<em><u>Gieger Counter is the correct answer.</u></em>
Explanation:
<u><em>Geiger counter</em></u> is an instrument used for measuring the ionising radiations such as beta and alpha particle or gamma rays. It is a hand held radiation instrument and can also be used as bench instrument. Its operating principle was discovered in 1908, Geiger-Muller tube was developed in 1928. It is very popular instrument due to good sensing detector and element and low cost. The sensor is a tube that emits electronic signal when the radiation is present and the counts displayed is the counts per second. The radiation dose is displayed in a unit <em>sievert.</em> The reading of the signal can be digital or analogue.
