To Radsafers from Walter Cofer -
I forwarded the inquiry regarding the discrepany in Cs-137 gamma ray constants that was recently posted on Radsafe to Dr. Birky, one of the authors of the 1998 edition of the Rad. Health Handbook. Here is the original inquiry and Dr. Birky's response:
I am trying to use gamma-ray constants for some of my calculations. I havefound a discrepancy between different books.
E.g. the gamma-ray constant for Cs-137 given in The Handbook of Health Physics and Radiological Health-Third Edition (p 6-11), 1998 is 1.032 E-04 mSv/h per MBq at 1 meter, which converts to 0.382 rem/h per Ci at 1 meter.
In Cember's third edition Health Physics (p 187), the gamma-ray constant for the same isotope is 0.33 R/h per Ci at 1 meter, which should be equivalent to 0.29 rem/h per Ci at 1 meter. Most of the gamma-ray constants in the Handbook are higher than in Cember's book.
University Hospital of Cleveland
The specific gamma-ray exposure constants listed by Cember in his most recent edition are taken from the old 1970 version of the Handbook. The most recent edition of the Handbook uses updated cap-gammas from Unger and Trubey of ORNL. The inquirer noted correctly that the Cember values are true "exposure" constants and the newer Handbook values are "dose" constants. Part of the discrepancy with Cs-137 may be that the Handbook value truly considers the Cs/mBa pair. This question has been put to me before, and I have it on my "to do" list to calculate an entire new set of cap-gammas using the latest emission information, and generate dose factors based on new dosimetry data. This is one of those nagging projects that may require using a month of vacation time for me to devote to its resolution.