As explained in the e-mail exchange copied below, the values found in Henke, Gullikson and Davis (1993) are erroneous for carbon at the energy of the C K line (277 eV). The

Subject: carbon photo absorption coefficient From: Martin ZombeckDate: Fri, 25 Oct 1996 10:47:11 -0400 Sender: mvz@sisko.harvard.edu During the calibration of the HRC-I subassembly we uncovered an error in the entry for the mass absorption coefficient for carbon at carbon k alpha in the Henke, Gullikson, and Davis 1993 tables (Atomic Data and Nuclear Data Tables v. 54, 181-342 (1993). This error is significant for anyone modeling the transmission of organic thin films or using organic gases (methane, propane, etc.) in proportional counters in order to make absolute qe measurements. What follows is e-mail correspondence between me and Eric Gullikson discussing our result. To: EMGullikson@lbl.gov Subject: carbon mass attenuation coefficients Date: Tue, 15 Oct 1996 09:55:32 -0400 From: Martin Zombeck We have been attempting to derive the effective path length of a gas proportional counter by the following method: 1. measure the count rate as a function of fill pressure using several incident energies and several fill gases. 2. monitor possible variations in source flux with a separate gas filled proportional counter 3. calculate the gas density using the fill pressure, the measured temperature of the gas, and the gas composition 4. calculate the mass absorption of the fill gas using the gas composition and the mass absorption coefficients of the elemental constituents (from Henke, et al., 1993) 5. Derive the thickness t from a best fit to the data using exponential absorption as a model. We control the gas pressure in both counters to within 1 Torr, monitor the temperature, and read the pressure with both Hg manometers and calibrated pressure transducers. We are also using certified fill gases. Here's what we obtain: Mn K-alpha (Fe55 source), P-10: 6.28 cm Al K-alpha (well filtered e-impact), P-10 6.22 cm C K-alpha (well filtered e-impact), Methane 7.96 cm !!! Physical measurement of offset counter window to back of counter (body diameter is 2") is 6.35 cm. We will make a further measurement at Al K-alpha with Methane. Is it possible that (u/p) for carbon at carbon K is in error? Your 1993 (and website) value is 1.96 x 10^3 cm^2 g^-1. Your 1982 value is 2.35 x 10^3 cm^2 g^-1 (20% higher than 1993) If we use our derived path length to derive a value for (u/p) for carbon, we obtain 2.54 x 10^3 , within 8% of your 1982 value. We have made the typical idiot checks: two idiots independently doing the calculations. We have also cross-checked our calculations with your website and get agreement when we use the same set of coefficients, path lengths, gases, energies, pressures, and temperatures. What's up? Thanks. Martin Zombeck ------------------------------------------------------------------------ Date: Sat, 19 Oct 96 18:30:51 PDT From: egull@grace.lbl.gov (Eric Gullikson ) To: mvz@sisko.harvard.edu Subject: carbon mass attenuation coefficients Dear Martin, Thank you for your email last week. It sounds like you guys have done some very careful measurements. I have checked the published data that was used in generating the last set of tables (1993) and found the following: Energy, mu, reference 277. 2106. 6 277. 2206. 11 277. 1720. 18 277. 2300. 87 277. 2808. 120 277. 2535. 128 277. 2051. 143 277. 1930. 144 277. 3700. 234 The last value is derived from relectance measurements and it is not too surprising that there are large errors associated with it. If you just take the average of the remaining eight values you get 2207 cm^2/gm. However, you can see the spread in the measurements and your value of 2540 is certainly within reason. In fact, reference 128 which gives a value quite close to yours appears to be one of the more thorough works. As for our value, it does appear to be too low compared to the average measured value. In part this may be due to an error in our transcribing the measurement from reference 144. Thank you very much for letting me know about this. I hope that when you're done you will consider publishing your results so that we can refer to them in the future. Best Regards, Eric ************************************************************************* Eric M. Gullikson Center for X-Ray Optics, 2-400 Phone: (510) 486-6646 Lawrence Berkeley Laboratory FAX: (510) 486-4550 1 Cyclotron Road email: EMGullikson@lbl.gov Berkeley, California 94720 ********************************************************************

Henke, B. L., Lee, P., Tanaka, T. J., Shimbukuro, R. L. and Fujikawa, B. K. 1982, "Low energy X-ray interaction coefficients: photoabsorption, scattering and reflection", Atomic Data and Nuclear Data Tables,27, 1-144.

Henke, B. L., Gullikson, E. M. and Davis, J. C. 1993, "X-ray interactions: photoabsorption, scattering, transmission, and reflection at E=50-30000 eV, Z=1-92", Atomic Data and Nuclear Data Tables,54, 181-342.

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