Question

Statement- 1 : The ionising power of $\beta$- particle is less compared to $\alpha$- particle but their penetrating power it more.
Slatement- 2 : The mass of $\beta$- particle is less than the mass of $\alpha$- particle.

• A. Both the statements are true and Statement 2 is correct explanation for Statement 1.
• B. Both the statements are true but Statement 2 is not the correct explanation for Statement 1.
• C. Statement 1 is true but Statement 2 is false.
• D. Statement 2 is true but Statement 2 is false.

Answer 1

The correct option is B Both the statements are true but Statement 2 is not the correct explanation for Statement 1.

The penetrating power of alpha rays, beta rays, and gamma rays varies greatly. Alpha particles can be blocked by a few pieces of paper. Beta particles pass through paper but are stopped by aluminum foil. Gamma rays are the most difficult to stop and require concrete, lead, or other heavy shielding to block them.

Alpha particles are strongly ionising but can be stopped by paper or skin.

Beta particles are also strongly ionising (perhaps 1 beta particle will cause 100 ionisations).

Gamma rays are very poor at ionising (about 1 to 1) but they are very difficult to stop (they are very penetrating). As they are not good ionisers, they are less dangerous to life.

Gamma rays are photons, so formally massless.
Beta decay typically releases an electron or positron and a neutrino (which for all practical purposes is massless). The mass of an electron in (amu) is : 5.49e-4 amu.
An alpha particle is a helium nucleus (2 protons, 2 neutrons). Its mass in amu is: 4.0012 amu.