# IB DP Physics E.5 Fusion IB Style Question Bank HL Paper 1

### Question

A gamma ray can split into an electron and a positron when it passes through certain materials. Which process describes this phenomenon?

A. Pair production

B. Pair annihilation

C. Nuclear fission

Ans:A

The phenomenon in which a gamma ray can split into an electron and a positron when passing through certain materials is described as “Pair production.” Pair production is a process in which a gamma ray of sufficient energy is converted into an electron and a positron. A fundamental law of mechanics, given by Newton, is that in any process total linear (as well as angular) momentum remains unchanged.

### Question

What is the variation of nuclear density $$\rho$$ with nucleon number $$A$$ ?

Ans:B

The nuclear density ($$\rho$$) in an atomic nucleus generally increases with increasing nucleon number ($$A$$). This relationship is described as a direct or positive correlation. As the number of protons (Z) and neutrons (N) in the nucleus increases, the total nucleon number (A = Z + N) also increases.

The nuclear density can be defined as the mass of the nucleus divided by its volume. Mathematically:

$$\rho = \frac{M}{V}$$

As $$A$$ increases, the mass ($$M$$) of the nucleus increases because it contains more protons and neutrons. The volume ($$V$$) of the nucleus remains relatively constant for a wide range of nucleon numbers. Therefore, the increase in mass with increasing $$A$$ leads to an increase in nuclear density ($$\rho$$).

So, the nuclear density ($$\rho$$) generally increases with nucleon number ($$A$$) in a positively correlated manner.

### Question

The graph shows the relationship between binding energy per nucleon and nucleon number. In which region are nuclei most stable?