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.     

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.     

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.     

Der Zerfall von Nb94 m

Using scintillation spectrometers and coincidence techniques the decay of Nb^{94 m} has been investigated. TheK-shell conversion coefficient of the 41.5 keV isomeric transition was found to be 570±100 indicating aM 3 transition. The maximum energy of theβ-decay to the 0.87 MeV level of Mo⁹⁴ is (1.15±0.03) MeV occurring (4·5±0·7)×10^?3 per disintegration, anotherβ-decay to the 1.57 MeV level was found to be (4·0±1·3)×10^?5. From this the parities and spins of the levels involved in the decay of Nb^{94 m} are determined.     

DasL/K-Einfangverhältnis von48Vanadium

We measured theL/K-capture ratio of⁴⁸V for all transitions simultaneously and foundP _L /P _K =0.104±0.004. Coincidence measurements with the γ-rays by scintillation counters led toP _L /P _K =0.115 ± 0.015. This latter value is not very exact, but the comparison of the number ofK-pulses in the two sets of measurements allows the statement that the⁴⁹V-impurity in the⁴⁸V was less than 1.1% at the time of delivery and less than 10% during the measurements. So a possible⁴⁹V-impurity did not disturb the results.     

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 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.     

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.     

Suche nach Zweiquantenprozessen beim Zerfall von Xe131m

The decay of Xe^131m was investigated in order to detect nuclear double decay processes, in which the transition energy is distributed either between twoγ-quanta or between oneγ-quantum and oneK-conversion electron or between twoK-conversion electrons. By analyzing the emittedγ-radiation in a two-dimensional way an upper limit of 2.2 · 10^?5 was derived for the ratio of theγγ- toγ-transition probability. An investigation of theγ-spectrum in coincidence withK-quanta yielded an upper limit of 3 · 10^?2 for the rate ofe _Kγ-transitions relative toγ-transitions. The simultaneous emission of twoK-quanta was actually observed. These doubleK-quanta result either from the doubleK-conversion that was sought or from the internal conversion of the internal Compton-effect. For the doubleK-electron emission toγ-emission probability a value of (3.6±0.7) · 10^?3 was obtained. TheK-conversion coefficient and the half-life of Xe^131m were measured to be 32.1±0.4 and 11.94±0.04 d, respectively.     

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.     

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.     

DieK-Fluoreszenzausbeute von Titan und der Zerfall des48Vanadium

TheK-fluorescence yieldΩ _K of Titanium has been measured using the coincidence method and investigating the electron capture decay of⁴⁸V. The detectors used have been a Si(Li)- and a Ge(Li)-detector for the X- andγ-rays. The experimental results areP _K Ω _K =0.2005 ±0.0030 andΩ _K (Ti)=0.224±0.003 usingP _K =0.896. For the branching ratios of the decay of⁴⁸V we obtainedEC (3.239) 7.9±0.6%EC (3.224) 2.9±0.4%EC (2.295) 35.6±2.0% Β⁺ (2.295) 52±1.0% all others 1.6%. Additionally someγ-ray-energies of the decay of⁴⁸V and the half-life,T _{1 2}=(16.23 ±0.03)d, have been measured.     

DasL/K- und dasM/L-Einfangverhältnis von65Zink

We have investigated theL/K- and theL/M-capture ratio of⁶⁵Zn. For the transitions to the first excited state of⁶⁵Cu we obtained (N _L/N _K) _A =0.120±3% and (N _M/N _L) _A =0.153±13% and for both transitions to the groundstate and the first excited state simultaneously we found (N _L/N _K) _G =0.118±3%. The values for (N _L/N _K) agree well with the results of Santos Ocampo and Conway but are higher than the results of Totzek and Hoffmann. All values are discussed in view of the different theoretical values obtainable.     

Electron capture intensities in the decay of133Ba

The ground state decay of¹³³Ba was investigated using NaI(Tl) scintillation crystals.P _L/P_K electron capture ratios were measured for the transitions to the 437 keV and to the 384 keV level of¹³³Cs. The results are: (P _L/P_K)₄₃₇=0.371±0.007 and (PP _L/P_K)₃₈₄=0.221±0.005. From these data a mass difference between the ground states of the¹³³Ba- and the¹³³Cs-atom of (515±3) keV was derived. Besides, these capture ratios yield an exchange correction of 1.03±0.03. Furthermore, the intensity of the transition to the 161 keV level was determined to be smaller than 0.5% of all decays.     

Experimentelle Untersuchungen am Elektroneneinfang des85Strontium und88Yttrium

The electron capture decay of⁸⁵Sr and⁵⁵Y has been investigated using NaI(Tl)-detectors. Spectroscopic-coincidence techniques have been employed to examine theK-electron capture rates. The experimental results areP _K ω _K (Sr)=.5959 ± 0.0035 andP _K ω _K (Y)=0.6340± 0.0032. Using theK-capture probabilities, derived from the capture ratios ofBrysk andRose with the exchange correction ofBahcall:P _K (Sr)=0.880± 0.008 andP _K (Y)=0.883 ± 0.008, one can derive from these results the fluorescence yieldsω _K (Rb)=0.677± 0.009 andω _K (Sr)=0.712± 0.010. Functions ofω _K (Z) were fitted to recent experimental data and tabulated forZ=5–90. In addition to these results the half life of the 514 keV state of⁸⁵Rb and the branching ratios and the positron rate of the⁸⁸Y-decay have been measured with the same techniques. The data obtained partly disagree from measurements of other authors.     

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.     

Determination of theK-shell electron capture probabilityP K in the decay of139Ce

A new coincidence procedure for the determination of theK-shell electron capture probability in simpleEC decays is described. By measuringγ-rays andK-shell conversion electrons separately and in coincidence with theK X-rays theK capture probability can be deduced only from counting rates. The method has been applied to¹³⁹Ce. The result ofP _K = 0.726±0.010 is in fairly good agreement with other experimental values reported previously.     

Messungen derK-Konversionskoeffizienten und der Aktivierungsquerschnitte der isomeren Atomkerne Se77m,Se79m,Ge75m und Ge77m

TheK-conversion coefficients α _K of the nuclear isomers Se^77m , Se^79m , Ge^75m and Ge^77m have been measured by detecting theK-röntgen- andγ-radiation from neutron-irradiated Se- and GeO₂-samples with the aid of scintillation counters to be α _K =0.79±0.06, 7.4±0.6, 1.44±0.13, and 1.2±0.6, respectively. In all cases, the values obtained, are in agreement with those taken from the tables ofRose under the assumption of anE3-transition, thus confirming this assignment which was proposed earlier by other authors. In addition, the cross sectionsσ for inducing the activities by slowed down neutrons have been measured to beσ=22±2, 0.40±0.04, 0.20±0.02, and 0.12±0.03 barns, respectively, and are compared with earlier data of several authors.     

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.     

Precise determination of the¯ P K ω K -value and the fluorescence yield ω K of Cu after electron capture decay of65Zn

The¯P _K ω _K -value of Cu following⁶⁵Zn decay has been determined to be 0.3866 ± 0.0017 using two independent methods for the measurements of theK-X-ray emission rate. With¯P _K =0.887 deduced from literature the fluorescence yield of Cu was found to beω _K =0.436±0.003.