Curium is synthesized by bombarding plutonium with alpha particles. The alpha particles are formed from two protons and two neutrons that are identical to the nucleus of the element helium. The particles are gathered by emissions from uranium or radium through alpha decay. Most alpha particles have a high amount of energy; they are dangerous in that they can be absorbed by human skin and tissue. In 1944 curium was first synthesized by bombarding the alpha particles onto the isotope, number 239, of plutonium. The experiment was carried out in a cyclotron; a cyclotron is a particle accelerator which works though high frequencies and alternating voltage. The hydroxide form of the isotope, number 242, of curium was synthesized by bombarding the isotope, number 241, of americium with neutrons. Isolated isotopes of curium do develop high amounts of gamma and beta radiation as they decay; this fact has reduced some of the interest in commercial uses of curium.