Re: Conversion of Half-life Years to Seconds

["Leo M. Lowe" <llowe@senes.ca>]

Hello,



Thanks to all who responded to my query (copied below), with most 

commenting "does it make any real difference?"



First however, my main point (which I wasn't too clear about) is that there 

must be some specific definition of the unit "year" that is used by 

standards organization i.e. there has to be some fixed unit.  Perhaps an 

academic question, but still of interest to some.  As another example, the 

unit "day" is defined as 24 hours or 86,400 seconds even though the actual 

earth day is not exactly 24 hours.



Second, relative to half-lives, the National Nuclear Data Center at 

Brookhaven (www.nndc.bnl.gov/nndc/nndcnsdd.html  under "Decay Radiations") 

quotes the half-life of U-238 (4.4689E+9(3) y or 5 figures) to a relative 

precision of 0.067%.  This is comparable to the relative difference between 

365 days and 365.25 days.  Therefore, which "year" is used does matter in 

this case.



 > I want to calculate relatively precisely the specific activities of

 > radionuclides with half-lives that are given in units of years.  This

 > requires a conversion from "years" to seconds.

 >

 > So which "year" should I use: the calendar year (365 days), the mean solar

 > year (365.24219 days), the sidereal year (365.25636 days), ....?  (where 1

 > day = 24 hours = 86,400 seconds).

 >

 > Which "year" is used by the standards organizations, such as NIST, when

 > publishing half-lives?



Leo M. Lowe, Ph.D., P.Phys.

Principal, Senior Health and

Environmental Physicist



SENES Consultants Limited

121 Granton Drive, Unit 12

Richmond Hill, Ontario

Canada L4B 3N4

Tel:	(905) 764-9380

Fax:	(905) 764-9386

llowe@senes.ca

www.senes.ca



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