Conditions for Population of Energy Levels Inversion when Active Medium Based on Gadolinium Isotopes Gd155 and Gd156 Couple Neutron Pumping

The paper theoretically studies the possibility of energy transformation of fast and epithermal neutrons to energy of coherent photon radiation at the expense of a neutron pumping of the active medium formed by nucleus with longliving isomerous states. The channel of the nucleus formation in isomeric state as a daughter nucleus resulting from the nuclear reaction of neutron capture by a lighter nucleus is taken into consideration for the first time. Assessment of neutron flux spectrum parameters providing transition from the main state into one of the excited ones for the nuclei of isotopes ₅₄Xe¹³⁰, ₁₀Ne²² is made. It was shown that to transit the isotope nuclei into the excited state by forward neutron scattering on the nuclei it is necessary to “select” the isotopes not only with great specific energy of nucleons coupling but also with a small value of the neutron absorption cross section. Moreover, the paper performs the analysis of cross sections dependence of radiative neutron capture by the nuclei of gadolinium isotopes Gd¹⁵⁵ and Gd¹⁵⁶. As a result, the speed of Gd¹⁵⁶ nuclei formation is stated to exceed the speed of their “burnup” in the neutron flux. It is provided by a unique combination of absorbing properties of two isotopes of gadolinium Gd155 and Gd156 in both thermal and resonance regions of neutron energy. We have formulated the conditions required for making isotope nuclei excited by forward neutron scattering on nuclei and for storing nuclei in excited states. The relation which allows estimating processes parameters of neutron capture by nuclei, formation and decay of nuclei isomeric states is obtained as a result of analytical solution of differential equations system of nuclide kinetics taking into account the decay of nuclei isomeric states. The paper makes the possibility analysis of neutron pumping of the participating medium created by the hafnium isotope nuclei. The properties of hafnium isotopes nuclei is found to do not allow providing conditions for population inversion of energy levels due to the formation of hafnium nuclei in isomeric state Hf^178m2 in the neutron flux. The paper shows the possibility of excess energy accumulation in the participating medium created by the nuclei of the pair of gadolinium isotopes Gd¹⁵⁵ and Gd¹⁵⁶ due to formation and storage of nuclei in isomeric state at radiative neutron capture by the nuclei of the stable isotope with a smaller mass. It is concluded that when the active medium created by gadolinium nuclei is pumped by neutrons with the flux density of the order of 10¹³ cm^-2·s^-1, the condition of levels population inversion can be achieved in a few tens of seconds. The wave length of the radiation generated by the medium is 0.0006 nm. Sintered ceramics Gd₂O₃ based on enriched in the 155-th isotope of gadolinium can be considered a possible active medium. Thus, there is a possibility of creation of the laser techniques of new generation with the parameters providing its application in pulse power engineering of the future.

1. Shamanin I.V., Bedenko S.V., Pavlyuk A.O., Lyzko V.A. The use of ORIGEN-APR code for reactor VVER-1000 spent fuel isotopic composition calculation (Ispolzovanie programmi ORIGEN-ARP pri raschete izotopnogo sostava otrabotannogo topliva reaktora VVER-1000). Bull. Tomsk Polytechnic Univ., 2010;317(4):25–28 (in Russ.).

2. Shamanin I.V., Kazaryan M.A. Nuclide Kinetics Involving Hafnium and Gadolinium Nuclei in Long– Lived Isomeric States. Bull. Lebedev Phys. Inst., 2017;44(7):215–217 (in Russ.).

3. Tkalia E.V. Induced decay of nuclear isomer 178m2Hf and “isomeric bomb” (Inducirovanniy raspad yadernogo izomera 178m2Hf i “izomernaya bomba”). Uspekhi Fizicheskih Nauk, 2005;175(5):555–561 (in Russ.).

4. Evaluated Neutron Data Library Fond-2.2 (Russian library of evaluated neutron data files for constant sets generation in the constant ensuring system BNAP) (Biblioteka Otsenennykh Neytronnykh Dannykh Fond2.2 (Rossiyskaya biblioteka failov otsenennykh neytronnykh dannykh dlya generatsii naborov constant v sisteme konstantnogo obespecheniya BNAP) [Eresource]. Available on: http://ultra.ippe.obninsk.ru:8097 (June, 2005) (in Russ.).

5. Audi G. et al. The NUBASE evaluation of nuclear and decay properties. Nuclear Physics A, 1997;624:1–124.