Due to the limitation of the Cerenkov Effect to higher βenergies, small amounts of high energetic radionuclides may be determined in presence of much higher amounts of low energy βemitters, whereas conventional measurement of dual βemitters in the same sample requires window setting and three quench correction curves.
Cerenkov counting therefore allows the rapid determination of both radioistrontium nuclides ^{89}Sr and ^{90}Sr in two single counting steps without time wasting ^{90}Y ingrowth. While both nuclides (^{90}Sr: E_{β}_{max} = 0.5 MeV, ^{89}Sr: E_{β}_{max} = 1.5 MeV) are accessible to scintillation measurement with window setting (see dual labelling, procedure 2.1.2.), only ^{89}Sr creates Cerenkov radiation in water with counting efficiencies of 40 to 60 % without chemical quenching (fig. 10). For ^{90}Sr, the Cerenkov light part is < 0.5 %, which allows its sufficient discrimination from ^{89}Sr in an excess of up to 20 fold.
Alternate procedures applying Cerenkov counting foresee the selective separation of ^{90}Y and its successive Cerenkov measurement, or ^{90}Sr separation e.g. by Sr SPEC columns, its elution with diluted HNO_{3} followed by repeated Cerenkov counting of the ingrowing ^{90}Y. For a detailed survey see [L’Annunziata 2012] and [Vajda 2010].
The method described below can be improved by applying TDCRCerenkov counting to avoid the efficiency calibration procedure, when a LS counter with three identical photomultipliers is available (HIDEX 300SL) (see chapter 2.3.5.).
Materials and Equipment
 Gelating cocktail
 Plastic vial
Procedure
The separation of Sr/Y is either done by oxalate precipitation or on Eichrom/ TrisKem SPEC extraction chromatographic columns (see 2.3.2.).
Measuring Procedure (a):

 Sample measurement in aqueous solution (only ^{89}Sr)
 Sample measurement with scintillator (^{89}Sr and ^{90}Sr)
(1) Measure 5 mL of the colorless aqueous sample in a plastic vial (energy window 015 keV)
(2) Add 10 mL of a gelating cocktail; mix well and remeasure in an open energy
Measurements have to be done immediately after chemical separation in order to neglect ^{90}Y ingrowth (1 % after 1 hour).
The Cerenkov efficiency for ^{90}Sr with E_{max} = 546 keV is less than 1 %.
Measuring Procedure (b):

 Sample measurement in aqueous solution (only ^{89}Sr)
 Sample measurement after storage and determination of the ^{90}Sr activity from the ingrowth of ^{90}Y
(1) Measure the colorless aqueous sample (up to 20 mL) in a plastic vial (energy window 0 to 15 keV)
(2) Repeat the measurement after different times of storage
Note: The Cerenkov counting window is typically 015 keV! Plastic vials are preferable compared to glass vials because of their higher Cerenkov counting efficiency.
Evaluation
Procedure (a):
Determine the Cerenkov efficiencies for ^{89}Sr and the scintillation counting efficiencies for both Srisotopes. While Cerenkov counting of colorless samples is absent of chemical quenching, scintillation counting needs internal standardization or other appropriate quench calibration methods according to chapter 1.2 and 2.1.1.
The activities are calculated according to:
Procedure (b):
The activity ingrowth of the ^{90}Y and accordingly the ^{90}Sr concentration follows the exponential ingrowth (fig. 29).
and in equilibrium condition (> 25 d)
where
t = time difference between measurement after separation and after equilibration and
A_{0}(^{89}Sr) = Activity after separation
For more details in calculation see [BMU 2000].
Figure 29: Activity conditions in the system ^{89}Sr and ^{90}Sr/^{90}Y
_{ }
Yield recovery for the chemical Sr/Y separation steps is determined by ICPMS or ICPOES through addition of 30 mg of Sr^{2+} carrier to the sample. The addition of a ^{85}Sr tracer interferes with LS counting and should be avoided, especially when TDCR Cerenkov Counting is applied.
This calculation method can also be applied for the analysis of dual mixtures of α and βemitting radionuclides, when E_{β}_{max} exceeds 0.5 MeV and the αnuclide does not emit γrays exceeding about 450 keV (e.g. ^{32}P / ^{241}Am).
Lower Limit of Detection LLD: about 25 mBq per sample, but lower with preconcentration
L’Annunziata M.F. 2012: “Handbook of Radioactivity Analysis”, Chapter 15, 3^{rd} Edition 2012, Elsevier
BMU 2000: Messanleitungen für die Überwachung der Radioaktivität in der Umwelt und zur Erfassung radioaktiver Emissionen aus kerntechnischen Anlagen; Der Minister für Umwelt, Naturschutz und Reaktorsicherheit, Urban und Fischer, München, HαGesamtAWASS01
BMU 2000: Messanleitungen Umweltradioaktivität HRn222TWASS01, 4.1
Kalibrierung; see also Sranalysis and others
Vajda N. and Kim CK. 2010: Determination of Radiostrontium Isotopes – A review of analytical methodology; Appl. Radiat. Isot. 68 (2010) 23062326