CA1124205A - Enrichment of carbon-13 by multiphoton dissociation - Google Patents

Abstract

TITLE

DISSOCIATION

INVENTORS

Peter A. Hackett Clive Willis Michel Gauthier ABSTRACT OF DISCLOSURE

A method of producing carbon-13 by multiphoton decomposition of gaseous CF3Br or CF3Cl wherein the gas is irradiated at a pressure below 10 Torr with a laser beam at a minimum fluence of 30 joules per sq. cm. and a frequency selected such as to optimize the excitation of one of the specified species relative to the other, and then passed through a plysical separation stage to obtain a 13C2F6 product.

Description

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This invention relates to a method for isotopic enxichment by laser radiation and more particularly to a method of producing carbon-13 by multiphoton decomposition of cF3Br and CF3Cl.
The use of carbon-13 as an industrial compound is not widespread at the preser.t time but is expected to increase. Extensive application of carbon-13 to medical screening prcgrams is anticipated. The present method of production is by low temperature distillation of carbon monoxide and this process is expensive, provides small throughput, needs large inventory of starting materials, and must be symbiotic with a liquid air plant.
A method of isotopic separation by photopredissociation is described in United States Patent No. 3,983,020 issued Sept. 28, 1976 to C.B. Mcore and E.S. Young.
A photochemical method for carbon isbtopic enrichment is disclosed in United States Patent No. 4,120,767 issued October 8, 1978 to S.N. Bittenson and P. Houston. This patent describes a process using, as a starting material a gaseous mixture of at least two isotopic CF3I species and irradiating this mixture in a reaction zone with laser radiation at a pressure below about 10 Torr to cause relative enrichment of one of the species. The enriched residual substrate is 13CF3I. This process is effective but yields are low and therefore production costs are high.
In drawings which illustrate an embodi-ment of the invention, Figure 1 is a flow diagram of the process, Figures 2 and 3 are ~graphs showing infra-~.Z~;205 red spectrum of CP Br and CF3C1, Figures 4 and 5 are graphs of a-values as a function of photolysing wavelength for CF3Br and CF3Cl, and Figure 6 is a graph of ~-values as a function of CF3Br and CF3C1 pressures.
Referring to figure 1, a beam of photons from a laser 10 (pre~erably a C02 las~r) is directed into a reaction chamber 11 containing gaseous CF3Br or CF3Cl.
These materials occur as mixtures of two isotopic species i.e. 12CF3Br, 13CF3Br and CF3Cl, 13CF3C1. The frequency A of the laser light is chosen to optimize the excitation of one of the specified species relative to the other species. The reactions that take place are as follows:

13CF3Br ~ 13CF3 ~ Br 213CF3 __~ C2 6 or CF3C1 ~ CF3 + Cl 213CF3 ~ 13C2F6 The enriched product that is obtained is hexafluorethane (13C2F6). It has been found that this method of enrichment of carbon-13 in the products of multiphoton dissociation of CF3BR and CF3C1 compounds results in high yields and reduced costs of carbon-13 production.
After irradiation the gas mixture is passed through an absorption tube 12 for removal of bromine or chlorine and then to separation stage 13 e.g. a still, jet cooler, for physical separat~on of the products:

-3C2F6 ~enriched~ and 12CF3Br or 12CF3Cl.
The irradiation system used would preferably ~.Z4~)5 involye focussed or parallel laser be`ams providing a minimum fluence of 30 ioules per sq. cm. CJ cm ~. The laser frequency for the CF3Br case is a~out 1040 wavenumbers [cm 1) and for the CF3Cl case about 1070 wavenumbers. The irradiation takes place at a pressure below 10 Torr. It has been found that effective action will take place over a wide temperature range i.e. between -80C and ~100C, with good results being obtained at room temperatures i.e. 20C.
Figures 2 and 3 are infrared absorption spectra for CF3Br and CF3Cl respectively, relating to absorption to ~-avenumber of the radiation. Figures 3 and 4 are graphs of ~-values plotted against photolysing wavelength for the two materials obtained at 0.19 Torr, at room temperature and with a focussed incident laser beam. Alpha-values are defined as follows:

~ = C~ C ratio in produ~ts I C/ ratio in starting material The graphs indicate the optimum frequency ranges required for the laser irradiation for the two materials.

Figure 6 is a graph relating a-values to the pressures for CF3Br and CF3Cl. These plots were obtained at room temperature with a focussed laser beam.

Claims (4)

CLAIMS:

1. A method of producing carbon-13 by multiphoton decomposition of CF3Br, said material containing carbon-12 and carbon-13 isotopic species, comprising:
a) irradiating gaseous CF3Br in a reaction chamber at a pressure below 10 Torr with a laser beam at a frequency of about 1040 wavenumbers and providing a minimum fluence of 30 joules per sq. cm. such as to optimize the excitation of one of the specified species relative to the other causing the following reactions to take place:

b) passing the irradiated gaseous mixture through means for removing the bromine component, and c) passing the material through a physical separation stage to obtain a 13C2F6 product.

2. A method as in claim 1 wherein the irradia-ting step is carried out at a temperature near 20°C.

3. A method of producing carbon-13 by multi-photon decomposition of CF3C21, said material containing carbon-12 and carbon-13 isotopic species, comprising:
a) irradiating gaseous CF3C1 in a reaction chamber at a pressure below 10 Torr with a laser beam at a frequency of about 1070 wavenumbers and providing a minimum fluence of 30 joules per sq. cm. such as to optimize the exci-tation of one of the specified species relative to the other causing the following reactions to take place:

b) passing the irradiated gaseous mixture through means for removing the chlorine component, and c) passing the material through a physical separation stage to obtain a 13C2F6 product.

4. A method as in claim 3 wherein the irradiating step is caxried out at a temperature near 20°C.