A student sets up an experiment to investigate the radiation emitted from a phosphorus-32 source, which is a pure beta (β−\beta^-β−) emitter. A Geiger-Muller (G-M) tube connected to a counter is positioned 4.0 cm away from the source. A 3.0 mm thick sheet of aluminium is placed in the gap between the source and the G-M tube.
With the aluminium sheet in place, the counter records 42 counts in 1 minute.
The aluminium sheet is then replaced with a thin sheet of paper of thickness 0.1 mm. The counter is reset, and a new measurement is taken for 1 minute.
Explain why the new count is significantly higher than 42.