MadSci Network: Engineering

Re: Is Gold better than lead as a radiation shield.

Date: Fri Aug 11 16:53:49 2000
Posted By: William Lorenzen, Staff, Radiation Safety, Children's Hospital
Area of science: Engineering
ID: 964968145.Eg

To answer the question gold would be slightly less effective than lead as a 
gamma/x-ray sheild.  No activation occurs with these interactions.  Only 
with neutrons do you see activation.

The sheilding of radiation is based on the type and energy of the 
radiation.  The alpha and beta radiations are particulate forms of 
radiation.  They have mass and an associated electrical charge.  Gamma and 
x-rays are electomagnetic radiation.  It has no mass or charge.

Simply put for alpha radiation it can not travel but a few millimeters in 
air and even less in other more dense materials.  A few sheets of paper 
will stop alpha particles.

Beta radiation is simply an electron and it can travel further in air and 
materials.  Most common beta emmiters are stopped by a few centimeters of 
wood or plastic.  

Gamma & x-ray are the most penetrating forms of these radiations.  Because 
they are forms of elecrtomagnetic radiation they do not directly "collide" 
with other materials to be stopped.  Their interaction is based on the 
probability that they will interact with the atoms contained in the 
material they are passing through.  To increase the probability they will 
interact you need to increase the atom density of the material they are 
passing through.  Lead has a high atomic number and thus has a high atom 
density so it makes a good gamma/x-ray sheild.  The higher the atomic 
number the better the sheild.  Uranium is a great sheild for gamma/x-ray 
however it is naturally radioactive so it is not often used except is the 
most exstream cases.

So if you look up atomic numbers you can rank the effectiveness of 
materials as shields for gamma/x-rays.

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