AM, CM PURIFICATION The chemical separation methods for Am and Cm used by Thompson et aZ. (1949) in the Manhattan Project to produce sufficient quantities of Am and Cm for studies of these elements might be considered the classical steps. These are fluorides, oxalates, hydroxides, phosphates, iodates, fluosilicates, oxidation reduction reactions, cation exchange with citrate eluant, and a few solvent extraction methods. Many of the above methods, i.e., oxalates, iodates, fluorides, and fluosilicates, were reported to be greatly influenced by interfering elements and precipitation conditions, and temperatures. The commentary provided therein points to many problems which are encountered in using such procedures in Am-Cm analysis, wherein La and Y are employed to carry Am and Cn but they later have to be separated to obtain weighless deposits of Am and Cm for alpha measurements. Penneman and Keenan's 1960-monograph on the Radiochemistry of Americium and Curium contains an abbreviated summary of the purification steps for Am and Cm. A collection of 15 detailed radiochemical procedures is given. None of them are for environmental procedures, and only one procedure provides for tracer yielding, either 2"3am or 24cm tracer. For repetitive analyses on a given sample type and matrix, good procedures and good operator competence is usually achieved. For different sample types, the problems are increased, with probably the greatest difficulty being experienced with large (> 10 g) soil samples of varying elemental content. The difficulty is further increased when the practical limitation of minimum cost is also imposed, since this could influence the methods chosen and development of a fail-safe method for a given problem. Over the years, the basis for Am and Cm analyses has changed. Through the 1950s and the 1960s, the primary analytical requirements existed within nuclear materials production and weapons testing programs. One continuing type of analyses in all of these programs was the need for bioassay of nuclear workers. Low-Beer (1973) surveyed a large number of laboratories in order to compile a review on bioassay procedures. She reports indications that at that time, 1973, the transplutonium elements command very little attention in routine bioassay programs. The procedures reviewed by Low-Beer are either gross alpha methods or specific tracer-free methods. In the gross alpha method, if activity is observed, further specific analyses were to be performed to identify and quantify them. These procedures were said to give high yields 80 to 95% and there is no mention of the use of any tracer in the specific methods, The present day approach seems to be to always use isotope dilution techniques with tracer. An advantage in the use of the tracer is that the isotope sought is positively identified and the chemical processing losses are accounted for, providing high accuracy and sensitivity. In a tracer-free analysis, in case zero activity is detected, there is no way to establish that the chemical processing yield was indeed not zero due to unexpected sample interferences or some processing anomaly. 562 A disadvantage of the use of tracers is that precautions must be taken to balance sample activity and tracer activity within certain limits, which are often set by a particular case. Also there is the chance that the tracer being used will be present in the sample. For instance, tabulations of the TU content of spent reactor fuels by Pigford and Ang (1975) and the EPA (Anonymous, 1974) show epgnt reactor fuels will contain most of. the long-lived TU nuclides, including 2"@Mam, 242m, and 245cm. If environmental samples also have similar compositions, the use of isotope dilution techniques to analyze for 24am and 244en, the usual isotopes of prime interest, must be done with care. Approximate information on the TU's expected in such samples will aid this evaluation. In the worst case, one single sequential analysis, using tracers, may not give optimum accuracy and the analysis will have to be done in parts; but in some cases, the more expensive method of additions will have to be used. PREPARATION FOR COUNTING Sample preparation, after purification, depends on the counting technique which is to be employed and the energy and type of radiation measured. A consideration of the radiations of the transuranics from spent fuel and tracers shows that the preponderance require alpha measurements but beta and gamma methods are sometimes applicable. Most samples are now measured by alpha spectroscopy in Frisch grid or surface barrier detectors. Sometimes beta counting, liquid scintillation counting, gamma spectroscopy, or mass spectrometry supplements or replaces alpha spectrometry. The choice of the method is also based upon the sensitivity required and the need for discrimination from other actinides. The capabilities and limitations of the methods must be kept in mind as many different mixtures of the transuranic elements may be encountered. The alpha-emitting actinides are prepared for counting by several techniques. Due to the short range of the alphas, then, preferably weightless, samples are required for 2 APHA measurements. Examples of the techniques that have been used are stippling of LaF3, Bokowski (1964), or PrF3, Perkins (1961); discussions of the transfer of aqueous and organic solutions for thin films, Hufford and Scott (1949), stippling of Fe(OH)3, Kooi and Holistein (1962), or the cupferride extract, Brooks (1950), and ignition to the oxide and electroplating, Mitchell (1960). The discs or trays are mostly of stainless steel or platinum although tantalum, Shipman and Weiss (1960), has been used and evaporation onto a watchglass reported, Evaporation under an infrared lamp is the usual technique. Care is taken to spread the precipitate uniformly. Trays as large as 3” have been used so as to obtain thin cakes. A drop of organic film, such as collodion or zapon, is added and the metal disc flamed. Hufford and Scott (1949) review in detail the techniques for preparing thin films such as evaporation from a variety of media, TEG and slurry spreading, electrodeposition, and sublimations. A variety of scintillation techniques have been applied to actinide measurements. Liquid scintillation methods for alpha counting of 239Pu have been reported by Fontaine and Baude-Malfosse (1961) and for 24 lam by Cline (1967). Szidon et al. (1968) compared LSC methods with other Pu standarization techniques. 563