Article The influence of ashing temperature on the determination of Pu in soil and biological samples

Wang, Zhongtang  ,  Zheng, Jian  ,  Tagami, Keiko  ,  Uchida, Shigeo

Plutonium is the second element in the transuranium element series. The current existence of Pu in natural environment originated from human nuclear activities, such as the nuclear explosion, nuclear industry and accidental release from nuclear accidents. The global fallout, as a result of the extensive atmospheric nuclear weapon tests in the last century, is the dominant Pu source in the environment. In recent years, there has been considerable concern regarding the behavior of the global fallout Pu in the environment because of the radiotoxicity associated with its alpha-emitting radioisotopes (239Pu, 240Pu) and the need of using Pu as a tracer to study geochemical processes, for example, soil erosion, sediment dating and desertification studies. In all these applications, an inevitable operation is to transfer Pu from environmental samples (e.g. soil, sediment and biological samples) to a liquid form which is compatible with the subsequent chemical treatment. In literature, many methods were presented to achieve this, such as, nitric acid leaching, total digestion method and alkali fusion method. Among these methods, nitric acid leaching is most popular because it is simple, fast and effective. Normally, the nitric acid leaching method consists of four steps: ashing, acid leaching, Pu separation and Pu measurement. The ashing step is intended to destroy the organic matter in the samples, which would have a negative impact on the Pu separation step. However, different ashing temperatures were used by researchers, from 400 to 900℃. Various ashing temperatures may cause additional uncertainty in Pu analysis. For example, low temperatures may not decompose the organic matter thoroughly; while high temperature may produce some refractory particles. Therefore, an appropriate ashing temperature should be identified and accepted by researchers to improve the reliability and accuracy of the nitric acid leaching method.Thus, in this study, efforts were made to investigate the effect of ashing temperature on accurate determination of Pu using nitric acid leaching method, for soil and biological samples. Furthermore, an optimum temperature was recommended for sample ashing.

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