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Ch.21 - Radioactivity & Nuclear Chemistry
Chapter 21, Problem 41b

Predict a likely mode of decay for each unstable nuclide. b. Al-34

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Identify the atomic number of aluminum (Al), which is 13.
Determine the neutron number of Al-34 by subtracting the atomic number from the mass number: 34 - 13 = 21 neutrons.
Compare the neutron-to-proton ratio to the stable isotopes of aluminum. Al-27 is stable with a neutron-to-proton ratio of 1.08, while Al-34 has a ratio of 21/13 ≈ 1.62.
Recognize that a high neutron-to-proton ratio suggests beta decay (β⁻ decay) as a likely mode of decay, where a neutron is converted into a proton, emitting a beta particle (electron) and an antineutrino.
Conclude that Al-34 is likely to undergo beta decay to increase its stability by converting a neutron into a proton, resulting in a new element with an atomic number of 14 (silicon).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Nuclear Decay

Nuclear decay is the process by which an unstable atomic nucleus loses energy by emitting radiation. This can occur in various forms, including alpha decay, beta decay, and gamma decay. Each type of decay results in the transformation of the original nuclide into a different element or isotope, often leading to a more stable configuration.
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Alpha Decay

Alpha decay is a type of radioactive decay in which an unstable nucleus emits an alpha particle, consisting of two protons and two neutrons. This process decreases the atomic number by two and the mass number by four, resulting in the formation of a new element. Alpha decay typically occurs in heavy nuclides, where the strong nuclear force is insufficient to hold the nucleus together.
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Beta Decay

Beta decay is a form of radioactive decay in which a neutron in an unstable nucleus is transformed into a proton, emitting a beta particle (an electron or positron) in the process. This increases the atomic number by one while keeping the mass number unchanged, resulting in the formation of a new element. Beta decay is common in nuclides that have an excess of neutrons.
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