A LARGE number of the known stable elements have been bombarded by neutrons of energies ranging up to 20 Mev. The transmutation reaction of the type involving the ejection of two neutrons is apparently evident with varying degrees of intensity in nearly all the elements of * Elizabeth Clay Howald Scholar. the periodic table. In addition, reactions of the type where a proton or an alpha-particle is ejected are observed. For bombarding neutrons of low energy these reactions are observed only for relatively light elements, but for very energetic neutrons such reactions are evidently quite common in elements of high atomic number. TABLE I. Radioactivity produced by very high energy neutron bombardment. At. No. 6 7 8
Determination of the ordinary and isotopic spin values belonging to a definite partition in the space coordinatesThe exclusion principle requires that the complete wave function vanish if more than one particle has a given set of orbital angular momentum, spin and isotopic spin quantum numbers. To obtain the total spin and total isotopic spin quantum numbers associated with the different partitions we first make a list, for each manifold separately, of the sets of individual particle quantum numbers compatible with the exclusion principle, classifying them according to Xm s and Sw T . Because of the symmetry about the origin, we may restrict ourselves to Sw s , Sw T^0 . Since Sw T = M" T and 3Zm 8 = M 8 , we immediately arrive at the total s and T necessary to account for these projections. To illustrate the method we again consider the case of three particles: I T has been observed by Fermi 1 that cadmium is relatively inactive after bombardment with neutrons. Since cadmium is a very effective absorber of slow neutrons its large capture cross section for this process is probably due to the formation of one or more stable isotopes. However, many elements not rendered radioactive by neutrons are readily activated under bombardment with high energy deuterons, and it seemed desirable to investigate the disintegrations of cadmium under such conditions.Targets of chemically pure metallic cadmium were exposed to a beam of deuterons of energy about 6.3 Mev. Exposures of the order of four microampere-hours rendered the bombarded specimens strongly radioactive. The deuteron 1 E. Amaldi, O. D'Agostino, E. Fermi, B. Pontecorvo, F. Rasetti, and E. Segre, Proc. Roy. Soc. 149, 522 (1935). Manifold ms m^ ms wT ms m? Sras 2m From the table it is obvious that there is only one pair of s, T values for the partition [3], namely s=|, T=|. After the partition [3 3 has been removed from the manifold (2 + 1) there remains the three sets of quantum numbers (s = f, T = §), (s = |, T = f), (s = I, T = i), associated with the partition [2 + 1]. A similar table for the manifold (1 + 1 + 1) together with Eq. (36) yields the result that the partition [1 + 1 + 1] has only two pairs of spin values, (s = f, T = f) and (s = ^, T=|).beam was obtained by the multiple acceleration of deuterium nuclei in the cyclotron. In order to determine with what elements the activity was associated, the bombarded specimen was dissolved in nitric acid. To this solution small quantities of solutions of the neighboring elements, silver, palladium, and indium were added.The silver was first precipitated from this solution as the chloride by the addition of hydrochloric acid. This silver was redissolved in ammonium hydroxide and reprecipitated by the addition of nitric acid. The palladium was next brought down from the original filtrate as palladium dioxime by the addition of dimethylglyoxime to the slightly acid solution. Ammonium hydroxide added to the filtrate next precipitated the indium as indium hydroxide. APRIL 15, 1937 The bombardment of a cadmium target by...
Although there are but two stable isotopes of indium whose mass numbers are 113 and 115, seven radioactive periods are shown to exist. Six of these whose half-life periods are 13 seconds, 72 seconds, 54 minutes, 2.3 hours, 4.1 hours and 50 days emit negative electrons, and one period of 20 minutes is radiopositive. By bombarding indium with slow neutrons, deuterons and very fast neutrons, and by bombarding cadmium with deuterons it is possible to assign with considerable confidence each period to a certain indium isotope. The conclusions are that the 54 minute and 13 second activities are both due to In 116 , the 4.1-hour and 50-day periods are both In 114 and the 20-minute, 72-second and 2.3-hour periods are from isotopes of mass 111, 112, and 117, respectively. Beta-ray energy limits are approximately 2.15 Mev for the 50-day period and 1.75 Mev for the 20-minute positive period.
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