K-shell Internal Conversion Coefficients Research Articles

Further Test of Internal-conversion Theory with a Measurement in 119Sn

Precise measurements are being used to test theoretical K-shell internal conversion coefficients (ICCs): in particular, our program has focused on examining whether the atomic K-vacancy formed during the conversion process must be incorporated into the calculations. We report here a measurement on the 65.66-keV, M4 isomeric transition in 119Sn. Our preliminary result is αK=1610(27), which confirms the importance of including the vacancy in the ICC calculations.

Precise tests of internal-conversion theory

Using the 165.9-keV M1 transition in 139La as a calibrant, we have determined the K-shell internal conversion coefficients (ICCs) for the 127.5-keV E3 transition in 134Cs and the 661.7-keV M4 transition in 137Ba to 0.6% precision. Unlike previous less-precise measurements of these ICCs, which differed significantly from calculated values, our results agree well with calculations that include the atomic K-shell vacancy and disagree with those that exclude it. These results, which are consistent with what we also found for 193Ir, confirm our earlier conclusions but for different energies, multipolarities and atomic numbers.

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.

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.

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.

Structure and decay of a three-quasiparticle isomer in153Eu

An isomer has been observed in the stable nuclide ${}^{153}\mathrm{Eu},$ which primarily decays via a 919-keV gamma ray to the ${17/2}^{+}$ level of the ground-state band. The structure of the isomer has been investigated using an array of eight germanium detectors and an electron spectrometer. The K-shell internal-conversion coefficient of the 919-keV transition has been measured to be $9.8(2.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ establishing that this transition has electric-dipole character. This measurement, and the observed decays of the isomer, indicate that the isomer has spin and parity ${19/2}^{\ensuremath{-}}.$ Using timing measurements against a pulsed beam, the half-life of the isomer has been measured to be 475(10) ns: this suggests high purity for the K quantum number and associated highly K-forbidden decays. The gamma-gamma coincidence data have revealed a rotational band built upon the isomer. The properties of the rotational band are consistent with the configurations $\ensuremath{\nu}[651]3/2\ensuremath{\bigotimes}\ensuremath{\nu}[505]11/2\ensuremath{\bigotimes}\ensuremath{\pi}[413]5/2,$ and $\ensuremath{\nu}[402]3/2\ensuremath{\bigotimes}\ensuremath{\nu}[505]11/2\ensuremath{\bigotimes}\ensuremath{\pi}[413]5/2,$ or a mixture of both.

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.

K-shell ionization of Dy atoms produced in [formula omitted] nuclear reactions

The K-shell ionization cross sections, σ K Z , are determined for Dy atoms produced in bombardments of several Gd targets with α-particles in the energy range 47–130 MeV and of 148, 150Nd targets with 12C ions at 65 and 90 MeV. The determination is based on the measured intensity ratios of the characteristic K X-rays of the product atoms to those of the target elements. Analysis of the simultaneously measured discrete in-beam γ-ray spectra allows one to determine ionization cross sections for Dy product atoms, σ Z K( der), derived as a sum of the products of the γ-ray intensities times the corresponding K-shell internal conversion coefficients. The measured and the total derived values are found to be identical to within the experimental errors. The partial ionization yields per reaction are analyzed as functions of the average angular momentum left in each exit channel. Strong dependence of these yields on the nuclear structure is found. Moreover, the variation of the yields with the angular momentum is also strongly structure dependent. Properties of the quasicontinuum γ-radiation deexciting the reaction residues are considered. Upper intensity limits are determined for the low-energy magnetic dipole components in this radiation.

Mass and low-lying levels ofGe67; trends in the structure ofNi63,65,Zn65,67, andGe67,69

/sup 6/7/sub 3/2Ge/sub 3/5 has been studied via the reaction /sup 6/4Zn(..cap alpha..,n..gamma..)/sup 6/7Ge. The mass excess was measured to be -62666 +- 12 keV, and four low-lying excited states have been identified. Among these newly identified levels is an isomeric state at 18.2 keV having a measured total mean lifetime of 18.5 +- 0.3 ..mu..s and a measured K-shell internal conversion coefficient ..cap alpha../sub K/ = 176 +- 29. In addition, the total lifetime of the 63.4 keV isomeric level in /sup 6/5Ni has been measured to be 104.9 +- 7.1 ..mu..s. The level schemes of the six nuclei /sup 63,66/Ni, /sup 65,67/Zn, and /sup 67,69/Ge are then compared, and similarities in their structure and in the decay characteristics of the isomeric states of each are discussed and interpreted in terms of a simple pairing model.

The decay of 85mKr

The allowed beta spectrum and internal conversion electron spectrum in the decay of 85mKr were measured with the high resolution π 2 magnetic spectrometer of the TRISTAN on-line isotope separator system, and the 85mKr gamma-ray spectrum was measured with a high resolution Ge(Li) detector. The half-life of 85mKr was found to be 4.480 ± 0.008 h. The allowed beta decay of 85mKr was found to have an end-point energy of 840 ± 2 keV, an intensity of 78.8 % and a log ft of 5.15. Using the PBS method for calculating internal conversion coefficients, the 150.99 ± 0.05 keV transition in 85Rb was found to be of pure M1 multipolarity with a K-shell internal conversion coefficient α k of 0.0400 ± 0.0008 and a K/L/M ratio of 89/10/2.2. The 304.47 ± 0.05 keV isomeric transition in 85Kr was found to be a pure M4 multipole with α k = 0.432 ± 0.020 and a K/L/M ratio of 67/10/2.0. The gamma-ray energies were determined by both Ge(Li) and spectrometer measurements.

On K-shell internal conversion coefficients

K-shell internal conversion coefficients have been obtained for E1 and M1 transitions in the point nucleus limit by using solutions of the Biedenharn symmetric Dirac-Coulomb Hamiltonian. Numerical results obtained for atoms having Z values between 20 and 65 with γ-ray energies from 0.15 MeV to 2.5 MeV are compared with results of earlier calculations.

High-energy internal conversion coefficients

The K-shell internal conversion coefficients were calculated for every fifth value of the atomic number Z from Z = 30 to Z = 100 for lowest four electric and magnetic transition multipoles. The finite nuclear size effect and screening by atomic electrons were considered precisely in the energy region from 6 to 9.5 mc 2 and approximately for energies from 12 to 20 mc 2. The K/(L + M) conversion coefficient ratios equal roughly 8.7, 6.6 and 4.3 for Z = 30, 60 and 95, respectively, independently of the transition energy and multipolarity. In the considered energy region, the internal conversion in the s-subshells is found to be dominant.

Measurements of αK for the 84.3 keV transition in 170Yb and the 80.6 keV transition in 166Er

The K-shell internal conversion coefficients for the 84.3 keV 2 + → 0 + transition in 170Yb and the 80.6 keV 2+ → 0+ transition in 166Er have been measured to 3% by the K X-ray/γ ratio method with a NaI(Tl) crystal, a bent-crystal spectrometer and a least-squares fitting technique. The experimental conversion coefficients of α K = 1.43 ± 0.04 and α K = 1.72 ± 0.6 for 170Yb and 166Er, respectively, agree with the presently available theoretical values for pure E2 transitions. In the case of 170Yb, it was also possible to determine the intensity of the K-capture branch to 170Er. The present value of (0.19 ± 0.04)% agrees with the previous determination of (0.15 ± 0.05) per cent by Day.

Decay of 145Eu to levels in 145Sm

The decay of 145Eu to levels in 145Sm was investigated. Singles γ-ray spectra were obtained with the use of Ge(Li) detectors, and β +- γ (NaI) and e-γ (NaI) coincidence measurements were performed. By intercomparison of the photon intensity data with published conversion-electron intensity data, K-shell internal-conversion coefficients were calculated for most of the transitions observed in the γ-ray spectra. From the β +- γ coincidence measurements, the 145Eu decay energy was found to be 2710±15 keV. A level scheme with 23 excited states in 145Sm was proposed based on results obtained from e-γ coincidence measurements, on transitions energies, intensities and multipole orders, on the measured decay energy and on data available from (d, p) reaction studies. Energies (in keV) and spin and parity assignments (enclosed in parentheses) for the proposed levels in 145Sm are as follows: 0( 7 2 −) , 894.1( 3 2 −) , 1423( 9 2 −) , 1437( 1 2 , 3 2 , 5 2 +) , 1548 3 2 +) , 1628( +), 1658( 3 2 , 5 2 −) , 1805( +), 1859( 1 2 , 3- 2 −) , 1877( 5 2 , 7 2 −) , 1972( 3 2 −) , 1997( 5 2 , 7 2 −) , 2111, 2134( 3 2 , 5 2 , 7 2 −) , 2156( 1 2 −) , 2193, 2276, 2293 ( ≦ 7 2 − ), 2329, 2346, 2388, 2427 ( ≦ 7 2 − ), 2482 and 2510. The (K-capture/ β +) ratio for the first-forbidden transition that populates the 894.1 keV state was measured to be 80(±50%) as compared to the theoretical ratio of 42 for an allowed transition. By the use of closed energy cycles and the measured 145Eu decay energy, the electron-capture decay energies for 153Ho and 149Tb are predicted to be 4.22±0.06 and 3.69±0.03 MeV, respectively.

Measurement of αK for the 91.5 keV E2 transition in 164Er

The K-shell internal conversion coefficient, α K, for the 91.5 keV 2 +→0 + transition in the decay of 164Ho to 164Er was measured by the K X-ray/γ ratio method with scintillation crystals. Photons seen by the NaI detector were required to be in coincidence with continuous beta rays in order to eliminate effects of the competing electron capture decay of 164Ho to 164Dy. The experimental conversion coefficient α K = 1.31±0.11 agrees with the presently available theoretical values for an E2 transition.

Ground state parity of 227Ac

The K-shell internal conversion coefficient and L-subshell electron ratios were measured for the transition from the 3 2 − 327 keV level to the I = 3 2 ground state in 227Ac. The results indicate that the transition is an M1 + E2 multipole mixture. Thus, the 277Ac ground-state parity is odd.

Investigation of gamma rays in the decay chain [formula omitted

Gamma-ray spectra were measured with a Ge(Li) detector for the decay chain 149 Gd(9 d)→ 149 Eu(106 d)→ 149 Sm . Results were compared with previously known data for transitions following the decay of the same two nucleides. By combining several sets of conversion-electron and γ-ray intensities, K-shell internal conversion coefficients were calculated for and probable multipolarities were assigned to 149Gd transitions that had been observed in both γ-ray and conversion-electron spectra. These transition intensities and multipole orders were found to be consistent with a partial decay scheme that features excited states in 149Eu at energies of 149.8, 496.6, 534.4, 666.6, 749.1, 795.1, 939.1, 956.1 and 1097.8 keV. Intensities measured in this study for γ-rays following 149Eu decay were found to agree with a recently published set of intensity values. Here again, K-shell internal conversion coefficeints were calculated by combining conversion-electron and γ-ray data. An e-γ[Ge(Li)] coincidence measurement yielded additional evidence for the existence of 149Sm excited levels at energies of 22.5, 277.0, 350.0 and 528.5 keV.

K-shell internal-conversion coefficients of the 122 and 136.4 keV gamma transitions of57Co

K-shell internal-conversion coefficients of the 122 and 136.4 keV gamma transitions of57Co

Alpha-particle and gamma-ray spectral studies of 149Gd and 149Eu

The alpha-particle and photon spectra of 9.5 d 149Gd and the photon spectrum of its daughter 106 d 149Eu were studied with a Si(Au) surface barrier detector, and with Ge(Li) and NaI(Tl) gamma-ray spectrometers. The 149Gd alpha particles were found to have an energy of 3.01±0.01 MeV while the α E.C. branching ratio was found to be (4.0±1.2) × 10 −6. The 149Gd gamma-ray transition energies, in keV, and relative intensities (placed in parentheses) were found to be: 150 (240), 216, (0.8), 253 (1.3), 261 (4.2), 273 (12.5), 299 (118), 347 (100), 461 (2.5), 497 (6.3), 517 (10.5), 535 (12.4), 646 (4.5), 666 (3.6), 750 (30), 790 (27), 812 (0.4), 934+939 (11.5), 949 (3.2). For 149Eu the photon energies, again in keV, and relative intensities were measured to be: 255 (12), 277 (100), 328 (118), 350 (9), 506 (14) and 529 (13). The K-shell internal conversion coefficients were calculated by intercomparison of the photon intensity data with conversion electron intensity data of other workers.

Measurements of conversion coefficients for transitions in 154Gd, 160Dy, 170Yb, 171Yb and 141Pr

Internal conversion coefficients were measured by observing with a well-type NaI(Tl) crystal the photon spectra emitted during the de-excitation from the first excited state to the ground state of 154Gd, 160Dy, 170Yb, 171Yb and 141Pr. The results were obtained by analysis of either the singles spectra, or spectra obtained by coincidence-sum techniques, or both. For the coincidence work gating was done either with high-energy gamma rays or with beta particles. The spectra from the Yb isotopes were analysed on a computer using a least-squares, curve-fitting program. The photon detection efficiencies were calculated with a computer by performing numerical integrations. The K-shell internal conversion coefficients directly measured were 0.632±0.016 for 154 Gd, 1.47±0.05 for 170 Yb, 6.9±1.0 for 171 Yb and 0.375±0.009 for 141 Pr . The total internal conversion coefficients directly measured were 1.20±0.02 for 154 Gd and 4.52±0.11 for 160 Dy , which yield respective K-shell internal conversion coefficients of 0.637±0.016 and 1.54±0.06 when multiplied by K to total ratios. In order to eliminate interpolation errors from the internal conversion coefficient tables, theoretical values were obtained with computer calculations (point nucleus, no screening) normalized, by use of an effective nuclear charge, to the tables of Rose and Sliv and Band. The results for the transitions in 154Gd, 160Dy and 141Pr are in good agreement with theory. The ratio of the experimental result to the theoretical value is 1.06±0.05 for the transition in 170Yb. The result for the transition in 171Yb implies a mixing ratio of E2/M1 = 0.45±0.08, assuming the theoretical internal conversion coefficients are correct.