Description of the Post Irradiation sample preparation for activated samples

Upon receipt all samples are counted for 10 minutes as received. This establishes an estimate of the total activity. The results are entered into a WWW-table for book keeping purposes.

The samples are inspected for leakage of the PPO out of the welded PE irradiation vial into the secondary containment bag. If leakage is observed a case to case decision is being made as to whether or not to proceed with the external cleaning described next.

The irradiation vials are removed from their bags. Each vial is then separately cleaned externally. The vial is placed into a mixture of 2 parts HCl and 1 part HNO₃, heated to 60 degree (slightly below the melting point of the PPO). Each vial remains in its acid bath for 30 minutes. It is then removed and placed into a new zip lock bag. The cleaning acid is put into small (4 ml) PE vials and counted. External activities can be detected in most cases.

All externally cleaned vials are again counted to establish a base line for the activity content. Counting length varies from 15 minutes to up to an hour, depending on the importance of the samples.

The PPO (and the radio isotopes it contains) is separated from the irradiation vial by means of acid extraction. 15 ml of 8 molar, high purity HNO₃ is heated to 70 degrees in a new (to avoid sample cross contamination) 50 ml glass beaker#1. Two samples are processed in parallel on the same hot plate at a time for an expedient preparation of short lived isotopes. Glass beakers are covered with Al foil to prevent cross talk.

The PE sample vial is cut open and put into the hot HNO₃. It is left in the acid on a hot plate for 30 minutes. At temperatues above 70 degrees the PPO melts. Only when molten the PPO is miscible in HNO₃. A yellow solution forms.

After 30 min the sample vial is recovered from the beaker#1 and moved into another 50 ml glass beaker#2, containing 15 ml pre-heated 8 molar HNO₃. The vial is left in there for another 30 minutes for a second recovery.

Beaker#1 is taken off the hot plate. When the temperature of the solution drops below 70 degrees the PPO precipitates as a fine powder. The radio isotopes stay in the HNO₃ in solution. The solution is allowed to cool down for one hour.

After 30 minutes beaker#2 is removed from the hot plate and the empty irradiation vial is recovered into a zip lock bag and counted. Using U-spiked sample UA37 we determined that less than 1% of the Np activity is left in the vial. Beaker#2 is put back on the hot plate.

An Eicrom TRU Resin ion exchange column, secured in a lab stand, is now prepared. It is opened and the fritted filter at its mouth is gently seated against the resin using a glass rod. The liquid in the column is drained and 15 ml of clean high purity 8 molar HNO₃ are poured through the column.

The content of beaker#1 is slowly and carefully poured through a disposable plastic filter into the column. Note that the filtering was added in June 2001. It was tested just with the spiked sample UA37. For the July 2001 activation run filtering was only done for the PPO samples, not with the blanks. The acid is collected in 4 ml PE vials. If care is taken most of the solid precipitate remains in beaker#1.

After all liquid has been transferred from beaker#1 into the column the hot acid in beaker#2 is transferred into beaker#1 for a second acid extraction of the remaining solid precipitate. Beaker#1 is kept at 70 degrees on the hotplate for 30 minutes for this second extraction.

After 30 minutes beaker#1 is taken off the hot plate and allowd to cool to room temperature for 1 hour.

The content of beaker#1 is then again poured through the same filter into the ion exchange column. The acid is again collected in 4 ml PE vials.

The empty beaker#1 is flushed with 15 ml of hot HNO₃ to take up the remaining solid residue. The liquid is transferred into 4 ml PE vials and counted. Using the UA37 we determined that about 13% of the ²³⁹Np remains in the solid residue. About 2% is left in the filter.

After all liquid has been put into the column it is flushed twice with 15 ml of fresh 8 molar HNO₃ to remove the radio isotopes left in the acid still trapped in the column. When using a filter no or very little solid PPO residue is observed in the column. The column does show a yellow discoloration.

About 75% of the Np/Pa (U/Th activation products) typically remains in the column. This has been verified with several spiked PPO samples using organic U/Th compounds and one sample using U/Th salt. The column is then counted. Counting results are reported as "PPO activities after ion exchange".

The acid discharged from the column and collected in small 4 ml vila is counted as well. It typically contains only 5% of the U-daughter Np. The counting results for this sample are reported as "PPO activities no ion exchange".