Neptunium isotopes, emissions from

A radioactive element is an element that disintegrates spontaneously with the emission of various rays and particles. Most commonly, the term denotes radioactive elements such as radium, radon (emanation), thorium, promethium, uranium, which occupy a definite place in the periodic table because of their atomic number. The term radioactive element is also applied to the various other nuclear species, (which arc produced by the disintegration of radium, uranium, etc.) including (he members of the uranium, actinium, thorium, and neptunium families of radioactive elements, which differ markedly in their stability, and are isotopes of elements from thallium (atomic number 81) to uranium (atomic number... 

After Abelson returned to Washington, McMillan pressed on. Unstable neptunium decayed by beta emission with a 2.3-day half-life he suspected it decayed to element 94. By analogy with uranium, which emits alpha particles naturally, element 94 should also be a natural alpha emitter. McMillan therefore looked for alphas with ranges different from the uranium alphas coming off his mixed luranium-neptunium samples. By autumn he had identified them. He tried some chemical separations, finding that the alpha-activity did not belong to an isotope of protactinium, uranium or neptunium. He was that close. 

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