Optimizing Lead Shielding for Gamma Radiation Protection

[NJV]

What thickness of lead is needed to neutralize brief exposure to gamma radiation, or at least reduce it to below 5 gray?

 

[DaleSwanson]

You need to provide more info about the source or strength of the gamma rays.

 

[pallidin]

Here's a link to provide some more info:

http://en.wikipedia.org/wiki/Radiation_shield

 

[DeShark]

What thickness of lead is needed to neutralize brief exposure to gamma radiation, or at least reduce it to below 5 gray?

As has been stated, you need to know the intensity and energy of the x-rays (or gamma rays). Essentially, the intensity of radiation as it passes through a thickness of lead diminishes exponentially with the thickness of lead.

i.e. I(x) = I(0) exp (- m.x) + c

where I(x) is the intensity as a function of x, the thickness of lead and m is what is known as the attenuation co-efficient of lead. c being the background radiation.

However, there's a problem, because m is a function of the energy of the source. You should be able to find an attenuation coefficient vs energy diagram for lead somewhere on the net.

If you have a specific source, then it will emit certain energies with a certain intensity. You'd have to find out how much each was attenuated to find the diminished activity and finally work out the number of grays in the usual manner.

 

[NJV]

Thank you for the information. The equation proves useful.

 

[Bob S]

The most penetrating x-ray (or photon) energy is about 1 or 2 MeV. Below about 0.5 MeV, the photoelectric effect off of bound electrons is significant, and above 2 MeV, pair production (of an electron and positron) becomes significant. I seem to recall that 2 inches of lead reduces Cobalt 60 radiation by about a factor of 10.

 

[Bob S]

The most penetrating x-ray (or photon) energy is about 1 or 2 MeV. Below about 0.5 MeV, the photoelectric effect off of bound electrons is significant, and above 2 MeV, pair production (of an electron and positron) becomes significant. I seem to recall that 2 inches of lead reduces Cobalt 60 radiation by about a factor of 10.

Cobalt 60 radiation has two gammas, 1.1 MeV and 1.3 MeV.

The lead gamma absorption cross section for 1 to 2 MeV gammas is in the range of 20 barns. For 50 KeV, the photoelectric cross section is a few kilobarns (compared to a few barns for carbon).