30Juii'4P MDDC - 938 UNITED STATES ATOMIC ENERGY COMMISSION OAK RIDGE TENNESSEE ON THE EXISTENCE OF A CALCIUM ISOTOPE WITH AN 8.5 DAY PERIOD by Roy Overstreet Louis Jacobson University of California Published for use within the Atomic Energy Commission. Inquiries for additional copies' and any questions regarding reproduction by recipients of this document may be referred to the Documents Distribution Subsection, Publication Section, Technical Information Branch, Atomic Energy Commission, P. O. Box E, Oak Ridge, Tennessee. Inasmuch as a declassified document may differ materially from the original classified document by reason of deletions necessary to accomplish declassification, this copy does not constitute authority for declassification of classified copies of a similar document which may bear the same title and authors. Date of Manuscript: November, 1946 Document Declassified: May 12, 1947 This document consists of 2 pages. -^ UNIV. OF FL lib" ■ DOCUMFMT.qncoT ."I Digitized by tine Internet Arcliive in 2011 witli funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/onexistenceofcalOOuniv - 1 - MDDC - 938 ON THE EXISTENCE OF A CALCIUM ISOTOPE WITH AN 8.5 DAY PERIOD Walke, Thompson, and Holt(l), in a study of the radioactive isotopes of calcium, have reported an isotope with an 8.5 day half -life which they have given the assignment of Ca 4^. It was prepared in greatest yield by the bombardment of calcium metal with 8 Mev deuter- ons. Also, very low yields of. the isotope were prepared by bombarding calcium oxide with fast neutrons. The authors conclude that Ca'* decays to K^^ by K-electron capture emit- ting primarily X rays (3500 ev) but some gamma rays and conversion electrons of high energy (1.1 Mev). An attempt to produce Ca^^ has been made in this laboratory using higher energy particles. Although the reported fraction of gamma rays and conversion electrons is small, it was thought that sufficiently high yields of the isotope could be obtained with 20 Mev deuterons to make feasible its use as a tracer in biological work. The following reactions were tried: a. Ca'^^' (d, p) Ca''^ : CaCl2 was bombarded with 20 Mev deuterons to the extent of 40 micro-ampere-hours. No activity with a half-life in the neighborhood of 8.5 days and electron energy greater than about .05 Mev (limit of the electroscope) was found in the calcium fraction. Approximately 0.3 M c of long-lived activity (> 60 days) was found which presumably was due to Ca ^ . This result was unexpected in view of the fact that high yields are obtained for the reaction K^ (d, p) K*^ at these energies (107 /^c per micro-ampere-hour). b. K'^^ (d, 2n) Ca''^ : KClwas bombarded with 20 Mev deuterons to the extent of 135 micro-ampere-hours. Thirty-six hours after the bombardment,the purified calcium fraction was examined for activity. The thickness of the sample was 0.75 milligrams per square centimeter. No activity could be detected upon placing the sample inside an ionization chamber. Also,the calcium fraction was examined with negative results by means of a thin window electro- scope and a GM counter (window thickness = 2 mgs. per cm^). As a final check, an X-ray film was placed over the sample for several days. No darkening was observed. c. A^° (oe, 3n) Ca^^: Argon gas (2.5 liters) was bombarded with 40 Mev alpha particles to the extent of 20 micro-ampere-hours. The radioactive products were collected on a negatively charged copper wire extending into the gas. No measurable amov(nt of radioactive calcium was produced. The only activity found on the wire was due to K . This isotope was produced in surprisingly good yield by means of the reaction A (a,pn)K'*^. The yield was 80yUc per micro-ampere-hour. (1) Walke, H., Thompson, F. C, and Holt, J., Phys. Rev., 57, 177 (1940') UNIVERSITY OF FLORIDA 3 1262 08907 9437 MDDC - 938 In each of the above preparations appropriate inert carriers were added and calcium was finally isolated as the oxalate. As a special precaution, barium and strontium precipi- tations were made in all cases. All precipitations were repeated several times in the presence of hold-back carriers in order to insure clean separations. Activities were measured with a Lauritzen electroscope. The air-gap plus the electroscope window was equivalent to 4 mgs per cm^ of aluminum. • I On the basis of the experiments described, it must be concluded that if a Ca^i iso- tope exists that emits beta or gamma rays or energetic conversion electrons, its half- life must be considerably less than one day or longer than one year. The possibility of an isotope that decays by means of K-electron capture to the ground state of the product nucleus K^^, thus emitting only very soft X rays (3500 ev) and no gamma rays or de- tectable electrons, also seems to be ruled out. On the basis of the observed yield of Ca^^ from the (d, p) reaction, an 8,5 day Ca^l should have been produced by the same bombard- ment in a yield of~300 //c. This amount of activity presumably would have been detected by the instruments used, in view of the fact that 3500 ev X rays have a half -thickness of ~1.5 mg Al per cm^ or~-6 mg air per cm^.