ИСТИНА

State-of-art of low energy nuclear excitation by high intensity femtosecond lasers is discussed. Recent experimental campaigns at JIHT provided additional experimental evidence for such a process, but excited nuclei yield exceeded the calculations dramatically. New possible experimental schemes are considered. Experiments on low energy nuclear excitation in hot dense plasma are underway for almost 40 years. All the successful experiments were questionable since experimentally assessed nuclear yield was quite higher than the calculated one. Plasma created by the high intensity femtosecond lasers is very attractive for such an experiments being hot and dense, emitting x-rays and fast electrons, etc. We performed two experimental campaigns to measure internal conversion electron from nuclear decay of low energy isomers of 57Fe and 181Ta using double and single target setup. New experimental data on the secondary electron yield from a thin layer of 57Fe irradiated by emission of the hot dense plasma source created by femtosecond laser pulses with intensity of 1017 Wcm2 is presented. Plasma source hard X-ray and electron fluxes are measured for the source characterization. Thorough statistical analysis of the delayed secondary electron spectrum from the 57Fe layer in the 20–100 ns temporal window allows exclusion of the null hypothesis of the random character of the differences of this spectrum with that obtained using a 56Fe target. Thus, statistically valid maxima at 5.8 and 7.4 keV can be attributed to the decay of the isomeric nuclear state of 57Fe (14.41 keV, 98 ns) by the internal conversion process through the atomic K-shell (maximum at 7.4 keV), followed by the Auger process (maximum at 5.8 keV). We also fulfilled an experimental study of delayed fast, negatively charged particles from femtosecond laser-plasma interaction at an intensity of 1017 Wcm����2. Thick plates made of Ta and W were used as a target. We distinguished certain events due to negative ion detection of H����, C���� and O����, but most events, delayed by 0.5–4.5 s with respect to the instant of plasma formation, were 3–7 keV electrons. The comparative study of energy spectra of these electrons for the Ta and W cases revealed close coincidence of the Ta spectrum to the spectrum of electrons arising due to the internal conversion decay of the 6.237 keV nuclear isomeric level of the 181Ta isotope (with natural abundance of almost unity).