Marinelli Beakers (ca. 1950) |
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The
following footnote regarding the Marinelli beaker is found in a report by
R.F. Hill, G.J. Hine and L.D. Marinelli (1950) of the Sloan-Kettering
Institute in In
the 1940s and 1950s, the main application of the Marinelli beaker was the
analysis of I-131 in liquids (e.g., urine). The original version of the
Marinelli beaker, pictured here, consisted of a pyrex laboratory beaker
with a central hollow tube projecting from the bottom. A detector, usually
a glass GM tube designed for gamma counting, was positioned in the central
tube while the beaker was filled with the sample. Since the sample
effectively surrounded the detector, the counting efficiency was greater
than would be the case if the sample were in any other type of container. |
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A
laboratory often used Marinelli beakers of
different sizes -
small beakers for small volume samples and large beakers for large
volume samples. While it was always possible to increase the volume of a
small sample by dilution so that it would fill a large beaker, this
sacrificed counting efficiency. Until
the mid-to-late1950s when liquid scintillation counters came along and
gamma scintillators (NaI crystals) became larger and more widely
available, the major options for counting liquid samples were Marinelli
beakers, jacketed (annular) GM tubes, and dipping GM tubes . Since
Marinelli beakers could hold larger volume samples than annular GMs, they
had a higher counting efficiency for gamma rays. On the other hand, their
efficiency for beta particles was lower than that of annular GM tubes
because the betas had to penetrate the glass of the beaker as well as the
GM tube wall. A
different type of alternative was to dry the sample and count it with an
end window GM or electroscope (e.g., the Landsverk Model L-75). However,
the preparation of dried samples was difficult to perform in a
reproducible manner and it risked the volatilization of the iodine. |
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As NaI detectors became more widely available, workers started to use the type of sample container that most people think of today as the Marinelli beaker: a relatively large plastic jar/beaker with an annular bottom that slid over the NaI crystal (e.g., Haigh, 1954 and Dratz, 1957). Sometimes referred to as a “well-bottom” container, the end of the well was sealed so that the container “hung” from the top of the detector. Kindly donated by Ron Kathren
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References Bruner,
H.D. and Perkinson, J.D. A
Comparison of Iodine-131 Counting Methods. Nucleonics October 1952, p.
57. Marinelli,
L.D. and Hill, R.F. in Brookhaven National Laboratory Conference Report
BNL-C-5, 1948, p.98. Dratz,
A.F. Well-Bottom Container Improves Gamma Counting, Nucleonics
August 1957, p. 83. Hill, R.F., Hine, G.J. and Marinelli, L.D. The Quantitative Determination of Gamma Radiation in Biological Research, Am. J. Roentg. and Radium Therapy, February 1950, p. 160. |
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