Teflon Mini FAQ
by Monica Jaszczak
What is Teflon?
Teflon (R) is Polytetrafluoroethylene (or Polyethylene Tetrafluoride).
Monomer Formula: C2F4
Monomer Molecular weight: 100.02
Density (g/cm3) = 2.20000E+00
IUPAC International Chemical Identifer: InChI=1/C2F4/c3-1(4)2(5)6
CAS Registry Number: 9002-84-0
Polytetrafluoroethylene's chemical structure is:
F F | | | | ?------------C------------C-----------? | | | | F F
What is "virgin Teflon"?
Virgin Teflon is "pure" Teflon, that is, it has no fillers (impurities) added. The solid, Teflon spine supplied with Data Spectrum's Elliptical Lung Spine Body Phantom (ECT/LUNG/P) is made of virgin Teflon. (Note that some special order requests in the past were supplied with a "mechanical" Teflon spine phantom.)
What are some radiological characteristics of Teflon?
To start with, please read the reference "X-Ray Attenuation and Absorption for Materials of Dosimetric Interest" by J. H. Hubbell and S. M. Seltzer.
According to Hubbell and Selzer Teflon (R) has the following properties:
- Material: Polytetrafluoroethylene, (Teflon)
- Z/A: 0.47993
- I (eV): 99.1
- Density (g/cm3): 2.250E+00
- Composition (Z : Fraction by weight):
- 6: 0.240183
- 9: 0.759818
How these data are used to compute the mass attenuation coefficients (in units of cm2/g) is explained at: http://physics.nist.gov/PhysRefData/XrayMassCoef/chap2.html
One needs the total (that is, the sum of the cross sections for the photoelectric absorption, Compton scattering, etc.) cross section as a function of energy.
FYI: The NIST has an interactive web program called XCOM that will compute the mass attenuation coefficient for elements, chemical compounds or mixtures. You enter the chemical formula (such as "C2F4" for Teflon (R)), specify an energy range and let it perform the calculations.
The linear attenuation coefficient (what we are most interested in) is simply the mass attenuation coefficient multiplied by the density.
For example, at 140 keV, the Mass Mu (from the output of the program XCOM) is 0.134 g/cm3. Thus the linear Mu is 0.2948 per cm.
At ~511 keV, the Mass Mu (from the output of the program XCOM) is 0.0829 g/cm3. Thus the linear Mu is 0.1822 per cm.