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An efficient method for γ‐spectrometric determination of radium‐226,228 via manganese fibers
Author(s) -
Dulaiova Henrieta,
Burnett William C.
Publication year - 2004
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.4319/lom.2004.2.256
Subject(s) - radium , seawater , fiber , radiochemistry , cartridge , radon , manganese , groundwater , chemistry , environmental science , materials science , analytical chemistry (journal) , environmental chemistry , geology , metallurgy , nuclear physics , physics , oceanography , organic chemistry , geotechnical engineering
Radium isotope activities are typically at such low levels in natural waters, especially in seawater, that their measurement requires preconcentration from very large samples. Many investigators accomplish this by passing large volumes (20 to 150 L) of seawater or groundwater through a cartridge loaded with MnO 2 ‐impregnated acrylic fiber. We describe here a new approach for converting “Mn fiber” into a form suitable for measurement of long‐lived 226 Ra and 228 Ra by γ‐spectrometry. The fiber is packed into custom‐made crucibles manufactured from stainless‐steel sheets. The fiber is then ashed at 550°C resulting in a sample mass reduction of approximately 90%. The crucibles are subsequently folded to enclose the ash, pressed using a hydraulic press, and sealed on top with silicon caulking to prevent radon escape. This procedure has an advantage over similar techniques because there is no sample transfer needed, and it is very time efficient. Radium‐228 is determined by counting photopeaks at 338 and 911 keV from its daughter 228 Ac (T 1/2 = 6.1 h). Radium‐226 is determined either by its photopeak at 186 keV (clear from interferences from 235 U as U is not extracted on Mn fiber from oxidizing waters) or by counting the more abundant photopeaks from the granddaughters 214 Bi and 214 Pb after a 3‐week in‐growth period. A recent International Atomic Energy Agency intercomparison study for radium determination in water as well as comparison to the traditional radon emanation method showed that this technique provided good results and is appropriate for radium measurements in natural waters.