An automated quality control system uses a radioactive source to monitor the density of a flowing polymer. A safety engineer carries out test measurements with various absorbers placed between the source and a Geiger-Müller detector. The background count rate in the laboratory is determined to be $15counts\; per\; minute\; (cpm)$.

The recorded count rates are:

• Source with no absorber: $1450cpm$
• Source with a thin sheet of cardboard: $320cpm$
• Source with a 3 mm aluminium plate: $318cpm$
• Source with a 50 mm lead block: $18cpm$

Which types of radiation are emitted by the radioactive source?