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Home , Einsteinium, Fermium

LETTERS TO THE EDITOR

Little can be said about the detailed shape of the ~ es 0 curve because of the large statistical errors. Bk Cm Am I *Research supported by a joint program of the Ofhce of Naval Research and the U. S. Atomic Energy Commission. Cartwright, and Rouvina, Rev. 806 'Oxley, Phys. 93, (1954). 6;75 MEV Chamberlain, Segre, Tripp, Wiegand, and Ypsilantis, Phys. Rev. 93, 1430 (1954). 'Marshall, Marshall, and de Carvalho, Phys. Rev. 93, 1431 (1954). MEV& e 6,6 J. M. Diclrson and D. C. Salter, Nature 173, 946 (1954). y OEC. l9-20, I952 ~ de Carvalho, Marshall, and Marshall, Phys. Rev. 96, 1081 (1954). Chamberlain, Segre, Tripp, Wiegand, and Ypsilantis, Phys. Rev. 95, 1105 (1954). 4'

O. I- V) New Elements and , l- Atomic Numbers W and 100 O O A. GHIQRso, S.G. THQMPsoN, G. H. HIGGINs) AND G. T. SEABQRG) Radiation Laboratory and Department of Chemistry, University of Califorrtia, Berkeley, California M. H. STUDIER) P. R. FIELDs, S. M. FRIED) H. DIAMQND, J. F. MECH, G. L. PYLE, J. R. HUIZENGA, A. HIRSCH, AND W. M. MANNING Argonne Eati onal 0.0l-- Laboratory, Lemont, Illinois 20 50 40 50 60 70 AND QROP NUMBER C. I. BRovlNE, H. L. SMITH, AND R. W. SPENcE& Los A/amos FIG. 1. Elution of element 99 relative to cahfornium (citrate eluant). Scientific Laboratory, Los Al'amos, %em 3fexico (Received June 20, 1955) identification for the newly discovered element was 'HIS communication is a description of the results completed (i.e., the correct choice between atomic in 1952 and numbers 99 and 100 had been made) a tentative assign- of experiments performed December, "100"4" the following months at the University of California ment to was made and this information was Radiation Laboratory (UCRL), Ar gonne National communicated to the ANL and LASL Laboratories. Laboratory (ANL), and Los Alamos Scientific Labora- Immediately following this, further ion-exchange elu- tory (LASL), which represent the discovery of the tion separations were carried out at both UCRL and elements with the atomic numbers 99 and 100. ANL resulting in essentially simultaneous identification The source of the material which was used for the of the 6.6-Mev alpha activity as belonging to the erst chemical identjt6cation of these elements was the element with 99 (i.e., elution in the eka- Los Alamos Scientific Laboratory which provided position). The results of these definitive elu- which had been subjected to a very high in- tion experiments are shown in Fig. 1. stantaneous Qux in the "Mike" thermonuclear Further measurements on material from the same explosion (November, 1952). Initial investigations at source by the LASL led to the observation of a ANL showed the presence in this material of the new 7.1-Mev alpha activity (at an intensity of about 4 Pu'~, ' and investigations at ANL and LASL ' percent of that of the 6.6-Mev alpha activity) without showed the presence of Pu"' and Arrl ', pointing to chemical identification beyond proving that it was due the presence of neutron excess in greater to a transplutonium element. This 7.1-Mev alpha ac- abundance than expected. tivity was first shown by the UCRL group in ion- the UCRL to look for isotopes of This led group exchange elution experiments of the type described transcalifornium elements in material from the same above to be an isotope of element 100 (i.e., elution in source. Samples were subjected to chemical procedures the eka- position just ahead of the 6.6-Mev to separate the from the fraction, ' element 99 alpha activity) and was shown to have a tracer Cf'4' (36-hour, 6.75-Mev alpha particle4) was half-life of about a sustained a longer-lived added and a separation of the tripositive was day by This establishment of the effected using the cation-exchange resin Dowex-50 element 99 parent. isotope and elution at 87'C with citrate solution. ' responsible for the 7.1-Mev alpha activity as having the These experiments showed the elution in a transcali- atomic number 100 was con6rmed in a similar experi- fornium position of a 6.6-Mev alpha activity and hence ment by the AXL group somewhat later. The elution proved conclusively that a new (transcalifornium) ele- data for the experiments that established this atomic ment had been found. Before the atomic number number are shown. in Fig. 2. The , , LETTERS TO THE EDITOR 1049

gratitide to R. A. Penneman and personnel of his group for their cooperation and the use of their pulse analyzer. MAR. f, l955 The UCRL group wishes to acknowledge the coopera- tion of K. Street, Jr., W. W. T. Crane, L. R. Zumwalt, L. B. Werner, N. E. Ballou, and I. J. Russell in pro- IOOO- viding samples, and to thank N. B. Garden, Rosemary Barrett, and R. A. Glass for active assistance. r Hess, Pyle, Fried, and Inghram (to be published). IOO- Asprey, Browne, Engelkemeir, Fields, Fried, Pyle, Smith, Spence, and Stevens (to be published). 'K. Street, Jr., and G. T. Seaborg, J. Am. Chem. Soc. 72, 2760 (1950). Ghiorso, Thompson, Street, and Seaborg, Phys. Rev. 81, 154 IO- (1951). Cf ~ See, e.g., Thompson, Street, Ghiorso, and Seaborg, Phys. Rev. 80, 790 (1950). ~Thompson, Ghiorso, Harvey, and Choppin, Phys. Rev. 93, I.O- 908 (1954). ~Harvey, Thompson, Ghiorso, and Choppin, Phys. Rev. 93, 1129 (1954). 7. I MEV Studier, Fields, Diamond, Mech, Friedman, Sellers, Pyle, 0 I- Stevens, Magnusson, and Huizenga, Phys. Rev. 93, 1428 (1954). Fields, Studier, Mech, Diamond, Friedman, Magnusson, and Huizenga, Phys. Rev. 94, 209 (1954).

l i II I t I 1 I t IO 50 50 70 90 I IO E LUTIO N DROP NUMBER Multiple Meson Production in Emulsions FIG. 2. Elution of element 100 relative to other actinide Exposed to the Bevatron Beam*) elements (citrate eluant). WILLIAM R. JOHNSON RuChution tuborutory, DePurtmerit of Physics, and radioactivities will be discussed in a forth- University of Cabfornia, Berkeley, California coming publication. (Received May 31, 1955) Isotopic assignments which were made as the result confirmed the later ' of this early work were largely by EASUREMENTS have been made on the shower- work on the intense neutron irradiation~' of Pu"'. - ~ particle production in nuclear stars formed in Thus can be said that the for the it 600-micron Ilford G.5 stripped emulsions. Production 6.6-Mev 99 alpha activity is 253, corresponding to the P decay sequence Cfs 99' s (~20-day, 6.6-Mev TABLE I. Observed and calculated— shower-particIe s:20 day multiplicity percentages Fermi model. ), the Cfs" originating from the beta of U'" and daughters. Also, the mass number for Energy in Extension of Fermi's Experimental decay Bev '+e calculations& observations the 7.1-Mev 100 alpha activity is 255 corresponding to P 3.2 0 20 42 the decay sequence 99"':100'ss (~16-hour, 7.1- 1 47 28 ~30 day 2 29 25 Mev alpha the 99"' originating from the 3 particle), ~ ~ ~ 1 of U'" and daughters. Av 1.17 0.94~0.09 We suggest for the element with the atomic number 0 16 25 99 the name einsteinium (symbol E) after Albert 1 41.5 38 Einstein, and for the element with atomic number 100 2 35 20 the name fermium (symbol Fm), after . 3 7.5 17 ~ ~ ~ 0 The primary acknowledgment is to the personnel of Av sg 1.34 1.3+0.11 LASL for the design and construction of the thermo- 17 which rise to the extreme 0 14 nuclear (Mike) weapon, gave 1 38 31 neutron Aux required to produce the very heavy nu- 2 38 30 clides. We wish to thank H. F. Plank for his very able 3 10 18 3 addition the ~ direction of the sampling operation. In 5 ~ ~ 1 ANI group wishes to acknowledge helpful discussions AV Nit 1.44 1.62~0.11 with A. Turkevich and its indebtedness to D. I'". Peppard and his group (George Mason, John Maier, and a In the computation of the percentages for each value of ee the tabulated number represents the shower tracks that would actually be observed, not Richard Wallace), who isolated a heavy element frac- the number of pions created. The numbers in column 3 for ne =2 include the following production schemes: pp+ —,n72++, pp+ —0, n72++0, and tion. The LASL group wishes to acknowledge its pn+ —0. (The +, —,and 0 refer to the charges of the created mesons. )