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10 October 2008

Answer to Question #6964 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding — Shielding

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

In France, we often use syringe shields made of tungsten. I am looking for HVT (half-value thickness) for ^99mTc in my books or on the Web and I'm finding nothing.

I am unaware of any reference that will list HVTs in tungsten. However, it can be calculated given the mass attenuation coefficient (µ/ρ) and the density (ρ) of tungsten. These values can be found in a number of references.

I used the data from the National Institute of Standards and Technology (NIST) (select X-Ray Attenuation and Absorption for Materials of Dosimetric Interest; Table 1 for densities, Table 3 for mass attenuation coefficients). The density of tungsten is given as 19.3 g/cm³ and the mass attenuation coefficient for 140 keV in tungsten is determined, by interpolation, as 2.152 cm²/g. The mathematical relationships are HVT = 0.693/µ and µ = (µ/ρ)ρ. Using this data, I calculate the HVT of ^99mTc in tungsten to be 0.0167 cm.

David Close, CHP

Answer posted on 5 November 2007. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of 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 specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.