Stepl
Choose a gamma emitting point source with a reasonably long half-life, having gamma line(s) in the medium energy range (the 662 keV line of 137Cs is a good choice).
Stepl
Define geometry for a spectrometric measurement, which is unambiguous and easily
reproducible; e.g. position the source in the detector axis at a fixed distance from the detector front surface.
Step 3
Perform a spectrometric measurement for a time needed to collect more than 10 000 counts in the peak of interest. Pay attention to spectrum and line shapes. Record the measurement conditions and the net peak area in spectrometer logbook.
Spectrometer QC check Procedure D3, Pg. 2 of 2
On the regular basis Step 4
Repeat the measurement on a regular basis (every month) and on special occasions (before measuring campaigns) and record the data obtained in spectrometer logbook.
StepS
Compare obtained results with the results of previous checks. If the result is within 10% the spectrometer is most likely functioning properly. If the result is outside these limits check the system settings and adjustments. If everything seems in order possibly repeat the efficiency calibration.
Discussion
Samples collected during fieldwork may not be directly measurable and must therefore be brought to a form suitable laboratory measurements. In emergency simple, straightforward physical methods are preferred - even at the expense of accuracy - to facilitate rapid hazard assessment and aid decisions on intervention.
Sample preparation may be performed by:
i. separation of different components (e.g. soil, stones, roots, grass, etc.), ii. diminishing the grain size of solid material,
iii. increasing the concentration by drying, ashing etc., iv. homogenisation of the sample,
v. separating a representative amount of the original sample (aliquot) and putting it into a container/holder (geometry) for which efficiency calibration data exist.
The changes of the sample quantity during sample preparation must be carefully followed and documented in order to trace the original environmental radionuclide concentration back to the measured laboratory sample activity.
Equipment/Supplies
> Sample holders
> Spill containment trays
> Scale
> Standard laboratory tools (scissors, spoons, knives, plastic bags etc.)
> Pipettes for liquid samples
> Labels, marker pen, aluminium and plastic foils
Sample preparation Procedure D4, Pg. 2 of 3
> Plates, trays and boxes for mixing samples
Step 1
Screen field samples by dose rate monitor to identify those with higher activity. Treat them separately. Avoid cross contamination.
Step!
Weigh field samples. Separate major components and weigh each of them.
Step 3
In order to create laboratory samples fitting in a pre-defined geometry (sample container) cut the sample components separated in Step 1 till their grain size is small enough compared to the holder size. This can be done by crushing with pestle and mortar, cutting with knife or scissors, using a blender etc.
Step 4
Blend the sample components separated in Step 1 till they are homogenised. This can be done by stirring the material with a spoon, shaking it in a closed box or by using a mixer/blender etc.
StepS
Take a representative amount of the original sample (aliquot) fitting in the pre-defined geometry (sample holder) for which calibration data exist. This sub-sample is called a
laboratory sample. Measure the size (mass or volume) of the laboratory sample and record the data in Worksheet D2.
Step 6
Close the sample holder with the appropriate lid. To prevent spill of the sample material and/or contamination of the counting device additional wrapping in plastic or aluminium foil may be advisable. Stick a label on the sample and write the following data on the label with a marker pen:
code of the sample, i.
ii.
iii.
size of the sample, date of the preparation.
1X3N
Samples collected are prepared for analysis in a liquid scintillation counter. A small amount of sample is distilled with a simple apparatus and then added to a liquid scintillation vial.
Liquid scintillation counting medium is added to the sample; the sample is allowed to stabilise and then it is counted along with a background sample, and a prepared standard. The liquid scintillation counter detects the low energy beta emissions of tritium (Pmax =18.6 keV).
Simple calculations are performed to determine activity per volume.
Tritium in water samples is most likely present as T2O or HTO. Background water (so called
"zero" water) used in counting should be collected from a very deep well, so the activity is
<0.5 Bq/L, or obtained from a commercial vendor. In an emergency, higher activity background samples can be used. In that case MDA values will be higher. Calibration samples should be prepared in the same counting vials with the same cocktail used for the samples. It is not recommended to use the unquenched calibration standard supplied with many liquid scintillation counters, or to purchase one specifically for this purpose. The liquid scintillation cocktail obtained should not be diluted with sample beyond the limits set by the manufacturer. An ideal cocktail for environmental counting can be diluted to 100% (or a 50:50 mix of cocktail and sample). Biodegradable scintillation cocktails are available and are recommended.
i?IN • i ^ i ; ™ *
Tritium analysis by simple distillation Procedure El, Pg. 2 of 4
Equipment/Supplies
r> Liquid Scintillation Counter, coincidence type, preferably with auto sample changer
Auto quench correction and chemoluminescence correction features are preferred. It is also recommended that the LS Counter is able to handle 20 mL liquid scintillation vials. A refrigerated unit is not required.
Software to measure/view spectrums is available and is desirable.
^ Liquid scintillation counting vials, of the correct size for the LS counter and preferably made of low potassium glass
Polyethylene vials may be used when dioxane liquid scintillation cocktail is used. Plastic vials may cause problems with static electricity and give erratic results. It is recommended that liquid scintillation vials be used once only.
^ Distillation Apparatus: 250 or 100 mL round bottom boiling flasks with ground glass fitting, Pyrex type; connecting side arm adapter with ground glass fitting, condenser with ground glass fittings, graduated cylinders, rubber tubing, marble boiling chips, and preferred heating device (Figure El)
> Worksheet El
Reagents
^ Sodium Hydroxide pellets
^ Potassium permanganate; solid
^ Calibration Standard 3H in water matrix, non-acidified, from a reputable supplier;
certification below secondary not recommended
> Background Water, preferably low in tritium activity, from a deep well or other verifiable source, or from a certified vendor. Distill a large quantity of this water using NaOH and KMnC*4 according to the procedure below and store for use in the analyses
^ Liquid Scintillation Cocktail, preferably commercially supplied and biodegradable with a dilution ratio up to 100%
Toluene or dioxane cocktails are available. Liquid scintillation cocktails can also be prepared according to the literature but usually are not of consistent quality and are not recommended.
FIGURE El
DISTILLATION APPARATUS FOR TRITIUM ANALYSIS
Stepl
Place 100 mL of sample (or whatever is available up to that amount but no less than 30 mL) in the round bottom boiling or distillation flask. If the amount is not 100 mL, measure the amount added precisely. It is also wise to distill the background supply with this batch.
Step 2
Add 0.5 g sodium hydroxide and 0.1 g potassium permanganate to the flask (this will destroy any organic compounds present in the water). Add a boiling chip.
Step3
Connect a side arm adapter to the flask and insert a small graduated cylinder or beaker to catch the distillate below the outlet.
Step 4
Connect a condenser to the adapter. Connect it to a water supply with rubber hoses as shown in Figure El.
StepS
Turn on the heating device. Begin boiling the sample. It is recommended that the technician remain within eyesight of the process at all times as it continues.
Step 6
Collect the first 10 mL of distillate and discard it. Collect the next 50 mL, or 20 mL if smaller volumes of samples are used.
Step?
Allow the distillate to cool and swirl well to mix.
StepS
Pipette the correct quantity of sample into a liquid scintillation vial, preferably 10 mL or according to what the liquid scintillation cocktail will hold.
Tritium analysis by simple distillation Procedure El, Pg. 4 of 4
Step 9
Add the correct quantity of liquid scintillation cocktail, coming to a final volume of 20 mL (for a 20 mL vial).
Step 10
Put on the cap, label the vial on the cap only, and shake the vial to mix the contents. Do not add smudges or fingerprints to the exterior of the vial; gloves or tissues are recommended to hold the vial.
Step 11
Prepare a background and calibration standard for the counting batch.
llir 1
II
II
1
in in
Step 12
Allow the samples to dark adapt for 1 hour. This may not be an issue with some types of cocktails; consult the manufacturer of the cocktail for more information.