Patent GB-1519358-A (GB)
Title: Method of and apparatus for separating components of an isotopic mixture
IPC: B01D59/34
Filed: 1976-01-13
Abstract: 1519358 Producing selective excitation by means of electromagnetic radiation COMPAGNIE GENERALE D'ELECTRICITE 13 Jan 1976 [15 Jan 1975] 02156/76 Heading G6P Apparatus for isotope separation by isotopically-selective excitation of a molecular gas comprises collectors R1, R2 so placed in relation to an excitation zone 4 as preferentially to collect the respective isotope components. Isotopes I1, I2 having respective absorption lines with frequencies F1, F2 are irradiated by light from a laser LE. whose frequency FL lies in the range F1-¢LD to F2+¢LD. The Doppler effect causes the absorption line width to increase (to a Doppler width LD) relative to its absolute, natural width LN. Preferably, the laser LE frequency FL lies between the frequencies F1, F2. Molecules of both isotopes I1, I2 will be excited. However, molecules with components of motion along the axis 3 of laser beam propagation will experience a Doppler shift of their absorption line frequencies (the shaft will be up or down depending upon whether the molecules' component along the propagation axis 3 is toward or away from the laser LE). The apparatus utilizes these considerations as follows: molecules of isotope I1 travelling with components towards the laser LE will experience a frequency upshift and, since the upshifted frequency will lie nearer the laser frequency FL than the frequencies of any unshifted or downshifted molecules of that isotope I1, exhibit a greater probability of excitation than other Isotope molecules. Similarly (but conversely) molecules of isotope I2 travelling with components away from the laser LE will exhibit a greater probability (than other isotope I2 molecules) of excitation. A second laser L1 (especially operating in the UV range) irradiates the excitation zone 4 to ionize selectively the excited molecules of both isotopes I1, I2. Collectors R1, R2 are placed in relation to the excitation zone 4 such that ionized molecules of the first isotope I1 (with components towards the excitation laser LE) will preferentially collect at the first (i.e. upsteam) collector R1: and ionized molecules of the second isotope I2 (with components away from the excitation laser LE) will preferentially collect at the second (i.e. downstream) collector R2. Conditions for such collection are met by so disposing the collectors R1, R2 and maintaining the operating pressure in the chamber 2 that the mean free path of ions is about the same as the distance from the zone 4 to the collectors R1, R2. Preferably, the collectors R1, R2 are held at negative potentials relative to an anode 12; but the collectors may, alternatively, "fix" the collected ions chemically. In setting up the apparatus, the excitation laser LE (whose line width of emission must be less than the difference between the frequencies F1, F2) first has its frequency set below F1. The frequency is then varied incrementally and visible fluorescence from the gas in the chamber 2 observed. This reaches peak intensity as the frequency passes through F1, passes through a minimum at FL and then increases again to F2. The laser LE frequency is set at FL for effecting excitation. An example describes separation of Se78 and Se80.