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.     

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.     

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.     

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.     

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.     

Accurate determination of the pKωK value and the fluorescence yield ωK of Sr after electron capture decay of88Y

Thep _K ω _K value of Sr following⁸⁸Y decay has been determined to bep _K ω _K =0.613±0.004 using two independent methods for the measurement of theK x-ray emission rate and a calibrated γ-ray spectrometer for the determination of the disintegration rate. With this result and aK-capture probabilityP _K =0.877±0.003 deduced from literature theK-shell fluorescence yield of Sr is ω _K =0.699±0.007.     

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.     

Reinvestigation of the decay scheme of the short-lived isomeric states in112In

The two short-lived isomeric states in¹¹²In have been reinvestigated by means of the¹¹²Cd(d, 2n) and¹⁰⁹Ag (α, n) reactions. Measurements of delayed X- andγ-ray, lifetime and TDPAD spectra have been performed. A 6.32(3) keVγ-ray has been identified in the isomeric decay and anM1 multipolarity has been assigned to it on the basis of the measured internal conversion coefficients:α _L =196(39) andα _tot=231(35). TheE1+M2(δ =+0.24(4)) andE2 multipolarities have been determined for the 263 and 188 keV transitions deexciting the 8^?(T _1/2=2.82(2) μs) and 7⁺ (T _1/2=0.93(2) μs) isomeric states, respectively. A revised isomeric decay scheme is presented.     

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.     

The levels of144Pr from the decay of144Ce

The level scheme of¹⁴⁴Pr has been studied from the decay of¹⁴⁴Ce. The intensities and energies of gamma rays have been determined with a X-ray Ge(Li) detector. TheK-shell internal conversion coefficients for γ-rays have been measured with theK X-ray/γ-ray ratio method using NaI(Tl)—X-ray Ge(Li) coincidence techniques.     

The electron capture decay of125I and145Pm

The productP _K ω _K of theK-capture probability and theK-fluorescence yieldω _K was measured in the EC decay of 17.7 y¹⁴⁵Pm and 60.14d¹²⁵I by means ofK x-ray-γ-ray coincidences with semiconductor detectors. Accepting a best value ofω _K =0.920 forZ=60 from the literature, values ofP _K =0.606±0.025 and 0.554±0.025 for decay of¹⁴⁵Pm to the 67.2 and 72.4 keV levels in¹⁴⁵Nd, respectively, were determined, from which the application of EC theory givesQ _EC=153±4 keV to the ground state. TheP _K ω _K ratio to the 67.2 and 72.4 keV levels also was determined independently to be 1.11±0.01, which serves as a good check on theγ-ray-gatedP _K values. Theγ-ray energies were determined more accurately to be 72.4±0.1 and 67.2±0.1 keV, together with a ratio of their relative intensities,I _72.4/I _67.2=3.35±0.09. In the decay of¹²⁵I, a value ofP _K ω _K =0.699±0.030 was measured, and by using an independent determination ofQ _EC=178±2 keV to the ground-state from the literature, a value ofP _K=0.801 is calculated from allowed EC theory, from whichω _K =0.873±0.017 atZ=52 is obtained. This value is in good agreement with theoretical values and with a value of 0.875±0.028 predicted by the best fit curve of Bambyneket al.     

Accurate determination of theP KωK-value and the fluorescence yield ω K of Rb after electron capture decay of85Sr

TheP _Kω_K-value of Rb following⁸⁵Sr decay has been determined to beP _Kω_K=0.586±0.003 using two independent methods for the measurements of theK-X-ray emission rate. With this result andP _K =0.877±0.003 deduced from literature the fluorescence yield of Rb is ω _K =0.668±0.006.     

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.     

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.     

Study of159Yb decay

Theβ ⁺-decay of 1.4 min¹⁵⁹Yb was studied at the YAS-NAPP-2 facility installed on the proton beam of the JINR Dubna phasotron. The singles γ-ray spectra and prompt and delayedγ-γ coincidences were measured on the multidetector system. The decay scheme of¹⁵⁹Yb was proposed on the basis of theγ-γ coincidence data. The low lying states of¹⁵⁹Tm were preliminary identified within the framework of the rotational model.     

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.     

The decay of 8.7 min237Pa

The beta and gamma radiations of²³⁷Pa have been investigated employing semiconductor and scintillation spectrometers and coincidence techniques. Sources of²³⁷Pa were obtained after bombardments of²³⁸U with bremsstrahlung and 14-MeV neutrons and subsequent chemical separation. From the total of 18γ-rays following the decay of 8.7±0.2 min²³⁷Pa 17 transitions, representing 99.9% of theγ-ray intensity, could be placed in a level scheme of²³⁷U. AQ _β- value of 2.25±0.1 MeV has been determined.     

Radiative neutrino decay and the unusual X-ray flux from Sn 1987A

The radiative neutrino decay in the mass and a lifetime range, m_v=10–100 keV and τ_v=10³–10⁵ s, is often argued to be forbid by γ-ray data from past supernovas. We demonstrate that this argument is not always correct, and accordingly attempt to explain via radiative neutrino decay the unusual soft component of the X-ray spectrum from SN 1987A, observed by the satellite Ginga. Our fit to the data suggests that τ_v=(1–3)×10⁴s·(m_v/50 keV).     

The decay of85As

The decay of isotope-separated⁸⁵As has been studied for the first time by means ofγ-ray spectroscopy. A level scheme for⁸⁵Se has been constructed on the basis ofγγ-coincidence measurements. Spin and parity were then assigned to the lowest excited levels. Two levels, weakly populated in⁸⁴Se after emission of delayed neutrons, were also identified. The results obtained here differ considerably from previously reported experiments with chemically separated sources.