He continued to construct pieces of laboratory equipment such as the ionisation chamber pictured below. Pierre taking the measurements. Together they discovered polonium and radium and used the word 'radioactivity' for the first time. This sensitive device was developed by Pierre Curie for investigations into radioactivity. The chamber consists of a positive and negative plate connected by an electrometer.
Radiation ionises the air in the chamber.
The breakdown of air molecules into positive and negative ion pairs allows them to act as carriers of electric current. The negative ions migrate to the positive plate and the positive ions to the negative plate. This causes a weak electric current to flow which can be measured on the electrometer. The level of radioactivity will determine the strength of the current. At a Royal Institution Lecture in London in 1903, Pierre described the amazing properties of radium and the medical tests he had been carrying out on himself.