Suburban Decay Mystery Cache

Our first attempt at a puzzle cache - constructive feedback welcome!

The cache is not located at the given coordinates: these are for the entrance to Highfield Park (on-street parking available nearby).

The cache can be located as follows:

N53 22.X W002 11.YZ where:

If ¹¹C = 24885 MBq at 00:00, then activity = X MBq at 02:00

and

If ¹⁸F = Y MBq at 00:00, then activity = 6 MBq at 01:04

and

If ¹⁵O = 3210 MBq at 00:00, then activity = 5 MBq at 00:Z

(X, Y and Z should all be rounded to the nearest whole number).

Good luck!

You can check your answers for this puzzle on GeoChecker.com.