High resolutionL- andM-subshell internal conversion studies of low energy transitions in149Sm and151Eu

The internal conversion subshell intensities of the (21.529±0.014) keV transition in¹⁵¹Eu and the (22.494±0.011) keV transition in¹⁴⁹Sm have been determined in a high resolution investigation using a double-focussing iron-core spectrometer. The subshell ratios yielded unambiguousM1+E2 multipole mixtures for both transitions. δ²(E2/M1) for the 21.53 keV transition was determined to be (8.8±0.7)·10^?4 and for the 22.49 keV transition to be (5.5±1.2)·10^?3.     

Internal conversion studies of transitions in96Mo

The internal conversion spectrum from the decay of⁹⁶Tc has been investigated using a 50 cm radius double-focussing beta-ray spectrometer. Relevant features of the internal conversion spectrum from the decay of⁹⁶Nb have also been reexamined in the same way. Special interest has been focussed on investigating a proposed doublet level structure at about 2.44 MeV and higher lying levels in⁹⁶Mo. Internal conversion coefficients have been obtained for most transitions by combining the measured conversion electron intensities obtained in this work with recently reported gamma-ray intensities from Ge(Li) detector measurements. A level scheme has been compiled and deduced transition multipolarities have been used for a discussion of spins and parities for the levels.     

β + ratio andβ-delayedγ-decay of146Eu

The positron decay of¹⁴⁶Eu was investigated, firstly to derive for the allowed transition to the 2046 keV state in¹⁴⁶Sm the electron capture to positron decay ratio. The experimental valueEC/β ⁺=43.7(42) is found to be in agreement within the respective error intervals with the ones calculated from the formalism of allowed decay using the recentQ-values of¹⁴⁶Eu. Further on, theγ-decay properties of¹⁴⁶Eu have been reinvestigated with emphasis on implied modifications of the hitherto accepted decay scheme: 42 new levels and 33 newγ-transitions were placed in the revised level scheme, 12 of the previously reported levels were deleted. The level distribution of¹⁴⁶Sm is discussed within a statistical model. The indication for a non-statisticalβ-strength function is observed.     

Transition probabilities in146Eu

Transition probabilities in the odd-odd nucleus¹⁴⁶Eu are measured. A recent determination of the lifetime of the 115.6 keV level has indicated a strong retardation of the 115.6 keVM1 transition. In contrast, the present results areT _1/2(230.3)≦165 ps,T _1/2(115.6)≦160 ps. TheE2 cross-over transitions of 269.5 and 230.3 keV were not found in the Ge(Li) gamma spectrum. All results are in agreement with the single particle model.     

Search for a 11/2−→3/2+ M 4 transition in141Sm

The electromagnetic decay of the 11/2^{? 141m} Sm is investigated. Internal conversion electron and X-ray-conversion electron coincidence measurements indicate that the state undergoesβ ⁺ and electron capture decay with 99.69% strength and the remaining 0.31% goes to a 174.2±0.3 keVM4 transition. TheK/L conversion electron intensity ratio for the transition is measured to be 1.7±0.4. The energy of the 11/2^? is established at 175.8±0.3 keV above the 1/2⁺ ground state in¹⁴¹Sm. Systematics of theM4 transitions in theN=79 and 81 isotones are discussed.     

Concerning internal conversion coefficients in Hf180

The gamma-ray relative intensities from transitions in Hf¹⁸⁰ following the 5.5 hour Hf^180m decay have been measured using a bent-crystal gamma-ray diffraction monochromator and a least-squares fitting technique. From these measurements it was possible to deduce a value for the internal conversion coefficient for the 93.3-keV transition of α _T ⁹³ =4.91±0.23. From previous measurements of conversion electron intensities byEdwards andBoehm and our gamma-ray relative intensities, internal conversion coefficients for all transitions except the 57.5-keV transition were obtained. These coefficients agree well with the previous determinations byEdwards andBoehm, however, our measurements have improved precision, particularly in the case of 501.3-keV transition. The present measurements of α _K for the 215.3-, 332.5-and 443.8-keVE2 transitions are 11% lower than theoretical values while α_K for 93.3 keV E2 transition agrees closely with the theoretical value. These results are in close agreement with the previous measurements ofEdwards andBoehm. The present experimental α_K for the 501-keV transition agrees closely with the theoretical α_K for an E3 multipolarity.     

Decay properties of139mSm and139Eu

The structure of¹³⁹Sm is investigated through the decay properties of^139mSm and¹³⁹Eu. The decay of^139mSm is measured to have a half-life of (10.7±0.6) s. Gamma-ray and internal conversion electron measurements lead to the construction of a decay pattern comprising seven transitions among five states. The decay of¹³⁹Eu with a measured half-life of (17.9± 0.6) s is studied with beta decay spectroscopy techniques. A decay scheme consisting fourteen states in¹³⁹Sm is proposed. Using deducedft values and transition multipolarities,J ^ρ assignments are made. Nuclear systematics of the odd-A, N=77 and 76 are discussed.     

Tentative level diagram of146Pm below 1.1 MeV

The level scheme of the doubly odd nucleus¹⁴⁶Pm was investigated by means of in-beam spectroscopy. The¹⁴⁶Nd(p, n) reaction in the 3.5–8 MeV proton energy interval on enriched targets has been used to populate the exited states of¹⁴⁶Pm. High resolutionγ-ray spectra using Ge(Li) and hyperpure Ge detectors and conversion electrons with a mini-orange spectrometer were measured. Withγ-exitation functions andnγ-coincidences usingnγ-discriminated NE231 neutron detectors transitions in¹⁴⁶Pm were identified,γγ-coincidences gave information aboutγ-cascades. With these data a level scheme of 38 levels below 1.1 MeV exitation energy has been deduced including 73 transitions. For 12 transitions experimental conversion coefficients have been evaluated, which agree with the expected values forM1/E2-transitions.     

Internal conversion coefficients of the transitions in Tm169

The conversion electron spectrum of Tm¹⁶⁹ has been measured by an iron-yoke double focusing spectrometer. Gamma-ray energies and gamma-ray intensities were measured by a bent crystal spectrometer. Conversion coefficients and conversion ratios were determined from the electron and gamma intensities. The conversion process of the retardedM 1 transitions of 177 keV and 198 keV was found to be normal, in agreement with our earlier directional correlation results. No penetration effects were found in the conversion process of the retarded 63 keVE1 transition.     

Detailed Ge(Li)-Ge(Li) coincidence studies of levels in152Sm and152Gd

The decay of 12.4 y¹⁵²Eu to¹⁵²Sm and¹⁵²Gd was studied in a high resolution singles measurement and two 4096×2048 Ge(Li)-Ge(Li) coincidence studies. Forty-five gates were analyzed in order to confirm or establish the placement of the γ rays as well as to accurately determine the intensities of the 12 doublets, which included several not previously reported. A new γ-β interband transition, 4 _γ ⁺ →2 _β ⁺ (561.4 keV), a possible 3 _γ ⁺ →2 _β ⁺ (423.7 keV) transition, and a new 330.9 keV transition between the 4 _γ ⁺ level and theI ^π K=3^?0 octupole level were established from coincidence data. Levels at 1757.0 keV in¹⁵²Sm and 1282.5, 1318.7, and 1692.2 keV in¹⁵²Gd are now established on the basis of coincidence data. These data also establish for the first time the population in the¹⁵²Eu decay levels at 1680.0 and 1047.9 keV in¹⁵²Sm and¹⁵²Gd, respectively, as well as a new level at 1700.8 keV in¹⁵²Sm.     

Conversion electron measurements in the decay of156Tb

The conversion electron spectrum from the decay of¹⁵⁶Tb to¹⁵⁶Gd was measured with an iron, double-focusing spectrometer. TheK conversion coefficient of the 1222.4 keV transition was measured relative to theK conversion coefficient of the 661.6 keV transition in¹³⁷Cs and found to be 0.00174±0.00013. This result was used to normalize electron and gamma-ray data to obtain theK conversion coefficients of 33 transitions in¹⁵⁶Gd. The 1009.6 and 1040.6 keV transitions have largeE0 components.     

The conversion electron spectrum in the decay of195Au

Twenty-four internal conversion lines in the decay of¹⁹⁵Au have been studied at high resolution by means of the Vanderbilt iron-free spectrometer. The electron intensities of this work and previously published photon intensities were used to calculate the percentage decay to each level in¹⁹⁵Pt. Conversion coefficients andL subshell ratios were used to assign the following multipolarities: 30.8 keV, pureM1; 98.8 keV, (99±1)%M1; 129.8 keV, pureE2; and 210 keV, pureE2. MeasuredL subshell ratios are not in good agreement with theoretical values.     

In-beam γ-ray spectroscopy of the neutron deficient 100Ag

Conversion coefficients and conversion ratios of someγ-transitions in²⁰¹Tl and²⁰³Tl were measured by means of simultaneous spectroscopy ofγ-quanta and conversion electrons employing intensity calibrated semiconductor detectors. The experiments aimed at a precision as high as possible within the limits of the experimental methode used. Theγ-transitions were of the typeM 1(+E2). From the measured values the penetration parameters of the internal conversion for theM 1 components (λ) together with the multipol mixing ratios (δ²) were deduced. The necessary theoretical coefficients were taken from the tables of Hager and Seltzer. The results are for the ?-forbidden 331 keV transition in²⁰¹Tl,λ=+4.0±1.0,δ ²=1.78±0.16; for the ?-allowed 361 keV transition in²⁰¹Tl,λ=+0.5±0.5,δ ²=0.02±0.02; for the ?-forbidden 279 keV transition in²⁰³Tl,λ=+ 5.71±0.45,δ ²=1.55±0.08.     

Internal conversion coefficients in the Hartree-Fock atomic model. Calculations and experiments for199Hg

The internal conversion coefficients were calculated for the transitions in¹⁹⁹Hg using both Hartree-Fock and Hartree-Fock-Slater atomic models. The relative conversion line intensities were measured with the magnetic spectrometers in Prague and Heidelberg. The multipolarities were determined to be:M1+(0.20±0.03)%E2, pure E2 and M 1+ (13.4 ±0.4)%E2 for the 50, 158 and 208 keV transitions, respectively. Allowing for the nuclear structure effect in M1 component we obtained: M1+(0.15±0.03) %E2,λ = 2.4±1.0 for the 50 keV and M1+ (10.9±0.7)% E2, λ=3.8±0.5 for the 208 keV transitions. Very good agreement was found between theory and experiment for the atomic subshells,K, L_1?3,M _1?5,N, andO + P.     

Experimental determination of penetration parameter forM1 conversion,and theE2 admixtures for 77 and 191 keV transitions in197Au

TheL-subshell conversion for 77 keV transition andK,L ₁,L ₂-shell conversion for 191 keV transition in¹⁹⁷Au, as well asK-shell conversion transition of 158 keV in¹⁹⁹Hg were measured by means of Π√2-iron free electron spectrometer. Relative gamma-ray intensities have been determined by Ge(Li) spectrometer. From these measurements the α _K conversion coefficient value has been deduced for 191 keV transition as α_K(191 keV)=0.86±0.03. This value shows that the spin of the level at 268 keV in¹⁹⁷Au is 3/2⁺. For the penetration parameter (λ) and intensity ratio \(\left( {\delta ^2 = \frac{{\left\langle {E2} \right\rangle ^2 }}{{\left\langle {MI} \right\rangle ^2 }}} \right)\) the following values are obtained: $$\begin{gathered} \lambda = 3.4 \pm _{1.5}^{1.9} \delta ^2 = 0.11 \pm 0.03for 77 keV transition \hfill \\ \lambda = 3.2 \pm _{0.6}^{0.8} \delta ^2 = 0.17 \pm 0.04for 191 keV transition. \hfill \\ \end{gathered} $$ The agreement of these results with the predictions of De Shalit model is discussed.     

On the octupole excitation in236U

Measurements of theK,L _I,L _II andM _I conversion lines of the 687.7 keV transition in²³⁶U are evaluated within the electron penetration formalism. The spin-parity assignment of the octupole bandhead is found to be 1^? in accordance with reaction data, and an assignment of 2^? to the 687.7 keV state is ruled out. The penetration matrix element ∥η∥ has the value of 13.5 for theK-shell and increases slightly for higher main shells. An estimate of the anomalous amplitudes is compared with values reported for transitions in the odd even actinide nuclei. Furthermore electron conversion data for the 1^?→2⁺ and 1^?→4⁺ transitions are given. Radioactivity²³⁶U from²³⁵U(n,e ^?); measured: conversion electron decay; deduced: conversion coefficients fromK, L andM shells; evaluated: dynamic matrix elements.     

Non-yrast level structure of121Xe via beta decay of121m+g Cs

The results of measurements of the gamma-ray and conversion-electron singles and coincidence spectra from the decay of the 122 s^121m Cs and the 155 s^121g Cs to levels of¹²¹Xe are reported. TheM 3 multipolarity of the 68.5 keV isomeric transition in¹²¹Cs has been deduced. Numerous low-lying levels below 1.6 MeV excitation energy are found. A negative-parity level at 355.9 keV is observed for the first time. The results supplement the low lying energy level systematics in odd-A xenons. A comparison is made with theN=67 barium isotone.     

Konversionskoeffizienten von γ-Übergängen in204Pb

Two semiconductor detectors with known efficiencies were employed to measure simultaneously the intensities of the γ-rays and the conversion electrons which are emitted by a mixture of²⁰⁴Bi and^204m Pb in radioactive equilibrium and by pure^204m Pb. Conversion coefficients, conversion ratios and also the relative intensities of many transitions in²⁰⁴Pb were obtained. Informations about transition multipolarities are deduced. Some conversion coefficients and conversion ratios which are measured with good precision are used to check theoretical values.     

A Si(Li) detector system for conversion coefficient measurements and application to the decays of51Cr and87Y

An electron detector system with a 3 mm × 100 mm² Si(Li) detector with a cooled FET and vacuum air lock for changing sources was constructed. The absolute efficiency was measured as a function of energy for use in the measurement ofK conversion coefficients. With the Si(Li) and a Ge(Li) detector, theK conversion coefficient of the 320 keV transition in⁵¹V was measured to be 0.00156 ± 0.00008 where theK conversion coefficients of the 661 and 279 keV transitions in¹³⁷Ba and²⁰³Tl were used as standards. From absolute detection efficiency measurements, theK conversion coefficients of the 388 and 483 keV transitions in⁸⁷Sr were measured to be 0.16 ± 0.02 and 0.0024 ± 0.0003, respectively.     

Internal conversion of the 6.2 keV transition in181Ta

The total conversion coefficient of the 6.2 keV Mössbauer transition in¹⁸¹Ta was measured by X- and gamma-ray spectroscopy. The result of 86 ± 20 disagrees with the literature value of 46, but agrees with theory if a nuclear penetration parameter deduced from relative conversion electron intensities is taken into account. The weak 6.2 keV gamma ray has intensity per decay that is less than the previous value by a factor of 8.5.