What's New?
.	December Journal
.	December Newsletter
.	Online Registration for HPS 2010 Midyear Meeting Now Available
.	NRC Academic Program Nuclear Education Grants, FY2010, Now Accepting Applications
.	EPA's STAR Graduate and GRO Undergraduate Fellowship Funding Now Accepting Applications

Upcoming Events
.	2010 HPS Midyear Topical Meeting Radiation Risk Communication to the Public 24-27 January 2010 Albuquerque, NM
.	2010 HPS Professional Development School Radiation Risk Communication: Issues and Solutions 27-29 January 2010 Albuquerque, NM

21 November 2009

Answer to Question #362 Submitted to "Ask the Experts"

Category: Doses and Dose Calculations — Internal dose calculations

The following question was answered by an expert in the appropriate field:

What is the biological half-life of ²³⁰Th and ²³²Th?

The biological half-life of ²³⁰Th and ²³²Th is the same. The International Commission on Radiological Protection gives the following information:

8,000 days for thorium in bone, and 70 percent of the uptake goes to bone.
700 days for thorium in the liver, and 4 percent of the uptake goes to liver.
700 days for thorium in all other tissues and organs, and 16 percent of the uptake goes to these locations.
The remaining 10 percent is assumed to be excreted with a half-life of 0.5 days.

These values are based on animal experiments and, although expected to be close, are not exact numbers. People vary and so do their metabolisms. For example, work in the Human Monitoring Laboratory on human volunteers has seen the biological half-life of iodine vary from 20 days to 200 days. The accepted average is 80 days. Note: Uptake refers to the amount of thorium that enters the blood. If an insoluble compound of thorium is inhaled it can stay in the lung for a long time and only slowly enters the blood stream.

Gary Kramer, PhD

The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.