5.2.3 Radioactive decay (3)
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1.
Consider a radioactive isotope that undergoes beta decay. Draw a simple diagram to illustrate the process, clearly labelling the reactants and products. In your diagram, indicate the change in the number of protons and neutrons in the nucleus. Also, state the charge and mass of the emitted beta particle.
Diagram:
| Reactant: Nucleus of a radioactive isotope (e.g., Carbon-14) |
| Product: Nucleus of a different isotope (e.g., Nitrogen-14) + Beta particle (electron) |
Change in Protons and Neutrons: The number of protons increases by 1 (from the original isotope) and the number of neutrons decreases by 1. The total number of nucleons (protons + neutrons) remains the same.
Beta Particle: The emitted beta particle is a high-speed electron. It has a charge of -1 (negative) and a mass very close to that of an electron (approximately 9.11 x 10-31 kg). It is often represented as β-.
2.
A scientist observes that a particular element has isotopes with very different masses. Explain why the heavier isotopes of this element are likely to be radioactive. Consider the forces acting within the nucleus in your explanation.
The heavier isotopes of an element are likely to be radioactive because the strong nuclear force is less effective at holding together a nucleus with a large number of protons and neutrons. As the mass number (number of protons and neutrons) increases, the electrostatic repulsion between the positively charged protons also increases significantly. This makes the nucleus increasingly unstable. The strong nuclear force, which attracts protons and neutrons, must overcome the electrostatic repulsion to maintain stability. However, for very heavy nuclei, the electrostatic repulsion can overwhelm the strong nuclear force, leading to the nucleus being unstable and undergoing radioactive decay. This decay process reduces the number of protons and neutrons, bringing the nucleus closer to a more stable configuration. Therefore, heavier isotopes are more prone to radioactive decay.
3.
Alpha decay and beta decay are types of radioactive decay. State, with a clear explanation, how the nucleus changes during each of these processes. Your answer should consider the resulting particle emitted and the change in atomic number and mass number.
During alpha decay, the nucleus emits an alpha particle (which is a helium nucleus, 4He). This process results in a decrease of 2 in the atomic number and a decrease of 4 in the mass number. The nucleus essentially transforms into a new element with a lower atomic number. For example, Uranium-238 (atomic number 92) decays into Thorium-234 (atomic number 90) by emitting an alpha particle.
During beta decay, a neutron within the nucleus transforms into a proton, emitting an electron (beta particle) and an antineutrino. This process results in an increase of 1 in the atomic number and no change in the mass number. The nucleus changes into a new element with a higher atomic number. For example, Carbon-14 (atomic number 6) decays into Nitrogen-14 (atomic number 7) by emitting a beta particle.