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Write the complete decay equation for the given nuclide in the complete $^A_Z\textrm{X}_N$ notation. Refer to the periodic table for values of Z:
$\alpha$ decay producing $^{228}\textrm{Ra}$. The parent nuclide is nearly 100% of the natural element and is found in gas lantern mantles and in metal alloys used in jets ($^{228}\textrm{Ra}$ is also radioactive).
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OpenStax College Physics Solution, Chapter 31, Problem 27 (Problems & Exercises) (1:01)

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This is College Physics Answers with Shaun Dychko. Thorium undergoes <i>α</i>-decay by creating an <i>α</i>-particle which consists of two protons and two neutrons. And so the daughter nuclide of this decay is going to have two fewer protons than the thorium and so that is 90 minus 2 making 88 and that's the element radium which has this atomic number 88 and the number of neutrons decreases from 42 to 40 and the number of nucleons in this particular nuclide is 228. But this 228 plus the 4 nucleons in the <i>α</i>-particle totals 232 so that is conserved, the number of nucleons is conserved. And there's nothing else to consider here in terms of conservation laws because there's no charges being produced and so on. So there we go. That's the <i>α</i>-decay of thorium into radium.