Caesium is a soft silvery-gold metal. Caesium-137 is one of the by-products of nuclear fission process in nuclear bombs, nuclear weapon testing, and nuclear reactor operations. It was discovered by and an undergraduate at UC Berkely, Margret Melhase in 1941. Historically, the most important use for cesium has been in research and development, primarily in chemical and electrical applications. Caesium-137 is water-soluble and extremely toxic in minute amounts. Once released into the environment, it remains present for many years as its radiological half-life is 30.07 years. It can cause cancer 10, 20 or 30 years from the time of ingestion, inhalation or absorption provided sufficient material enters the body. Cesium-137 is widely used throughout the construction industry for level, moisture, and thickness gauging applications. Cesium is also commonly used in medical research & treatment and oil well drilling.