Technical Guidance

Ga-68 (Gallium-68) radiation safety data from Ionactive.

Se-75 (Selenium-75) radiation safety data from Ionactive.

Kr-85 (Krypton-85) radiation safety data from Ionactive.

The TVT (10th value thickness), and HVT (1/2 value thickness) are easy to use simplifications in radiation shielding calculations. They are a good approximation to the solution desired, and in many cases will give shielding results as good (i.e. as accurate) as the more complicated and expensive models (e.g. MicroShield and MCNP etc). However, they should be used with caution and especially where thin shields are required with low energy photons. The TVT may over estimate the shielding required, but not always. This resource will explore these issues and answer questions like 'is build up (B) accounted for in published TVT / HVT data' and similar. You will also note that there is a requirement to interpolate publicly available data (e.g. for linear attenuation coefficients) and this alone can explain why published TVT for a particular gamma emitter and shielding material can vary.

There is much data over the WWW and in books regarding TVT and HVT (10th value thickness and 1/2 value thickness) for radiation shielding of gamma emitting radionuclides. There are also a few online calculators, and the soon to be released Ionactive Radiation Protection Online Calculator. Furthermore, in some cases TVT and HVT are not suitable for shielding evaluation and computer codes may be required (e.g. MicroShield or MCNP). However, for simple issues and radiation protection training, the TVT and HVT are still reliable. This resource presents data that Ionactive would be willing to use, subject to the clarifications just given.

Using exact values of TVT (10 value thickness) is quite easy - just work in 1/10ths. However, a little more work is required when you have fractions of a TVT, or you want to know precisely the attenuation of a given radiation shield, or precisely how many TVT is contained within a given thickness of material. This article provides the information you need!