Reducing Short-Term Uncertainty

When performing calibrations for the Reader Calibration Factor (RCF) or Element Correction Coefficient (ECC), Harshaw recommends:

• Wait 24–48 hours after annealing before irradiation.
• Wait 24–48 hours after irradiation before readout.

The purpose of this timing is to allow low-temperature (short-term) peaks to fade. This leaves the more stable high-temperature peaks, reducing short-term uncertainty in the measurement.

The same consideration applies when performing controlled experimental exposures, performance testing, or blind irradiations. While field dosimeters often experience natural transit delays, laboratory exposures may not—making fade an important factor.

A Common Method That Can Increase Uncertainty

Some users attempt to reduce fade effects by applying a preheat or selecting a partial calibration region (instead of integrating the full 1–200 region for LiF:Mg,Ti).

However, as TLD cards age, the glow curve may shift due to less efficient heating, Teflon™ encapsulation degradation, or air pocket formation. This can cause more low-temperature peaks to contribute to the total integral, increasing uncertainty.

Advantage of Harshaw Model 6600 & 8800

If you are using the automatic calibration feature in the Harshaw Model 6600 or 8800 with LiF:Mg,Ti material, fade timing is kept consistent between anneal, exposure, and readout. This controlled workflow minimizes variability.

Additionally, Harshaw TLD dose calculation algorithms for LiF:Mg,Ti-based dosimeters incorporate an 8-day pre- and post-fade factor into their calculations. Your Cs-137 relative response calibration must account for this timing structure.

Read our related post: Why the Harshaw TLD Dose Algorithms Use 8 Days for Fade