Zs. Németh

Origin of Ta-180m and the temperature of the s-process

The origin of 180m Ta, natures rarest isotope, represents a persisting puzzle of nuclear astrophysics. Recent studies indicate that it may be produced at a variety of nucleosynthesis sites, that is, by the s-process during stellar helium burning, or by the p- and v-processes, which occur in supernova explosions. Among these scenarios, the s-process is, at present, best suited for reliable predictions. For the quantitative discussion of a possible s-process origin of 180m Ta, the required input data were improved in two directions : (1) By photoexcitation experiments it was found that the decay of 180m Ta is not affected at typical s-process temperatures. (2) The stellar (n, γ)-rates for 179 Ta and 180m Ta were calculated with a refined statistical model approach. The results show that the 180m Ta abundances yields a lower or an upper limit for the temperature at the s-process sire, depending on whether it is produced in stellar helium burning or in supernovae

Comparison of experimental and theoretical high multipole-order internal conversion coefficients

Sixty-four accurately measured (1σ ⩽ 5%) internal conversion coefficients (ICCs) of high multipole-order (E3, M3, E4, M4) gamma-transitions have been compared with the theoretical values of Rosel et al. and Hager and Seltzer. Individual measurements were carefully examined and modified, if necessary. The discrepancies among the experimental values and the Rosel calculations tend to fall within a narrow band and do not reveal any dependence on atomic number, shell or transition energy. However, discrepancies between the experimental data and the calculations of Hager and Seltzer depend on transition energy, viz., increases up to 10% occur when the transition energy approaches the K binding energy. The calculations of Rosel et al. are preferred, and it is proposed that their third and fourth order ICCs are multiplied by factors of 0.975±0.010 and 0.975±0.005 respectively, to give better agreement with the experimental data. The accuracy of the corrected theoretical values is higher than most of the experimental data. This comparison also implies that the recommended source of ICCs and total transition probabilities needs to be reconsidered by the International Nuclear Structure and Decay Data Network.

Half-lives of 111mCd, 113mIn and 115mIn

Abstract Bremsstrahlung from 4.5 MeV electrons on a platinum target was used to produce nuclear isomers in three nuclides through (γ,γ′) excitation of higher lying states and their half-lives were measured. The obtained values are 48.54±0.05 min for 111m Cd, 1.660±0.005 h for 113m In and 4.485±0.004 h for 115m In. The intensity ratio of 497 keV/336 keV gamma transitions in the decay of 115m In was determined as 1.04±0.05 × 10 −3 . The methods of analysis and the results are discussed.

A new detection method of99Tc by nuclear excitation

A new nuclear excitation process,99Tc (γ, γ′)99mTc reaction, was applied for the first time to radioactivation analysis of technetium. Bremsstrahlung irradiation of99Tc samples gave the reaction product99mTc which emits γ-ray measurable with ease by a semiconductor detector. The production rate of99mTc per μg99Tc was linearly correlated with the flux of bremsstrahlung. The detection limit of99Tc was estimated to be nanogram order (0.63 Bq99Tc) under the optimum irradiation condition. Possible interference by100Ru(γ, p)99mTc reaction was also studied, which could be discriminated from the (γ, γ′) reaction by simultaneously occurring98Ru (γ, p)97Ru reaction.

Half-life of 77mSe, 167mEr and 197mAu

Abstract Isomer states of three nuclides were excited by bremsstrahlung from a 4.5 MeV linear electron accelerator, and their half-lives were measured by counting their γ radiation with a well-type NaI(Tl) detector. A pneumatic rabbit system was used for fast sample transport. The obtained half-life values in seconds are 77 m Se : 17.31 ± 0.08, 167 m Er : 2.269 ± 0.006 and 197mAu: 7.73 ± 0.06. The results are compared with literature data. New half-life measurements were performed on three short lived odd-A nuclear isomers, since the uncertainty of the values published earlier is very striking. The isomeric states were excited by (γ, γ′) reaction. A relatively low exciting energy (below the energy required for particle emission) was chosen to obviate excitation of other nuclides.

Investigation of gamma and neutron fields around spent reactor fuel by 115In activation

Activation methods based on (γ,γ′) and (n,γ) processes have been developed for investigating hard γ and thermal neutron radiation fields in the vicinity of spent fuel assemblies stored in water. Based on experiments and practical considerations 115In was suggested as a target material both for γ and neutron activations. Fission product and actinide content of irradiated fuel can be assayed by these methods. The use of (γ,n) conversion in Be or D provides an additional tool for analyzing hard γ components. The methods may find application in non-destructive fuel assay. Results suggest the suitability of the methods for reactor operational and nuclear material safeguard purposes.

Half-life of 116m1In

The half-life of 116m1In was measured with a Ge(Li) detector. Measurements were repeated three times, and decays were followed for five half-lives. Analyses of γ-ray spectra, least squares fitting and dead-time correction were carried out. A half-life of 55.77 + 0.10 min was obtained.

Electron capture decay of 203Pb

Abstract Intensities of γ-transitions emerging from the EC decay of 203 Pb were measured precisely. The obtained relative γ-intensities are 100% (279.2 keV), 4.14 ± 0.08% (401.3 keV) and 0.932 ± 0.022% (680.5 keV). The 279.2 and 680.5 keV level feeding β-branching ratios were deduced to be 95.3 ± 0.1 and 4.7 ± 0.1% respectively. 203 Pb is suggested for calibration purposes.

K and total internal conversion coefficients of the 1063.6 keV M4 transition of 207Pb

Abstract Precise K and total internal conversion coefficients for the 1063.6 keV transition as well as γ- and K conversion electron intensity ratios of the 1063.6 and 569.6 keV transitions of 207 Pb are derived from earlier measurements. The recommended values are α K 1063 = 0.0945 ± 0.0022, α T 1063 = 0.126 ± 0.003, I γ 1063 I γ 569 = 0.758 ± 0.004 and I e 1063 I e 569 = 4.58 ± 0.05 . Both internal conversion coefficients deviate slightly from the theoretical values as expected.