Cyclotron bombardments

Mass-spectroscopic technique has also been used with non-fissile targets after pile or cyclotron bombardment to determine the mass-numbers of radioactive nuclides. In one case, the branching ratios of certain isotopes for and electron capture decay (where different elements are produced by the two routes) were determined from the amount of the stable end-products of radioactive decay, using the mass-spectrometer to identify the isotopes concerned and to correct for any stable impurities of the elements concerned (98). For some purposes, mass-spectroscopic separations could be very valuable technically such as the... 

When the cyclotron bombardment method became available, H. B. Law, M. L. Pool, J. D. Kurbatov, and L. L. Quill at Ohio State University bombarded samples of neodymium and samarium and obtained radioactive preparations which they believed might contain some 61 (18). C. S. Wu and E. Segre confirmed this (19). F. A. Paneth pointed out that they probably actually had obtained 61 in their mixtures, but the cyclotron method was not sufficiently powerful to give conclusive evidence of its existence (10). Nevertheless, the Ohio State group proposed the name cyclonium for the element. 

Continuation of the study of the radioactive elements produced by cyclotron bombardment of lower elements led in 1950 to isolation by tracer techniques of numbers 97 and 98. Bombardment of Am241 with helium ions by S. G. Thompson, A. Ghiorso, and G. T. Seaborg produced 97243 which resembled its analogue, terbium, in its elution from ion-cxchange resins. Since terbium was named from the city of Ytterby, 97 was named from the city in which so many new elements had been discovered, Berkeley, and the name berkelium and symbol Bk have been accepted (89, 90). 

Immediately after the cyclotron bombardment, the tar- 2-3 min get (size 13 x 19 mm - thickness 43p) is placed under an infra-red leap to be beated. A few drops of a... 

The isotope 242Cm was first isolated among the products of a-bombardment of 239Pu, and its discovery actually preceded that of americium. Isotopes of other elements were first identified in products from the first hydrogen bomb explosion (1952) or in cyclotron bombardments. Although Cm, Bk, and Cf have been obtained in macro amounts (Table 20-2), much of the chemical information has been obtained on the tracer scale. For the later elements, i.e., those with Z > 100, identification of a few atoms of short lifetime has required the use of very rapid separation techniques and detection based on their nuclear properties. 

In cyclotrons charged particles such as protons, deuterons, and a-particles bombard the target nuclei, and after emission of one or more particles to remove the excess excitation energy, a radioactive product nuclide may result. In the capture of positively charged particles and the subsequent emission of neutrons the product radionuclides are neutron deficient compared to the stable isotopes of the elemoit see Fig. 3.1 and 4.7. Another important point in cyclotron bombardments is that normally the product is not isotopic with the target. As a result, after chemical separations a product of high specific activity is obtained since it is not diluted by the target material. An example of an important cyclotron-produced radionuclide is Na (ti 2.6 y) formed by the reaction ... 

Let us take the production of radioactive sodium by reactor irradiation and cyclotron bombardment as examples of the application of these equations. Na2C03 (M = 106) is irradiated in a reactor to produce Na, which has a half-life of 14.66 h and emits /S and 7-rays. The reaction cross-section of Na (100% in natural sodium) is 0.53 b for thermal neutrons. For a 5 g sample, 60 h irradiation time, and a thermal flux of 10 n cm s, the activity at the end of the irradiation time will be ... 

Within a year, element 99 was again synthesized by cyclotron bombardment of uranium with nitrogen... 

Sufficient Be (4 10 gm) can be produced by cyclotron bombardments to enable reaction cross sections to be measured. Hanna found a cross section of (5-3 0.8) X10 cm for the Be (np) reaction with thermal neutrons and a cross section of less than 10 cm for the (ncc) reaction. These results are consistent with odd parity for Be". Comparison with the cross section for the inverse reaction Li (pn) suggests an odd parity level near the neutron binding energy in Be . 

After their success with neptunium and plutonium, Seaborg and his collaborators continued to look for more transuranics. (These collaborators included other scientists and graduate students who contributed many ideas and most of the work, and we regret that they must be consigned to a footnote.) They used cyclotron bombardment, a variety of targets, and microchemical techniques developed by Hahn. Americium and curium (elements number 95 and 96) were discovered in wartime at the Metallurgical Laboratory of the University of Chicago,... 

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