DISCLAIMERGindler'') lists eleven methods and reports on the range of quantity of uranium in micrograms for which each method is applicable. These methods and the lower limits of analysis are listed in Table I. An alternate approach to the neutron activat'ion analysis of uranium is to count the delayed neutrons emitted by the fission products of U-235. Echo and Turk(6) first described the application of this technique to the determination of By a systematic irradiation and counting procedure, they made determinations of u~~~ in a number of liquid samples containing known q~antities of which -2 varied from 10 to. lom3 micrograms. Three synthetic ore samples containing known amounts of $35 were also analyzed. They reported 0.05 microgram of u~~~ as a lower limit for a determination. They found the method to be rapid, and accurate, to require very little sample preparation, and to be free of any interferences except from those materials which have high neutron fission cross-sections (such as ?u 239 and $33) or high-neutron capture cross-sections (such as mie el'^) has made a more extensive study of delayed neutron emission for the determination of fissionable materials. He applied the method.to the determination of uranium in a large number of geolog'ical'~samp1es and to samples of pure uranium reagents, as well as the determination of the isotopic composition of a uranium sample. from the fission of $35, $33, and Pu239 by both thermal and fast neutrons and from the fission of U238 and d32 by fast neutrons.It was found that the delayed-neutron activity resulting from the fission of each of these nuclides could be resolved into six groups with fair agreement in the half-lives of corresponding groups.Slight differences in the half-lives of corresponding groups were obtained when-different nuclides were fissioned as well as when the method of fission was different, as for example, when U-235 was fissioned first with thermal neutrons and then with fast neutrons.Quite.large differences between corresponding groups for absolute group yields were obtained when different nuclides were fissioned.The data obtained, by Keepin, et a1, (9) for thermal neutron fission of 335, $33, and l?u239 is given in Table 111 Table IV lists An analysis for uranium is made by irradiating a test sample in a nuclear reactor for a period of time ranging from seconds to minutes, rapidly removing the sample to a neutron counting facility, allowilig b~b s o l u t e group y i e l d (dp) means t h e number of delayed neutrons per 100 f i s sians .t h e counter t o c o l l e c t counts f o r a period of time and recording t h e ' c o l l e c t e d count, A blank sample and a comparator sample a r e then t r e a t e d p r e c i s e l y a s was t h e t e s t sample. The blank sample u s u a l l y c o n s i s t s of an empty r a b b i t . In those cases i n which a uranium a n a l y s i s i s desired on a material t o which uranium has been added, t h e o r i g i n a l matrix material t o which no uranium has been added can serve a s the blank along wi...

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