On the stimulation of the de-excitation of nuclear isomers in plasma of a high-current electric discharge

Vladimir Koltcov

doi:10.14311/ppt.2021.1.5

Abstract

The prospects of stimulated de-excitation of nuclear isomers (SDENI) with a trigger transition energy ∆E up to ∼ 1 keV in a plasma of a high-current electric discharge (HCED) with an electron temperature θ ∼ ∆E are discussed. An estimate of the probability of the SDENI process in plasma by the mechanism of nuclear excitation by electron capture (NEEC) is obtained. Themost promising for the SDENI study are isomers 229mTh (∆E ≈ 8 eV), 235mU (∆E = 76 eV), 110mAg (∆E = 1128 eV). To create an energy source most promising isomer is 186m Re (∆E is unknown) with a half-life of 2 × 105y, for which stimulated de-excitation in the laser plasma had beenalready observed at θ ∼ 1 keV.

Highlights

For more than 60 years, but so far unsuccessfully, attempts have been made to create a controllable source of γ-radiation or an energy source based on stimulated de-excitation of long-lived nuclear isomers
Only a brief overview of these studies is given, which is necessary for assessing the prospects for studying the stimulated de-excitation of nuclear isomers (SDENI) using the plasma of a high-current electric discharge
The reason for the lack of this effect is the difficulty of creating the resonance conditions for stimulating the radiation for long-lived isomers. Another reason is that long-lived nuclear isomers spontaneously decay mainly due to internal electron conversion, but, as shown in [6, 7], the conversion transition can be resonantly stimulated by photons, as well as a transition with emission of a γ-quantum

Summary

Introduction

For more than 60 years, but so far unsuccessfully, attempts have been made to create a controllable source of γ-radiation or an energy source based on stimulated de-excitation of long-lived nuclear isomers (hereinafter referred to as SDENI). For nuclear transitions of energy no more than a few keV, laser pulses of lower intensity but longer duration and grater energy, which form plasma with a temperature of θ ∼ 1 keV, are more efficient, in this case the plasma lifetime τ can increase up to nanoseconds In such plasma, the SDENI effect was observed on the 186m Re isomers [32] (see Section 3.2). The most powerful HCED facilities, such as the “Angara-5” facility at the Troitsk Institute for Innovation and Thermonuclear Research (TRINITI) (in Moscow, Russia) with a maximum discharge current Imax = 6 MA and a pulse duration up to τ = 150 ns [34] or the “Z-machine” of Sandia National Laboratories (in Albuquerque, USA) with Imax = 26 MA, τ = 100 ns [35] make it possible to obtain an HCED plasma with a temperature of θ ∼ 1 keV This temperature is lower than the record temperatures in the laser plasma, and it can be expected that the temperature of the HCED plasma will be lower than the energy of nuclear trigger transitions ∆E. The probability of excitation of the 235mU isomer in such a plasma was PSDENI ∼ 10−14, which is close to the calculated value by formula (3)

Detecting the SDENI process in pulsed plasma

Nuclear isomers for studies in HCED plasma

Findings

Conclusions