New Evaluation of Mean Excitation Energies for Use in Radiation Dosimetry

Atomic mean excitation energies (I values) have been obtained from stopping-power and range data in twelve experiments. The analysis incorporates new values of shell corrections that include contributions made by electrons in all shells. Except for one set of data, the values of I obtained from different experiments are consistent with one another. Empirically, it is found that the following formulas fit the 1 values obtained here: I(eV)=11.2 + 11.7 Z, Z<13, I(eV) = 52.8 + 8.71 Z, Z > 13. The numerical values found from the experiments analyzed are in agreement with those suggested in the National Academy of Sciences-National Research Council Report 1133. It appears that a few of the I values given in the National Bureau of Standards Handbook 79 (1961) are now out of date. A table of 1 values for some thirty-six materials of particular importance in radiation dosimetry is given in addition to the elemental I values found from the new data analysis.