Question

1, In an admixture of particles of different species, all with same kinetic energy

		A, lighter particles have the Bragg peak in deeper interiors
		B, Heavier particles have the Bragg peak in deeper interiors
		C, Bragg peak location is independent of the particles species

2, In a medium of chemical compound

		A, The stopping power does not depend on the relative composition of different elements
		B, The stopping powerof an element in a compound is proportional to the fractional weight of the element in the mediuim
		C, The stopping powerof an element in a compound is proportional to the atomic number of the element in the medium
		D, The stopping powerof an element in a compound is proportional to the mass number of the element.

Answer 1

1. Option (B)

Explanation - For lighter particles such as photons, most of the radiation is delivered only a short depth. The particle gradually loses this energy after actively interacting more with outer cells and drops only a small remaining dose of ionizing radiation on the deeper diseased cells.

On the contrary, a heavy particle such as a proton gradually loses its speed as it interacts with human tissue. It is controlled more easily and delivers maximum dose at a desired and precise depth. The absorbed dose increases very gradually with greater depth and lower speed, suddenly rising to a peak that we call as the Bragg peak. Hence heavier particles have Bragg peak in deeper interiors.

2. Option (C)

Explanation - The stopping power is of a material for an ion is defined as the rate of change of the energy of a particle with material thickness.

The measured stopping powers show a dependence on particle velocity and on the atomic number of the stopping element.