Conversion Line Intensities Research Articles

Quantitative conversion spectroscopy of the ultrasoft isomeric transition of uranium-235 and the electronic structure of uranium oxides

Combined measurements of conversion electron spectra and the decay constant (76.5 eV, (1/2)+→(7/2)−) of the E3-isomeric transition of the uranium-235 nucleus have been performed with collection of the isomer atoms on an indium surface. The conversion spectra are interpreted as corresponding to a mixture of two different oxides A and B of uranium, one of which (A) is similar to UO2, and the other (B) consists of a uranium-oxygen cluster based on the linear uranyl group O-U-O. From a set of mixed experimental spectra conversion spectra have been found corresponding to the chemical states A and B of the isomer atoms, and the variation of the absolute intensities of the conversion lines has been quantitatively investigated for them by varying the chemical composition of the isomer atoms and the ratio between the intensities of various conversion lines of the B spectrum. Experimental ratios between the intensities of the conversion lines are compared with the expected ratios in accordance with the distribution of the 6p electron density in the uranyl group. It is concluded that the experimental data agree with the calculation and that abrupt violations of proportionality of the partial probabilities of conversion of the electron density near the nucleus are absent. In accordance with the hypothesis of proportionality of the partial probabilities of conversion, an experimental estimate is given of the degree of localization of the deep-lying uranium 6p1/2 shell during formation of the chemical bond in the uranyl group: around 70% of the 6p1/2 electron density remains in the quasi-atomic uranium shell and around 30% is transferred to hybrid molecular orbitals.

Precise intensity measurements of internal conversion lines in the decay of 207Bi and systematic comparison with theoretical predictions

Relative intensities of internal conversion lines of the 569.6, 897.3, 1063.6 and 1770.2 keV transitions in the decay of 207Bi were precisely determined by spectrographical measurements with position-sensitive electron detectors installed on the focal plane of the INS iron-free π√2 β-ray spectrometer. Internal conversion coefficients were deduced with the measured relative electron intensities and with the recent precise γ-ray data, where we assumed that the ICC of the 569.6 keV K-line is equal to the theoretical α k(E2) value. The experimental ICC thus obtained were systemati- cally compared with those by Rösel- Fries-Alder- Pauli (RFAP) and found to be satisfactorily in agreement with the theoretical values. L- and M-subshell ratios, and K- through O+P-shell ratios of the 569.6 and 1063.6 keV transitions determined for the first time in the present work were also found consistent with the predictions by RFAP.

Nuclear structure and chemical effects in internal conversion of the 35 keVM1+E2 transition in125Te

The relative conversion line intensities of the 35 keV transition in125Te were measured using the 50 cm π√2 iron-yoke magnetic spectrometer. The transition was proved to be ofM1+(8.7±1.5)×10−4 E2 multipolarity, the magnetic component being affected by the nuclear structure with λ=2.4±1.4. The conversion intensity ratio,0/N 1 , was determined to be 0.115+0.005 for both Ag125 I and Cu125 I sources. It is in accordance with previous measurements for the Zn125m Te and Pb125m Te sources and differs from those for the125mTeO2 and Na2H 4 125 TeO6 ones. The conversion coefficients were calculated for 32 configurations of the valence shell of free tellurium atom and ions and were compared with the experimental results.

L- and M-subshell conversion line intensity ratios for pure E2 transitions in 168Er

Measurements of the conversion electron spectrum from the 167Er(n, e −) 168Er reaction show L I L III = 0.0859(6) , L II L III = 0.963(4) , M I M III = 0.696(7) , and M II M III = 0.934(5) for the 79.804 keV, 2 + → 0 +, E2 transition and L I L III = 0.663(4) , L II L III = 1.270(6) for the 184.285 keV, 4 + → +, E2 transition in 168Er. For the 79.8 keV transition the L II L III ratio is (5.7 ± 0.7)% higher and the M I M III ratio (7.0 ± 1.1)% lower than predicted by theory. The L II L III and M II M III ratios for this transiton and the L-subshell ratios of the 184 keV transition agree with the theory. An explanation of the observed discrepancies is sought in the sensitivity of the calculated L I and M I conversion coefficients on the lower energy region to a partical cancellation in the leading matrix element for E2 conversion.

The nature of M1 admixtures in intra-band transitions in the γ-vibrational band

Abstract The M1 admixtures in the 74.6 keV (3+ → 2+), 122.8 KeV (5+ → 4+) and 146.3keV (6+ → 5+) transitions in the γ-vibrational band of 168Er have been determined to be 33 ± 1, 29 ± 2 and 22 ± 6 percent from measurements of L subshell conversion line intensity ratios. It is shown that the M1 admixtures in the intra-band transitions in the γ-band are a general and suprisingly constant feature in deformed rare-earth nuclei. This suggests that they are the result of a collective effect. The theory of Greiner, which takes the diferent deformation of the proton and nuetron cores into account, is found to be able to give a quantitative explanation of the observed M1 admixtures.

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, L1−3,M1−5,N, andO + P.

Proton states, anomalous conversion, andK-Auger spectra inAm241fromCm241(electron capture) andBk245αdecays

$\ensuremath{\gamma}$ and conversion-electron spectra of mass-separated $^{241}\mathrm{Cm}$ (32.8 day) samples were measured at high resolution with Ge(Li) detectors and a magnetic $\ensuremath{\beta}$-ray spectrometer; 28 $\ensuremath{\gamma}$ rays and 76 conversion lines were identified. The multipolarities of most of the 28 transitions in $^{241}\mathrm{Am}$ were deduced. Two-parameter $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidences confirmed a level scheme incorporating all transitions in six rotational bands. The observed half-life of $^{241}\mathrm{Cm}$ via the decay of the 471.8 keV $\ensuremath{\gamma}$ ray was 32.8 \ifmmode\pm\else\textpm\fi{} 0.2 day. The $\ensuremath{\alpha}$ branching deduced from the measurements of ${L}_{2}$ and ${L}_{3}$ electron lines of the 145.5 keV transition in $^{237}\mathrm{Pu}$ was (1.0 \ifmmode\pm\else\textpm\fi{} 0.1)%. The $\ensuremath{\alpha}$ singles spectrum of $^{245}\mathrm{Bk}$ (5 day) decay to $^{241}\mathrm{Am}$ showed 12 $\ensuremath{\alpha}$ groups feeding the 3 lowest bands. On the basis of these measurements six single-particle states in $^{241}\mathrm{Am}$ have been identified. The ground state of $^{241}\mathrm{Am}$ is known to be $\frac{5}{2}\ensuremath{-}[523]$. The following Nilsson band-head assignments have been made: (keV, $K\ensuremath{\pi}[N{n}_{z}\ensuremath{\Lambda}]$: 205.9, $\frac{5}{2}+[642]$; $\frac{3}{2}\ensuremath{-}[521]$; $623.1,\frac{1}{2}+[400]$; 652.1, $\frac{1}{2}\ensuremath{-}[530]$; and 670.2, $\frac{3}{2}+[651]$. The 266.0 keV $E1$ transition $\frac{3}{2}\ensuremath{-}[521]\ensuremath{\rightarrow}\frac{5}{2}+[642]$) was found to have the most highly anomalous conversion coefficients yet observed, with anomaly factors of 100-200, consistent with $E1$ penetration conversion parameter sets ${\ensuremath{\lambda}}_{1},{\ensuremath{\lambda}}_{2}$ = (18.5,283) or (-19.3, -63); the exiting 205.9 keV $E1$ transition ($\frac{5}{2}+[642]\ensuremath{\rightarrow}\frac{5}{2}\ensuremath{-}[523]$) shows normal $E1$ conversion. The 471.8 keV $M1+\ensuremath{\sim}7% E2$ transition $\frac{3}{2}\ensuremath{-}[521]\ensuremath{\rightarrow}\frac{5}{2}\ensuremath{-}[523]$ also shows anomalous (factor of 3) conversion, with an $M1$ penetration parameter \ensuremath{\sim}5.5. There is some indication of anomalously low $K$ conversion for transitions near $K$ threshold. Observed ${P}_{1}$ conversion line intensities are about twice the theoretical ${P}_{1}$ conversion coefficient predictions. Seven $\mathrm{KLL}$- and two $\mathrm{KLM}$ - Auger electron lines were observed and the $K$-shell fluorescent yield was deduced as (96.5 \ifmmode\pm\else\textpm\fi{} 0.4)%.RADIOACTIVITY $^{241}\mathrm{Cm}$ [from $^{239}\mathrm{Pu}(\ensuremath{\alpha},2n)$]; measured ${T}_{\frac{1}{2}}$, ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, ${X}_{K}$, ${\ensuremath{\omega}}_{K}$, ${E}_{\mathrm{ce}}$, ${I}_{\mathrm{ce}}$, ${e}_{\mathrm{AKLL}}$, anomalous $E1$ and $M1$ conversions, deduced penetration parameters and retardation, deduced ${\ensuremath{\alpha}}_{{P}_{1}}$, $\ensuremath{\gamma}\ensuremath{\gamma}$-coin, $\ensuremath{\alpha}$ branching, $^{245}\mathrm{Bk}$ [from $^{244}\mathrm{Cm}(\ensuremath{\alpha},p2n)$; measured ${E}_{\ensuremath{\alpha}}$, ${I}_{\ensuremath{\alpha}}$; deduced hindrance factors. $^{241}\mathrm{Am}$ deduced levels, $log\mathrm{ft}$ (EC), $\ensuremath{\gamma}$ multipolarity, $I$, $\ensuremath{\pi}$, 6 single-particle states. Mass-separated $^{241}\mathrm{Cm}$. Toroidal $\ensuremath{\beta}$ spectrometer at 0.05% FWHM.

Internal conversion of two low-energy transitions in195Au

Conversion electron spectra of the low-energy transitions in195Au taken with a magnetic spectrometer were analysed numerically. Derived conversion line intensities were found to agree with recent calculations of internal conversion coefficients for the subshells,Li,Mi,Ni and O+P. Transition energies and multipolarities were determined to be 61·35±0·06 keV [M1++ (15·7±0·6)% E2] and 56·60±006 keV [pure E3]. A description is given of the employed computer program DECOS 1 which makes use of an analytical function to express the conversion line shape.

Chemical effects on internal conversion in 125Te

Internal conversion line intensities were measured for the 35.5 keV M1 transition in 125Te with the use of different chemical compounds. Differences in valence-shell intensities lead to the evaluation of electron densities at the nucleus and to an interpretation of Mössbauer chemical isomer shifts

Relative intensity and internal conversion coefficient measurements in the decays of 51Cr, 137Cs, 192Ir, and 207Bi

An “internal conversion coefficient spectrometer” utilizing Ge(Li) and Si(Li) detectors has been used to make precision measurements of relative gamma-ray intensities for transitions following the decay of 192Ir and 207Bi, relative internal conversion line intensities for some transitions from 192Ir, and conversion coefficients for some transitions from the decays of 51Cr, 137Cs, and 192Ir. Limits and values are given for E2 M1 mixing ratios and penetration effects for the 320.1-keV transition in 51V, the 484.5-keV transition in 192Os, and the 604.4-keV transition in 192Pt. The consequences of the results for nuclear structure are discussed.

Internal conversion investigations for the 127·37 keV E3 transition in134Cs

Relative conversion line intensities of the 127·37 keV E3 isomeric transition in134Cs have been measured for ten atomic subshells, using the (π/2) √13 beta-ray spectrometer. The multipolarity E3 + (0·07±0·04)% M4 was determined. Internal conversion coefficients were calculated in different physical approximations. Precise calculations were performed for two atomic models (non-relativistic Hartree-Fock-Slater and relativistic Hartree-Fock-Slater). Experimental data were found in agreement with tabulations of Hager and Seltzer and mentioned calculations. An upper limit for the γ-branching ratio γ(138·6 keV M4)/γ(127·37 keV E3) was found to be 0·2%. The measurement of the half-life of the isomeric state has been carried out with a NaJ(Tl) crystal. The result obtained isT1/2 = (2·95 ± 0·02) h.

Nuclear structure effect in internal conversion of the isomeric transition in 191Os

Measurements have been performed on relative conversion line intensities of the hindered 74.38 keV isomeric transition in 191 Os with the 1 2 π√13 iron-free β-ray spectrometer. Anomalies were observed for the L, M and N subshell intensity ratios and were explained with a nuclear structure parameter λ = 9.4 ± 0.5 and a mixing ratio ¦δ( E4/M3 )¦ = (3.0 ± 0.3) × 10 −3 .

Relative internal conversion electron intensities of the 113 keV transition in177Hf

The intensities of the internal conversion lines of the 113 keVM1 +E2 transition in177Hf have been measured. From comparison with theoretical conversion coefficients the transition has been found to be (95.2 ± 0.5)%E2 corresponding to ¦δ¦=4.5 ± 0.3. The theoreticalLI andMI conversion coefficients used in the comparison have been increased by 5% according to the result that for pureE2 transitions in the deformed region theLI/LII,LI/LIII,MI/MII, andMI/MIII theoretical ratios are too low (∼5%). Moreover, the present result indicates that theLII/LIII andMII/MIII ratios obtained from the tabulations by Hager and Seltzer and from the computer program by Pauli are too high (1–2%).

Experimental test of conversion coefficient ratios for M-, N- and O-shell electrons

Abstract Relative conversion-line intensities have been measured for five E2 transitions of energies from 81 to 412 keV in nuclei with Z ranging from 55 to 80 using the iron-free 1 2 π√ 13 β-ray spectrometer. The results for M-, N- and O-shells were found to agree with the calculations where screening is taken into account. The atomic screening and finite nuclear size effects in internal conversion of the N-subshell electrons were investigated. Two previously measured conversion electron spectra were analysed with four different computer codes and the consistency of the results was examined.

Energy levels in 191Ir

The electron capture decay of 191Pt has been studied using Ge(Li) detectors singly and in coincidence to identify fifty-one transitions in 191Ir. The energies and intensities of the internal conversion lines associated with eighteen of these transitions have been determined and used to establish multipolarities and mixing ratios. Thirteen transitions have been excited in Coulomb excitation using oxygen ions of energy ranging from 25 to 65 MeV and B(E2)↑ values determined for six excited states. The results of the measurements have been embodied in a decay scheme involving levels in 191Ir with energies (in keV), spins and parities as follows: 0( 3 2 +), 82.398 ( 1 2 + ), 129.400( 5 2 +) , 171.32( 11 2 −) , 178.93( 3 2 +), 343.2(72 +), 351.15( 5 2 +), 390.97( 7 2 −), 502.5 ( 9 2 + ), 538.85( 3 2 + ), 587.95( 5 2 + ), 624.06( 1 2 + ), 658.87( 3 2 − ), 686.3( 7 2 + ), 747.74( 5 2 + ), 762.56( 3 2 + ), 799.75( 5 2 −), and 935.33( 3 2 +?).

Internal conversion investigations on the 42 keV E3 transition in 191Ir

Abstract Relative conversion line intensities of the 41.85 keV E3 transition in 191Ir have been measured for twelve atomic subshells, using the iron-free 1 2 π √13 β-ray spectrometer. The transition energy of 41.85 ± 0.03 keV and multipolarity E3 + (0.001 ± 0.01)% M4 were determined. Internal conversion coefficients were calculated in different physical approximations. Precise calculations were performed for three atomic models. Experimental data were found in agreement with recent tabulations and present calculations based on the relativistic potential.

A method for the high precision measurement of relative intensities and internal conversion coefficients

The development of a method for the precision measurement of relative intensities and internal conversion coefficients is discussed. The success of this method primarily depends on a series of interconnecting computer analysis routines which are designed to preserve the significance of the propagated uncertainties. High precision fitting is used to determine photopeak and conversion line intensities. A pair of relative efficiency curves is derived, one for gamma rays and one for electrons, with the property that the ratio of the electron efficiency to the gamma-ray efficiency is known absolutely. Relative electron and gamma-ray intensities are determined from their respective curves and the uncertainties in the intensities are given in their complete matrix form. Internal conversion coefficients are determined directly from the absolute ratio of the two efficiency curves. Sample results are given from the analysis of the decays 192Ir, 207Bi and 137Cs.

Nuclear structure effect in internal conversion of the 57.54 keV E1 transition in 180Hf

Measurements have been performed on relative conversion line intensities of the highly K-forbidden E1 transition (8 − → 8 +) of 57.54 keV in 180Hf. Anomalies observed for the L, M, N subshell and O total intensity ratios were explained with the nuclear current parameter η = −7.0 ± 0.3 and nuclear charge parameter ξ = 10 ± 50.

Construction and application of a [formula omitted] high-resolution β-ray spectrometer connected with a tandem accelerator

A high-resolution iron-free β-ray spectrometer with a focusing angle of π√(13) 2 =324.5° has been constructed and connected with a 6 MV tandem accelerator. The focusing principle of this “flat” spectrometer involves radial focusing and axial defocusing at the exit slit which is curved. The “image” of a point source is a curved line, and the image of a line source is identical with that of a point source. The extra degrees of freedom due to this focusing principle are used to obtain a resolving width independent of all aperture angle terms up to the third power, and the only fourth-order term is that with ϕ 2 r × ϕ 2 z ( ϕ r and ϕ z are radi and axial aperture angles, respectively). The dispersion is D = 6.5. The stationary orbit has a radius of r 0=30 cm. The magnetic field is produced by five pairs of coils. The maximum electron energy is 4.5 MeV and the corresponding electric power 45 kW. A typical pair of values for resolution (fwhm) η and fractional solid angle ω is η=2.2 × 10 −4 and ω=0.6 × 10 −2. The spectrometer is situated in an iron-free brick building nearby a 6 MV tandem accelerator whose beam can be focused at the source position of the spectrometer to a spot of 0.5 × 5 mm 2. The spectrometer was widely applied to study conversion line energies and intensities both from radioactive sources and from Coulomb-excited nuclei. At favorite cases momentum ratios can be measured with 2 × 10 −6 precision (internal error), and intensity ratios with 1 per cent. In this paper results are mostly given for energy values.

Gamma-radiation of193Au

The gamma-radiation of193Au has been studied by means of a Ge(Li) semiconductor detector. In addition to the transitions observed by Svahn et. al. (Z. Physik210 (1968), 466), 21 new transitions have been found. With the use of the relative conversion line intensities from the above reference and the γ-ray intensities of this work, the number of internal conversion coefficients αK has been determined. The multipolarities of the transitions have been deduced from a comparison of the experimental and theoreticalα K -values. Some additions to the193Au decay scheme were made on the basis of new experimental results.