7/30/2019 Cs AMP MEL

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Pre-concentration of caesium with ammonium molybdophosphate (AMP)

The supernatant solution from the manganese dioxide precipitation of the previous step is re-

acidified to pH 1.5 - 2 with about 350 ml of concentrated HCl. Addition of a few ml of 30% H 2O2 to

dissolve a small amount of MnO2 suspension carried over from the previous step is sometimes done. A

slurry of 30 g of AMP in water is added and the suspension stirred for 30 minutes by bubbling topermit efficient sorption of caesium carrier and radioisotopes by the AMP. The AMP is permitted to

settle out for 4 -5 hours in the tank, then the supernatant solution is pumped out into another tank (for

subsequent precipitation of Ca(Sr) oxalate). The AMP(Cs) precipitate is removed from the bottom of

the tank into a 20-liter container as a suspension for transportation to the home laboratory for final

analytical work-up.

From the shipboard pre-concentration step with ammonium molybdophosphate (AMP), caesium

carrier and radionuclides in several hundred liters of sea water have been efficiently collected on 30 g

of AMP. A suspension of this AMP in 10 20 liters is received in the laboratory for final analysis.

The AMP is allowed to settle, and the supernatant solution is decanted or siphoned away. The

remaining amount of suspension is centrifuged, and the AMP solid can be washed a few times with

small volumes of water acidified to pH = 2.

The separated AMP is then dissolved in a minimum amount of 10M NaOH. The yellow color

disappears, leaving usually a small amount of insoluble matter which is often due to manganese

dioxide. This fine-particle suspension of MnO2 was carried over in the supernatant solution of the first

pre-concentration step (MnO2 precipitation for Pu and Am) and subsequently taken down by the AMP.

The insoluble matter is separated by centrifugation and/or filtration. The Cs-AMP solution in NaOH is

transferred to a beaker, heated and boiled to drive off ammonia. This will minimize precipitation of

AMP when the solution is re-acidified.

The boiled Cs-AMP-NaOH solution is cooled and diluted to about 500 ml with water.

Concentrated HCl is added to neutralize the NaOH and to acidify the solution to about pH = 2. The

transition from basic to acidic is signaled by the re-appearance of yellow color from the

molybdophosphate; however, because the ammonia has largely been removed in the previous step,

very little AMP will precipitate directly. To the acidic solution, 1 g of fresh AMP is added and stirred

in to collect the Cs (2nd AMP-Cs precipitation).

After settling and decantation, the 2nd AMP-Cs is separated by centrifugation and washed. It is

again dissolved in a minimum amount of 10M NaOH, and any insoluble can be centrifuged or filtered

off. Precipitation of a third AMP-Cs is optional; normally, for gamma spectrometry, two AMP-Cs

precipitations are sufficient. The dissolved 2nd AMP-Cs is adjusted to a standard volume geometry for

which an efficiency calibration has been performed with a particular detector. One or more gamma ray

measurements are done to determine the Cs-137 content by way of its photon emission at 661 keV

energy. The caesium chemical recovery is determined by measurement of the Cs-134 major gamma

ray emissions at 605 and 796 keV. Because of serious coincidence summing effects in well counters,the Cs-134 efficiency calibration must be done with a known activity of Cs-134. Alternatively, a direct

comparison with a standard containing the same amount of Cs-134 which was originally added to the

sample before chemical processing can be done to assess the fraction of Cs-134 remaining in the

purified Cs sample.

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