Question

Give examples of a primary standard and a local radiotherapy secondary standard how they relate to the measurements within a clinic? How is the calibration factor for a secondary transferred from primary. Why might be necessary to recalibrate your secondary standard?

Answer 1

Analytical standards ae divided into two: primary standards and secondary standards. A primary standard is 100% pure and stable reagent, that has high molecular weight and no water of hydration. Examples of a primary standard are: with molecular weight equivalent to 105.99 gram/mol and with molecular weight 294.19 gram/mole. On the other hand, a secondary standard is that which may absorb water from the atmosphere, is not extremely pure or unstable. For example, base is a secondary standard, as it contains impurities of , , etc. and it also absorbs water from the atmosphere. It is absolutely necessary to recalibrate secondary standard as they teend to change their composition with time. In case of , which is a secondary standard, it might absorb more from the atmosphere, leading to change in its overall composition, and concentration with the passage of time. So, in order to ensure that the calibration is same as the real mixture at that point of time, it is necessary to recalibrate them. This is not the case with the primary standards.

In the radiotherapy and Oncology processes, laser beam calibration-both directional and absolute, are done for quality purpose in a clinic. To achieve absolute minimum in uncerainty, there is a need for the calibration. The wavelength of the laser light is compared with th dynamic vibration for the asolute calibration. To minimise the reference sensor uncertainty, transfer standards are created.