hown to consist of fast moving particles, each with a mass about the same as a helium atom. Alpha particles emitted a radioactive gas called thoron. The alpha particles emitted by the thoron could pass through the wall of the tube that it was being held in.
             Beta radiation was shown to consist of fast moving electrons. They can be deflected into a circular path by using a uniform magnetic field. Measurement of the specific charge of beta particles gave the same value as for the electrons, so scientist concluded that beta particles are electrons, produced in a way, which was yet to become clear.
             Gamma radiation was shown to be electromagnetic radiation with a wavelength of the order of 10 m or less. Gamma radiation can be analysed using a 'crystal grating'. A crystal is a regular arrangement of layers of atoms at very close spacing so it looks diffraction grating, provided the wavelength is of the same order as the atom spacing.
             Background radiation comes from many sources. Natural
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