# The Gamma Ray Constant (Video)

**Published:** May 10, 2024

**Source:** Ionactive Radiation Protection Resources

#### Prelim

The expression subject to discussion in this video is as follows: \[ \begin{align} D_{\mu Sv hr^{-1}} &= \frac{ME}{6 r^2 } \end{align} \]

The terms are:

**M**(radioactivity in MBq)**E**(energy in MeV)**r**(distance in m)**6**(the gamma ray constant, one of many possibilities)

The video resource presented here was written over 10 years ago, but the main findings / comments are still very relevant, namely that the above expression is somewhat of a compromise, especially for gamma emissions below about 60 keV (0.06 MeV).

Please stay and watch the video (!), but ultimately you may then wish to consider the following Ionactive resource: **Formula for calculating dose rates from gamma emitting radioactive materials**. [**Ionactive comment**: in this referenced resource the **M** (*radioactivity in MBq*) is replaced by **A** (*radioactivity*) ]. This subject area is then further explored by an interactive widget where you can see the above expression working for four different radionuclides (and note in particular that the value of the gamma ray constant changes) - this resource is: **Gamma dose rate (D=AE/6r2) - or is it? A widget to calculate the validity of this formula**.

Now on with the video.