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RE: Mass attenuation coeff for Beta
I always thought that mass attenuation is consistent for all materials for
absorbing beta energy (let's forget Bremstrahlung for now). Isn't this
true? Similar density thicknesses (mg/cm^2) would have equivalent
transmission regardless of the material. Density thickness would be
essentially electron density.
???
Rob
Robert J. Gunter, CHP
East Tennessee Technology Park
Operations Support Manager
Safety and Ecology Corporation
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-----Original Message-----
From: owner-radsafe@list.vanderbilt.edu
[mailto:owner-radsafe@list.vanderbilt.edu]On Behalf Of Tom O'Dou
Sent: Wednesday, May 08, 2002 10:03 PM
To: radsafe@list.vanderbilt.edu
Subject: Fw: Mass attenuation coeff for Beta
Subject: Re: Mass attenuation coeff for Beta
> I have an equation that provides the mass absorption coefficient for beta
> particles of energy 0.1 MeV to 4 MeV.
>
> The reference of this form for the equation escapes me at this time but a
> similar form appears for the Half Value Layer for beta absorption in
> Radiation Protection by Dr. Shapiro (1990).
>
> The equation is as follows:
>
> mu = 17/E^1.14
>
> where mu is the absorption coefficient in mg/cm^2 and E is the beta energy
> in MeV. For your situation where Tl-204 has a maximum beta energy of
763.4
> keV with polyethylene density at 0.92 g/cc.
>
> mu = 17/(.7634)^1.14 = 23.1 cm^2/gram
>
> x = 0.12 mm of polyethylene (1.1E-2 g/cm^2)
>
> e^(-mu*x) = fraction penetrating = .78
>
> A similar calculation will yield a penetrating fraction of 0.93 for Y-90
> betas at 2.28MeV.
>
> I constructed an excel spreadsheet for the results of your comparison for
> the different thicknesses of polyethylene. These are the fractions
> pentrating the material thickness specified.
>
> for x = 0.12 mm: Tl-204 : 0.78 Y-90 : 0.93
> for x = 0.16 mm: Tl-204 : 0.71 Y-90 : 0.91
> for x = 0.24 mm: Tl-204 : 0.60 Y-90 : 0.86
>
> Enjoy!
>
> Tom O'Dou, CHP, RRPT
>
> ----- Original Message -----
> From: "Frikkie Beeslaar" <beeslar@sabs.co.za>
> To: <radsafe@list.vanderbilt.edu>
> Sent: Wednesday, May 08, 2002 8:36 AM
> Subject: Mass attenuation coeff for Beta
>
>
> > Radsafers
> >
> > I am looking for a table of mass-attenuation coeff. for beta-particles.
> > I want to determine the RELATIVE effect of different thicknesses of
> > plastic (Polyethylene) on the transmitted fraction of beta-particles
> > (Sr/Y and Tl204).
> > (How will the fraction of transmitted beta-particles through a 120
> > micrometer plastic differ from 160 um and 240um ? )
> >
> > I will be using the following equation:
> > T(X) = exp(-u/p . X)
> >
> > Alternatively, one can use the transmission kernel equation:
> > T(X)= [1+exp(-k Xo)] / [1+exp(kX - kXo)]
> > but then I need the practical range(which differ from CSDA ??) of beta
> > particles in Polyethylene or at least the atomic number of
> > Polyethylene.
> >
> > Is my thinking correct? Is there an easier way of calculating it?
> >
> >
> > Thanks for the help.
> >
> > Regards
> >
> >
> > Frik Beeslaar
> > Medical Physicist
> > Radiation Protection Service (SABS)
> > e-mail: BEESLAR@SABS.CO.ZA
> >
> > Tel: 027-12-428 6882
> > Fax:: 027-12-428 6685
> > Cell: 082 829 9613
> >
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