Chemistry/Physics Question?

Question

I am working on my college chemistry class and I am stuck on these questions.

At 2.00 m from a radioactive source the intensity of its gamma radiation is 307 roentgen. What is the intensity at a distance of 37.6m?

At 3.00 m from a radioactive source the intensity of its gamma radiation is 230 roentgen. How far away would we need to be to breduce the intensity to 5.19 roentgen?

Answer 1

Intensity of radiation is inversely proportional to the square of the distance.

I=k/(r^2) then
k= I(r^2)=(307(4))=1228 roentgen meters square

Problem #1

I=I(r^2)/(R^2)= 1228/(37.6 ^2)=0.87 roentgen

Problem #2
Similarly determine k
k=230(3^2)=230(9)=2070 roentgen meters square

R=SQRT(k/I)= SQRT (2070/(5.19))=20 meters

Different values for k signify sources of different intensity (radioactivity).