Gammaübergänge und Energieniveaus in Dy 165

220 neutron capture Gamma rays of Dy 165 were measured with the Risø curved crystal spectrometer. The intense transitions permitted the construction of a level scheme for this oddN nucleus. The rotational bandsK=7/2⁺[633],K=1/2^?[521] andK=5/2^?[512] were precisely localized, including the spin 11/2 states. Gammavibrational bands built on these Nilsson orbits were observed with their band heads at 538.6, 573.5 and 570.2 keV. TheI=5/2 term at 533 keV can be considered as the 5/2^?[523] Nilsson state. The branching ratios allowed the determination of (g _K?g^R)²-factors for the [633], [521] and [512] bands and yieldedE 1-hindrance factors.     

E1,ΔK=0−Übergänge in deformierten Kernen ungerader Massenzahl

The half lives of the 5/2 5/2^?[523] level at 25.7 keV in ₆₆ ¹⁶¹ Dy and the 5/2 5/2⁺[642] level in ₆₈ ¹⁶³ Er, found in this work to lie at 69.2 keV, have been determined by the delayed coincidence method to be T_1/2=27.8± 1.5 nsec, and T_1/2=8.8± 0.5 nsec, respectively. The following hindrance factors relative to the single particle Weisskopf estimate (F _W and the Nilsson estimate (F_N were obtained: ₆₆ ¹⁶¹ Dy 5/2 5/2^?[523] → 5/2 5/2⁺[642]:F_W=(6.6± 1.3) × 10³, F_N=0.48± 0.10 ₆₈ ¹⁶³ Er 5/2 5/2⁺[642] → 5/2 5/2^?[523]:F_W=(2.4± 0.5)× 10⁴, F_N=1.8 ± 0.4 A systematic difference between transitions in odd proton nuclei and odd neutron nuclei was found: E1, ΔK=0 transitions in odd neutron nuclei have hindrance factors F_N from 2.9 to 0.16, this means, these transitions are in agreement with the predictions of the Nilsson model within a factor of 10. For transitions in odd proton nuclei one has hindrance factors F_N from 75 to 9.9 × 10^?4. It is shown that a small difference between the deformation of the initial and the final state changes the transition probability of both, proton and neutron transitions, considerably.     

Neutroneneinfangs-Gammaspektrum und Niveauschema von Erbium 167

The (n, γ)-spectrum of Er 167 was investigated by means of the Risø bent crystal spectrometer. The energies and intensities of 47 transitions were measured. 22 of them were fitted into a level scheme. The rotational bands of theK=7/2⁺[633],K=1/2^?[521], andK=5/2^?[512] states were found up to the spin valuesI=11/2⁺, 9/2^?, and 7/2^?. Gammavibrational states of these Nilsson orbitals were determined or proposed. The energy of theK=5/2^?[523] state was suggested. Branching ratios of gamma transitions were compared with theoretical predictions.     

Low-lying intrinsic energy levels in the nucleus170Ho

The band-head energies of the two-quasiparticle states expected in the doubly odd deformed nucleus¹⁷⁰Ho are calculated for a zero range residual interaction. The results are compared with the available experimental information. It is concluded that the ground state has the Nilsson configuration 6⁺{7/2^?[523↑] _p }+5/2[512↑] _n being the 2.76m isomer whereas the 43s isomer is the 1⁺ ∑=0 state arising from the same configuration and lies at about 100 keV excitation energy in agreement with the experiment. The first excited state in this nucleus is predicted to be the 4^?{3/2⁺[411↑] _p +5/2^?[521↑] _n } state close to the ground state with the corresponding 1^? ∑=0 member expected to appear well above the 1⁺ isomer.     

Rotational properties of the odd-Z transfermium nucleus 255Lr by a particle-number-conserving method in the cranked shell model

Experimentally observed ground state band based on the 1/2-[521] Nilsson state and the first exited band based on the 7/2-[514]Nilsson state of the odd-Z nucleus ~(255)Lr are studied by the cranked shell model(CSM) with the paring correlations treated by the particle-number-conserving(PNC) method. This is the first time the detailed theoretical investigations are performed on these rotational bands. Both experimental kinematic and dynamic moments of inertia(J~(1)and J~(2)) versus rotational frequency are reproduced quite well by the PNC-CSM calculations. By comparing the theoretical kinematic moment of inertia J~(1) with the experimental ones extracted from different spin assignments, the spin 17/2~-→13/2~- is assigned to the lowest-lying 196.6(5) ke V transition of the 1/2~-[521] band, and 15/2~-→11/2~- to the 189(1) ke V transition of the 7/2~-[514] band, respectively. The proton N = 7 major shell is included in the calculations. The intruder of the high- j low-? 1 j_((15)/2)(1/2~-[770]) orbital at the high spin leads to band-crossings at ω≈0.20( ω≈0.25) Me V for the 7/2~-[514] α =-1/2(α = +1/2) band, and at ω≈0.175 Me V for the1/2~-[521] α =-1/2 band, respectively. Further investigations show that the band-crossing frequencies are quadrupole deformation dependent.     

Investigation of the reaction Dy164 (n, γ) Dy165

The level structure of Dy¹⁶⁵ has been investigated at the Karlsruhe research reactor using thermal neutron capture in Dy¹⁶⁴. The target was Dy₂O₃ enriched to 92.71% Dy¹⁶⁴. Neutrons were either monochromized by Bragg reflection from a lead crystal or transmitted through a bismuth single crystal filter. High-resolution measurements of the capture spectrum have been performed by means of a Ge(Li) 5-detector pair spectrometer and a Ge(Li) anti-Compton assembly. A large number of new lines has been observed. Cascade relationships were studied by using several techniques: a double coincidence apparatus with 4″ Ø×5″ NaI(Tl) detectors, a coincidence system containing a scintillation detector and a 34 cm³ Ge(Li)-diode as well as a two-parameter system involving the pair spectrometer (with NaI (Tl) as the primary detector) and a single 4″Ø×6″ NaI (Tl) counter. In the framework ofNilsson's model and simple microscopic pictures of vibrational states the results are consistent with the following spectroscopic interpretation: 0 keV, 7/2⁺[633]; 108.2 keV, 1/2^?[521]; 184.3 keV, 5/2″[512]; 533.5 keV, 5/2″ [523]; 538.6 keV, 7/2⁺[633] +Q₂₂; 570.3 keV, 5/2^?[512]+Q₂₂+1/2^?[510]; 573.6 keV, 3/2^? [521]+1/2^?[521]+Q₂₂; 1103.3 keV, 1/2^? [521]+Q₂₂+3/2^? [521]. For comparison preliminary results are given for the isotonic nucleus Yb¹⁶⁹.     

Half-life measurements of intrinsic states in deformed odd-mass nuclei

The half-lives of the following intrinsic states in deformed odd-mass nuclei has been measured by delayed coincidences with a time-to-amplitude converter:

1. 5/2 5/2⁺[642] at 86.5 keV in¹⁵⁵Gd:T _1/2=6.7±0.3 ns, which results in the determination of theE1,ΔK=1 transition probability to the ground state 3/2 3/2^?[521] and first rotational state 5/2 3/2^?[521], yielding hindrance factors ofF _N ≈5.5 and ≈1.8 (F _W =3.1×10⁴ and 2.3×10⁴) respectively.
2. (3) 5/2 5/2^?[512] at 191.4 keV in¹⁶⁹Yb:T _1/2=3.35±0.15 ns and at 122.39 keV in¹⁷¹Yb:T _1/2=265±20 ns which results in the determination of the transition probabilities of theE1,ΔK=1 transitions to the ground states 7/2 7/2⁺[633], of theK-forbiddenM1 transitions to the 5/2 and 3/2 1/2^?[521] and of theE2 transitions to the 5/2, 3/2 and 1/2 1/2^?[521] states in both nuclei.

TheE1 transition probabilities are compared to the transitions between the same Nilsson states in¹⁷³Yb and¹⁷⁵Hf discussing the influence of the position of the Fermi surface — obtained from recent stripping and pick-up reactions — on these transition probabilities. Additional information on the decay scheme of¹⁷¹Lu→¹⁷¹Yb is obtained by delayed coincidence measurements. For testing the used time-to-amplitude converter the well known half-lives of the 482 keV level in¹⁸¹Ta (T _1/2=10.4±0.3 ns) and of the 279 keV level in²⁰³Tl (T _1/2=0.285 ±0.015 ns) were measured, in good agreement with other measurements.     

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

The strongly shape driving πh_9/2[541]l/2^? configuration with α=+1/2 exhibits some anomalous, and so far unexplained, features concerning the crossing frequency, ?ω_c, the aligned angular momentum, i_x, and interaction strength, at the alignment of the first pair of i_13/2 quasineutrons in several odd-Z rare earth-nuclei. The h_9/2[541]1/2^? and h_11/2[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 ?. Theγ-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 theγ-transition energies are identical within ～0.2 keV below the vi_13/2 crossing.     

Time constants of radiative transitions from the 5<Emphasis Type="Italic">d</Emphasis>[3/2]<Subscript>1</Subscript> level of a xenon atom

Integral yields of spontaneous emission at wavelengths of 1.73, 2.03, and 2.65 μm have been measured upon excitation of pure xenon by a pulsed electron beam. These yields have been analyzed and experimental data have been obtained on time constants of radiative transitions 5d[3/2]₁ → 6p[5/2]₂, 5d[3/2]₁ → 6p[3/2]₁, and 5d[3/2]₁ → 6p[1/2]₀ of XeI, which appeared to be equal to (2300 ± 400) × 10^?9, (300 ± 40) × 10^?9, and (1300 ± 200) × 10^?9 s, respectively. It is shown that the experimental data are in a qualitative agreement with the results of computational and theoretical investigations. The results of averaging the experimental and calculated data are proposed for use as recommended values of the corresponding constants.     

Investigation of neutron-deficient tungsten isotopes168−174W

The decays of^168?174W were observed in the reactions of³⁶Ar and⁴⁰Ar beams with enriched targets of¹³⁶BaF₂ and¹³⁸BaF₂. The measured half-lives are 53(2) s, 76(6) s, 2.42(4) min, 2.38(4) min, 6.6(9) min, 6.3(4) min, and 35.3 (5) min, respectively. Decay schemes were derived from theγ ^? and X-ray coincidence data. Spin assignments of ground- and excited states are discussed within experimental level systematics and compared with the results of microscopic-macroscopic model calculations. Excitation energies of modeled one-quasiparticle states were found in reasonable agreement with the experimental data. Allowed unhindered beta decay from the 5/2^? [523] to the 7/2^? [523] configuration was identified in¹⁷¹W and this transition is also proposed for the decays of the even-even isotopes^{168, 170}W.     

Anomalous shift in crossing frequency for the proton 1/2[541] band in175Ta

High-spin states in¹⁷⁵Ta have been populated in the¹⁶⁰Gd (¹⁹F,4n)¹⁷⁵Ta reaction with beams provided by the HI-13 tandem accelerator at the Institute of Atomic Energy in Beijing. A level scheme was constructed from γ-γ coincidence experiments. Seven decay sequences built on 5/2⁺[402], 1/2^?[541], 7/2⁺[404] and 9/2^? [514] proton Nilsson configuration have been extended to higher spin. An anomalously large delay of the neutron AB crossing built on the h_9/2 proton Nilsson State 1/2^?[541] is discussed.     

Behavior of the excitation cross sections of the perturbed series of the xenon atom

Behavior of the excitation cross sections of the perturbed 6s[3/2]_n°?np[1/2]₀ spectral series of the xenon atom is experimentally studied. By using the methods of extended electron beam and optical spectroscopy, the cross sections are measured and the optical excitation functions are recorded for the transitions of this series with n=6–13. A deviation of the dependence Q=f(n) from a power-law function is revealed, as well as changes in the form of optical excitation functions and in the nature of the branching caused by perturbation of the 7p[1/2]₀ level by levels of the 5p ⁵(² P _1/2°)6p configuration.     

Backbendings of superdeformed bands in ~(36,40)Ar

Experimentally observed superdeformed(SD) rotational bands in ~(36)Ar and ~(40)Ar are studied by the cranked shell model(CSM) with the pairing correlations treated by a particle-number-conserving(PNC) method.This is the first time that PNC-CSM calculations have been performed on the light nuclear mass region around A=40.The experimental kinematic moments of inertia J~((1))versus rotational frequency are reproduced well. The backbending of the SD band at frequency around ω =1.5 Me V in ~(36)Ar is attributed to the sharp rise of the simultaneous alignments of the neutron and proton 1 d_(5/2)[202]5/2 pairs and 1 f_(7/2)[321]3/2 pairs, which is a consequence of the band crossing between the 1 d_(5/2)[202]5/2 and 1 f_(7/2)[321]3/2 configuration states. The gentle upbending at low frequency of the SD band in ~(40)Ar is mainly affected by the alignments of the neutron 1 f_(7/2)[321]3/2 pairs and proton 1 d_(5/2)[202]5/2 pairs.The PNC-CSM calculations show that besides the diagonal parts, the off-diagonal parts of the alignments play an important role in the rotational behavior of the SD bands.     

Level schemes of163, 165Yb and backbending behaviour of neutron deficient Yb-isotopes

High spin states in^{163, 165}Yb have been populated using (¹⁶O,xn) reactions with^{152, 154}Sm targets. Several rotational bands are observed and the lifetime of highly converted transitions have been measured utilizing a solenoid-Si(Li) spectrometer and Ge(Li) detectors. Thei _13/2 and 3/2^? [521] bands do not backbend, whereas the 5/2^? [523] bands do, indicating additional processes besides the rotational alignment of one i_13/2 neutron pair that are responsible for the backbending.     

Nuclear levels in 238Np

Low and high energy spectra from thermal neutron capture in ²³⁷Np have been studied over the energy ranges 25 to 650 keV and 2600 to 5500 keV. Primary transitions from neutron capture in four resonances have been observed between about 4800 and 5400 keV. Using 12 MeV deuterons, (d, p) spectra at three angles have been observed with a magnetic spectrograph. A nuclear level scheme for ²³⁸Np has been constructed by combining the results of the above measurements with previous data from a study of the ^242mAm α-decay. The Nilsson model has been used to interpret the level structure. Including results from the previous α-decay study, nine rotational bands can be assigned. The Nilsson configurations (K^π [Nn₃ΛΣ]) and band-head energies are: 2⁺π[642↑]?ν[631↓], 0.0 keV; 3⁺π[642↑]+ν[631↓], 86.6 keV; 3^?π[523↓]+ν[631↓], 136.0 keV; 2^?π[523↓]?ν[631↓], 182.8 keV; 5⁺π[642↑]+ν[622↑], 278.1 keV; 0⁺π[642↑]?ν[622↑], 332.5 keV; 5^?π[523↓]+ν[622↑], 342.6 keV; 0^?π[523↓]?ν[622↑], 286.0 keV; 6^?π[642↑]+ν[743↑], 301 keV. The measured (d, p) reaction cross sections are compared with theoretical calculations based on these assignments. The Gallagher-Moszkowski rule is found to be valid in the four cases where we have observed both parallel and antiparallel coupled bands with $\text{K}{}^{\mathrm{+}}\text{= Ω}{}_{\mathrm{<mtext>p</mtext>}}\text{+Ω}{}_{\mathrm{<mtext>n</mtext>}}$ and $\text{K}{}^{\mathrm{?}}\text{= |Ω}{}_{\mathrm{<mtext>p</mtext>}}\text{?Ω}{}_{\mathrm{<mtext>p</mtext>}}\text{|}$. The lowest levels of the two K = 0 bands have spin I = 1; Newby odd-even shifts can be determined in both cases.     

Signature splitting in two quasiparticle rotational bands of <Superscript>180,182</Superscript>Ta

The signature splittings in K^π = 1 ⁺: 7 /2[404] _π?9 /2[624] _ν, K^π = 0^?: 9 /2[514] _π?9 /2[624] _ν bands of ¹⁸⁰Ta and K^π = 0^?: 7 /2[404] _π?7 /2[503] _ν, K^π = 1^?: 5 /2[402] _π?3 /2[512] _ν, K^π = 1⁺: 7 /2[404] _π?9 /2[624] _ν bands of ¹⁸²Ta are analysed within the framework of two-quasiparticle rotor model. The phase as well as magnitude of the experimentally observed signature splitting in K^π = 1⁺ band of ¹⁸⁰Ta, which could not be explained in earlier calculations, is successfully reproduced. The conflict regarding placement of a 12 ⁺ level in K^π = 1 ⁺: 7 /2 ⁺[404] _π?9 /2 ⁺[624] _ν ground-state rotational band of ¹⁸⁰Ta is resolved and tentative nature of K^π = 0^?: 7 /2[404] _π?7 /2[503] _ν, K^π = 1⁺: 7 /2[404] _π?9 /2[624] _ν bands observed in ¹⁸²Ta is confirmed. As a future prediction for experimentalists, these two-quasiparticle structures observed in ¹⁸⁰Ta and ¹⁸²Ta are extended to higher spins.     

Low-lying two-particle states in the nucleus236Np

The ambiguities and the uncertainties about the energy levels of the doubly odd actinide nucleus ₉₃ ²³⁶ Np₁₄₃ are sought to be removed by determination of the bandhead energies of various two-particle configurations expected to appear in the low energy spectrum of this nucleus. The calculations involve quantitative evaluation of the zero range neutron-proton residual interaction energy contribution to the bandhead energy for each configuration. It is concluded that the ground state is the long-lived isomer with spin-parityI ^π=6^- arising from the configuration {5/2⁺[642] _p +7/2^?[743] _n }. Bandhead energies for eight two-particle states appearing upto an excitation energy of 400 keV are presented and the results are discussed in the context of the available and further experiments.     

Energy levels of the nucleus248Bk

The ambiguities and contradictions in presently available experimental information on the energy levels of the doubly odd deformed nucleus²⁴⁸Bk are sought to be cleared through calculation of the band head energies of the two-particle states based on evaluation of the residualn-p interaction energy for a zero range interaction. The applicability of the Gallagher-Moszkowski rule for the relative ordering of the spin triplet and singlet states is critically examined. It is concluded that the 8^? state from the {7/2⁺[633]p; 9/2^?[734]n configuration is the long lived isomer and forms the ground state of this nucleus. The 1^? state of the same configuration is the short lived isomer and an excited state in accordance with the GM rule and so is the 6⁺ state of the {3/2^?[521]p; 9/2^?[734]n configuration. The expected location of 20 two particle states comprising 10 GM pairs is calculated and compared with the available experimental information.     

Study of band structures and crossings in179Re

High-spin states in¹⁷⁹Re have been populated by the¹⁶⁵Ho(¹⁸O, 4n) and¹⁷⁰Er(¹⁴N,5n) reactions. A level scheme is constructed from the studies ofγγ-coincidences using anti-Compton spectrometer arrays. The previously known 5/2⁺[402], 1/2^? [541] and 9/2^? [514] bands have been extended to 35/2⁺, 45/2^? and 39/2^?, respectively. In addition a 1/2⁺ [660] band, a three-quasiparticle band and two isomers were established. Furthermore several level sequences were identified decaying into the 5/2⁺ [402] and 1/2^? [541] bands. This allowed to determine the excitation energy of the 9/2^? member of the latter band. The band crossing features of the bands have been explained as the rotation alignment of ani _13/2 quasineutron pair taking into account shape changes.     

Levels of233Pa excited in helium-induced single-proton transfer reactions

The²³³Th(³He,d)²³³Pa and²³³Th(α, t)²³³Pa reactions were studied with 28.5-MeV³He and 30-MeV α-particles, respectively. The reaction results are interpreted in terms of a distorted-wave Born-approximation analysis. Transferred angular momenta are deduced from (α, t) and (³He,d) cross-section ratios,R=dσ(α, t)/dσ(³He,d). Theoretical cross sections, calculated in the framework of the Nilsson model with pairing and Coriolis interactions included, are in reasonable agreement with experiment. Rotational bands built on the following Nilsson proton configurations are identified in²³³Pa: 1/2_?[530↑], 3/2⁺[651↑], 1/2⁺[660↑], 5/2⁺[642↑], 5/2_?[5231↓], and 3/2_?[521↑].