Orsay: how to predict detector damage?

So here's what I'm doing about cross sections in the elastic scattering simulation:

1. Choose a random direction for the outgoing particle (⁸Be).
2. Calculate the c.m. theta corresponding to that direction.
3. Calculate the Rutherford cross section for that angle, normalized to 1 at 5':
   

   double RCS=Math.pow( Math.sin(theta/2) , -4);
   double cross_section=RCS/276237;
   

4. Choose a random number between 0 and 1 ("test").
5. If "cross_section" is greater than "test" then proceed (with energy loss calculations and direction tests and other assorted nonsense); otherwise discard this event and start again.
   

Using this approach I get however-many hits per strip, from elastic scattering, for every however-other-many simulated events.

(In a separate calculation, I determined the solid angle for each strip in whatever configuration.)

My question: How do I go from that ratio (and solid angle) to a reasonable estimate of time to damage the detectors?

Other information I have: from Tom's notes:
2.51E+18 atoms/cm2 in target (for 50 ug/cm2 12C target)
1.25E10 particles per second for 2 particle nanoamps
72495.9 mb/sr for elastic scattering at 5'

Someone please tell me how not to be a numpty, and how to combine all this information in a useful way.

Update: I think I might have come up with something.

1. Use the Rutherford cross section to calculate the number of events, per second of beam time, into annuli of width 1', centred on 1',2',...55'.
2. Simulate elastic scattering and count how many events go into the same annuli, for a given number of particles on target.
3. Compare the resulting hits-per-degree curves, and find a normalization coefficient that takes us from "simulated hits per X simulated events" to "hits per second".
4. Apply the normalization coefficient to the "hits per strip" calculated above.
5. Deduce the lifetime of each individual strip (i.e. the number of seconds/hours/days for it to get 1e9 hits, with the given beam current).

...I'm too sleepy to go into the gory details right now--maybe tomorrow--but it looks like "configuration 5", my current favourite, will result in the middle half-dozen strips of the detectors that are at lowest angles dying within 5 days. This is good: it gives me another constraint to work with when picking detector positions.

(I figured this out this evening instead of (a) marking the papers I need to hand back first thing tomorrow, (b) working on my Manchester talk, or (c) going to bed early, so maybe I'm still a numpty.)