A deuterium nucleus and a tritium nucleus fuse together to form a helium nucleus and a particle X - AQA - A-Level Physics - Question 30 - 2019 - Paper 2

To determine the missing particle X, we need to consider the conservation of nucleons (protons and neutrons) and charge during the fusion process.

1. Identify the nucleons and charge before the reaction:

   • Deuterium nucleus (2H) has 1 proton and 1 neutron.
   • Tritium nucleus (3H) has 1 proton and 2 neutrons.
   • Total before fusion: 2 protons and 3 neutrons.

2. Identify the products of the reaction:

   • A helium nucleus (4He) has 2 protons and 2 neutrons.
   • The total after fusion must still equal 2 protons and 3 neutrons.

3. Calculate the nucleons for X:

   • Helium contributes 2 protons and 2 neutrons.
   • To balance the nucleon count:
     • Protons: 2 (Helium) + X(protons) must equal 2, suggesting that X must have 0 protons.
     • Neutrons: 2 (from Helium) + X(neutrons) must equal 3, suggesting that X must have 1 neutron.

From the particle composition, we can conclude that particle X is a neutron. Hence, the answer is:

• X is a Neutron (B).