Calculating the Equivalent Dose Rate for an Unprotected Radiation Worker

[melissaaa]

Homework Statement

An unprotected radiation worker walks into a room which she knows is sometimes
used to store high activity sources. She is unaware that, on that particular day, it
contains an unshielded Co-60 γ source. The source is encapsulated in a material which
filters out β emissions, but with negligible reduction to the γ emissions. The activity
of the source is 2.0 × 104
MBq. Each decay releases two γ photons with individual
energies 1.17 MeV and 1.33 MeV - a total photon energy E = 2.50 MeV per decay.
She is standing 6.0 m from the source. Assume the source is approximately a point
source.
(a) Calculate the equivalent dose rate (in µSv/h) delivered to the position of the
worker

Homework Equations

I don't know which equation to use

The Attempt at a Solution

I didn't understand how to do the question but I checked the answers and I don't understand how they did this:

H [µSv/h] = 0.14 × 2 ×104 ( MBq) ×(2.50 MeV)/ (6 m)^2
=194 µSv / h
≈190 µSv / h

 

[mfb]

This is just [factor that takes units and absorption probability into account] * [activity of the source] * [released energy per decay] / [distance squared]. You should find this formula in your book/script/... Which part is unclear?