Nuclear Radiation as you move away from a source 2

[boreholelogger]

Here's one for the nuclear guys!.

Does anyone know where I can find equations for the radioactivity emitted from a CS137 source as you move directly away from it in a straight line?.

 

[andyenergy]

Follows the inverse square law -

http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html

http://www.ndt-ed.org/EducationResources/CommunityCollege/Radiography/Physics/inversesquare.htm

 

[electricpete]

A note on terminology - radiation is emitted, not radioactivity.

Depending on the size of the object and your distance, it might be more usueful to view it is a point source or a plane source or a line source.

From far away - point source - acts like 1/r^2
From close up - plane source - no change with distance
Line geometry close up - acts like 1/r

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[boreholelogger]

That simple huh!

 

[electricpete]

as in all things, how simple depends on how exact you want your answer

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[dclarklu58]

Any elementary text on Nuclear Engineering would provide you with point source equations. As is stated above radiation follows the inverse square law, similar to light and gravity propagation.
You will need the initial source concentration to calculate the intensity.

 

[electricpete]

It is an area spreading phenomenon. Let's say there are x units of radiaion emiited per second from the source.

If it acts like a point, we can draw sphere's of equidistance points from the source at radius r of area 4*pi*r^2. The photons per second per square meter crossing the sphere at radius r is x/4*pi*r^2. Hence the inverse square relation.

If it acts like an infinite line (distance to the line is much less than the length of the line), we can draw cylinders of equidistance poitns from the source at radius r of area 2*pi*r*dl. The photons per second per square meter crossing that cylinder at radius r is x/2*pi*r*dl hence the 1/r dependence.

If it acts like an infinite plane (distance to the plane is much less than the length and width of the the plane), we can draw planes of equidistance poitns fom the source at distance z of area dx*dy. The photons per second per square meter crossing that cylinder at radius r is X/dx dy. hence no distance dependence.

In the real world we have a lot of other shapes besides poitns and lines and we aren't always at the proper distance for the ideal behavior.

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