Intensity follows the inverse square law, meaning it is proportional to 1 over the distance squared from the source. If the initial intensity from a source is I1 at a distance r, when the distance increases to 2r, the intensity decreases to I1/4, as the equation is proportional to 1/r^2. Intensity is a measurement of energy per unit area, measured in Watts per square meter, and decreases with distance from a point source as the same amount of energy spreads out over a larger spherical area.

1. Iα1
Intensity is proportional to 1 over the distance squared
(inverse square law).

2. As a mass moves away from a larger mass
with a radial gravitational field, the force
felt is proportional to one over the radius
squared.
So, if the initial radius is r and the force felt
is F, when the radius increases to
2r, because the equation is 1/r^2 the force
becomes F/4.
The same applies for the intensity of
radiation from a source.

3. 2 2
IX=IX
1 1 2 2
Therefore:
2
I1 = X2
2
I2 X 1

4. Intensity – I – is the energy that flows
through a certain area in a second. It is
measured in Watts per metre. W/m^2.
The gamma rays from a point source
spread out to cover a sphere shape.
The further the distance, the same
energy is spread out over a bigger
area, so the intensity decreases.