Recently, laser isotope separation has emerged as the most practical method for isotope separation compared to other separation methods, and research into it has been conducted intensively. There are several methods for laser separation, among which atomic vapor laser isotope separation is accepted as a promising method for both wide range of applications and possibility of expansion.
In this method, the first step of separation process is atom vapor and collimating. If the vapor source is heated to the target temperature under complete vacuum conditions, feed metal is melted to liquid state and starts evaporating. According to the temperature of vapor source, the rate of evaporation and vapor pressure of feed metal are controlled, which adjusts the atomic density of collimated atomic beam. At the laser pumping region, the atomic density of atomic beam is critical to the absorption cross section of laser beam.
Kang Chol Jin, a researcher in the General Assay Office, simulated the distribution of lithium vapor as a function of the length-to-diameter ratio of the source nozzle for laser isotope separation of lithium, and experimentally determined the atomic density distribution of lithium atomic beams in the collimated region.
It was found that when the heating temperature of the lithium vapor source was kept at 500℃, the atomic density near the nozzle central axis increased relatively rapidly with increase in the length-to-diameter ratio of the outlet nozzle, i.e., the atoms flying at an angle similar to the central axis of the tube flew almost linearly out of the nozzle.
According to the calculations, when the L/D value of the nozzle at 500℃ was 10 and the diffusion angle of the atomic beam was 10°, the collimation efficiency was above 46%.
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