On Sep 13, 2011, at 12:55 PM, Peter Heckert wrote:
Am 13.09.2011 22:47, schrieb Man on Bridges:
Hi,
On 13-9-2011 20:44, Horace Heffner wrote:
<snip calculation of lead shielding>
Hmmm, is there a way to start and stop a gamma radiation source,
as it may be used only to trigger the process?
There is no other way than shielding or increasing the distance.
Rossi could inside use a shield that is moved electrically or by
heat (bimetal).
Or he could control the distance to the gamma source.
If it is a very small point source the /local/ intensity of
radiation could be changed by factor 10^2 or 10^3.
Peter
The above is incorrect. A 2 cm thick lead shield will only reduce
Co-60 gammas by 75%.
I = I0 * exp (-0.694 * x)
So we want I/Io = 0.01 to achieve 1/100 reduction factor.
I/I0 = exp (-0.694 * x)
0.01 = exp (-0.694 * x)
ln(0.01) = -0.694*x
x = ln(0.01)/(-0.694) = 6.63
It takes 6.6 cm of lead to divide Co-60 gamma intensity by 100.
Similarly, it takes about 10 cm of lead (on all sides) to attenuate
CO60 gammas by a factor of 1/1000.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
