Answer to Question #8865 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Instrument Calibration (IC)

The following question was answered by an expert in the appropriate field:

Q

Can we use LiF TLD-100 for high-energy beams, for example, up to 1.2 MeV?

A

TLD-100 is certainly usable for high-energy photon measurements. LiF TLD-100 does exhibit some energy dependence in its dose response, with the largest variations occurring at rather low energies. If you are making dose measurements, the relative dose response depends, in part, on what energy has been used in calibrating the dosimeters. If the dosimeters have been calibrated with a relatively high energy source, such as 137Cs (662 keV), the response at 1.2 MeV will be very close to that at the calibration energy (i.e., TLD [thermoluminescent dosimetry] light output per unit tissue dose will be very close at both energies). If you attempt to measure doses at low-photon energies (below 100 keV or so) you will find that the response of the dosimeter, calibrated at 137Cs energies, is higher at the lower energies, often being 30 to 40% higher in the 10s of keV region. The TLDs have often been used for measurements of high photon energies available, for example, in medical therapy installations where photon energies may exceed 10 MeV. Many experimentalists have found that the TLD-100s, calibrated at 60Co energies (average of 1.25 MeV), yield a somewhat depressed response to the higher-energy photons, responses often being 8 to 10% lower than that observed at 60Co energies.

George Chabot, PhD, CHP

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 5 February 2010. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.