Investigations on Nuclear Spectroscopy at the Reactor and Their Applications

Physical launch of the WWR-M reactor in the branch of Physical-Technical Institute of AS of the USSR in Gatchina took place on the 29th of December in 1959. However the first work on nuclear spectroscopy was carried out before the reactor was launched; namely, gamma-radiation was measured of short-lived isomeric nucleus with lifetime of some tens of minutes produced by irradiation in the reactor mock-up processed at a power of 1-2 Wt. The internal conversion coefficient measured from Xand γ-ray intensity ratio coincided with the one measured earlier and L.I. Rusinov delivered a report about the beginning of scientific activities at the WWR-M reactor [1]. This was a new level of work with short-lived isotopes, as earlier the most short-lived nucleus investigated in the laboratory of L.I. Rusinov was Hf with T1/2=5.5 h. Earlier this isotope irradiated in the reactor of Kurchatov Institute in Moscow was brought to PhysicalTechnical Institute in Leningrad by plane. That work was undertaken in order to bring a contribution in a study of K-forbiddenness. Indeed, it was wonderful that the 57.6 keV transition of E1 type determines such a large half-life [2]. Launch of a new reactor in Gatchina has given a possibility to deal with very short-lived isotopes using various pneumatic and other posts in which the minimal time of delivery of sample to measuring installation amounted to 40 ms [3]. Generally speaking, the works on nuclear spectroscopy in Physical-Technical Institute began as early as in 1934, when an investigation of properties of Br decay was carried out with participation of L.I. Rusinov [4]. That work was a push for development of studies about nuclear isomerism. So, all the following works of Laboratory of nuclear isomerism in PhTI in some way or other were connected with this interesting phenomenon. The first works in this direction made at the WWR-M reactor under the leadership of D.M. Kaminker were developed to the measurements of lifetimes of nuclear levels of doubly odd nuclei after radiative capture of neutron. It should be noted that the excited states of doubly odd nuclei are excited in the decay of radioactive nuclei very seldom, therefore, one nucleon transfer reaction are nearly the only source of information about such nuclear states. In these works carried out by A.M. Berestovoj and Yu.E. Loginov eight new nuclear isomers were found and investigated [5, 6].