Elements

The second most abundant element in the universe, helium is rare on Earth. In liquid form it is used as a coolant in super conducting magnets in MRI scanners – so should this rare element be used in something as frivolous as party balloons? And what happens to the helium when that balloon inevitably escapes the clutch of a small child? (Picture: US National Helium Reserve; Credit: Jonny Dymond/BBC)