populated by the reaction⁷⁶Ge(¹²C,α2n) were measured with the recoil distance method. In addition upper lifetime limits were obtained for nine states. The measured lifetimes and energies indicate a band crossing at aboutI ^π =8⁺, probably arising from the alignment of twog _9/2 neutrons. For the 3.04 MeV 6^? state as a second member of a band built on the 2.65 MeV 4^? state the measured lifetime points to a two-quasiparticle configuration. The positive-parity states have been discussed in the frame of the interacting boson approximation, nuclear field theory and the cranked shell model.     

Coulomb excitation of 85Rb and 87Rb

Energy levels of ⁸⁵Rb and ⁸⁷Rb have been studied via de-excitation γ-rays following Coulomb excitation with ³⁵Cl ions. In addition to the known negative-parity states at 151.2 keV and 868.2 keV in ⁸⁵Rb, two states at 281.0 keV and 731.8 keV have been found with fourγ-ray transitions of 129.8, 281.0, 450.8 and 731.8 keV. Only one Coulomb excited state at 402.6 keV in ⁸⁷Rb has been observed. The B(E2↑) values (in units e² · b²) have been determined as 0.0035±0.0004 (151.2 keV), 0.0016±0.0002 (281.0 keV), 0.0101 ±0.0010 (731.8 keV), and 0.036±0.004 (868.2 keV) for the states in ⁸⁵Rb, and as 0.0054±0.0006 (402.6 keV) for the state in ⁸⁷Rb. The mean lifetimes of the 731.8 keV and 868.2 keV states have been measured by the Doppler shift attenuation method as 6.4±0.7 psec and 4.2±0.5 psec respectively. Angular distribution measurements allow unique spin and parity assignments of $\text{1}\text{2}{}^{\mathrm{?}}$ and $\text{3}\text{2}{}^{\mathrm{?}}$ to the 281.0 keV and 731.8 keV levels respectively. The spin and parity of the 868.2 keV level has been restricted to $\text{5}\text{2}{}^{\mathrm{?}}$ or $\text{7}\text{2}{}^{\mathrm{?}}$.     

Vibrational band structure in 184W populated in the decay of 184Re

The decay of ^184mRe has been investigated through γ-ray and conversion electron studies. The band head of the K^π = 2^? octupole band has been established at 1130.0 keV. The E2/M1 mixing ratios of three transitions from the γ-vibrational band to the ground state band have been determined by angular correlation measurements. A mixing of El, M2 and E3 multipolarity has been derived for the 921 keV transition combining angular correlation and conversion electron data. A value B(E3, 0⁺ → 3^? = (25 ± 5) × 10⁴e² · fm⁶ was obtained from the measured E2/M1 mixing of the 91 keV 3^? → → 2^? transition and γ-branchings. The data are discussed in terms of the collective model taking into account band mixing.     

Decay of 8.0-day131I to levels of131Xe and 11.77-day131mXe

The decay characteristics of¹³¹I have been determined with high accuracy. The total branch from¹³¹I to^131mXe has been measured to be 1.086±0.007%. The half life of^131mXe has been measured as 11.770±0.012 days. Theγ-ray spectrum has been determined and new transitions at 85.92, 232.17, 295.83, 302.44, and 449.57 keV established. The position, spin and parity were established for a 9/2^? level at 341.140 keV and spin and parity of 7/2^? established for a level at 666.921 keV. The log f₁t for the unique firstforbiddenβ transition from 7/2^{+ 131}I to 11/2^{? 131m}Xe has been calculated to be 9.78.     

Investigation of the decay rate for71Ge in chemical compounds and calibration of the Mössbauer isomer shift of the 67 keV γ-transition of73Ge

Changes of the radioactive decay rate of⁷¹Ge (T _1/2=11.43 days) have been studied experimentally for⁷¹Ge in some compounds of bivalent and quadrivalent germanium. Relative changes Δλ/λ of the electron capture probability have been measured, and the chemical changes Δρ(0) of the electron density at the germanium nuclei have been determined from these measurements. Values for the Mössbauer isomer shift calibration constants for the 67 keV γ-transition of⁷³Ge have been estimated:C=δ/Δρ(0)=(0.061±0.020) mm·s^?1/a.u., Δ〈r ²〉=(21±7)·10^?3 fm², ΔR/R=(6.9±2.3)·10^?4.     

Gamma-gamma directional correlations in69Ga

Employing a Ge(Li)-NaI(Tl) detector system, gamma-gamma directional correlations for nine cascades in⁶⁹Ga have been measured. The result of the present measurements combined with other existing data allowed the adoption of a 5/2^? spin and parity for the 1106.4 keV level, and a 7/2^? for the 1 336.1 and 1487.5 keV levels. A tentative 7/2^? spin and parity has been adopted for 1923.1 keV level. Mixing ratios have been determined for six transitions. The data obtained are utilized to extractM1 andE2 reduced transition probabilities. A comparison of the experimental data is made with the predictions of the one particle-core and three particles-core coupling models.     

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.     

Levels in 156Gd studied in the (n, γ) reaction

Levels up to 2.3 MeV in ¹⁵⁶Gd have been studied using the (n, γ) reaction. Energies and intensities of low-energy γ-rays and electrons emitted after thermal neutron capture have been measured with a curved-crystal spectrometer, Ge(Li) detectors and a magnetic electron spectrometer. High-energy (primary) γ-rays and electrons have been measured with Ge(Li) detectors and a magnetic spectrometer. The high-energy γ-ray spectrum has also been measured in thermal neutron capture in 2 keV resonance neutron capture. The neutron separation energy in ¹⁵⁶Gd was measured as S_n = 8535.8 ± 0.5 keV.About 600 transitions were observed of which ~50% could be placed in a level scheme containing more than 50 levels up to 2.3 MeV excitation energy. 42 of these levels were grouped into 15 excited bands. In addition to the β-band at 1050 keV we observe 0⁺ bands at 1168, 1715 and 1851 keV. Other positive-parity bands are: 1⁺ bands at 1966, 2027 and 2187 keV; 2⁺ bands at 1154 (γ-band) and 1828 keV; and 4⁺ bands at 1511 and 1861 keV. Negative-parity bands are observed at 1243 keV (1^?), 1366 keV (0^?), 1780 keV (2^?) and 2045 keV (4^?). Reduced E2 and E0 transition probabilities have been derived for many transitions. The ground band, the β- and γ-bands and the 0⁺ band at 1168 keV have been included in a phenomenological four-band mixing calculation, which reproduces well the experimental energies and E2 transition probabilities.The lowest three negative-parity (octupole) bands of which the 0^? and the 1^? bands are very strongly mixed, were included in a Coriolis-coupling analysis, which reproduces well the observed energies. The E1 transition probabilities to the ground band are also well reproduced, while those from the higher-lying 0⁺ bands to the octupole bands are not reproduced. Absolute and relative transition probabilities have been compared with predictions of the IBA model and the pairingplus-quadrupole model. Both models reproduce well the E2 transitions from the γ-band, while strong disagreements are found for the E2 transitions from the β-band. The IBA model predicts part of the decay features of the higher lying 2⁺₂, 4⁺₁ and 2^?₁ bands.     

Mössbauer effect study of hyperfine interactions in145Nd

The magnetic hyperfine splitting of the 72.5 keV γ rays of¹⁴⁵Nd was investigated in intermetallic compounds of Nd and in the paramagnetic salts Nd _x Y _1-x Cl₃·6H₂O (withx=0.02 andx=0.05) at 4.2 K. With the magnetic hyperfine tensorA of Nd_0.01Y_0.99Cl₃·6H₂O known from EPR spectroscopy, the analysis of the unresolved magnetic hyperfine spectra yieldsI _e =5/2 for the spin of the 72.5 keV state, in contradiction to a previous result. The multipolarity of the 72.5 keV γ transition was found to be essentiallyM1 with δ²=0.010±0.014, and the magnetic moment of the 72.5 keV state was determined as μ(5/2)=?0.319±0.004 nm. For various divalent and trivalent Nd compounds as well as for metallic Nd the isomer shift IS of the 72.5 keV γ line was measured. A value for the change of the mean square nuclear charge radius during the 72.5 keV γ transition of Δ〈r ²〉=+(1.9±0.9)·10^?3fm² was deduced using electron density differences from free-ion Hartree-Fock calculations.     

Unusual Light Spectroscopic Properties of a 2-Pyridone-Based Multi-Ring-Fused Fluorescent Scaffold

UV-VIS absorption and fluorescence spectroscopic properties of six related polyaromatic 2-pyridones have been studied. Excitation of the lowest and rather weak and structure-less transition [ε _max (430 nm)?≈?3,000 mol^?1dm³cm^?1] gives rise to a broad fluorescence band in the visible region, for these compounds. These S ₀ ? S ₁ transitions are compatible with symmetrically forbidden transitions, promoted by intensity borrowing, as is revealed by fluorescence depolarisation data. With one exception, all compounds exhibit strong fluorescence, with quantum yields in glycerol varying between 40% and 70%. The corresponding fluorescence lifetimes range from 11 ns to 17 ns, while the radiative lifetimes are very similar (≈26 ns), for all compounds. Interestingly and rarely observed, the calculated radiative lifetimes for the weak absorption band are significantly longer, i.e. between 37 and 40 ns.     

Electromagnetic transition strengths in 24Na

Mean lifetimes, excitation energies and branching ratios of ²⁴Na states, populated in the ²³Na(d, p)²⁴Na reaction have been measured. Gamma-ray spectra were measured at three angles in coincidence with proton groups at θ_p = 169°. Mean lifetimes obtained from DSA are (excitation energy in keV, lifetime in fs): 563, > 1000; 1341, 95 ± 30; 1344, 38 ± 11; 1346, > 1500; 1512, 38 ± 11; 1846, 260 ± 50; 1885, 36 ± 9; 2513, 15 ± 7; 2563, < 25; 2904, 50 ± 15; 2978, < 25; 3216, 22 ± 8; 3372, 19 ± 5. For higher levels up to 4207 keV upper limits of 30 fs were set. In combination with earlier work the following unique spin(-parity) assignments could be made: J^π(1846) = 2⁺, J(2513) = 3, J^π(3745) = 3^?. A new level at E_x = 3681.7 ± 0.6 keV is reported.     

Deformations and shape changes in81Y

High spin states in⁸¹Y up to the probable 33/2⁺ and 29/2^? yrast states have been measured via the reaction⁵⁸Ni(²⁸Si,αp, using the Cologne tandem accelerator. Directional correlations of oriented nuclei were determined and the level scheme was extended with lifetimes measured by means of DSA and recoil distance techniques. Reduced transition strengths inferred from lifetimes were consistent with the results of Hartree-Fock-Bogolyubov calculations, which predict a nearly axially symmetric deformation ofβ ₂≈0.37 for theπ=+ band. Predictions reveal an alignment driving the system to a smaller and triaxial deformation withβ ₂=0.23 andγ=?30°, although the data show this crossing to be somewhat delayed. Particle-rotor calculations for the one-quasiparticle bands corroborate the predictions of deformation parameters based on the cranking model.     

Isomeric state at 945.3 keV in237Np

A new isomeric state in²³⁷Np has been discovered at an excitation energy of (945.3±0.2) keV withT _1/2 =(711±40) ns. Six gamma-ray lines have been measured depopulating the isomeric state to known levels in²³⁷Np. The comparison of the measured absolute gamma-ray transition probabilities with empirical values yields as most probable spinI andK assignmentI=K=13/2 for this isomeric state. It is most likely a 1-proton-2-neutron quasiparticle state 13/2^?π5/2⁺ [642] +ν7/2^? [743] + ν 1/2⁺ [631]. However, a one-quasiparticle 11/2^? [505] configuration for the isomer cannot be excluded.