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RE: Mass attenuation coeff for Beta
The difference is that there are values for charged and uncharged particle
tranport through materials. for examples photons, betas, and alphas of the
same energy will have different values for the same material. They are all
of different masses and charges and should be expected to have different
attenuation values for the same materials.
Glen
> -----Original Message-----
> From: Rob Gunter [SMTP:rgunter@SEC-TN.COM]
> Sent: Friday, May 10, 2002 7:50 AM
> To: Radsafe
> Subject: 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
> Bldg 1020, Rm 18
> Oak Ridge, TN 37830
> Ph: (865) 241-9748
> Cell: (865) 548-9910
> Pager: (865) 873-0078
>
> -----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
> > >
> > > Private bag X191
> > > Pretoria
> > > 0001
> > > South Africa
> > >
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