首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 23 毫秒
1.
The decay of 4 min 158Tm has been investigated with on-line mass-separated samples obtained from the Orsay ISOCELE separator. Measurements of γ-rays, conversion electron lines and γ-γ bi-dimensional coincidences were performed. About 180 transitions were ascribed to the decay and two thirds of them were placed in a decay scheme. The β-band and the γ-band were identified with bandheads situated at 806.40 and 820.13 keV respectively. In addition, a number of other vibrational bands (β-γ, β-β, Kπ = 0? and 1?) are proposed. The decay properties of those bands are discussed in the framework of current nuclear models. The log ft values suggest a 2? assignment for 158Tm with the possible configuration (p404J↓-n521↑).  相似文献   

2.
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 Sn = 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.  相似文献   

3.
Levels in 162, 164, 166Er have been studied using the (α, 2nγ) reaction at an energy of 24 MeV. Singles spectra, γ-γ coincidence spectra, and angular distributions were obtained using Ge(Li) detectors. Transitions from levels in the γ-vibrational bands up to the 8+' in 162, 164Er and 10+' in 166Er were observed and M1/E2 mixtures were determined for many of these transitions. There is a relative shifting upward of the even-spin levels in the γ-band of 166Er while the analogous levels of 162, 164Er are shifted downward with the effect being most pronounced for162Er. The standard phenomenological band-mixing parameters z2 and z02 were obtained from γ-ray branching ratio data and the values are probably correlated with the staggering of levels in the γ-bands. The ratios of the intraband and interband E2 transition strengths which are related to the intrinsic quadrupole moments of the ground-state and γ-bands are discussed. A number of other levels are observed in 162, 164Er and some of these correspond to negative parity states reported in decay studies.  相似文献   

4.
The decay of 161Yb (T12 = 4.2 min) has been investigated with Ge(Li) and Si(Li) detectors and a toroidal β-spectrometer. Isobarically separated samples produced by the YASNAPP facility at Dubna Institute were used. The singles γ-ray spectrum, the conversion electron spectrum, γ-γ-τ and e-γ coincidences have been measured. In all, 67 γ-ray transitions have been observed. A decay scheme for 161Yb is proposed involving 12 excited states in 161Tm. The 72+[404], 72?[523] and 52+[402] levels have been identified. The interpretation of the high-lying levels is discussed. The Q-value of 161Yb decay has been determined to be 3850 ± 250 keV. The A-dependence of the energies of the one-quasiparticle states in odd-A Tm isotopes is demonstrated.  相似文献   

5.
Coulomb excitation studies have been performed to measure transition probabilities of collective quadrupole vibrational states in 180Hf. The I = 2 level of the Kπ = 2+ collective γ-band is established at 1200.5 keV with B(E2)exc = (11.0 ± 1.1) × 10?50e2 · cm4 (3.6 ± 0.4 s.p.u.). The angular distribution of the de-exciting γ-rays from this level yields δ = 9.6+22?5.8 or, less likely, 0.7 ± 0.2 for the 1107.2 keV 2γ+ → 2g+ transition. The B(E2)exc for any KπI = 0+2 stateorother 2+ states up to 1500 keV is less than 5 × 10?51e2 · cm4 (< 0.2. s.p.u.).  相似文献   

6.
Rotational sidebands in 166Er were observed using the 24 MeV 164Dy(α, 2nγ) reactions. The ground-state band was observed up to spin 16+ and does not backbend. A strong backbend is, however, observed in a Kπ = (O+) sideband, indicating that the 12+ state of the previously unknown S-band is at 2656 keV. The γ-band shows significant rotational alignment above I = 10+. Levels of at least two negative-parity bands, one of which is primarily the Kπ = 2? octupole vibration, are also observed.  相似文献   

7.
The decay of 159Tm (T12 = 9.0±0.4min) has been investigated with Ge(Li) andSi(Li) detectors, B-spectrographs and a toroidal spectrometer using isotopically separated samples produced by the YASNAPP facility at Dubna. The singles γ-ray spectrum, the conversion electron spectrum, the positron spectrum, prompt and delayed γ-γ coincidences were measured. Using strong thulium activities, conversion electrons were also measured with high resolution b-spectrographs. In the 159Tm decay 81 new γ-ray transitions were observed. A decay scheme of 159Tm is proposed involving 12 excited states in 159Er. The first members of the rotational bands 32?[521], 52?[523], 32+[402 + 651], 112?505 and 72?[514] and the 52, 72 and 92 states of a strongly perturbed positive parity band were identified. The Q-value of 159Tm was determined to be 3.4±0.3 MeV.  相似文献   

8.
T. Seo 《Nuclear Physics A》1977,282(2):302-316
The level scheme of 151Pm populated by the β-decay of 12 min 151Nd has been studied using Ge(Li) detectors as singles and coincidence γ-ray spectrometers. Most of the new γ-rays have been included in a partial level scheme of 151Pm involving four new levels. Angular correlation measurements on the 170.752–255.678 keV and 170.752–138.882 keV cascades have been made with the result A2 = 0.088±0.005 and ?0.02 – +0.05, respectively. A PAC measurement on the 170.752–255.678 keV cascade has yielded the g-factor of the 255.676 keV level as g = 1.18 ±0.16. A Nilsson-model calculation including Coriolis coupling has been made and the experimental level energies have been well reproduced by the Nilsson orbitais [413]↓, [411]↑, [420]↑, [532]↑, [541]↑ and [550]↑. Theoretical transition rates, E2/M1 mixing ratios, branching ratios and g-factors are in good agreement with experimental values.  相似文献   

9.
The circular polarization P of γ-rays from unpolarized sources of 75Se, 171Er, and 175Yb of strengths ? 500 Ci has been measured with a Compton polarimeter of the radial transmission type. Eight NaI crystals and a four-fold current integration system were used to simultaneously record the data in four independent channels. The results are: P = ?(1.8 ± 6.0) × 10?5 for the 401 keV transition in 75As (the experimental error is ± 1.5 × 10?5, the remaining part is due to the uncertainty in the decay scheme of 75Se), P = (0.8 ± 1.5) × 10?4 for the 296 keV and 308 keV transition in 171Tm, and P = (5.7 ± 0.8) × 10?5 for the 396 keV transition in 175Lu. The last value confirms the parity non-conservation in nuclear forces. The polarimeter was calibrated with bremsstrahlung from 170Tm. The correction for polarized bremsstrahlung was given special attention. Correction factors are derived for 51Cr, 177Lu, and 198Au from a comparison of the measured and calculated bremsstrahlung yields.  相似文献   

10.
Excitation functions for the (α, γ) and (p, γ) reactions leading to 10B have been measured at θ = 0° in the energy range from Ex = 6.7 to 7.6 MeV. Two resonances corresponding to levels at 6.88 and 7.44 MeV are observed. Branching ratios extracted from γ-ray spectra are the same in both reactions for the 6.88 MeV (1?, T = 0 + 1) level, but different at 7.44 MeV. The T = 0 + 1 level at 7.44 MeV (Γ = 90±10keV) is assigned 2? or 2+ from its strong branch to the 3+ ground state. We find no evidence for a second isospin mixed 1? state.  相似文献   

11.
The γ-rays following the β?-decay of 228Fr have been studied by means of γ-ray singles including multi-spectrum analysis and γ-γ coincidence measurements using Ge(Li) spectrometers. Most of the observed γ-transitions could be placed in the level scheme of 228Ra. The accuracy the energy of the first-excited state in 228Ra has been improved and 35 new excited levels have been established, 11 of them grouped into the ground-state band, the low-lying Kπ = 0? band with the head at 474.14 keV and two excited Kπ = 0+ bands with heads at 721.17 and 1041.9 keV. Candidates for two close-lying Kπ = 2+ bands have also been found. It is concluded that the ground state octupole deformation, if any, is less pronounced in 228Ra than in lighter radium isotopes.  相似文献   

12.
The level structure of 184W has been studied from the prompt γ-rays emitted following the capture of both thermal and 2 keV neutrons by 183W. Energies and intensities were measured for both the primary and the secondary (low-energy) prompt γ-rays. From these data, a level scheme is proposed for 184W in which all the Iπ = 0+, 1+ and 2+ states below ≈ 2.0 MeV are observed. Where possible, rotational-band assignments have been made to these and other levels. Additional evidence is presented which confirms the 1130 keV state as being the band head of a Kπ = 2? octupole vibrational band. Admixed Kπ = 0+ and 2+ bands are established at 1322 and 1386 keV, respectively, with the Iπ = 2+ states (at 1431 and 1386 keV) having a mutual admixture of ≈ 12%. In the energy region above 1.5 MeV, the following bands and band-head energies are identified: Kπ = 1+, 1613 keV; Kπ = 0+, 1614 keV; Kπ = 1+, 1713 keV; Kπ = 2+, 1877 keV. The neutron binding energy in 184W has been determined to be 7411.1±0.6 keV. The band structure of the 1613 keV (1+) and 1614 keV (0+) bands is observed to be strongly distorted, the observed A ( h?2/2I) values being ≈ 3.6 keV and ≈ 32 keV, respectively. This strong distortion is shown to be explainable in terms of Coriolis coupling of reasonable strength between the two bands. A similar explanation is shown to account for the somewhat less anomalous A-values (22.8 keV and 14.0 keV, respectively) of the 2+ band at 1386 keV and the 3+ band at 1425 keV. The results of a phenomenological fiveband-mixing analysis involving the Kπ = 0+ and 2+ bands below ≈ 1.5 MeV are presented and discussed. These calculations indicate, among other things, that the direct E2 matrix element connecting the 1322 keV, Kπ = 0+ band and the ground-state band is quite small, possibly zero. They also indicate that a nonzero E2 matrix element exists between this excited Kπ = 0+ band and the γ-vibrational band and that the magnitude of this element is comparable with that between the γ-vibrational and ground-state bands. Arguments favoring and apparently refuting the interpretation of the 1322 keV, 0+ band as a “two-phonon γ-vibration” are presented.  相似文献   

13.
A complete set of conventional γ-ray spectroscopic techniques has been applied to investigate the level structure of 156Gd. A total of twenty-five new levels has been established; unambiguous spin assignments could be given for twelve of them on the basis of angular distributions and conversion electron measurements. The proposed level scheme contains 49 levels, which can be ordered in seven rotational bands. The ground-state band was excited up to Jπ = 14+, the β-band up to 10+, the γ-band up to (11+), the second Kπ = 0+ band tentatively up to (10+), the Kπ = 4+ band up to (8+). Two negative-parity bands, one with even spins and one with odd spins, were excited to Jπ = (12?) and (13?). An isomeric state was established with T12 = 1.3 μs, Jπ = 7?, Ex = 2137.7 keV. The properties of the Kπ = 4+ band and the isomeric state can be well explained by two-quasiparticle configurations. The negative-parity bands are interpreted as aligned octupole bands. Positive and negative-parity bands have been calculated in terms of the IBA model. Good agreement with the experimental results is obtained.  相似文献   

14.
The level structure of 158Gd has been studied using the prompt γ-rays and conversion electrons emitted following neutron capture in 157Gd. The γ-ray energy and intensity measurements were made using both Ge(Li) detectors and a curved-crystal spectrometer. Conversion-electron energy and intensity measurements were made using two separate magnetic spectrometers: one to measure the primary electron spectrum and the other to measure the lower energy secondary electron spectrum. Some γ-γ coincidence measurements were also made among the secondary γ-rays. From these data, a neutron separation energy of 7937.1 ± 0.5 keV has been determined for 158Gd. A level scheme containing 59 excited states with energies < 2.25 MeV, for which de-excitation modes have been identified, is proposed for 158Gd. Many of these states have been grouped into rotational bands. A total of thirteen excited rotational bands with band-head energies below 2.0 MeV are contained in the level scheme. Features of the proposed level scheme include: the Kπ = 0?, 1? and 2? octupole-vibrational bands with band-head energies of 1263, 977 and 1793 keV, respectively; the γ-vibrational band at 1187 keV; three excited Kπ = 0+ bands with band-head energies of 1196, 1452 and 1743 keV; several two-quasiparticle bands with band-head energies in keV (and Kπ assignments) of 1380 (4+), 1636 (4?), 1847 (1+), 1856 (1?), 1920 (4+) and 1930 (1+). An analysis of (d, p) reaction data is presented which permits definite two-quasiparticle configuration assignments to be made to most of these latter bands. Evidence is presented which suggests strong mixing of some two-neutron and two-proton bands. A phenomenological four-band mixing analysis is made of the energy and E2 transition-probability data for the ground-state band and the three lowest-lying excited collective positive-parity bands. Good agreement with experiment is obtained. A Coriolis-mixing analysis of the octupole bands has been carried out and good agreement with the data on level energies and E1 transition probabilities to the ground-state band has been achieved. Values of Z, the ratio of the E1 transition matrix element with ΔK = 1 to that with ΔK = 0, involving the octupole bands and the first four 0+ bands are derived. For three of these 0+ bands, absolute values of these matrix elements are deduced. An interesting alternation in the sign of Z is observed for these four 0+ bands.  相似文献   

15.
The intrinsic structure of 168Tm has been studied using the (3He, d) and (α, t) proton stripping reactions as well as the (d, t) and (3He, α) neutron pick-up reactions. The beams of 24 MeV 3He particles, 25 MeV α-particles and 12 MeV deuterons were obtained from the McMaster tandem Van de Graaff accelerator. The reaction products were analyzed with an Enge-type magnetic spectrograph and detected with photographic emulsions. The spectra have been interpreted in terms of the coupling of an odd proton and an odd neutron, each moving independently in a spheroidal potential, which gives rise to intrinsic two-quasiparticle states with K = ¦Ω1±Ω2¦. The identification of the intrinsic states was made by comparing the experimental cross-section patterns with those predicted with the aid of Coriolis coupling and distorted-wave Born approximation (DWBA) calculations. Rotational bands superimposed on the Kπ = 3+ and Kπ = 4+, {72+ [633]n±12+ [411]p} configurations, the first of which is the ground state, ha been observed in the spectra of all four reactions. New assignments have been made for configurations resulting from coupling the 12? [541], 72+ [404], 54+ [402] and 12? [530] p to the 72+ [633] neutron state. The neutron pick-up measurements confirmed the earlier assignments based on (d, t) reaction studies and suggested tentative assignments for the {12+ [400]n±12+ [411]p} and {32+ [402]n±12+ [411]p}  相似文献   

16.
The decay of 184mRe has been investigated through γ-ray and conversion electron studies. The band head of the Kπ = 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.  相似文献   

17.
The decay properties of the 31 y 178Hf isomeric state have been investigated by means of a Ge(Li)-NaI(Tl) Compton suppression device and a Si(Li) detector, as well as with Ge(Li) and Ge(Li), intrinsic Ge and Si(Li) coincidence arrangements. From the E3 character of the unobserved isomeric transition (11.7 ≦ EIT ≦ 16.7 keV), deduced from L-subshell and M/L ratios, Iπ, K of the isomeric level was determined as 16+, 16. The {p[404] ↓ + p1514] ↑ + n[514] ↓ + n[624]↑}16+ + four quasi-particle configuration was assigned to this level at 2447.5 ± 2.5 keV. As proposed earlier the isomeric E3 transition decays to the 13? level of the band built upon the Iπ = 8? isomer. The |gK?gR| values derived from E2M1 ratios of interband transitions show that the 8? isomer contains about 36 % of the p[404] ↓ + p[514] ↑ configuration and about 64 % of the n[624] ↑ + n[514] ↓ configuration.  相似文献   

18.
Levels of 184W populated in the decay of 8.7 h 184Ta have been studied by a variety of experimental techniques. As a result of β and γ-ray energy and intensity determinations and extensive β-γ and γ-γ coincidence measurements, a detailed 184Ta decay scheme accommodating more than 99.5% of the decay intensity has been established. Intense β-ray groups of end-point energies 1165±26 and 1123±26 keV populate levels in 184W at 1699 and 1746 keV, which de-excite predominantly to the 8.3 μs isomeric level at 1285 keV, recently identified as the 12?[510]ν?112+ [615]ν Kπ = 5? band origin. The 1699 keV level also de-excites to members of a 12?[510]ν?72 [503]ν Kπ = 3+ band based at 1425 keV. New information about the properties of the γ-vibrational and K = 2 octupole bands in 184W is presented and the possible configurations of the levels directly populated in the β? decay are discussed. The configuration 72+[404]π ?32? [512]ν Kπ = 5? is indicated for the 184Ta ground state.  相似文献   

19.
Measurements of γ-ray yield functions, γ-γ coincidence spectra and y-ray angular distributions following the 64Ni(α, n) and (α, 2n) reactions have been made. Beam energies of 17 to 25 MeV were used. Among the new levels observed, with their proposed spin-parity assignments, are: in 66Zn, 3708 keV, (5)+; 3896 keV, 5?; 4812 keV, (7?); 5110 keV, (8?); 6417 keV; (10?); 7516 keV, (12+); and in 67Zn, 2937 keV, 132+; 3491 keV, 172 or 192; 3492 keV, (132(si+)); 4221 keV, (192?); 4631 keV, (212+); 4685 keV, (212?). Comparison between the ground-state sequence, 0+ to 6+, in 66Zn and the first 92+ to 212+ levels in 67Zn strongly suggests that the latter be described as a g91 neutron orbital weakly coupled to the 66Zn core. Other sequences of high-spin 66Zn states are proposed to be formed from two-quasiparticle states containing the g92 excitation, coupled to the same ground-state sequence.  相似文献   

20.
The γ-ray decay spectrum of 82 s 59Cu produced by the 58Ni(p, γ) 59Cu reaction has been studied with a 40 cm3 Ge(Li) detector. The number of γ-rays now known for this decay has more than doubled. Additional direct β+ branches to the 1679.7(52?), 2414.8(32?) and 2681 keV states of 59Ni have been identified with log ft values of 5.5, 5.5 and 6.0, respectively. A major change is the reassignment of the 1340.4 keV γ-ray to a 1679.7 → 339.3 keV transition. A limit of log ft ≧ 6.9 is given for the direct feeding of the 1337(72?) keV state, together with limits for direct population of other energetically available states. The new weak γ-ray branches found for the 878.0, 1301.5 and 1679.7 keV levels are in excellent agreement with the recent theoretical calculations of Glaudemans et al.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号