Speaker
Description
A study of the cross-sections and level filling yields of high-spin isomeric states provides information about the structure of excited levels in the continuous and discrete regions of excitation, as well as about the mechanisms of nuclear reactions. Therefore, the aim of our work is to study the $^{178m}$Ta and $^{180m}$Hf yields in reactions with bremsstrahlung with energies ranged in the giant dipole resonance energy region.
The study of the weighted average yields was carried out by the activation method using a bremsstrahlung γ-beam of electrons with a 20 MeV maximum energy and natural tantalum targets.
The spectra of irradiated targets were measured by Canberra and Ortec gamma spectrometers with ultra-pure semiconductor detectors with a (15–40)% detection efficiency compared to a 3′×3″ NaI(Tl) detector. The energy resolution of the spectrometers was 1.8–2.0 keV on the 1332 keV $^{60}$Co γ-line.
The gamma transitions from the decay of $^{178m}$Ta and $^{180m}$Hf are reliably identified in the spectra.
The bremsstrahlung simulation was carried out with the Geant4 software code.
For the first time, the weighted average level filling yield of $^{178m}$Ta in the $^{180}$Ta(γ, 2$n$)$^{178m}$Ta-reaction and the weighted average level filling yield of $^{180m}$Hf in the $^{181}$Ta(γ, $p$)$^{180m}$Hf-reaction at a 20 MeV bremsstrahlung maximum energy were obtained. For $^{180}$Ta(γ, 2$n$)$^{178m}$Ta-reaction weighted average yield is equal 48(5) mbn and for $^{181}$Ta(γ, $p$)$^{180m}$Hf-reaction weighted average yield is equal 60(4) mbn.
According to the simulation results, within the TALYS-1.9 and EMPIRE-3.2 program codes, the dominance of non-statistical processes is established. The theoretical integral cross sections are significantly lower than the experimental values.
A discussion of the findings is ongoing.
