1. Fill in the gaps in the following statements:

• The nucleus of the atom that emits ionising radiation is           .

• The elements that emit ionising radiation are called           .

• The behaviour of radioactive elements cannot be changed by            or            processes.

     2. List the natural sources of background radiation.

     3. List the artificial sources of background radiation.

     4. Fill in the missing words:

         Some rocks, like              gives off the radioactive gas            . If this gas is trapped in houses,

         it may cause            . The danger from this radioactive gas can be minimised by              the

         rooms of the house.

     5. How is background radiation detected and measured?