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.     

The decay of 0.57 s114Cs

Fusion reactions between⁵⁸Ni projectiles and⁵⁸Ni target nuclei were used to produce¹¹⁴Cs activity, which was studied by on-line mass separation and decay spectroscopy. The obtained half-life of 0.57±0.02 s and the probability ratio of 44±3 between betadelayed proton and beta-delayed alpha emission represent data with improved precision. The absolute branching ratios for both particle decay modes were determined to be (7 ±2)×10^?2 and (1.6±0.6)×10^?3, respectively. These branching ratios and the shapes of particle spectra are discussed with reference to the statistical model calculations. Groundstate alpha decay of¹¹⁴Cs was observed with an alpha energy of 3,226±30 keV and a branching ratio of (1.8±0.6)×10^?4. An upper limit of the branching ratio for a possible ground-state proton decay was set at 5×10^?4. Fromγ-ray singles andγ-γ coincidence measurements, excited states in¹¹⁴Xe are proposed.     

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.     

The decay of115 mIn

The decay of^115m In has been investigated using accurate counting methods. The emission rate of conversion electrons plusβ ^?-particles was determined with a 4π proportional flow counter. The total andK-shell internal conversion coefficients of the 336 keVγ-ray in¹¹⁵In were measured by the electron X-ray coincidence method using combinations of a Si surface barrier with a NaI(Tl) detector and of a magneticβ-spectrometer with a high energy resolution Si(Li) detector, respectively. The conversion ratioR=K/(L+M+...) was deduced from electron spectra recorded with the magneticβ-spectrometer. The 336 keVγ-ray emission rate of all used sources was determined with a calibrated NaI(Tl)γ-ray spectrometer. A Ge(Li) detector has been used to determine the relative intensity of the 497 keVγ-ray in¹¹⁵Sn. As results have been deduced the 336 keVγ-ray emission per decay (N _γ1/N ₀=(45.9 ± 0.1)%), the total internal conversion coefficient (α=1.073 ± 0.014), theK-shell internal conversion coefficient (α _K=0.843±0.012), the conversion ratioR=3.63±0.07, theβ ^?-transition per decay going to the ground state (N _β1/N ₀=(5.0 ± 0.7)%) and to the first excited level in¹¹⁵Sn¹¹⁵Sn(N _β2/N ₀=(0.047 ± 0.002)%), and the 497 keVγ-ray emission (N _γ2/N _γ1=(0.103 ± 0.004)%). From the obtained internal conversion data it follows that the 336 keVγ-ray transition is ofM4 character with anE5 admixture of less than (3.5±1.5)%. The half-life of the isomeric state¹¹⁵ mIn has been determined with four different methods. The result isT _1/2=(4.486±0.004) h.     

Anomalous conversion of 127 keV (E3) transition in134Cs

The total conversion coefficient of the 127.49 keV E3 isomeric transition in the decay of^134mCs was measured using the gamma intensity balance method with the help of a high resolution low energy photon detector. Theα _Tvalue was found to be 5.84±0.47 as against the theoretical value of 6.96, thus showing an anomaly of (16.1±6.7)%. TheK-conversion coefficient,α _kwas also measured using the X-ray peak to gamma ray intensity method and found to be 2.24±0.04 as against the theoretical value of 2.72, which shows an anomaly of (17.6±1.4)% consistent with the experimental anomaly inα _T. TheE3 hindrance factor of the isomeric transition was estimated to be (3.44±0.23) ·10⁴.     

Low-lying 134Cs excited states from the (n, γ) reaction

Low-energy γ-ray and conversion electron spectra from the ¹³³Cs(n,γ)¹³⁴Cs reaction have been investigated with a bent cyrstal spectrometer, β-speetrometer, Ge(Li) and Si(Li) detectors. Gamma-gamma coincidence measurements were made with the Ge(Li)-Ge(Li) arrangement. Gamma-gamma delayed coincidences have been studied with the use of the Ge(Li)-NaI(Tl) coincidence set-up. The decay of 2.9 h ^134mCs has been investigated with the prism β-spectrometer and Ge(Li) detector. The half-lives of the 176.403 and 257.112 keV levels have been measured to be 49.7 ± 0.8ns and 12.3 ± 1.1 ns respectively. The neutron binding energy B_n have been calculated to be 6891.4 ± 1.3 keV. Spin and parity assignments have been made for almost all the levels. The possible structure of the levels deduced is discussed.     

States inN=80140Nd populated in the decay of140Pm

The level structure of theN=80,¹⁴⁰Nd has been investigated through the beta decay of^140m Pm and^140g Pm, whose decay half-lives were measured to be 5.95±0.05 min and 9.1±0.5 sec, respectively. Decay schemes for the two isomers have been constructed fromγ-ray measurements. With the help of the beta decayft values and internal conversion electron measurements, spins and parities were deduced for levels in¹⁴⁰Nd. Among the levels a 7^? state at 2222.0 keV and a 5^? state at 2273.3 keV are identified as two-neutron quasiparticle states. The (ie233-01) for^140m Pm and^140g Pm have been deduced as 7^? and 1⁺, respectively. From beta end-point measurements, the decay energies of the two isomers have been determined asQ _EC=6.48±0.07 MeV^140m (Pm) andQ _EC=6.08±0.10 MeV (^140gPm). The results are discussed in the light of nuclear systematics of theN=79 and 80 isotones.     

Life-times of the 4 1 + -states in134Te and136Xe

The half-lives of the first excited 4⁺-levels in theN=82 isotones ₅₂ ¹³⁴ Te and ₅₄ ¹³⁶ Xe have been determined tot _1/2=(1.50±0.13) ns andt _1/2=(1.32±0.10) ns, respectively, through the measurement of delayedγ,γ-coincidences. The value for¹³⁴Te is in agreement with the assumption that the low lying levels of this nucleus are based mainly on theg ₇ ^{2 /2} proton configuration. In¹³⁶Xe the half-life is unexpectedly small which indicates a more strongly admixed structure of the levels involved in this case.     

Transition probabilities and the structure of some negative-parity states in126,130Xe and132Ba

The lifetimes of several negative-parity states in^126,130Xe and¹³²Ba have been determined by means of the generalized centroid-shift method. The reactions^124,128Te(α,2n) and¹²²Sn(¹³C, 3n) have been used. Following results were obtained:T _1/2(2758 keV)=1.3±0.2 ns in¹²⁶Xe,T _1/2(2060 keV)=0.20±0.10 ns,T _1/2(2104 keV)=0.50±0.10 ns,T _1/2(2376 keV)=0.30±0.10 ns andT _1/2(2973 keV)=4.6±0.4 ns in¹³⁰Xe as well asT _1/2(2120 keV)=0.40 _?0.10 ^+0.20 ns in¹³²Ba. A systematics of the B(E2; 7 _? ¹ ?5 ₁ ^? ) values in theN=76 nuclei is presented. Electric dipole and quadrupole transition rates are discussed in terms of octupole and quadrupole collectivity. The structure of the 5 ₁ ^? and 7 ₁ ^? states is considered. Nuclear reactions:^124,128Te(α, 2 _n ),E=26 MeV,¹²²Sn (¹³C, 3n),E=53 MeV; measuredE _γ I _γ , γ-r.f. DeducedT _1/2, B(σL) in^126,130Xe and¹³²Ba. Ge detectors. Generalized centroid-shift analysis.     

Search for an isomer in94Rb

Measurements of theβ-ray half-life,γ-ray and X-ray spectra andγ-ray half-lives have been done with a plastic scintillation detector, a high resolution Ge(HP) detector and a 142 cm³ Ge(Li) detector to search for an isomeric state in⁹⁴Rb. Mass-separated activities of⁹⁴Rb were obtained from the He-jet type on-line mass-separator at the Kyoto University reactor. No isomeric transition was found in theγ-ray and X-ray measurements with the upper limits of 3×10^?4 and 8×10^?5, respectively, as compared with the 836.9 keV transition. Half-lives obtained from theγ-ray decay measurements are discussed in the light of classification given byQ _β -value measurements.     

Nuclear levels in228Th populated in the decay of228Pa

The electron-capture decay of²²⁸Pa to levels in²²⁸Th has been studied using mass-separated sources and high-resolutionγ-ray and conversion-electron spectroscopy. A level at 979.5 keV is assigned as 2⁺ member of a second excited K_π=0⁺ band, with the 0⁺ band head at 938.6 keV. The 2⁺ and 3⁺ members of a second excited K_π=2⁺ band at 1153.5 and 1200.5 keV, which decay by strongE0 transitions to the 969 keVγ-vibrational band, are confirmed. In addition we tentatively propose a K_π=1⁺ band at 944 keV. The K_π=0^?, 1^? and 2^? members of the octupole quadruplet are confirmed, and theγ decay of these levels is analysed in an approach, in which the mixing of the octupole bands by the Coriolis interaction is taken into account. It is suggested that octupole correlations might be important for theE1 transition moments. A total of 29 levels is observed between ～1.4 and ～2.0 MeV, for which the nuclear structure, and the possible assignment to rotational bands, is unclear.     

The decay scheme of the 3-s Isomer of100Nb and the properties of levels in100Mo

Theβ ^? decay of the longer-lived isomer in¹⁰⁰Nb has been studied at the fission-product separator JOSEF. Measurements ofγ-ray singles spectra, ofγ-γ coincidences and ofγ-γ angular correlations have been performed. A value oft _1/2=2.99(11)s has been determined for the isomer which probably hasI ^π=4⁺ or 5⁺. A scheme of the levels of¹⁰⁰Mo which are populated in the decay of this isomer has been established. Information on the spins of several states of¹⁰⁰Mo has been obtained. Thus,I=0 levels have been identified at 1,505, 2,038 and 2,087 keV. The mixing ratios have been determined for the 2₂ ⁺→2₁ ⁺ and 2₃ ⁺→2₁ ⁺ transitions. The results provide evidence for a vibrational structure of¹⁰⁰Mo with separate bands based on the ground state and on the first excited 0⁺ level.     

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.     

Theβ-decay of100Y: Discovery of a very low lying 0+ state in100Zr

Theβ-decay of¹⁰⁰Y has been investigated at the gas filled recoil separator JOSEF by means ofγ-ray and conversion electron spectroscopy. Twoβ-decay modes, of half lives 0.94±0.03 s and 0.55±0.15 s, have been observed. Using Xγ-, Xce-, γγ- andγce-coincidences the level scheme of¹⁰⁰Zr has been constructed. An excited 0 ₂ ⁺ state at 331.3 keV has been discovered in this nucleus. Theβ-decay from the 0.55 s decay mode in¹⁰⁰Y shows a strong preference for the ground state compared to the 0 ₂ ⁺ state in¹⁰⁰Zr. The structure of¹⁰⁰Zr and the nature of the 0 ₂ ⁺ level is discussed in the light of the present results.     

Internal conversion coefficients and penetration effect for the 279 keV transition in203Tl

The internal conversion process of theM1+E 2 mixed 279 keVγ-ray transition in the decay of²⁰³Hg has been reinvestigated. The emission rate of theK-shell internal conversion electrons was determined with an electron X-ray coincidence measurement using a magneticΒ-spectrometer and a Si(Li) detector of high energy resolution. Conversion electron ratios were obtained from electron spectra recorded as a function of momentum. The disintegration rate has been taken from measurements with a calibrated NaI(Tl)γ-ray spectrometer. Following results have been deduced: α=0.2279±0.0024, α _K =0.1653±0.0017, α _L =0.0475±0.0013,K/(L+M+?)=2.64±0.03,K/L=3.48±0.12,L/(M+N+ ?)=3.14±0.12. On the basis of the experimental results on theK-shell internal conversion coefficient,α _k , and the conversion ratioK/(L+M+?) the penetration effect on the internal conversion of theM1 part and the mixing ratio,δ ², of the 279 keVγ-ray transition in²⁰³Tl have been studied. Calculations were made using Hager and Seltzer's formalism and their theoretical internal conversion coefficients. The results are consistent with a mixing ratio ofδ ²=1.32±0.11 and a penetration parameter ofλ=6.8 ±0.8.     

Directional correlation measurements withL I andL II conversion electrons of the 31 ke V transition in195Pt

The (31L ₁?99γ) and (31L _II?99γ) directional correlations have been measured in¹⁹⁵Pt. The results give the mixing ratio for the 31 keV transition,δ+0.012±0.004.     

A determination of the CKM-matrix element ratio |V ts |/|V cb | from the rareB-decaysB→K *+γ andB→X s +γ

Implications of the recent CLEO observation [1] of the rare decay modeB→K ^*+γ having a combined branching ratio BR(B→K ^*+γ)=(4.5±1.5±0.9)×10^?5 and an improved upper limit on the inclusive branching ratio BR(B→X _s +γ)<5.4×10^?4 (95% C.L.) [2] are discussed in the context of the Standard Model (SM). Using the unitarity of the CKM-matrix and taking into account QCD radiative corrections in the decay rate and the inclusive photon energy spectrum we obtain an improved upper limit on the inclusive branching ratio BR(B→X _s +γ)<4.8×10^?4 (95% C.L.). This can be used to constrain possible non-SM contributions to the inclusive branching ratio, giving BR(B→X _s +γ) (non-SM)<3.0×10^?4 form _t >-108 GeV. Within the SM, we show that the resulting experimental upper limit can be interpreted as a corresponding limit on the CKM-matrix element ratio yielding |V _ts |/|V _cb |<1.67, with the top quark mass assumed to weigh less than 200 GeV. We calculate the relative exclusive to inclusive branching ratioR(K ^*/X _s )≡Γ(B→K ^*+γ)/Γ(B→X _s +γ), based on the inclusive hadronic invariant mass distribution inB→X _s +γ. Estimating theK ^*-contribution from this distribution in the threshold region (m _K +m _π)≤m _{X s} ≤0.97 GeV and using experimental measurements from the semileptonicD-decaysD→K+π+?v _? in the same mass interval, we obtainR(K ^*/X _s )=0.13±0.03. This enables us to put a lower bound on the ratio |V _ts |/|V _cb | from the 95% C.L. lower limit on the branching ratio BR(B→K ^*+γ)>1.6×10^?5 [1,2]. Combining the exclusive and inclusive decay rates, we determine 0.50≤|V _ts |/|V _cb |≤1.67 (at 95% C.L.).     

Determination of the K-shell internal conversion coefficient for the 37.2 keV transition in the decay of121mSn

TheK-shell internal conversion coefficientα _K for the 37.2 keV transition (7/2⁺→5/2⁺) occuring in¹²¹Sb afterβ ^? decay of¹²¹ mSn has been redetermined applying theX- toγ-peak method (XPG). Measurements of photon spectra from thin sources have been performed at various source-detector distances with a high resolution, efficiency calibrated Si(Li) detector. Values ofα _K have been deduced from the number of emittedKX rays compared to that of the emittedγ rays. TheK-shell fluorescence yield for antimony has been taken from the literature. From in total 14 experimental runs a mean result ofα _K =9.52±0.27 has been obtained. The quoted uncertainty comprising statistical and systematic parts is discussed in detail. The present result is compared with the few existing earlier experimental values and with the theoretical value interpolated from the most recent tabulations.     

Beta-delayed neutrons and high-energy gamma-rays from decay of137I

Beta-delayed neutrons and high-energyγ-rays following decay of¹³⁷I have been studied in order to characterizeβ-decay to and deexcitation of neutron-unbound levels in¹³⁷Xe. The totalγ-ray intensity observed accounts for at least 20% of theβ-intensity to levels aboveB _n . No evidence was found for neutron andγ-ray emission from the same levels. With the experimentalβ-strength function aboveB _n detailed tests were performed on the reproduction of the experimental neutron spectrum, the level density and Porter-Thomas fluctuations of the reducedβ-transition probabilities to highly excited states in¹³⁷Xe.     

Resonant and intrastate transitions to the 2+ state in8Be

We have studied resonant, intrastate and non-resonant bremsstrahlungγ-ray transitions leading to the 2⁺ state in⁸Be atE _x=2.94 MeV. We find aγ-width of Γ _γ =0.45 eV for the 4⁺ state in⁸Be, corresponding to anE 2 strength of 19 W.u. For the intrastateγ-ray transition within the 2⁺ resonance we predict a maximum cross section of 2.5 nb atE≈3.3 MeV. An experimental observation of this novel type ofγ-ray emission, however, appears to be difficult due to the dominance of competing resonant and direct capture processes.