[ RadSafe ] How are half-lives determined? Summary of methods from Lederer et al

[Du Toit Volschenk]

A summary of methods used for Half-life determination is given in the
introduction of "Tables of isotopes" edited by Lederer, CM and Shirley,
VS
a Wiley Interscience Publication
John Wiley & Sons Inc, New York

I looked at the 7th Edition (1978)

Methods listed (not specifically listed for the length of the half
life, although the U-235 half-life listed of 3.5 x 10^17 y was
determined with methods 2+3 below):
1) Measurement of time-decay
2) Mass spectroscopy - Direct determination of the decay rate by
measurement of the decrease in the number of atoms (or the increase of
number of atoms of a daughter isotope) relative to another isotope of
the same element
3) Disintegration rate of a sample containing a known mass of the
active substance (mass spectrometric analysis of the sample to correct
for other isotopes present)
4) Calorimetry - Heat rate production from a known mass of active
substance
5) Measurement of decay rate of a parent substance by periodic removal
and radioassay (or mass spectrometric assay) of a decay product
6) Specific activity determination by chemical and/or isotopic analysis
of natural samples, involving assumptions about sample history 
7) Measurement of radioactivity from a sample containing a number of
atoms calculated from the expected yield of the reaction by which it was
produced
8) Estimation based on decay energy, level structure and theoretical
considerations (Usually used for alpha emitters)
9) Other methods (e.g. nuclear recoil, delay coincidence, doppler shift
attenuation, etc)

Du Toit Volschenk
Radiation Protection Service
South African Bureau of Standards
dutoit at sabs.co.za 

>>> Steven Dapra <sjd at swcp.com> 2007-01-18 04:46 >>>
Jan. 17, 2007

	How are half-lives determined?  I am particularly interested in
the 
determination of very long half-lives, such as the uraniums.  What are
the 
measurement techniques, or whatever is used?  Citations to standard 
reference books explaining the techniques would be useful and
appreciated.

	You are welcome to answer here, or by private e-mail.

	Thank you.

Steven Dapra
sjd at swcp.com 





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