[2]	U. Fantz J. Nucl. Mat. 337-339 (2005) p1087 - 1091, and: U. Fantz priv. comm. 2005
Fit	<ex> = 3.93e-15 * exp(-3.51/Te) / Te**0.27 * 1.e6
[3]	U. Fantz, D. Wuenderlich, Atomic and Plasma-Material Interaction Data for Fusion, Vol 16 (2011), p 75, IAEA, Vienna, and: D. Wuenderlich priv. comm. 2011
Fit	<ex> = 9.00e-15 * exp(-3.61/Te) / Te**0.27 * 1.e6