The detector and counter are used in an experiment to show that a radioactive source gives out alpha and beta radiation only. Two different types of absorber are placed one at a time between the detector and the source. For each absorber, a count is taken over ten minutes and the average number of counts per second worked out. The results are shown in the table. Absorber used. Average counts per second No absorber. 33 Card 1 mm thick. 20 Metal 3 mm thick. 2 Explain how these results show that alpha and beta radiation is being given out, but gamma radiation is not being given out.​