Spectroscopy of nuclear systems. Progress report, January 1--December 31, 1974 Page: 51 of 53
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mass is distributed bimodally; the lower mass, or fine particle mode being
in the size range between 0.1 and L 1m, while the upper, or coarse
particle mode was found to be over 5 pm. The saddle point between the two
mass (or volume) modes is between 0.8 and 3.0 im. It is anticipated that
within the next few years these findings will be recognized by establishing
new standards requiring the determination of aerosol mass and composition
as a function of particle site. Independent determination of the mass con-
centration of only two size fractions, divided at about 1 to 3 um will
probably be adequate for monitoring purposes.
The high volume filter technique and other gravimetric weighing methods
currently in use for atmospheric monitoring are inadequate for future moni-
toring purposes. Slow time response and tedeous manual operation are the
principal disadvantages of these methods.
We have developed a two stage on-line mass monitor with aerosol Size
separator (TWaMASS) employing the beta attenuation technique for high reso-
lution monitoring of atmospheric aerosols. This instrument independently
analyzes the mass concentration of two particle size fractions. Coarse
particles are inertially separated by impaction on mylar film coated with
a silicon adhesive. The fine particle fraction is collected on a high effi-
ciency glass-fiber filter. Carbon-14 is used as a source of beta particles
which are detected by a solid-state silicon s.rface-barrier detector
coupled to fast low-noise nuclear electronics. The output of this system
is sent to a high speed counter interfaced to a progranable calculator
which controls TWOMASS, calculates mass concentration of each size fraction,
plots, prints and stores the data on tape. The instrument has been gravi-
metrically calibrated using laboratory aerosols. It has subsequently been
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Macias, E. S. Spectroscopy of nuclear systems. Progress report, January 1--December 31, 1974, report, January 1, 1974; St. Louis, Missouri. (https://digital.library.unt.edu/ark:/67531/metadc1020885/m1/51/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.