Date: Wed, 29 May 1996 
From: James K Cochran 
 
"0.5 micron cartridge PF" refers to particulate Th-234 retained
on a 0.5 micrometer-equivalent pore size wound polypropylene fiber
cartridge.  These cartridges were used throughout this work.

The most appropriate reference to methodology is: 

Buesseler, K.O., J.K. Cochran, M.P. Bacon, H.D. Livingston, S.A. Casso,
D. Hirschberg, M.C. Hartman and A.P. Fleer (1992).  Determination of
thorium isotopes in seawater by non-destructive and radiochemical
procedures.  Deep-Sea Res. 39, 1103-1114.