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United States Patent 0 1C6 Patented June 25, 1968

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United States Patent 0 1C6 Patented June 25, 1968 r P 3,390,161 United States Patent 0 1C6 Patented June 25, 1968 1 2 for the separation of gamma emitting isotopes of cobalt from a mixture of nickel isotopes whereby the removed 3,390,161 PROCESS FOR SEPARATING TRACE QUANTITIES radioactive cobalt is in compact form thereby minimiz OF AN IMPURITY ISOTOPE FROM A MIXTURE ing the expense in disposing of it. 0F ELEMENTS Another object of the present invention is to provide Anthony V. Fraioli, Essex Fells, N.J., assignor to The a process whereby the removal of a radioactive impurity Bendix Corporation, Teterboro, NJ., a corporation of can be performed more quickly, more economically, and Delaware with smaller investment in equipment and supplies than No Drawing. Filed Sept. 30, 1963, Ser. No. 312,341 by conventional ion exchange techniques or convention 8 Claims. (Cl. 260—439) al techniques of magnetic separation. 10 These and other objects and features of the inven The present invention relates to a process for separat tion are pointed out in the following description in terms ing trace quantities of an impurity isotope from a mix of the embodiments thereof. ture of elements and more particularly, to a process for Neutron irradiated natural nickel has a gamma to beta separating gamma emitting isotopes from neutron ir 15 ratio of approx. 1/5000 and is composed of stable iso radiated nickel. topes of nickel (approx. 95%), the radioisotope Ni63 Radioactive Ni“ is produced by neutron bombard (approx. 3%), and arti?cial isotopes of cobalt and iron ment of natural nickel, or nickel isotopically enriched (approx. 2%) including the gamma emitting isotopes with Ni?z. Naturally occurring nickel is composed of Co58 and Co60 (less than 1% ). The ratio and percentages four isotopes; namely, Ni58 (approx. 68%), Ni60 (ap~ 20 given will vary depending, e.g., on the neutron ?ux in a prox. 27%), Ni61 (approx. 1.2%), and Ni62 (approx. the reactor during bombardment, and duration of bom 3.8% ). When Ni62 is subjected to neutron bombardment, bardment and aging. The values given here are merely a fourth isotope Ni63 is formed which is a beta emitter. to illustrate a typical composition of commercially avail~ In addition to the formation of Ni“, there is simul able irradiated nickel. taneously produced trace quantities (at most 1%) of 25 In accordance with the preferred embodiment of our arti?cial radioisotopes of cobalt which are gamma emit invention, the neutron irradiated nickel to be processed ters. is dissolved in a hydrochloric acid solution. Naturally The radioactive isotope Niea, as a beta emitter, has occurring cobalt is then added to the solution as a chlo many commercial uses. For example, it may be used as ride. Alpha-nitroso beta-napthol in 50% acetic acid is a cold cathode electron emitter in an ionization gauge. 30 then added to the solution to form a precipitate com It may also be used to underlie a phosphor coating to prising cobalt alpha-nitroso beta-naptholate. The equilib excite the phosphor for luminescent panelling. However, rium concentration of unprecipitated cobalt which exists in order to utilize the high and relatively stable ac in solution in contact with the precipitate is thereby en tivities of Ni“ for instrument purposes, personnel must riched with the natural isotopes and diluted with respect be protected from harmful gamma radiation. The total 35 to the radioactive isotopes in exact proportion as the gamma radiation emanating from a device using Ni63 ratio of their concentrations prior to precipitation. The should be less than 40 milliroentgen per week. precipitate is then ?ltered, digested and washed with Cobalt can be separated from a solution containing 12% HCl, with the wash being added to the ?ltrate. The nickel by conventional precipitating agents such as alpha ?ltrate then contains the unprecipitated nickel isotopes nitroso beta-napthol. However, separation of the gam 40 and the residual equilibrium concentration of cobalt ions, ma emitting isotopes of cobalt from irradiated nickel by isotopically mixed in a ratio of their concentrations prior precipitation is unsatisfactory because the residual equi to precipitation. To further decrease the concentration librium concentrations of the gamma emitting isotopes of the gamma emitting isotopes, the above steps are re of cobalt in solution after precipitation leaves the gam peated. More naturally occurring cobalt is added to the ma to beta ratio much too high. _ ?ltrate to increase the ratio of the stable isotopes to Brie?y, the process of the present invention for remov 45 gamma emitting isotopes in the ?ltrate. The cobalt is ing the gamma emitting istotopes of cobalt from a mix again precipitated by the addition of alpha-nitroso beta ture of nickel isotopes comprises adding the stable iso napthol which results in the equilibrium concentration of tope of cobalt to a solution of the mixture so that after the unprecipitated cobalt existing in solution in contact precipitation of the cobalt, the equilibrium concentra with the precipitate being further enriched with the nat tion of the unprecipitated cobalt which exists in solution 50 ural isotope and further diluted with respect to the radio in contact with the precipitate is enriched with the nat active isotope. The steps of dilution and precipitation urally occurring isotope and diluted with respect to the may be repeated again, if necessary, until the distribu radioactive isotopes in exact proportion as the ratio of tion of cobalt isotopes remaining in solution approaches their concentrations in solution prior to precipitation. the distribution present in naturally occurring cobalt. An object of the presentinvention is to separate trace 55 The pH value of the solution to be treated should be quantities of an impurity isotope from a mixture of below 4 in order to prevent precipitation of the nickel as elements. the hydroxide. While other inorganic acids such as HNO3 Another object of the present invention is to provide may be employed to dissolve the mixture, HCl is pre a process for separating gamma emitting isotopes of ferred so as to facilitate a subsequent plating process. cobalt from a mixture of nickel isotopes. 60 While alpha-nitroso beta-naphthol in 50% acetic acid Another object of the present invention is to provide is the preferred precipitating reagent, because of the sta a process for separating the gamma emitting isotopes of bility and keeping properties of the reagent, alpha-nitro cobalt from a mixture of nickel isotopes by adding the beta-napthol is also operative. Generally, the quantity of stable isotope of cobalt to a solution of the mixture'so 65 reagent added should be 1.2 times the theoretically neces that after precipitation of the cobalt, the equilibrium con sary quantity to precipitate the cobalt present. centration of the unprecipitated cobalt which exists in Precipitation is expedited and separation of the pre solution in contact with the precipitate is enriched with the naturally occurring isotope and diluted with respect cipitate is facilitated if agitation and digestion (for approx. to the radioactive isotope in exact proportion as the ratio 3 hours) are employed prior to separation of the precipi of their concentrations prior to precipitation. 70 tate from the supernatant solution. While precipitation It is also an object of the present invention to provide may be carried out at a temperature of between 25° and li,390,16l 3 4 boiling temperature of the solution, a temperature of it is to be understood that all matter contained in the about 80° C. is preferred. above description and example shall be interpreted as il Generally, the quantity of stable cobalt added to the lustrative and not limitative of the scope of this inven solution should be such that the ratio of stable isotopes tion. Reference is, therefore, to be had to the appended to radioactive isotopes prior to precipitation is approxi claims for a de?nition of the limits of the invention. mately 104 parts to 1 part. This results in an equilibrium ‘What is claimed is: concentration of less than 10_12 grams of the gamma emit 1. A process for separating trace quantities of gamma ting isotopes of cobalt after three successive dilution pre emitting isotope of a metal selected from the group con cipitation steps which is well within safe handling re sisting of cobalt and mixtures of cobalt and iron from quirments. Of course, the larger the amount of stable iso acid solutions having a pH value below 4 containing tope added, the greater the dilution of gamma emitting7 nickel and a metal selected from the group consisting of isotope, thereby allowing the process to be carried out in cobalt and mixtures of cobalt and iron, comprising add one step. However, it is preferred to carry out the proc ing an inactive isotope of the metal to said solution so that ess by a series of dilution-precipitation steps rather than the ratio of inactive isotope to gamma emitting isotope is adding a larger amount of stable isotope and perform at least 104 parts to 1 part, adding to said solution a pre ing the process in one step because carrying out the proc cipitating reagent selected from the group consisting of ess in a series of steps requires addition of a minimum alpha-nitroso beta-naphthol and alpha-nitro beta~naph amount of natural cobalt and allows working with a prac thol to precipitate in said solution said gamma emitting tical quantities. The inactive isotope preferably is added isotope and said added inactive isotope, and separating in a quantity such that there remains in the solution an , the precipitate from the supernatant solution. inactive isotope to gamma emitting isotope ratio of at 2. The process of claim 1 wherein said added inactive least 10 to 1.
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