Calibration Info

To fully understand the relationship between PMT (photo multiplier tube) Counts and total exposure for the Nanodot OSLs, a custom calibration is needed. This calibration is used in lieu of the calibration created by the OSL reader, which is created using the pre-dosed OSLs from the manufacturer. To begin the calibration, a set of fifteen unexposed Nanodot OSLs is chosen at random and exposed to a 9.3Ci [math] ^{137}Cesium[/math] source. Using a distance of 30cm from the faceplate of the source and also including the distance from the faceplate to the surface of the source, [math]{D}=(\text{Distance to faceplate} + 11.2cm)=41.2cm [/math] , the exposure rate is calculated in Roentgen using [math] \dot R = \frac {\Gamma A }{ D^2} [/math]. A gamma factor of [math] {\Gamma} = 0.33 \frac {(m^2)(R)}{(Ci)(hr)} [/math] and activity of [math]{A} = 9.3 Ci [/math] is used for these calculations. Using the exposure rate found in the previous calculation, it is possible to find the total exposure of the Nanodot OSL by integrating the exposure rate over the time the OSL was exposed to the source, [math]\int\limits_{t_0}^{t_f}\dot R\ dt [/math].

The Landauer Microstar reader used to analyze the OSLs outputs the accumulated dose in terms of milliRad (mRad), which would require a conversion from Roentgen to Rad. By converting units, it was found that [math] 1.14554\ \text {Roentgen} = 1\ \text{Rad}[/math]. Using this conversation allowed for a linear fit calibration to be created to visualize the relationship between background subtracted PMT counts and calculated dose. This calibration is then used to get well understood measurements during experiments involving the OSLs.

---

Click here for calibration data

Thesis