Investigation of the active medium of H₂–HCl gasdynamic lasers in the anharmonic approximation

-=SUP=-15-=/SUP=-N isotope enrichment of the atomic nitrogen component in atomic-molecular exchange reactions in the post-discharge zone

“…The primary processes occurring in the measurement tube are the loss of vibrational energy of molecules as a result of deactivation on tube walls and vibrational-translational (V −T ) relaxation, the dissociation of vibrationally excited molecules, the recombination of atoms on tube walls, and the atomic-molecular exchange. Let us consider the example of nitrogen and see how the concentration of 14 N and 15 N atoms at given distance L from the post-discharge zone inlet varies in these conditions with time t of flow through this zone.…”

“…The aim of the present study is to identify the mechanism of a more than thirty-fold enrichment of the atomic nitrogen component with isotope 15 N in the post-discharge zone of a pulsed discharge and develop a kinetic model that illustrates consistently how the relative concentrations of atoms 15 N and 14 N vary in the course of flow of excited gas along a quartz tube and how this variation depends on the degree of vibrational excitation of gas; its density and temperature; the rates of dissociation of molecules, vibrational relaxation of molecules, and recombination of atoms on tube walls; and the atomic-molecular exchange rate. The atomic-molecular exchange has not been taken into account in numerical simulations and analytical studies of isotopic effects in an electrical discharge in earlier research [9,10,14]. Upon close examination, it was found that the mechanism of two-stage enrichment involving electronically excited states (A 3 + u and B 3 g ), which was proposed in our study [13],…”

“…Valves adjusting the flow of nitrogen were used to keep the pressure in tubes constant throughout the experiment within the range from 333 to 733 Pa (2.5−5.8 Torr). The measurement tube temperature was kept close to T = 300 K. Atoms of 14 N and 15 N were identified in the flow of partially dissociated nitrogen by their EPR signal. Nitrogen molecules do not contain uncompensated electron spins and produce no contribution to the EPR signal.…”

“…Since the typical spectrum recording time was no shorter than 10−15 min (i.e., exceeded considerably the interval between generator pulses), the probable perturbations of the EPR signal due to fluctuations of average discharge power W T in the course of gas flow along the discharge tube (at high flow velocities) were smoothed out. The ratio of concentrations of 15 N and 14 N atoms in the nitrogen flow through the spectrometer cavity was determined by comparing the results of double integration of the obtained lines. The spectrometer was calibrated against the EPR signal of molecular oxygen [18,19] to determine the absolute concentrations of 14 N and 15 N atoms.…”

“…The interest in 15 N has been on the rise in recent years in relation to the projects of fast power reactors with nitride fuel (U, Pu)N. Nitride fuel has the following advantages: high density, high thermal conductivity, and compatibility with the primary materials of fuel-element cladding and liquid-metal coolants (sodium and lead). However, nitrogen isotope 14 N, which accounts for 99.7% of naturally occurring nitrogen, is converted under the influence of reactor neutrons into long-lived radioactive carbon isotope 14 C that has a negative effect on the neutron physics of nitride fuel and leads to excessive gas release. The mentioned drawbacks of nitride fuel may be eliminated by substituting natural nitrogen with nitrogen enriched with 15 N [5,6].…”