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Across 2. The changing of one element into another by radioactive decay, nuclear bombardment, or similar processes. 3. The counter tube in which light flashes when exposed to ionizing radiation 9. Radiation in the form of elementary particles emitted by an atomic nucleus, as alpha rays or gamma rays, produced by decay of radioactive substances or by nuclear fission 14. A nuclear reaction in which an atomic nucleus, especially a heavy nucleus such as an isotope of uranium, splits into fragments, usually two fragments of comparable mass, releasing from 100 million to several hundred million electron volts of energy. 17. Obtained from leach solutions, in an intermediate step in the processing of uranium ores. 18. The process or result of joining two or more things together to form a single entity. 19. A subatomic particle with the same mass as an electron and a numerically equal but positive charge. 20. A helium nucleus emitted by some radioactive substances, originally regarded as a ray.

Down 1. Occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating series of these reactions. 4. Radioactive elements with atomic numbers greater than the atomic number of 92. 5. Of or relating to the nucleus of an atom. Denoting, relating to, or powered by the energy released in nuclear fission or fusion. 6. Measurement of the amount of radioactive material that an object contains 7. A fast-moving electron emitted by radioactive decay of substances. 8. The time required for something to fall to half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate 10. A change in the identity or characteristics of an atomic nucleus that results when it is bombarded with an energetic particle 11. A stream of high-energy electromagnetic radiation given off by an atomic nucleus undergoing radioactive decay 12. The process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles 13. The process or fact of irradiating or being irradiated. 15. A unit of effective absorbed dose of ionizing radiation in human tissue, equivalent to one roentgen of X-rays. 16. The positively charged central core of an atom, containing most of its mass.