B. van Nooijen

Experimental values of internal-conversion coefficients of nuclear transitions: total and K-shell coefficients and L-subshell coefficient ratios

A tabulation is presented of experimentally measured values of internal-conversion coefficients for the K -shell, α K , L -subshells (mostly ratios only, L 1 : L 2 : L 3 ), and for all shells, α total . Results reported prior to November 1965, whose uncertainties are ≦ 25%, are listed and compared with theoretical values. Transition energies and spins an parities of initial and final levels, when known, are included. The theoretical values were obtained from computer interpolation, and in some cases extrapolation, of the tables of Sliv and Band. A brief discussion of the methods of measuring conversion coefficients is given.

Evidence for ground and both neutron and proton rotational aligned bands in 68Ge

Abstract From in-beam, γ-ray spectroscopy, the yrast band in 68Ge is found to branch into three positive parity bands at 8+. Bands built on both the yrast 8+ and second 8+ levels show strong backbending in I while the third is apparently a continuation of the ground band. The two lowest 8+ bands provide the first evidence for both proton and neutron rotation-aligned bands built on the same configuration in the one nucleus, here g 9 2 ) 2 . Rotational aligned model calculations confirm these assignments.

Note on the β-circularly polarized γ-angular correlations in the decays of 46Sc and 58Co

Abstract The β-γ circular polarization correlations of the (357 keV, 4 + → 4 + , β − ) − (1.121 + 0.889 MeV, γ ) cascade in 46 Sc and the (475 keV, 2 + → 2 + , β + ) − (0.810 MeV, γ ) in 58 Co have been measured by using the standard forward scattering technique for the detection of circular polarization of γ-rays. The energy selection of the β-rays was performed with a magnetic lens spectrometer. The measured asymmetry coefficients, Fermi to Gamow-Teller matrix element ratios, values of the Fermi matrix elements, isospin impurity coefficients and the effective Coulomb matrix elements are as follows: A =M F /M GT |M F | × 10 3 |α| × 10 3 |〈H C 〉|keV 46 Sc 0.06±0.03 0.03±0.04 1.9±2.5 0.95±1.25 6.7±10 58 Co 0.18±0.04 0.02±0.05 0.7±1.8 0.3 ±0.7 1.8± 4.7

L Subshell Ratios for E2 Transitions in Deformed Heavy Elements

Publisher Summary This chapter presents the discrepancies between theory and experiment for the L subshell ratios of pure E2 transitions. A study of the L subshell ratios in deformed heavy elements help to clarify the systematics of the reported deviations. It discusses the L subshell ratios of the 2 + → 0 + first excited state to ground state transitions of 42.9-keV in Pu 240 populated by the α decay of Cm 244 and of 57.9 keV in Th 228 populated by the α decay of U 232 . The measurements were made on the Vanderbilt iron-free double focusing spectrometer. Thin-window GM counters with cutoffs less than 5 keV were used as detectors to ensure uniform transmission and efficiency of detector. The sources were prepared by electrode position onto platinum foils and had areas of 1 × 16 mm 2 . The source strengths were of the order of 10 microcuries to keep the source thickness small. These weak sources required long measuring periods of 24 to 48 hours for each complete run to obtain good statistics. The three L lines of each transition were measured in a continuous run.

Beta-decay of 99mTc and dose calculations

A search for the non-unique once forbidden direct β-decay of 99mTc to the 89.36 keV level in 99Ru has been carried out with Ge(Li) detectors and a curved crystal spectrometer. The γ-ray intensity ratio of the 89.36 keV transition in 99Ru to that of the 140.5 keV transition to the 99Tc ground state is equal to or less than 3.6 × 10−4 for a 99Mo equilibrium source. Corrected for internal conversion and the percent 99Mo decay to the 142.6 keV isomeric level in 99Tc, the ratio of β-decay to the 89.36 keV level to γ-decay of 99mTc is less than or equal to 8.7 × 10−4. This limit is sufficiently small as to not seriously alter present local energy absorption dose calculations for 99mTc administered to humans.

Experimental Methods for the Determination of Internal Conversion Coefficients

Publisher Summary This chapter presents a survey of the important experimental techniques that are available at present for the measurement of internal conversion coefficients. The measurement of internal conversion coefficients is a powerful tool in nuclear spectroscopy to gain information about spins and parities of nuclear levels, about mixing ratios in mixed gamma transitions, and about nuclear structure in the case of retarded transitions. To measure the relative gamma and conversion intensities, a combination of different types of spectrometers can be used. Methods have been developed to such a degree that they can all give internal K-conversion coefficients with about the same accuracy (2–3%) in favorable cases. For nuclear decay scheme studies, only the peak-to-gamma-peak method (NPG method) and the internal-external conversion method (IEC method) can be used. The NPG and IEC methods are of great importance to nuclear spectroscopists and a part of their efforts should be directed toward further development of these methods.

Conversion Coefficient Measurements Employing Magnetic and Solid-State Spectrometers

Publisher Summary This chapter describes the conversion coefficient measurements employing magnetic and solid-state spectrometers. The development of lithium-drifted germanium detectors with moderate efficiency and good energy resolution has made the determination of relative intensities of the gamma rays possible with good accuracy in complex decays. If the relative conversion electron intensities are measured in a precision β-ray spectrometer, it is possible to use these in conjunction with relative gamma-ray intensities. It helps to determine the internal conversion coefficients either by accepting the theoretical conversion coefficient of a transition of known multipolarity or by measuring the conversion coefficient of one of the stronger transitions by the internal-external conversion (IEC) method. The relative gamma-ray intensities are calculated from the peak heights and the photoefficiency curve obtained by measurements on isotopes emitting two electromagnetic transitions of known relative intensity.