### Video Transcript

Using the equation that follows, which type of ionizing radiation, x, was used to bombard beryllium-9 and aid James Chadwick in the discovery of the neutron in 1932? (A) Positrons, (B) 𝛾-rays, (C) 𝛽-particles, or (D) 𝛼-particles.

The question tells us we are dealing with bombardment, the process by which a nucleus is bombarded with smaller particles to form a larger nucleus. In the equation given, beryllium-9 is being bombarded by unknown radiation x to form the larger nucleus of carbon-12 as well as a neutron. We will uncover the identity of ionizing radiation x using nuclide notation, where x is the chemical symbol for the nucleus or particle, A is the mass number, and where Z is the number of protons for nuclei or charge for particles.

We will also use the information that in a nuclear equation, the reactants and products must be equal in total mass number and total number of protons. Let’s first compare the total mass numbers of the reactants and products to determine the mass number of ionizing radiation x. While we do not know the mass number of x, we know that the mass number of beryllium-9 is nine. And the mass numbers of our products are 12 from carbon-12 and one from the neutron.

We can calculate the total mass number of the products by finding the sum of our mass numbers 12 and one, which is equal to 13. This means the total mass number of the reactants is also equal to 13. So, we can calculate the mass number of ionizing radiation x by subtracting nine from the total mass number, which gives us the missing mass number is equal to four. So, for the total mass number of the reactants to be equal to the total mass number of the products, ionizing radiation x must have a mass number of four.

Let’s repeat this process for total number of protons. Let’s start with the products where we know the total number of protons will be equal to the number of protons in carbon-12 plus the charge of a neutron, which is zero. Therefore, the total number of protons in the products is six plus zero, which equals six. We know that the total number of protons in the reactants must also equal six. So, we can solve for the number of protons in ionizing radiation x by using the number of protons in our reactant beryllium-9, which is four, which we can subtract from the total number of protons to find the number of protons in x. If we subtract six minus four, we find that ionizing radiation x contains two protons.

We now have the mass number and number of protons for ionizing radiation x. So now, let’s have a look at the answer choices to identify what type of radiation is occurring. Answer choice (A) positrons in nuclide notation are represented using the symbol for an electron with a mass number of zero and a charge of plus one. We can eliminate answer choice (A).

Answer choice (B) 𝛾-rays are represented using the 𝛾 symbol and are rays of energy, not particles, and therefore have no mass and no charge. We can eliminate answer choice (B). Answer choice (C) 𝛽-particles are represented using the symbol for an electron with a mass number of zero and a charge of minus one. We can also eliminate answer choice (C).

Answer choice (D) 𝛼-particles are represented using the chemical symbol for helium, He, as they are identical to a helium nucleus with a mass number of four and contain two protons. We can see that 𝛼 particles have the same mass number and number of protons as ionizing radiation x. Therefore, the type of ionizing radiation that was used to bombard beryllium-9 and aid James Chadwick in the discovery of the neutron in 1932 are (D) 𝛼-particles.