Bevington 2002

Bevington, Philip R., and D. Keith Robinson. 2002. Data Reduction and Error Analysis for the Physical Sciences. 3rd ed. Science/Engineering/Math. Boston: McGraw-Hill. http://www.worldcat.org/oclc/865237466.

Bevington (1969) was my go-to reference to fitting and analyzing data for my master’s and doctorate degrees. In this updated edition, he introduces the FWHM as the parameterization of the Lorentzian Distribution, pp 31–33.

Canberra 1985

Canberra. 1985. “Series 35 plus: Operator’s Manual: Appendix D: Computational Methods.” Canberra Industries.

Canberra presents their FWHM algorithm in Appendix D of their operator’s manual. They use three-point smoothing for peaks wider than 20 channels. Since this reference is not the easiest to find, I have reproduced “Appendix D.4 FWHM” and “Appendix D.7 Smooth,” http://www.mark-jensen.org/blog/2021/4/2/appendix-d4-fwhm.

Encyclopedia Britannica

Editors. N.D. “Radiation Measurement - Counting and Spectroscopy Systems.” In Encyclopedia Britannica, Online. Chicago: Encyclopædia Britannica, Inc. https://www.britannica.com/technology/radiation-measurement.

The Encylopedia Britannica highlights the use of FWHM as the energy resolution of spectroscopy.

Markevich and Gertner 1989

Markevich, N., and Isak Gertner. 1989. “Comparison among Methods for Calculating FWHM.” Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 283 (1): 72–77. https://doi.org/10.1016/0168-9002(89)91258-8.

Markevich and Gertner evaluate five methods of calculating the full width at half maximum [I was surprised that there were five methods to evaluate the FWHM].

Weisstein 2020

Weisstein, Eric W. 2020. “Full Width at Half Maximum.” Text. Wolfram MathWorld. Wolfram Research, Inc. May 1, 2020. https://mathworld.wolfram.com/FullWidthatHalfMaximum.html.

Weisstein provides the Full-Width at Half Maximum for selected functions. One of the examples he presents is the FWHM of a Gaussian as a function of standard deviation:

$$ \Gamma = 2 \sqrt{\ln{2}}\sigma $$

where $\Gamma$ is the full width at half max of the Gaussian and $\sigma$ is the standard deviation of the Gaussian.