Final shaping of the sample

The primary aim of final shaping is of course to transform the sample to its final form as required for analysis. At the same time it reduces the surface contamination to a minimum. As far as the form is concerned, spherical samples would be ideal since their surface to volume ratio is minimal. This is however unpractical, and in general the accepted compromise between small surface to volume ratio and difficulty of preparation consists in making cylinders or cubes. 

Cylindrical samples are machined from the crude samples by turning on a lathe, whereby also the base surfaces have to be rectified. For this purpose steel, hard metal or diamond tools can be used. The operating parameters may differ from one metal or alloy to another, but must always end up in flat and clean surfaces. As a result of several years of international cooperation within BCR, the Central Bureau for Nuclear Measurements (C.B.N.M.), Geel, 

Belgium, proposed a standardized tool form, which is schematically represented in Fig. II1-4 (3). The specific tool materials and turning parameters to be used to remove the last 0.1 to 0.2 mm are summarized in Table III-3. 

Cubic samples are generally prepared using thin cutting wheels coated wi th hard metal, but such techniques are only allowed if the metal is sufficiently hard. 

In some cases, surface contami- Fig. III-4 Standardized tool parame-nation is sufficiently low after ters for turning (3) 

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