Chemistry · Structure Of Atom · NEET
Gamma rays have the highest penetrating power. The full order from lowest to highest is: alpha < beta < gamma. Alpha is the weakest and gamma is the strongest. NCERT gives the exact ratio: beta is about 100 times more penetrating than alpha, and gamma is about 1000 times more penetrating than alpha. For NEET, always remember gamma > beta > alpha.
An alpha particle is a helium nucleus, so it is big and heavy and carries a +2 charge. Because it is large and highly charged, it collides with atoms very often and pulls electrons off them (strong ionisation). Every collision makes it lose energy fast, so it stops after a very short distance. That is why even a sheet of paper or your skin can stop it. Being a strong ioniser and being a weak penetrator go together.
Gamma rays are high-energy electromagnetic radiation (like X-rays), not particles. They have no charge and no mass. Because they have no charge, they do not get pulled by the electrons or nucleus of atoms, so they pass through matter easily without many collisions. They ionise very weakly, so they lose energy slowly and travel deep. This is why you need thick lead or concrete to stop them.
Alpha rays are stopped by a sheet of paper (or a few cm of air, or your skin). Beta rays pass through paper but are stopped by a thin sheet of aluminium (a few mm). Gamma rays pass through aluminium and need thick lead or thick concrete to be reduced. This is a very common NEET matching question, so memorise: paper stops alpha, aluminium stops beta, lead stops gamma.
No, they are opposite. Ionising power is how strongly a ray knocks electrons off atoms. The order of ionising power is the reverse: alpha > beta > gamma. A strong ioniser (alpha) loses energy fast, so it does NOT penetrate far. A weak ioniser (gamma) keeps its energy, so it penetrates far. Rule to remember: more ionising means less penetrating.
Yes. Alpha has the most charge (+2) and the most mass (helium nucleus), so it interacts most and penetrates least. Beta has less charge (-1) and very little mass (electron), so it goes further. Gamma has zero charge and zero mass, so it interacts least and penetrates most. The chain is simple: more charge and mass means more collisions means less depth.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Gamma > Beta > Alpha. NCERT states beta is about 100 times more penetrating than alpha, and gamma is about 1000 times more penetrating than alpha.
Alpha > Beta > Gamma. This is the exact reverse of penetrating power. The most ionising ray penetrates the least.
About 1000 times, according to NCERT. Beta is about 100 times more penetrating than alpha.
Gamma has no charge and no mass, so it barely interacts with atoms and passes deep into the body. Alpha is big and +2 charged, so it collides a lot and is stopped by the skin itself.
Gamma, because its high penetrating power lets it reach internal organs from outside. Alpha is dangerous mainly if swallowed or inhaled, because outside the body it is stopped by skin.
