A Method of Measuring Emission Spectra from Thermoluminescent Materials

It is always difficult to measure the emission spectrum of a thermoluminescent material, because the emission is transient, of low intensity, and the spectrum may change from one glow curve to another. Methods used in the past have involved making extremely fast spectral scans 1 , or heating multiple samples and recording a single wavelength band for each sample. 2 The second method is very time consuming and both methods are limited in’resolution. This note describes a method which is applicable to at least some materials. The experimental arrangement was as shown in Figure 1. The monochromator was a 50 cm McPherson. For our investigation we chose LiF (Harshaw TLD-700) in the form of a powder seived to 100-200 mesh. The LiF was placed in the hopper (A) and allowed to flow through the sloping tubing past the monochromator entrance window. The nichrome wire wrapped around the tubing was heated by passing ac current from a variable transformer through it. The vibrator (B), which touches the tubing and assists in obtaining uniform flow; is a vibrator type engraving tool. The LiF emits light as it passes the entrance window and the spectrum can be s&armed at any desired speed consistent with the flow rate and capacity of the hopper. Not shown is a light tight box to prevent room light entering the entrance window. The vibra_tor generates considerable electrical noise and it was necessary to wrap it in a grounded aluminum foil. It is vital that the flow be uniform for this method to work. Flow is governed by the diameter and slope of the tubing and the a&plitude and coupling of the vibrator. We found that a slow but heavy flow gives best results. The uniformity of the flow can be checked by stopping the monochromator drive and observing the steadiness of the resulting trace. The