Which decay process is represented by the following equation? (A) Positron emission, (B) beta emission, (C) alpha emission, (D) gamma emission, or (E) electron capture?
The question tells us that the equation given represents a decay process. Radioactive decay is the process by which an unstable nucleus spontaneously emits particles or radiation. The given equation shows that boron-8 is decaying to form beryllium-8, and a particle or form of energy is also emitted. In the first four answer choices, we see that the decay process is described as emission. Emission means that the distinguishing particle or radiation of the type of decay must be written as a product in the nuclear equation, while the final answer choice (E) uses the word capture, which means the particle, in this case an electron, is taken into the nucleus and must be written as a reactant in the nuclear equation.
It is worth noting that electron capture is still considered radioactive decay, since gamma rays and X-rays are emitted during this process. Since the particle being emitted is expressed here as a product, we can eliminate answer choice (E). Let’s identify our emitted particle using nuclide notation, where X represents the symbol of the element or particle, where A represents the mass number, which for nuclei is the sum of the protons and neutrons, and where Z represents the charge, which for nuclei is the number of protons. Our emitted particle’s symbol represents an electron with a mass number of zero and a charge of positive one.
Let’s compare what we know about our emitted particle to the remaining answer choices. Answer choice (A) positron emission occurs when a positron is emitted, which we can represent with an e representing an electron with a mass number of zero and a charge of positive one, while answer choice (B) beta emission occurs when a beta particle is emitted, which we can represent using an e for an electron with again a mass number of zero but a charge of negative one.
Next, answer choice (C) alpha emission, which occurs when an alpha particle is emitted from the nucleus. An alpha particle has the same composition as a helium nucleus. So, we can use the symbol He for helium, which has a mass number of four and an atomic number of two. And finally answer choice (D) gamma emission occurs when gamma rays are emitted, which are a form of radiation and therefore have no mass number and no charge.
We can see that the symbol for a positron matches the symbol for the particle being emitted in the given equation. So we know that this equation represents positron emission. Therefore, the correct answer is (A) positron emission.