Radiation calculation confusion

[murdrobe]

Homework Statement

6. If the exposure rate from 137Cs at one metre is 2.50 mGy/h, how many bequerels are present?

Homework Equations

Exposure is a quantity that expresses the radiation delivered to a point at a certain distance.

I1d12 = I2d22
I1 = the radiation intensity at distance d1 from the radiation source.
d1 = the shorter distance from the source where the radiation intensity is I1.
I2 = the radiation intensity at distance d2 from the radiation source.
d2 = the longer distance from the source where the radiation intensity is I2.

I1 I2
source* ------------>|----------> |
------------>| |
d1 d2

The Attempt at a Solution

my issue is that it seems we are being asked to convert miliGrays to becquerels and I am not sure how that's done, they seem to be a measure of different things from what i was taught so surely a conversion will be imperfect?

from looking around on the internet, it seems possible but via conversion through several intermediatry units. is that how this is meant to be achieved or is there a simpler method?

 

[murdrobe]

*shameless bump*

this 1 has stumped me a little sorry.