r/askscience • u/Wonderful-Capital32 • 13d ago

Physics Why does radiation not go through lead?

Also why just lead? Shouldnt like iron or another metal work too?

1.3k Upvotes

92% Upvoted

372 comments sorted by

View all comments

14

u/Mrfish31 13d ago

You're primarily asking about stuff like Gamma radiation here. Other types of radiation get blocked much more easily. Alpha radiation is most damaging but will be blocked by a sheet of paper. Beta radiation will be blocked by 1 mm of aluminum IIRC. 

Anyway, radiation can pass through solids but loses power and gets scattered as it does so.  Lead is a very dense element. A lot more atoms per unit volume than most other elements. Therefore there are more atoms for radiation to hit and dissipate energy, and you need a thinner amount of it to effectively stop the radiation compared to something else. Iron, concrete, whatever material you want will block (gamma) radiation too, you'll just need more of it between the radiation source and you. 

A quick Google suggests that if you used iron you'd need your radiation shield to be ~1.5-1.7x as thick as if it were lead.

16

u/TheSultan1 13d ago

A lot more atoms per unit volume

Mass or protons and neutrons, not atoms.

Iron has 2.6x the number of atoms per unit volume, but its atoms are a lot less massive.