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.     

The decay of141Ce

The decay of¹⁴¹Ce has been reinvestigated using different experimental methods. The efficiency extrapolation technique applied to 4πβ —γ coincidence measurements has been employed for the determination of the disintegration rate of the sources and of the total internal conversion coefficient. TheK X-ray andγ-ray emisssion rates have been measured with a calibrated Si(Li) and an intrinsic germanium detector. Additionally the photon intensities have been determined from the internal conversion coefficients. Electron experiments with a magneticβ-spectrometer yielded the relative intensities, the shape factors and the maximum energies of the two β^?-transitions and the internal conversion ratiosK/L andK/(L + M+...). TheK-shell internal conversion probability has been determined with an electronK X-ray coincidence technique using the magneticβ-spectrometer together with a high energy resolution Si(Li) detector. New values for the following decay properties have been deduced:β ^?-intensities (p ₁ =0.306 + 0.006,p ₂= 0.694±0.006), shape factorsC = const (1+Aε) (A ₁ = ?(0.24±0.03),A ₂=?(0.22±0.04)), maximumβ ^?-energies (E ₀₁ = (582.2±2.6) keV,E ₀₂= (436.7±4.6) keV),K- shell internal conversion coefficient (α _K = 0.376±0.008), total internal conversion coefficient (α = 0.438±0.010), internal conversion ratios (K/L = 7.29±0.24, K/(L + M + ...) = 5.78±0.18),γ-ray intensity (I _γ = 0.482±0.003),K X-ray intensity (I_{K X} = 0.168±0.002) and the photon intensity ratio (I _{K X} /I _γ = 0.349±0.005). The procedure of uncertainty quotation is presented in some detail. The results are discussed with respect to existing experimental data.     

Die Lebensdauer des 23/2-Dreiteilchenniveaus des Hafnium 177 und sein Zerfall durchK-verbotene Gamma-Übergänge

An isomeric state of Hf¹⁷⁷ withT _1/2=(1,12±0,10)s was found by a fast chemical separation of the hafnium daughter from the 155d Lu^177m activity. We measured the same half-life by observing the delayedβ-γ-coincidences. A systematic investigation of the whole region 5s≧T _1/2≧10^?7s by the technique of delayed coincidences gave no further isomerism. We assign the observed half-life to the 23/2 three particle state of Hf¹⁷⁷ at 1315 keV and assume that the second hypothetical three particle state at 1337 keV does not exist. The 21/2 rotational state of theK=9/2 band is populated by a strongly converted 14,16 keVγ-transition from the isomeric state at 1315 keV. The 14,16 keVM _I andN _I conversion lines were observed by use of a double focusing magneticβ-spectrometer. The isomerism is caused by theK-selection rule. The retardation of the following threeγ-transitions by different degrees ofK-forbiddeness is discussed. The pulse height spectrum, measured by means of a Li-drifted Ge-detector, does not show the 36,52 keV-γ-transition which was previously assumed to populate the 1301keV-state. In addition to the knownγ-transitions we found a 40,9 keV-line. This is probably the transition between the 1301,1 keV and the 1260,3 keV-states.     

Zerfallsschemata, β-Matrixelemente und γ-Multipolordnungen für die Übergänge Co56→Fe56 und J131→Xe131

In the decay of Co⁵⁶ the following quantities have been measured:γ-ray intensities,β-γ directional correlation, andβ-(circularly polarizedγ) correlation. The directional correlation anisotropy was found to be, forβ energies above 300 keV,A ₂=0.5±0.4 per cent, corresponding to small or vanishing twice forbidden contributions to the allowed decay. The asymmetry parameterA of theβ-(circularly polarizedγ) correlation was measured to beA=?0.01±0.05 which implies a ratiox between Fermi and Gamow-Teller contributions to the decay ofx=?0.10±0.07, in agreement with the isospin selection rule. In the decay of J¹³¹ the following quantities have been measured: shape of the 606 keVβ-ray group,γ-ray intensities, conversion coefficients, andβ-(circularly polarizedγ) correlations. The measuredK/L ratio of the 364 keVγ-transition,K/L=6.0±0.2, is compatible with the conversion tables of Sliv and Band only. The multipolarities of theγ rays of 364, 637, and 723 keV were deduced. The 606 keVβ-364 keVγ cascade was used as a new calibration standard for analysers of circularly polarizedγ-rays.     

TheEC-decay of170Tm

The spectrum ofK X-rays andγ-rays following the decay of¹⁷⁰Tm has been reinvestigated using a high resolution Si(Li) detector. The intensities of theEC-branches from the ground state of¹⁷⁰Tm to the ground state as well as to the first excited level in¹⁷⁰Er have been measured. The total intensity of theEC-decay is (0.25 ± 0.05)% of all¹⁷⁰Tm disintegrations with (0.18 ± 0.05)% leading to the ground state and (0.07±0.02)% leading to the first excited level of¹⁷⁰Er. The energy of the de-excitingγ-ray has been determined to (78.7±0.5) keV. Its intensity is (0.28 ± 0.06)% of that of the 84.3 keVγ-ray in¹⁷⁰Yb.     

The electron capture decay of85Sr-measurements of theK X-Ray emission probability,half-life,and decay scheme

TheK X-ray emission probabilityP _K ω _K for the decay of⁸⁵Sr has been measured to be 0.5866 with a standard error of 0.05% and a systematic uncertainty of 0.65%. The X-ray emission and total disintegration rates were measured by 4π proportional counting in a pressurized detector and by 4π(A, X)-γ coincidence counting respectively. In addition, a high-pressure ionization chamber has been used to measure the⁸⁵Sr half-life giving a value of 64.84 d with a standard error of 0.01% and a systematic uncertainty of 0.02%. An investigation of the decay scheme was performed which confirmed the presence of a weak decay branch to a state at 869 keV in the⁸⁵Rb daughter nucleus. A value of (1.25 ±0.05)×l0?4 was measured for the intensity of the 869 keVγ-ray relative to the predominant 514 keVγ-ray.     

The beta branching ratio and conversion coefficients in the137Cs decay

The decay of¹³⁷Cs has been reinvestigated using several precision counting methods. The emission rate ofβ-particles plus internal conversion electrons was measured by the 4π-proportional counter method using vacuum evaporated sources free of self-absorption and checked by the liquid scintillation method. TheK-conversion coefficient was determined by the electron X-ray coincidence method using a magnetic spectrometer and a high resolution Si(Li) detector. TheK/(L+M+...) conversion ratio and a second less accurate value for the β-branching ratio were obtained from the recorded electron spectra. Theγ-ray emission rate of all sources was determined to within ±0.14%, on the average, with a calibrated NaI(Tl) crystal detector. As results the intensity of theβ-decay to the ground state of¹³⁷Ba could be determined to (5.4±0.3)% of the¹³⁷Cs decays, theK-conversion coefficient to 0.0916±0.0004, and theK/(L+M+...) conversion ratio to 4.41±0.04. From these values the γ-ray emission intensity is (85.1±0.4)% of the¹³⁷Cs decays and theK X-ray emission intensity is (8.13±0.10)% of the emittedγ-rays. All errors are discussed in detail.     

Measurements of someK-internal conversion coefficients near threshold

TheK-internal conversion coefficients have been measured by the XPG technique for a number of low energyγ-ray transitions whose energies do not exceed theK-binding energies by more than 4 keV. Using Si(Li) detectors in singles and coincidence arrangements, the following results were obtained: 63.1 keV El in¹⁶⁹Tm(α_K=1.02±0.15), 72.0 keV E1 in¹⁸⁷Re (0.75±0.05), 57.8 keV M1 in¹⁶²Ho (11.42±0.67), 56.6 keV M1 in¹⁶⁴Ho (12.04±0.70), and 67.1 keV M1 in¹⁷⁴Lu(10.25±0.58). The experimental results are compared with the theoretical calculations which include transition energies down to 1 keV above threshold.     

Spins und γ-Multipolordnungen beim Zerfall Fe59→Co59

In the decay of Fe⁵⁹ the following quantities have been measured:γ-ray intensities, conversion coefficients andβ-(circularly polarizedγ) correlations. The conversion coefficients were found to be: for the 1.10 MeVγ-transition, α_tot.=(1.36±0.10)·10^?4 and for the 1.29 MeVγ-transition, α_tot.=(1.07±0.08)·10^?4. The asymmetry parameterA of the correlationβ(0.27 MeV)?γ(1.29 MeV) were measured to beA= ?0.17±0.10, and forβ(0.46 MeV)?γ(1.10 MeV),A=?0.13±0.04. From these data and publishedγ?γ angular correlation measurements the following spins of Co⁵⁹ levels could be deduced: 1.10 MeV,I=5/2^?; 1.29 MeV,I=5/2^?; and 1.43 MeV,I=3/2^?. The two strongβ-ray groups are pure Gamow-Teller transitions (ΔI=1). The multipolarities of all fiveγ-rays are given.     

Internal conversion coefficient for the 165.8 keV transition in139La

The internal conversion process of the 165.8 keV-ray transition in the decay of¹³⁹Ce has been reinvestigated. The emission rate of the K-shell internal conversion electrons was determined by an (electron)-(X-ray)-(X-ray) triple coincidence experiment using a magnetic-spectrometer and two Si(Li) detectors. From electron spectra recorded as a function of momentum conversion electron ratios were also determined. The disintegration rate of the sources has been taken from 4- coincidence experiments. The following results were obtained: the probability for internal conversion in theK-shellk _K =0.1719±0.0020 and the conversion ratiosK/(L + M+...=5.84±0.17,K/L=7.45±0.20, andL/(M+...)=3.63±0.29. The internal conversion coefficients deduced area=(0.2520+0.0050), _K =(0.2152±0.0033), and _L =(0.0289±0.0012). The results are in good agreement with previous experimental values and with theoretical data calculated for a M1 transition of 165.8 keV in¹³⁹La.     

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 resonance fluorescence in121Sb

Usingγ quanta from a⁵⁶Co source, resonance fluorescence from a 3,452 keV level in¹²¹Sb was observed. Four deexcitingγ transitions were identified. The profile of theγ emission line, investigated by means of a high speed centrifuge, yields with a novel variety of Doppler shift analysis a lifetime of τ_4,298=(110±50)fs for theγ emitting 4,298 keV level in⁵⁶Fe. The lifetime of the 3,452 keV level was determined to beτ _3,452 =(200±100)fs.     

Levels in182W populated in the decay of182Ta

Theγ-rays emitted in theβ-decay of¹⁸²Ta have been reinvestigated with improved statistics in attempting to clarify the reported new levels at 1460.41, 1592.98, 1620.36, 1712.29 and 1762.91 keV in¹⁸²W observed in theβ-decay of¹⁸²Ta. The present study demonstrated that the fifteen newγ-rays, which were used to support the existence of the five new levels, are not relevant to theγ-decay of¹⁸²Ta. Therefore the five new levels are not populated in this decay. Additionally, theγ-ray with an energy of 1035.6 keV (0 ₂ ⁺ →2 ₁ ⁺ ) deexciting theβ-band head in¹⁸²W is observed for the first time in the present decay study and the previous tentative placement of the 351.0 keVγ-ray in the level scheme is confirmed by the present coincidence measurements.     

TheK-conversion coefficient near threshold of the 30 keV isomeric transition in108mAg decay

With calibrated Ge(Li) x-ray detectorsK x rays in the conversion of the 30 keV isomeric transition in the decay of^108mAg were observed in coincidence with 79 keV γ-rays. Thus, the fraction of 30 keV transitions which take place byK conversion was measured to be (2.44±0.23) × 10^?2. Making use of a theoretical total conversion coefficient (K conversion contributes only a minor part of the total conversion coefficient), an experimental value of theK-conversion coefficient was obtained, α_K=(1.07 ± 0.10) × 10⁴ (where the error represents twice the standard deviation to which the error in the detector efficiency has been added linearly). This value agrees with the theory of Hager and Seltzer forM4 conversion. The energy of the cascading γ-ray was remeasured to be 79.20 ± 0.05 keV.     

Verzweigungsverhältnisse und Konversionskoeffizienten von angeregten Zuständen des208Tl

The branching ratios of theγ rays of the second and fourth excited states of²⁰⁸Tl have been investigated by coincidence measurements between the α rays of²¹²Bi and subsequent 40keVγ ray. The detectors employed were a silicon surface barrier counter for α particles, and a 1.5 in ×2 mm NaJ (Tl) crystal forγ rays. It has been found that (75.6±3.7)% of all transitions of the 328 keV state and (94±7)% of all transitions of the (492 keV+473 keV) states populate the first excited state of²⁰⁸Tl. The 40 keV state is excited to (3.4±0.3)% by transitions of higher excited states relative to the direct excitation by α particles. The number of α particles with energyE _α = 6.047 MeV and the number of subsequent 40keVγ rays resulted in a conversion coefficient α(40keV)=22.55± 0.46. Similarly coincidence measurements between Tl-x rays and α particles have been used to determine theK- conversion coefficients α_K(328 keV)=0.31±0.03 and α_K(492 keV+ 473keV)=0.100±0.015. The experimental results are in good agreement with the theoretical values ofSliv.     

g-Faktoren und Multipol-Mischungsverhältnisse in156Gd

By integral perturbedγ-γ-angular correlation the gyromagnetic ratios of a 2-quasi-particle state at 1,513 keV and the 4⁺ state of the ground state rotational band in¹⁵⁶Gd were measured, using sources prepared by¹⁵⁹Tb(γ, 3n) and¹⁵⁶Gd(d, 2n) reactions:g _{1;513 keV} ⁴⁺ =0.78±0.05;g _R ⁴⁺ =0.37±0.05. In addition we obtain the multipole mixing ratiosδ _{535 keV}(M2/E1)=?0.09±0.01;δ _{1,225 keV}(E2/M1)=+1.83±0.10 for the 535 keV and 1,225 keVγ-rays. The classification of the 1,513 keV state is discussed. The internal field of Gd in Tb metal at 77 °K was found to beH=(?192±16)kOe.     

Theβ-decays of99Y and99Zr and the level schemes of99Zr and99Nb

Theβ-decays of⁹⁹Y and⁹⁹Zr have been investigated with the two recoil fission product separators JOSEF and LOHENGRIN. Half-lives of 1.51±0.08s and 2.1±0.1s respectively, have been determined. Aβ-decaying isomeric state has been observed in⁹⁹Y. The level schemes of ₄₀ ⁹⁹ Zr₅₉ and ₄₁ ⁹⁹ Nb₅₈ have been established fromγ-ray spectroscopy. Absoluteγ-intensities have been obtained by means of two independent techniques. Halflives of 293±10 ns for the 251.9 keV state and 10.2±1.5 ns for the 614.0 or 667.2 keV level in⁹⁹Zr have been measured through delayedβ,γ- andγ,γ-coincidence experiments. Values for the spins and parities of the low lying levels in⁹⁹Zr are proposed in accordance with the systematics of lighter odd Zr isotopes. Spins and partities are assigned to some levels in⁹⁹Nb fromγ,γ-angular correlation measurements. In this nucleus there is evidence for three-particle configurations of some excited states, where the odd proton is coupled to two neutrons which are in different orbits.     

Internal conversion studies of the 114 keV transition in175Lu

Measurements of the conversion line intensities, the directional correlation and the conversion probability for the 114 keVM1+E2 transition in¹⁷⁵Lu are reported. TheE2 admixture, determined from relativeK andL intensities, is (19.2±0.2)%. The theoreticalL _I internal conversion coefficient is found to be about 8% too low relative theK,L _II andL _III conversion coefficients.     

Decay of the134Cs isomers and the levels of134Xe,134Cs,and134Ba

A precision study of the decay of¹³⁴Cs ^g and¹³⁴Cs ^m has been made, using ordinary Ge(Li) spectrometers and ā Compton-suppression spectrometer. The logft value of the second forbidden nonuniqueβ-decay to¹³⁴Xe has been measured to be 13.0±0.2. TheM4γ-ray transition in¹³⁴Cs^m(8^?) decay has been measured to haveα _K= 73±7 and a hindrance of 7.0 over the Moskowski estimate. This is discussed in terms of the level configurations and the analogous transition in¹³³Xe. A new intensity limit of 2×10^?6 has been set for the zero-phonon transition between the 4⁺ and 2⁺ members of the two-phonon triplet. This leads to an upper limit forB(E2)_4→2′, greater than 905. This and the more preciseγ-ray intensity values are discussed in relation to presently available nuclear models.     

Die Konversion des Hg199m

Hg^199m was produced from natural HgO by fastn irradiation. The cascade decay was investigated with scintillation spectrometers by application of the summing technique. The following results were obtained: half-lifeT _1/2=(43±0,5) min; energy of the isomeric transitionE _γ1=(375±3)keV; conversion coefficients α _K375=3,05±0,25; α_total=5,45±0,25; yielding the multipole order of the isomeric transition to beM4+(25±15)%E5; energy of the second transitionE _γ2=(159±2)keV; conversion coefficients α _K159=0,30±0,03; α_total=0,9±0,1, confirming the multipolarityE2 of this transition.