Next, Marie and Pierre studied particles and energy as atoms decayed that was given off by radioactivity. It was first discovered when Marie saw that the radioactive gas had escaped somehow. Radioactive decay happens when there is a loss of energy, then, the nucleus transforms as the atom changes its shape. It occurs when a nucleus of an unstable atom loses energy by exuding particles of ionizing radiation. Passing the radioactivity through a thin, glass window allowed Marie and Pierre to study the radioactive decay of the atom. During the radioactive decay, it also emerged other types of decay including nuclear isomers. Lastly, Marie and Pierre invented the electrometer. The electrometer is used to measure electric charge. The electrometer was very sensitive against measuring electrical currents. The electrometer is used by making voltage to charge measurements with low currents. It