Calculating Absorber Thickness for Radiation Intensity Reduction - x=0.693/(miu)

[asdf1]

for the following question:
show that the thickness x of an absorber required to reduce the intensity of radiation by a factor of 2 is given by x=0.693/(miu)

my problem:
what is meant by "a factor of 2"?

 

[Tide]

It means that the energy is reduced to one half its starting value. BTW - 0.693 looks suspiciously close to \ln 2. ;)

 

[asdf1]

thanks! :)
so usually, factor=mutiple?