Calculating Gamma Ray Count Rate Error in 20 secs

[swaha]

Homework Statement

A detector is used to count the number of gamma rays from a radioactive source if the number of counts is 10000 in exactly 20 secs then what is the error in counting rate per sec?

Homework Equations

- no idea.

The Attempt at a Solution

- As per our syllabus we had only done Geiger muller counter which gives a dead time & from that we can calculate the error. However that is not given here. SO I got no idea to approach. Please help.

Options given- 5%, 22.4%, 44.7%, 220% (absolute values all).
Question source TIFR GS 2010.

 

[Simon Bridge]

Counting statistics follow a Poisson distribution.
http://level1.physics.dur.ac.uk/skills/poisson.php
... the standard error bears a simple relationship to the number of counts.