Nuclear Physics

(a) 1. Element for shielding aprons:
The element used for lining radiation-shielding aprons is Lead (Pb).
(a) 2. Reason for preference:
Lead is preferred for radiation shielding for two main reasons: - High Density and High Atomic Number: Lead has a very high density and a large number of electrons per atom. This dense structure is extremely effective at absorbing the energy of high-energy photons like gamma rays and X-rays, significantly reducing their intensity. - Cost-Effectiveness and Malleability: It is relatively inexpensive, abundant, and easy to work with, making it practical for constructing shielding materials.
(b) 1. Type of nuclear radiation:
We are given two clues:
1. The radiation does not alter the mass number (A).
2. The radiation is deflected by a magnetic field, which means it consists of charged particles.
Let's analyze the common types of radiation:
- Alpha ( ) decay: Emits a helium nucleus ( ). It is charged but changes the mass number by -4. So, it's not alpha.
- Gamma ( ) decay: Emits a high-energy photon. It does not change the mass number but is not charged, so it is not deflected. So, it's not gamma.
- Beta ( ) decay: Emits an electron ( ). An electron is a charged particle, so it will be deflected. Its mass number is 0, so emitting it does not alter the mass number of the nucleus. This matches both conditions. Therefore, the radiation is a Beta particle.
(b) 2. Equation for the decay:
In beta decay, a neutron within the nucleus converts into a proton and an electron. The electron is ejected as a beta particle.
- The mass number (A) remains unchanged: .
- The atomic number (Z) increases by 1: .
- The element with atomic number 12 is Magnesium (Mg).
The balanced nuclear equation is:
(where is an electron antineutrino, often omitted in introductory-level equations). The required equation is: .

Here are two key differences between nuclear fission and nuclear fusion:
1. Nature of the Process:
- Nuclear Fission: It is the process where a single heavy, unstable nucleus (like Uranium-235) splits into two or more smaller, lighter nuclei.
- Nuclear Fusion: It is the process where two or more very light nuclei (like hydrogen isotopes) combine or 'fuse' together to form a single, heavier nucleus.
2. Conditions Required:
- Nuclear Fission: This process can occur at normal temperatures and pressures. It can be initiated by bombarding a heavy nucleus with a slow-moving neutron, leading to a chain reaction.
- Nuclear Fusion: This process requires extremely high temperatures (of the order of K) and immense pressure to overcome the strong electrostatic repulsion between the positively charged nuclei and force them to fuse.

The force experienced by a charged particle moving in a magnetic field is given by . The subsequent acceleration is . The amount of deviation or the radius of the circular path depends on the charge-to-mass ratio ( ).
- Alpha particles ( ) are relatively heavy (4 amu) and have a charge of +2e.
- Beta particles ( ) are extremely light (approx 1/1836 amu) and have a charge of -1e.
The charge-to-mass ratio for a beta particle is much larger than for an alpha particle. Due to their much larger mass (and thus inertia), alpha particles are deflected much less than beta particles for a given magnetic field and velocity. Therefore, alpha radiation deviates the minimum.