Internal Conversion Coefficients Research Articles

Test of internal-conversion theory with measurements inCs134andBa137

We have measured the ratio of K-shell internal conversion coefficients, {alpha}{sub K}, for the 127.5-keV E3 transition in {sup 134}Cs and the 661.7-keV M4 transition in {sup 137}Ba. Previous measurements of these {alpha}{sub K} values led to a ratio that differed from calculated internal conversion coefficients. Our measured result, 30.01(15), disagrees with, but is a factor of three more precise than, the previous average of all experimental results. Our new result is consistent with calculations.

On the decay of 44Ti

The decay of 44Ti was investigated. The coefficients of internal conversion for γ transitions on the K shell were determined. For the M1 and E1 transitions, αc = 0.011(3) and 0.076(4), respectively. The absolute probabilities of γ transitions with energies of 68 keV (Iγ = 92.0%) and 78 keV (Iγ = 98.1%) were measured with an accuracy of 0.6%.

Nuclear Data Sheets for A = 94

Experimental data on ground- and excited-state properties for all known nuclei with mass number A = 94 have been compiled and evaluated. States populated in radioactive decay, as well as in nuclear reactions, have been considered. For these nuclei, level and decay schemes, as well as tables of nuclear properties, are given. The Hager-Seltzer internal conversion coefficients are listed for gamma rays of known multipolarity. This work supersedes the 1992 evaluation by J.K. Tuli (1992Tu02). Since 1992, many articles have been published which were incorporated in this evaluation. In summary, high-spin data using large arrays of Ge detectors have been obtained for 94Kr (2000Rz02), 94Sr (1995Ha20), 94Zr (2002Fo03,2005Pa48), 94Nb (2000Ma63), 94Mo (1998Kh04), 94Tc (2000Gh01), 94Ru (1994Ju03,1994Ro08), 94Rh (1994Ar33), and 94Pd (2003Ma24). A new isomer was observed in 94Y (1999Ge01). The low-spin levels in 98Mo were systematically studied using a variety of experimental techniques (2003Fr02). Considerable effort was spent investigating the decay of 94Ag and the levels of 94Pd (2006Mu03,2005Mu15,2004BaZY,2004Pl01,2002La18), in particular, the (21+) level in 94Ag is the first level observed to undergo both single and double proton radioactivity.

A practical method for assessment of dose conversion coefficients for aquatic biota

Radiological impact assessment for flora and fauna requires adequate dosimetric data. Due to the variability of habitats, shapes, and masses of the non-human biota, assessment of doses is a challenging task. External and internal dose conversion coefficients for photons and electrons have been systematically calculated by Monte Carlo methods for spherical and ellipsoidal shapes in water medium. An interpolation method has been developed to approximate absorbed fractions for elliptical shape organisms from absorbed fractions for spherical shapes with reasonable accuracy. The method allows an evaluation of dose conversion coefficients for arbitrary ellipsoids for photon and electron sources with energies from 10 keV to 5 MeV, and for organism masses in the range from 10(-6) to 10(3) kg. As an example of the application of the method, a set of dose coefficients for aquatic organisms discussed as reference animals and plants in a draft of an up-coming publication of the International Commission on Radiological Protection has been determined.

Activity standardization and nuclear decay data of 109Cd

The activity of a 109Cd solution has been accurately determined without using 109Cd nuclear decay data such as emission probabilities. An ampoule containing this calibrated 109Cd solution was sent to the Bureau International des Poids et Mesures to include the activity result in the database of the International Reference System (SIR). The emission rate of conversion electrons was measured by means of pressurized proportional counters as well as by a liquid scintillation spectrometer. The combination of the results with the photon emission rate measured with the aid of γ-ray spectrometers yields the activity concentration. The measurement results were also used to deduce emission probabilities with high accuracy. For the 88 keV transition, a photon emission probability of p γ = 0.03663 ( 33 ) and a total internal conversion coefficient of α t = 26.30 ( 25 ) were determined.

Test of internal-conversion theory with precise γ- and X-ray spectroscopy

Precise measurements of K-shell internal conversion coefficients (ICCs) are being used to determine the best method for calculating these coefficients. A recent result for the M4 transition from 193Ir m has been refined, demonstrating conclusively that the atomic vacancy created by the ejected electron must be properly accounted for in the calculation of ICCs. Measurements of additional cases are discussed.

Internal conversion and the photoelectric effect

It is demonstrated how data for internal-conversion coefficients may be decomposed with good accuracy into terms scaling with different powers of the atomic number. The individual terms are identified as a near-field contribution, a contribution due to photon emission and subsequent atomic photoionization, and interference. The photoeffect channel is generally important for high atomic numbers. The ratio of the photoeffect component to the near-field contribution is consistent with a localization of the relativistic photoeffect to distances from the nucleus not substantially exceeding the Compton wavelength of the electron irrespectively of atomic number and shell. Such localization is in accordance with results of an impact-parameter study. As a by-product a fitting formula is produced for electric dipole transitions involving the $K$ shell. The formula which is accurate to the level of $\ensuremath{\simeq}1%$ covers a variation of the conversion coefficient over nearly four decades.

Ratios of internal conversion coefficients

We present here a database of available experimental ratios of internal conversion coefficients for different atomic subshells measured with an accuracy of 10% or better for a number of elements in the range 26 ⩽ Z ⩽ 100. The experimental set involves 414 ratios for pure and 1096 ratios for mixed-multipolarity nuclear transitions in the transition energy range from 2 to 2300 keV. We give relevant theoretical ratios calculated in the framework of the Dirac–Fock method with and without regard for the hole in the atomic subshell after conversion. For comparison, the ratios obtained within the relativistic Hartree–Fock–Slater approximation are also presented. In cases where several ratios were measured for the same transition in a given isotope in which two multipolarities were involved, we present the mixing ratio δ 2 obtained by a least squares fit.

Experimental Identification of Spin-Parities and Single-Particle Configurations inNo257and Itsα-Decay DaughterFm253

alpha-gamma and alpha-electron coincidence spectroscopy for a short-lived heavy actinide nucleus (257)No (T(1/2) = 24.5 s) has been performed using a gas-jet transport system and an on-line isotope separator. Spin-parities of excited states in (253)Fm fed by the alpha decay of (257)No have been identified on the basis of the measured internal conversion coefficients. The nu3/2(+)[622] configuration has been assigned to the ground state of (257)No as well as to the 124.1 keV level in (253)Fm. It was found that the ground-state configuration of (257)No is different from that of lighter N = 155 isotones.

Nuclear Data Sheets for [formula omitted

Detailed level schemes, decay schemes, and the experimental data on which they are based are presented for all nuclides with mass number A = 241 . The experimental data are evaluated; inconsistencies and discrepancies are noted; and adopted values for excitation energies, γ–ray energies and intensities, as well as for other nuclear properties are given. This evaluation supersedes the earlier nuclear data sheets for A = 241 (1994Ak06,1985El03). New data include an extensive study of the levels, gammas, and band structure in 241Pu via (n,γ), (d,p), and (d,t) (1998Wh01) and in 241Am via ( 209Bi, 209Bi'γ) (2004Ab16,2002AbZV). Levels in 241Cm have been studied via ɛ decay (2003As01,2003AsZY) and α decay (1996Ma72). All experimental internal conversion data have been reanalyzed by the evaluator using the “frozen orbital hole” internal conversion coefficients of 2002Ba85.

Isomers of astrophysical interest in neutron-deficient nuclei at masses A = 81, 85 and 86

Decay properties of neutron-deficient exotic nuclei close to A=80 have been investigated at the IGISOL facility. The studied nuclei, 81Y, 81Sr, 81mKr, 85Nb, 85Zr, 86Mo and 86Nb, were produced by a 32S beam from the Jyväskylä isochronous cyclotron on 54Fe and natNi targets. The internal conversion coefficient for a 190.5 keV isomeric transition in 81mKr has been measured and the internal transition rate has been determined. The internal transition rate has been used to estimate a neutrino capture rate on 81Br, which yields a log ft of 5.13±0.09 for the reaction 81Br( ν, e -)81mKr. A new isomer with a half-life of 3.3±0.9 s has been observed in 85Nb. The existence of an earlier reported isomer with a half-life of 56 s in 86Nb has not been confirmed.

Precise measurement ofK-shell fluorescence yield in iridium: An improved test of internal-conversion theory

We have measured the total intensity of K x rays relative to 129.4-keV \ensuremath{\gamma} rays from decay of the second excited state in $^{191}\mathrm{Ir}$. This ($M1+E2$) transition was observed following the \ensuremath{\beta} decay of 15.4-d $^{191}\mathrm{Os}$. Our measured ratio yields the result ${\ensuremath{\alpha}}_{K}{\ensuremath{\omega}}_{K}=2.044(11)$. When combined with a recent measurement of the same ratio for the 80.2-keV $M4$ transition from $^{193}\mathrm{Ir}{}^{m}$, this result strongly confirms the need for the K-shell hole to be included in calculations of internal-conversion coefficients ${\ensuremath{\alpha}}_{K}$. Since the ${\ensuremath{\alpha}}_{K}$ value calculated for the $^{191}\mathrm{Ir}$ transition is virtually independent of the hole treatment, our result also yields a model-independent value for the iridium fluorescence yield, ${\ensuremath{\omega}}_{K}=0.954(9)$.

The βdecay of 147Cs to 147Ba

The β--decay of 147Cs to 147Ba has been studied by means of γ- and X-ray spectroscopy. A new level scheme of 147Ba is significantly modified and extended in comparison to the one previously reported. The Advanced Time-Delayed βγγ(t) method has been applied to measure half-lives of the 46.2 and 85.4 keV levels in 147Ba yielding T 1/2 of 510(80) ps and 370(100) ps, respectively. The lifetime results combined with the deduced internal conversion coefficients allowed to assign M1 multipolarity to three γ transitions. The B(M1) values obtained for the 39.2, 46.2 and 85.4 keV transitions range from 0.017 to 0.043 W.u. and represent typical B(M1) strength in the Ba-Er region. Model calculations using a shell correction approach with the axially deformed Woods-Saxon potential predict for 147Ba an octupole deformed ground state with β3 = 0.11.

Evaluation of 233Pa decay data

An evaluation of the complete scheme and data for 233Pa decay, including results of the recent measurements, is presented. Several data evaluation procedures were used in the analysis of the half-life data. The half-life has been determined to be 26.971±0.013 days. All the gamma-ray emission probabilities ever published have been examined, and the gamma-ray emission probability for the reference 312-keV γ line is recommended as 38.35±0.28%. The calculated internal conversion coefficients and their uncertainties have been used to obtain the complete decay intensity balance. Other decay characteristics have been calculated using the ENSDF analysis program. Finally, a new 233Pa decay scheme has been built.

Precise measurement ofαKfor theM4transition fromIrm193: A test of internal-conversion theory

The 10.5-day isomer in {sup 193}Ir decays by a single 80.2-keV M4 transition directly to the ground state of that nucleus. We have measured the total intensity of K x rays relative to 80.2-keV {gamma} rays for this transition to be 98.7(6). With the K-shell fluorescent yield for iridium taken to be 0.958(4), this result yields {alpha}{sub K}=103.0(8) for the K-shell internal conversion coefficient (ICC). The calculated {alpha}{sub K} for this transition is particularly sensitive to the treatment of the hole that is created by conversion in the atomic K shell. Recent ICC tables, which ignore the hole, yield {alpha}{sub K}=92.0. We demonstrate that calculations incorporating the hole produce values between 99.6 and 103.3 depending on the approximation used. Our result strongly supports the need to include the hole.

Internal conversion in hydrogen-like ions

The probability of internal gamma-ray conversion is theoretically investigated for hydrogen-like ions versus the corresponding neutral atoms. The relevant calculations are performed by the relativistic Dirac-Fock method. The results reveal that the effect of multiple ionization on the coefficients of internal conversion in the K shell is maximal near the ionization threshold and for transitions of high multipole order, where this effect can be as great as a few orders of magnitude. The distinction between the coefficient of internal conversion in the K shell of a neutral atom and that in the respective hydrogen-like ion decreases with increasing transition energy, but it remains sizable for transitions of practical importance. It is found that the ionization of an atom to a hydrogen-like ion with allowance for conversion in external atomic shells may change significantly (by up to eight orders of magnitude) the lifetime of the nucleus being considered. The predicted effects can be observed in experiments with beams of relativistic heavy ions.

Observation of high spin levels in131Cs from131Ba decay

The γ- and conversion electron spectra following131Ba e-decay are investigated, using HPGe detector and mini-orange electron spectrometer. Attention is particularly focussed on identifying weak transitions associated with low energy high spin levels in131Cs level scheme earlier inferred in reaction studies but not yet observed in131Ba decay. Our experiment identifies 15 new gammas and 6 new conversion lines in this decay. Internal conversion coefficients and multipolarities of several transitions are determined. Five new levels (3 with Iπ = 7/2+ and one each with Iπ 9/2+ and 11/2−) are introduced in the131Cs level scheme based on our observations taken together with the results from reaction studies. Spin-parity assignments to a few other levels are also suggested

Low-spin studies of theπh11/2νh11/2structure in134Pr

Low-spin states built on the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\nu}{h}_{11/2}$ configuration in ${}^{134}\mathrm{Pr}$ have been studied using a ${}^{119}\mathrm{Sn}{(}^{19}\mathrm{F},4n)$ fusion-evaporation reaction. A planar low-energy photon spectrometer along with a low-$Z$ target chamber was utilized in an array of five high-purity Ge detectors for the purpose of measuring low-energy $\ensuremath{\gamma}$ rays. A 39.3-keV $\ensuremath{\gamma}$ ray was discovered as a new transition at the bottom of the band. The transition was found to have an $M1$ multipolarity, determined from the internal conversion coefficients evaluated from the missing transition intensity. The new bandhead was assigned and was identified as an isomeric state with a mean lifetime of $\ensuremath{\tau}=4.6(1)\mathrm{ns}.$ This bandhead decays by a 306-keV $\ensuremath{\gamma}$-ray transition that was found to have an $E1$ multipolarity through the analysis of the angular distribution asymmetry.

How good are the internal conversion coefficients now?

How good are the internal conversion coefficients now?

A Tale of Two Compilations: Quadrupole Deformations and Internal Conversion Coefficients

(i) The deformation of the nuclear ground state is a fundamental property that can be deduced in even-even nuclei from the B(E2) value for the first 2+ (21+) state. In 1987, we published a compilation of such B(E2: 01+→ 21+) values for ~ 280 even-even nuclei. Very recently, we have updated the 1987 compilation and have compared the adopted B(E2: 01+ → 21+) values (for ~ 330 even-even nuclei) with those given by various theoretical models (Finite-Range Droplet Model, Woods Saxon Model, Relativistic Mean-Field Calculations, Extended Thomas-Fermi Strutinski Integral Method, Hartree-Fock+BCS Calculations, and Dynamical Microscopic Model). Agreement between theory and experiment varies from “reasonable” to “excellent”.(ii) Currently, the most widely used Internal Conversion Coefficient (ICC) compilations are those by Hager and Seltzer, Rösel et al., and Band and Trzhaskovskaya. In all three cases, the calculation of electron wave functions is carried out in the framework of the Hartree-Fock-Slater (HFS) method. It has been suspected for some time that there is a “2–3% problem” — that is, the HFS models give results that are systematically larger than the experimental data by 2–3%. ICCs are now available from relativistic self-consistent Dirac-Fock (DF) calculations in which the exchange terms of DF equations are included exactly. The DF model gives results that are very close to the experimental data. The long-standing “2–3% problem” has apparently now been solved.