Problem 14 - Chemistry: The Central Science

Question

What particle is produced during the following decay processes: (a) sodium-24 decays to magnesium-24; (b) mercury-188 decays to gold-188; (c) iodine-122 decays to xenon-122; (d) plutonium-242 decays to uranium-238?

Step-by-Step Solution

Answer

In the given decay processes, the following particles were produced: (a) Sodium-24 to Magnesium-24: Beta plus decay (positron, \(\beta^+\)) (b) Mercury-188 to Gold-188: Beta minus decay (electron, \(\beta^-\)) (c) Iodine-122 to Xenon-122: Beta plus decay (positron, \(\beta^+\)) (d) Plutonium-242 to Uranium-238: Alpha decay (alpha particle, \(\alpha\))

Step 1: Compare atomic and mass numbers

Sodium (Na) has atomic number 11, so sodium-24 is written as \(^{24}\text{Na}\), where 24 is the mass number. Magnesium (Mg) has atomic number 12, so magnesium-24 is written as \(^{24}\text{Mg}\). To identify the particle emitted, we need to compare the mass and atomic numbers of the parent and daughter nucleus. Since the mass number stays the same at 24 and the atomic number increases by 1, this implies that a beta plus particle (anti-electron, or a positron, denoted as \(\beta^+\)) was emitted. This process is called beta plus decay. (b) Mercury-188 decays to Gold-188

Step 2: Compare atomic and mass numbers

Mercury (Hg) has atomic number 80, so mercury-188 is written as \(^{188}\text{Hg}\). Gold (Au) has atomic number 79, so gold-188 is written as \(^{188}\text{Au}\). In this decay, the mass number remains the same, and the atomic number decreases by 1. This implies emission of a beta minus particle (electron, denoted as \(\beta^-\)). This process is called beta minus decay. (c) Iodine-122 decays to Xenon-122

Step 3: Compare atomic and mass numbers

Iodine (I) has atomic number 53, so iodine-122 is written as \(^{122}\text{I}\). Xenon (Xe) has atomic number 54, so xenon-122 is written as \(^{122}\text{Xe}\). In this decay, the mass number remains the same, and the atomic number increases by 1. This implies emission of a beta plus particle (positron, denoted as \(\beta^+\)). This process is called beta plus decay. (d) Plutonium-242 decays to Uranium-238

Step 4: Compare atomic and mass numbers

Plutonium (Pu) has atomic number 94, so plutonium-242 is written as \(^{242}\text{Pu}\). Uranium (U) has atomic number 92, so uranium-238 is written as \(^{238}\text{U}\). In this decay, the mass number decreases by 4, and the atomic number decreases by 2. These changes imply the emission of an alpha particle (consisting of 2 protons and 2 neutrons, denoted as \(\alpha\)). This process is called alpha decay.

Step 5: Summary

In the given decay processes, the following particles were produced: (a) Sodium-24 to Magnesium-24: Beta plus decay (positron, \(\beta^+\)) (b) Mercury-188 to Gold-188: Beta minus decay (electron, \(\beta^-\)) (c) Iodine-122 to Xenon-122: Beta plus decay (positron, \(\beta^+\)) (d) Plutonium-242 to Uranium-238: Alpha decay (alpha particle, \(\alpha\))

Key Concepts

Beta Plus Decay

Beta Plus Decay, also called positron emission, is a type of radioactive decay where a proton inside the nucleus is transformed into a neutron while releasing a positron and a neutrino. For example, when sodium-24 decays to magnesium-24, it emits a positron, which is denoted as \(\beta^+\). This is because sodium-24 has one more proton in its nucleus than magnesium-24. Hence, the process reduces the atomic number by one but leaves the mass number unchanged.

Positron emission is a natural way for isotopes with a high proton-to-neutron ratio to stabilize. Since the positron is the antimatter counterpart of the electron, its interaction with an electron leads to annihilation, releasing energy in the form of gamma rays.

Beta Minus Decay

Beta Minus Decay, commonly referred to as electron emission, is a decay process by which a neutron in an atomic nucleus is transformed into a proton with the simultaneous emission of an electron and an anti-neutrino. For example, mercury-188 undergoes beta minus decay to become gold-188. The atomic number increases by one, indicating the addition of a proton, but the mass number remains the same.

This type of decay occurs in isotopes with an excess of neutrons, allowing them to achieve a more stable configuration. Beta minus decay is significant in the context of nuclear physics, as it is a common decay mode for many radioactive isotopes.

Alpha Decay

Alpha Decay is a nuclear decay process where an unstable atom ejects an alpha particle, which consists of two neutrons and two protons (the same as a helium-4 nucleus). This results in the transformation of the atom into a different element with a mass number decreased by four and an atomic number decreased by two. An example of alpha decay is the transition of plutonium-242 to uranium-238.

Alpha decay typically occurs in heavy elements that have large atomic numbers, and it is a process that reduces the number of particles in the nucleus, leading to a more stable atomic configuration. Alpha particles, due to their relatively larger size, have low penetration depth and can be stopped by a piece of paper or human skin.

Radioactive Isotopes

Radioactive Isotopes, or radioisotopes, are variants of elements with unstable combinations of neutrons and protons that result in excess energy in their nuclei. This excess energy can lead to nuclear decay, with the nucleus releasing particles or electromagnetic radiation to achieve a more stable state. Radioisotopes can undergo various types of decay processes, such as alpha decay, beta minus decay, and beta plus decay, transforming themselves into more stable isotopes.

Radioactive isotopes have numerous practical applications in fields like medicine, industry, and archaeology. They are used in cancer treatments, radiometric dating, and as tracers in biochemical research. Understanding and managing nuclear decay processes is crucial for safely utilizing these isotopes in different areas.