Soil Sample Preparation for Methods That Do Not Require Extensive Treatment

2 Soil Sample Preparation for Methods That Do Not Require Extensive Treatment 

Determination of uranium in soil samples can be carried out by nondestructive analysis (NDA) methods that do not require separation of uranium (needed for alpha spectrometry or TIMS) or even digestion of the soil for analysis by ICPMS, ICPAES, or some other spectroscopic methods. These NDA methods can be divided into passive techniques that utilize the natural radioactive mission (gamma and x-ray) of the uranium and progeny radionuclides or active methods where neutrons or electromagnetic radiation are used to excite the uranium and the resultant emissions (gamma, x-rays, or neutrons) are monitored. In many cases, sample preparation is simpler for these nondestructive methods but the requiranent of a neutron source (from a nuclear reactor in many cases) or a radioactive source (x-ray or gamma) and relatively complex calibration and data interpretation procedures make the use of these techniques competitive only in some applications. In addition, the detection limits are usually inferior to the mass spectrometric techniques and the isotopic composition is not readily obtainable. 

A comprehensive review of the sample pretreatment strategies for total reflection x-ray fluorescence (TRXRF) analysis was published in the form of a tutorial review surveying several preparation methods for a variety of samples (De La Calle et al. 2013) however, specific determination of uranium is only episodic in that review. 

The ASTM has published a method, based on x-ray fluorescence (XRF), for the determination of uranium and thorium in soil or rock samples (C1255 2011). The samples are dried and ground and the content of uranium is determined by a wavelength-dispersive x-ray fluorescence (WDXRF) device. The method is suitable for a concentration range of 20-1000 pg U (or Th) g soil, and the limit of detection of 20 pg g is pronounced to be sufficient for clean-up verification. 

Methods based on neutron activation analysis (INAA and DNAA) were used for the determination of uranium in a variety of geological samples from Egypt (El-Taher 2010). The samples were crushed and sieved so that the particle diameter 

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