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What is the half-life of neptunium-237?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — transuranium element Modern version of the periodic table of the elements (printable).

The stablest isotope of neptunium, known as neptunium-237, has a half-life of 2,144,000 years.1