A radioactive material is placed near a detector.

The detector shows a count rate of $counts/min45\,000\text{ counts/min}$ .

When a sheet of paper is put between the material and the counter, the reading decreases to $counts/min38\,000\text{ counts/min}$ .

When an aluminium sheet is put between the material and the counter, the reading decreases to $counts/min15\,000\text{ counts/min}$ .

When a thick lead block is put between the material and the counter, the reading remains at $counts/min15\,000\text{ counts/min}$ .

What is being emitted by the radioactive material?

$α\alpha$ , $β\beta$ and $γ\gamma$ -radiation

$α\alpha$ and $β\beta$ -radiation only

$α\alpha$ and $γ\gamma$ -radiation only

$β\beta$ and $γ\gamma$ -radiation only