Distinguish between an X-ray image of a body structure and a CT scan.
Data for the linear absorption (attenuation) coefficient 
of X-ray radiation of energy 
are given in figure I below.
I
A parallel X-ray beam is incident on a copper filter, as shown in figure II below.
II
The intensity of the incident beam is 
.
Calculate the thickness of copper required to reduce the intensity of the emergent beam to 
.
An aluminium filter of thickness 
is now placed in the X-ray beam, together with the copper filter in (i). Calculate the fraction of the incident intensity that emerges after passing through the two filters.
Express your answer in (ii) as a gain in decibels (
).
.
.
