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Ch.21 - Nuclear Chemistry
Chapter 21, Problem 19b

Predict the type of radioactive decay process for the following radionuclides: (b) 6829Cu.

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1
Step 1: Understand the concept of radioactive decay. Radioactive decay is a process by which an unstable atomic nucleus loses energy by radiation. There are three common types of radioactive decay: alpha decay, beta decay, and gamma decay.
Step 2: Identify the type of radioactive decay. The type of decay can be predicted by looking at the neutron-to-proton ratio. If the ratio is too high, the nucleus will undergo beta decay to decrease the number of neutrons. If the ratio is too low, the nucleus will undergo positron decay or electron capture to increase the number of neutrons.
Step 3: Look at the atomic number and mass number of the given radionuclide. For <sup>68</sup><sub>29</sub>Cu, the atomic number is 29 and the mass number is 68.
Step 4: Calculate the neutron-to-proton ratio. The number of neutrons is the mass number minus the atomic number. So, for <sup>68</sup><sub>29</sub>Cu, the number of neutrons is 68 - 29 = 39. The neutron-to-proton ratio is 39/29.
Step 5: Compare the neutron-to-proton ratio with the stable range. For lighter elements (atomic number less than 20), the stable neutron-to-proton ratio is about 1. For heavier elements, the ratio is slightly greater than 1. Since the neutron-to-proton ratio for <sup>68</sup><sub>29</sub>Cu is greater than 1, it is likely to undergo beta decay to decrease the number of neutrons.

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Key Concepts

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

Radioactive Decay

Radioactive 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 characterized by the type of particle or energy released. Understanding the nature of the radionuclide helps predict the decay mode it will undergo.
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Rate of Radioactive Decay

Alpha and Beta Decay

Alpha decay involves the emission of an alpha particle (two protons and two neutrons), resulting in a decrease in atomic number by two and mass number by four. Beta decay occurs when a neutron is transformed into a proton, emitting a beta particle (electron or positron), which increases the atomic number by one. The type of decay depends on the neutron-to-proton ratio in the nucleus.
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Stability of Nuclei

The stability of a nucleus is influenced by the balance between protons and neutrons, known as the neutron-to-proton ratio. Nuclei with too many or too few neutrons compared to protons tend to be unstable and undergo radioactive decay to achieve a more stable configuration. For copper-68, analyzing its neutron-to-proton ratio helps determine its decay process.
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