At the end of the actinium nuclear decay series, polonium-215 decays in an alternating sequence of alpha and beta decays. What are the nuclei produced in the nuclear decay sequence listed in order of formation from first to last?

Question

At the end of the actinium nuclear decay series, polonium-215 decays in an alternating sequence of alpha and beta decays.  What are the nuclei produced in the nuclear decay sequence listed in order of formation from first to last?

Quizplus · Accepted Answer

11ecba2d_1247_9bca_a3bf_a38a13ad3829_MD0008_00 Radioactivity is the spontaneous emission of radiation (photons or particles) from an unstable atomic nucleus. Although several types of nuclear radiation exist, the three most common are alpha decay, beta decay, and gamma emission. During alpha decay, an unstable nucleus ejects an alpha (α) particle consisting of 2 protons and 2 neutrons (a helium-4 nucleus without its electrons). The nucleus formed following alpha decay has a mass number that is 4 units less and an atomic number that is 2 units less than the nucleus that underwent alpha decay. Beta decay can occur in three forms: β⁻ decay (electron emission), β⁺ decay (positron emission), and electron capture. In all three forms, the mass number is unchanged, whereas the atomic number either increases (β⁻ decay) or decreases (β⁺ decay) by 1 unit. Consequently, alpha decay of an atom of polonium-215 would form lead-211 by the following nuclear reaction: 11ecba2d_1247_9bcb_a3bf_c1872ffac112_MD0008_00 Subsequent β⁻ decay of the ²¹¹Pb nucleus would eject a nuclear electron (e⁻) and an antineutrino 11ecba2d_1247_9bcc_a3bf_f5c20d9ca950_MD0008_00 , yielding a bismuth nucleus with the same mass number: 11ecba2d_1247_9bcd_a3bf_7754b6fad578_MD0008_00 Alpha decay of the ²¹¹Bi nucleus would, in turn, produce a thallium-207 nucleus: 11ecba2d_1247_c2de_a3bf_931b8529e854_MD0008_00 Bi83211→Tl81207+He24 Finally, β⁻ decay of the ²⁰⁷Tl nucleus would give a stable lead-207 nucleus: 11ecba2d_1247_c2df_a3bf_fb0325378366_MD0008_00 Tl81207→Pb+e-82207+ν¯e Therefore, the nuclei produced in the nuclear decay sequence listed in order of formation is: 11ecba2d_1247_c2e0_a3bf_2b50f4fa4341_MD0008_00 Po84215→αPb82211→β-Bi83211→αTl81207→β-Pb82207 (Choices A and D) These sequences show a decrease in the atomic number after each β⁻ decay, but in a β⁻ decay, the atomic number increases 1 unit. Also, the atomic number of polonium is 84 rather than 88. (Choice C) This sequence shows an increase in the atomic number following each alpha decay. However, in alpha decay, the atomic number should decrease by 2 units and the mass number should decrease by 4 units. Educational objective: In alpha decay, the mass number of an atomic nucleus decreases by 4 units and the atomic number decreases by 2 units. In all forms of beta decay, the mass number of an atomic nucleus remains unchanged, but the atomic number increases (β⁻ decay) or decreases (β⁺ decay) by 1 unit.

At the End of the Actinium Nuclear Decay Series, Polonium-215