The table shows the activity of a radioactive sample changed as it decayed.

Time $/$ h $0$ $2$ $4$ $6$ $8$

Activity $/$ counts per second $500$ $280$ $160$ $95$ $55$

On the grid, draw a graph of activity against time and use it to deduce the half-life of the substance.

Show your method on the graph.

The half-life is approximately $____$ .

Important Questions on Radioactivity

HARD

Upper Secondary-IGCSE

IMPORTANT

A source contains two different elements with unstable nuclei. Isotope

A

has a half-life of

16

hours, isotope

B

has a half-life of

8

hours. The count rate from each is

128

per second, to begin with. Calculate the count rate after

32

hours.

MEDIUM

Upper Secondary-IGCSE

IMPORTANT

The first column of the table shows some uses of radioactive substances.

In the second column, write the appropriate code letter or letters from the list below :

$A$ Some radiation is very penetrating.

$B$ Some radiation is readily absorbed.

$C$ Ionising radiation damages cells

$D$ Radiation is easily detected.

$E$ Radioactive substances decay at a known rate.

Use of radioactivity	Code letter(s)
finding the age of an ancient object
diagnosing cancer and destroying cancerous tissue
sterilising medical equipment
controlling the thickness of paper in a paper mill
detecting smoke in the air
tracing leaks from underground pipes
irradiating food