Lebensdauermessungen am 341,2keV-Zustand und am 404,8 keV-Zustand in131Xe

Lifetime measurements of two excited states in¹³¹Xe populated by the decay of¹³¹I have been carried out. Analysis of data, delivered from a delayed γ-γ-coincidence experiment with a Ge(Li)-Plasticdetector combination, resulted in the following values:T _1/2 of 341.2 keV level in¹³¹Xe: (2.15 ± 0.07) nsT _1/2 of 404.8 keV level in¹³¹Xe: <0.5 ns.     

Nuclear orientation of negative parity states of 131Xe

The anisotropies of the 177, 326, and 503 keV γ-transitions between negative parity states of ¹³¹Xe have been remeasured in the decay of oriented ¹³¹I nuclei. In addition the linear polarization of the 503 keV radiation has been determined with a Compton polarimeter consisting of two Ge(Li) detectors. A combined analysis of the reported experiment and earlier internal conversion and angular distribution data yields the unique assignments $\text{9}\text{2}{}^{\mathrm{?}}\text{and}\text{7}\text{2}{}^{\mathrm{?}}$ for the levels at 341 and 667 keV. The $\text{E2}\text{M1}$ mixing ratios of the 177 and 326 keV transitions are δ(177) = ?4.5 ± 1.5 and δ(326) = ?4.4 ± 1.6. The intensity of the L = 2 component in the first forbidden β-decay to the 667 keV level is at most 60 %.     

Der Zerfall des125m Xe,des127m Xe und des127g Xe

The decay of^125m Xe produced by the reaction¹²²Te(α, n)^125m Xe using a target enriched in¹²²Te (95.4%) and the decay of^127m Xe produced by the reaction¹²⁷J(d, 2n)^127m Xe have been investigated: ^125m Xe decays with a half-life ofT _1/2=(56±3) sec by ayy- cascade withE _γ1=(140.4 ±0.5) keV andE _γ2=(110.5 ±0.5) keV. The experimental conversion coefficients yield multipolarities ofE3 for the 140.4 keV isomeric transition and predominantlyM1 for the 110.5 keV-transition. ^127m Xe decays with a half-life ofT _1/2=(71±2) sec. The decay also proceeds by aγγ-cascade with an isomeric E3 transition ofE _γ1=(172.5±0.3) keV and a predominantlyM1 transition ofE _γ2=(124.6±0.3) keV. In the decay of^127g Xe an additional branching of the electron capture to a level at (618.1±0.3) keV was observed. The relative probability forK-captureP _K618/P_K375=0.40 ±0.07 yields a total transition energyQ _EC=(664 ±4)keV. A spin of 1/2⁺ was assigned to the ground state.     

Nuclear magnetic resonance on oriented 11/2− 129mXe and131mXe in Fe

The magnetic hyperfine splitting frequenciesν _M=¦gμ _NB_HF/h.¦ of the 11/2^? isomeric states^129m Xe (T_1/2=8.9d) and^131mXe (T_1/2=11.8d) in Fe were measured with nuclear magnetic resonance on oriented nuclei at temperatures of 10–15 mK as 188.0(1) MHz and 209.8(1) MHz, respectively, the samples being prepared with the technique of recoil implantation after (α, x n) reactions. The magnetic moments of^129m Xe and^131m Xe are deduced to be (?)0.8914(6)μ _N and (?)0.9943(6)μ _N, respectively. The missing γ-anisotropies for allγ-transitions following the decay of 36.4d ¹²⁷Xe indicateI=1/2 for the ground state spin of¹²⁷Xe.     

Nuclear orientation measurements of the magnetic dipole moments of the 11/2− Isomeric states in129Xe,131Xe and133Xe

The low-temperature nuclear orientation technique was used to measure the magnetic moments of¹²⁹ mXe,¹³¹ mXe and¹³³ mXe implanted in iron by isotope separator. The magnitudes of the magnetic dipole moments, extracted from the gamma-ray anisotropy measurements areμ=?0.80(10)μ _N for^129m Xe,μ=?0.80(10)μ _N for¹³¹Xe andμ=?0.87(12)% for¹³³Xe. The results for these 11/2^? isomers agree with theoretical calculations by the spin polarization procedure using wave functions from the pairing-plus-quadrupole model.     

Die Gamma-Gamma-Winkelkorrelation der 326-177 keV-Kaskade in Xe131

The angular correlation of the 326-177 keV gamma-gamma cascade in Xe¹³¹ has been measured with 2 Ge(Li)-detectors. For the corrected correlation coefficients we obtainedA ₂=0.002±0.011 andA ₄=0.097±0.012. Estimating possible spins of 7/2, 9/2 and 7/2, 9/2, 11/2, 13/2 for the 667.0 and 341.2 keV states respectively, our experimental value agrees with the following spin sequences: 7/2^?→ 9/2^?→11/2^?, 7/2^?→11/2^?→11/2^? and 9/2^?→13/2^?→11/2^?.     

Angular correlation measurements in 131Xe

An experiment is described determining the angular correlations of five γ-γ cascades in ¹³¹Xe appearing in the decay of ¹³¹I. Using a 12-channel goniometer the following results were obtained: 325.8–177.2 keV, A₂ = 0.018(11), A₄ = ?0.003(10); 318.1–404.8 keV, A₂ = ?0.18(4), A₄ = ?0.05(3); 272.5–364.5 keV, A₂ = 0.15(4), A₄ = ?0.03(3); 284.3–80.2 keV, A₂ = ?0.005(7), A₄ = 0.005(15); 318.1–324.6 keV, A₂ = 0.24(5), A₄ = ?0.01(5). The result for the 318.1–324.6 keV cascade has not been corrected for a small influence from the 318.1–404.8 keV cascade. Four E2/M1 mixing ratios are deduced from the angular correlation coefficients (energies in keV): $\text{?0.28 ≦ δ(325.8) ≦}\text{t}\text{?}\text{0.20}$, ?0.19 ≦ δ(318.1) ≦ ?0.035, ?1.5 ≦ δ (324.6) ≦ ?0.05, δ(272.5) = ?0.38(17). Transition strengths and limits to transition strengths are calculated for several transitions. The properties of negative parity states in ¹³¹Xe are investigated theoretically in a model where three neutron holes in the $\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ orbit are coupled to the quadrupole vibrations of the even core. The experimental energies of the lowest negative parity states and the strengths of the transitions between these states are very well accounted for by the calculation.     

A new beta decaying isomer of131Sn; partial level scheme of131Sb

Gamma spectrum and half life of¹³¹Sn decay have been measured using the unslowed fission fragment separator Lohengrin at the high flux reactor of the Institute Laue-Langevin, Grenoble. Two beta-decaying isomers are evidenced, with half-lives of 39±2 s and 50±2 s. Additional confirmation of this isomerism is given by fission fragment-γ delayed coincidence, leading to a partial level scheme of¹³¹Sb including an isomeric level of 50±8 μs life-time at 1676.6 keV.     

Levels and transitions in 131Xe studied by the decay of oriented 131I

Sources of ¹³¹I were prepared by implantation in iron foils. Nuclear orientation of these sources was obtained by cooling them to temperatures of 30 to 50 mK using a dilution refrigerator and saturating the iron by an external magnetic field. Anisotropies of angular distributions of eleven γ-transitions in ¹³¹Xe have been measured, yielding the following results: the levels at 405 and 637 keV are $\text{3}\text{2}$⁽⁺⁾ and $\text{7}\text{2}$⁽⁺⁾ states and the assignment $\text{5}\text{2}$⁽⁺⁾ for the level a keV is confirmed. Deduced values of E2/M1 multipole mixing ratios are (energies in keV): ?0.5 ≦ δ(318) ≦ + 0.2; δ(364) = ?4.53±0.12; + 0.2 ≦ δ(405) ≦ +2.0; δ(723) = +0.207 ± 0.005. The allowed β-decay branch to the level at 637 keV is for at least 90% of the Gamow- Teller type.     

Richtungskorrelationsuntersuchungen an den γ-Kaskaden des131Cs

The¹³¹Cs decay has been studied by angular correlation measurements of the (404-216), (832-216), and (247-373) keV γ-cascades using NaJ(Tl)-detectors in connection with a two parameter multi-channel analyzer. Unique spin assignments are obtained for the 216 (Jπ=3/2⁺) and 373 (Jπ=3/2⁺) keV levels. A previously discussed value ofJπ=5/2⁺ for the 1048 keV level is ruled out. The multipole character of the 404 keV transition is found to beE2 with less than 2%M1.     

Isomeric states in180Os

Two new isomers have been observed in¹⁸⁰Os. A high-K isomer withI, K ≧20 and a half-life ofT _1/2=12+4 ns have been established. It deexcites via two transitions into the 18⁺ level of the yrare band indicating an unusually smallK-hindrance factor. Evidence for an isomer withI, K>16 and a half-life ofT _1/2=41±10 ns was found. A half-life of 17±3 ns was measured for the previously known 7^? state at 1862 keV. The decay scheme of the previously known 7^? isomer at 1928 keV has been extended and a revised version is presented.     

Messung von HalbwertszeitenK-verbotener Übergänge ingg-Kernen der Seltenen Erden

The half-life of the 1,490 keV level in¹⁶²Dy has been measured in the decay of¹⁶²Ho^m (68 min) by delayed coincidences ofKX rays and (900-1,300) keV gamma radiation to be (1.94 ± 0.19) nsec. A half-life in¹⁷⁶Hf has been remeasured in the decay of¹⁷⁶Ta (8.1h) by delayed coincidences of KX rays and (1,100–1,200) keV gamma radiation to be (4.75 ± 0.25) nsec. In order to fix the level with this half-life in the level scheme of¹⁷⁶Hf, the gamma spectrum delayed to KX rays was measured. It is suggested that probably the 1,227.4 keV-level of¹⁷⁶Hf is delayed and has the spin 2^? or 3⁺.     

γγ-Richtungskorrelationsmessungen am79Br

Using gaseous and solid sources of⁷⁹Kr the γγ directional correlations of the 208.6–397.6 keV-, 299.6–306.6 keV- and 389.1-217.1 keV γγ cascades of⁷⁹Br were measured. The results allow the unambiguous assignment of spin and parity to the levels at 397.6 keV (1/2^?) and 306.6 keV (1/2^?). In addition, they confirm the assignment to the level at 217.1 keV (5/2^?).     

New excited states of the nucleus129Xe

Excited states of¹²⁹Xe have been investigated through the¹²⁶Te(α,n)¹²⁹Xe reaction at the incident energy E=16MeV by means of in-beam gamma ray spectroscopy. Numerous levels below the excitation energy of 2.5MeV were found. Spin assignments were made from side feeding excitation functions. A new level at 274.2keV, which is suggested as spin 9/2 negtive parity bandhead, was observed for the first time.     

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 $\text{7}\text{2}{}^{\mathrm{?}}$.     

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.     

Low spin structure of128Xe

The low spin structure of¹²⁸Xe has been studied by means of the (α,n) reaction using beam energies near the Coulomb barrier. An extended level scheme with spins I≤10? and many new spin and parity assignments could be established. The results point to the completeness of the reaction at low spins and excitation energies below 2.5 MeV.     

Messung des Elektroneneinfangs am Kern176m Lu

The electron capture of^176m Lu to the ground state and to the first excited state of¹⁷⁶Yb has been observed by measuring the YbK x-rays and the 82,2 keV gamma-rays from the gamma decay of the first excited state in¹⁷⁶Yb. With the data of the 88,36 keV gammarays following the beta decay of^176m Lu to the first excited state of¹⁷⁶Hf the electron capture/beta decay ratio of^176m Lu was found to be (0,95±0,16)·10^?4. The electron capture branching ratio to the ground state and to the first excited state of¹⁷⁶Yb was found to be 40/60±30%. By analyzing the 88,36keV gamma-rays and the HfKx-rays the halflife of^176m Lu was evaluated to be 3,66±0,04 h. The value for theK-conversion coefficient of the 88,36keV transition was determined from the x-ray/gamma-ray ratio to be 1,19±0,09.     

Directional correlations of gamma cascades in153Gd

TheEC-decay of¹⁵³Tb to the levels of¹⁵³Gd has been studied in singles and coincidence mode using high resolution x-ray andγ-ray Ge(Li) detectors. The results, in general, are in agreement with the recent findings of Tuurnalaet al. showing a very high density of low-spin states in¹⁵³Gd. The results of theγγ directional correlation experiment using two Ge(Li) detectors together with the I.C.C. data have been used in assigning the spin and parity of 5/2^?, 5/2^?, 3/2^?, 3/2⁺, 5/2⁺, 3/2⁺ and 3/2⁺ to the 41.6, 109.8, 129.1, 212.0, 303.5, 945.6 and 1102.0 keV states respectively. Multipolarity assignments to majority of theγ-transitions have been made from the I.C.C. data obtained through the knowledge of ourγ-ray intensities and the published conversion-electron intensities. From the multipole characters of theγ-transitions, parity assignments have been made to seven states in¹⁵³Gd. Our results have been discussed and compared with that of Tuurnalaet al.     

Die Konversion des86mRb

^86mRb was produced by irradiation of natural Rb and Rb enriched in⁸⁷Rb (99.2%) with fast neutrons. The half-life ofT _1/2=(61.2±1.0) sec and the energy ofE _ρ=(556.03±0.25) keV were remeasured. The experimental conversion coefficients α_tot=0.0184±0.0015 andα _K =0.0158±0.0015 yield the multipolarity of E4 for the isomeric transition. The spin of 6^? was assigned to the isomeric state. It is proposed that the spin 6^? is formed by coupling ap _3/2-proton and ag _9/2-neutron according to Nordheim's “weak” rule.