Question is in the attachment.

3. While a detector is recording the passage of a particle, it is "dead" - i.e., insensitive to the passage of further particles. This can become a problem when rates are high. Assume that a counter has a dead time of 200 ns, and is exposed to a beam of 1 x 10" particles per second, so the mean number of particles hitting the detector in a 200 ns window is # = 0.2. Find the average number of particles recorded in a 200-ns period (hint: no particles are recorded if zero pass through; otherwise one particle is recorded), and hence the efficiency of the counter