by nonphysical
 P: 15 [b]1. If the radiationlevel is 400mGy/hr at 2m from a point radiation source, what will be the radiation level at 6m [b]2. I figured that if the radiation was 400mGy/hr at 2m it have been 1600mGy/hr when emmitted from the sorce. [b]3. If the inverse square law works like at 2m from the source it covers an area of 4m2 and at 3m it covers an area of 9m2 i figured that at 6m it covers anarea of 36m2 so the radiation would be less by the same proportion?
P: 596
 Quote by nonphysical [b]1. If the radiationlevel is 400mGy/hr at 2m from a point radiation source, what will be the radiation level at 6m [b]2. I figured that if the radiation was 400mGy/hr at 2m it have been 1600mGy/hr when emmitted from the sorce. [b]3. If the inverse square law works like at 2m from the source it covers an area of 4m2 and at 3m it covers an area of 9m2 i figured that at 6m it covers anarea of 36m2 so the radiation would be less by the same proportion?
Hi,

Do you want to determine the radiation level 6 m from the source ? If yes, then you no need to find the source strength (just to avoid confusion with units!).
May I know how did you get the source strength as 1600 mGy/hr?
Any why dont you take pi (=3.14) value in your computation for finding the source strength?
 P: 15 Hi, Thanks for the reply Yes i want to know the radiation level at 6m The only thing i know is the level is 400mGy/hr at 2m from a point radiation source. I do not know how to calculatate the rest. I thought 400mGy/hr at 2m might be a quarter of the original strength??
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P: 26,167

hi nonphysical!
 Quote by nonphysical 2. I figured that if the radiation was 400mGy/hr at 2m it have been 1600mGy/hr when emmitted from the sorce.
i'm sorry, this is nonsense …

and anyway you don't need to find the source strength
 3. If the inverse square law works like at 2m from the source it covers an area of 4m2 and at 3m it covers an area of 9m2 i figured that at 6m it covers anarea of 36m2 so the radiation would be less by the same proportion?
(try using the X2 icon just above the Reply box )

as Rajini points out, the surface area of a sphere is 4πr2, not r2

but the important point is the ratio

all you need say is, if you double the radius, you quadruple the area, so if you triple the radius (3 = 6/2), then … ?
P: 596
 Quote by nonphysical Hi, Thanks for the reply Yes i want to know the radiation level at 6m
Okay 6 m away from source
 The only thing i know is the level is 400mGy/hr at 2m from a point radiation source.
 I do not know how to calculatate the rest. I thought 400mGy/hr at 2m might be a quarter of the original strength??
No!
Apply inverse square law first to 2 m distance. From this you get the source strength. You no need to compute and get numerical value..just substitute in the inverse square formula with their units. Then for 6 m distance again using inverse square law substitute for source strength that you obtained for 2 m and get your answer in mG/hr.
 P: 15 Thanks Tiny-Tim, i think i'm getting closer 400mGy/hr at 2 meters should still be 400mGy/hr at 6m? then 400mGy/hr divided by the square of the distance ie 6m is that how it works?
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P: 26,167
hi nonphysical!

(just got up …)
 Quote by nonphysical 400mGy/hr at 2 meters should still be 400mGy/hr at 6m?
you're still thinking of mGy/hr as a measure of the source (the "original strength") …

it isn't, it's only a measure of the intensity at the receiver
 then 400mGy/hr divided by the square of the distance ie 6m is that how it works?
not exactly …

you have to divide by the ratio of the squares of the distances.

ie not by 62, but by (6/2)2
(btw, the "original strength" would be the intensity at distance r times 4πr2

that is a constant for any value of r )
P: 596
 Quote by nonphysical Thanks Tiny-Tim, i think i'm getting closer 400mGy/hr at 2 meters should still be 400mGy/hr at 6m? then 400mGy/hr divided by the square of the distance ie 6m is that how it works?
can you write the inverse square law formula?
 P: 15 Thanks again Tiny-Tim/Rajani Firstly Rajani, no i'm lost i cannot write the inverse square law formula. Secondly, Tiny-Tim again i'm lost in the meaning of (6/2)2 if you could put it more simply maybe i could grasp it and go from there. Thanks again
P: 596
 Quote by nonphysical Thanks again Tiny-Tim/Rajani Firstly Rajani, no i'm lost i cannot write the inverse square law formula.
Why you are not showing any interest in finding the formula? If you have access to internet you can easily google with 'inverse square law'..In fact tim already gave good ints for you and please understand what a inverse square law means.
 P: 596 Hi, I guess your answer is correct. How i usually derive: For 2 m: $$400 mGy/hr=\frac{S}{4\pi(2m^2)}\rightarrow S=(400 mGy/hr) 4\pi(2 m)^2$$ For 6 m: $$?mG/hr=\frac{S}{4\pi(6m^2)}$$ Substitute 'S' from 1st equation into 2nd equation to obtain '?'. If you want to find the source strength take care of units!