Lake Michigan environmental survey : final report / [edited] by John C. Ayers.

elements not listed. We have not been able to analyze routinely for ruthenium,
tellurium, molybdenum and phosphorus. Their concentrations are too low to detect nondestructively in.5 gram samples. It is our hope that when all the
analyses are completed there may be some sample material from certain stations
left over. If this is the case we will attempt to do destructive analyses on
them for these four elements. Our analytical procedure is as follows.
The samples, frozen on board ship, are dried in the laboratory overnight
at 80~C. One half gram, or whatever is available, is weighed into a polyethylene vial which is then heat sealed. A standard reference solution containing
all the elements of interest is sealed in a similar vial. The sample and
standard are irradiated together for two minutes in a thermal neutron flux of
3x1012 neutrons/cm2-sec. The standard is then counted immediately for 200
seconds on a 35cc Ge(Li) crystal and the data accumulated in a Nuclear Data
4096 memory. After counting, the data are transferred to magnetic tape and
the sample counted for 400 seconds. These data are also stored on tape and
the standard recounted for 400 seconds and the sample again for 2000 seconds.
The first set of counts enables us to obtain aluminum and vanadium and
occasionally copper and titanium. The second counts give us calcium, magnesium,
chlorine, iodine, manganese, dysprosium and in sediment, strontium.
We then irradiate the sample and standard for 10 minutes at a thermal
neutron flux of 1.5x1013 neutrons/cm2-sec. The sample and standard are allowed
to decay for 24 hours and are counted for several hours. We obtain bromine,
sodium, potassium, arsenic, lanthanum and occasionally molybdenum at this time.
The samples are repackaged in aluminum foil as are the standards. Approximately 15-20 of these standards and samples are packaged in an aluminum holder
and irradiated for 50 hours at a thermal flux of 1013 neutrons/cm2-sec. The
samples are allowed to decay for 5 days and are repackaged to remove the aluminum foil and counted for several hours. Concentrations of lanthanum, gold,
samarium, ytterbium and lutetium can usually be obtained.
The samples are allowed to decay for three to five weeks and are counted
12 hours for the final results. Here we obtain rubidium, zinc, mercury, iron,
antimony, cobalt, chromium, silver, thorium, selenium, scandium, neodymium,
europium, terbium, cesium, and barium.
All of the data are stored on seven-track magnetic tape and analyzed by
the University of Michigan IBM 360 computers.

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