DE102005016792B4 - Simplified procedure for Sr90 activity determination - Google Patents

Abstract

Simplified procedure for SR90 activity determination with the following process steps:
- Dry and grind raw sample material (particle size: <0.2 mm)
- Gammaspektrometrische measurement of the sample material to determine the specific activity a _{β / γ} (N _i ) in Bq / g of the beta / gamma emitters
- Unique determination of the measurement sensitivities ε (N _i ) for the nuclide mixture Sr90 / Y90 and for the other beta emitters
- For beta count rate measurement Sample material with a mass assignment of max. 40 mg / cm ² and the mass M evenly distributed on measuring surface F _D
- Measure the total beta count rate n _n / IPS / at the mass M on the measuring surface F _D
- Conversion of gamma-spectrometrically measured specific activities a _{β / γ} (N _i ) in beta count rates n _{β / γ} (N _i ) according to n _{β / γ} (N _i ) = ε (N _i ) · a _{β / γ} (N _i ) · M
By taking the difference from the total beta count n _n and the sum of the beta count rates of the beta / gamma emitters Σn _{β / γ} (N _i ), the contribution of the beta count rate n (Sr90 / Y90) to Sr90 is given. Y90
Determination of Sr90 specific activity a (Sr90) in / Bq / g / according to n (Sr90 / Y90) / ε (Sr90 / Y90) * M * 2 = a (Sr90)

Description

The The invention relates to a simplified method for Sr90 activity determination.

The activity determination of pure beta emitter Sr90 in samples of environment or from nuclear is due to the variety associated with it chemical operations consuming and difficult. The evaluation only a rehearsal lasts at least a week and requires profound ones Knowledge of chemistry. The price is accordingly high A simple soil sampling is already at about 1000.00 Euro. The economic one But coercion can quickly lead to too low a sample density the result of a statistically insufficient description of the radiological Situation.

task The invention is now a simpler method such as that of To have patent claim, with the fast and inexpensive and without the previous disadvantages for The statistical safety measures a sufficiently large number of samples can be.

This object is achieved in that the sample material is not chemically processed for Sr90 activity determination; Instead of the chemical separation of strontium for beta count rate measurement, the beta count rate contribution of the other beta emitters after a mechanical sample treatment is measured purely by measurement by combining a beta counter rate measurement and a gamma spectrometric measurement. For this purpose, the sample material is brought by grinding into a measuring form (uniform application as a granular powder on measuring surface), in which regardless of the chemical and physical properties of the sample material, the activity of each isolated beta-emitter Ni can be determined by Betazählratenmessung. In this measurement form, the measurement sensitivity ε (N _i ) of the beta count rate measurement for all beta emitters N _{i is} determined by a one-time calibration. With knowledge of the measurement sensitivities ε (N _i ) and the gamma-spectrally measured specific activity a _{β / γ} (N _i ) of the beta emitters, which are also gamma emitters, the beta count rate component Σn _{β / γ} (N _i ) of the beta / gamma can be determined on any sample material Emitters are calculated. The difference between the measured total beta count rate n _n and the sum of the calculated beta count rates Σn _{β / γ} (N _i ) is then the contribution of the nuclide mix Sr90 / Y90 to the total beta count rate.

In the following versions the invention will be closer explained.

2 measuring method of the claim

2.1 Fundamentals

n_b

die Bruttozählrate in /IPS/,

n₀

die Nulleffektrate in /IPS/,

n_n

die Nettozählrate in /IPS/,

ε_D(N_i)·ε_S(N_i) = ε(N_i)

die Messempfindlichkeit der Probenmessung und

A(N_i)

die Probenaktivität des Nuklids N_i in /Bq/

sind.The prerequisite for the new Sr90 measurement process is the ability to determine the activity of each beta emitter with a beta counting meter. For this, the response of the detector ε _D (N _i ) for the beta radiation of the nuclide N _i and the efficiency of the radiation source ε _S (N _i ), which is predetermined by the self-absorption of the beta radiation of the nuclide N _i in the sample, must be known. The context applies AT i ) = (n b - n 0 ) / Ε D (N i ) · Ε S (N i ) = n n / Ε (N i ) by doing

n _b

the gross count in / IPS /,

n ₀

the zero effects in / IPS /,

_n

the net count in / IPS /,

ε _D (N _i ) ε _S (N _i ) = ε (N _i )

the measuring sensitivity of the sample measurement and

A (N _i )

the sample activity of the nuclide N _i in / Bq /

are.

The response ε _D (N _i ) can be determined very precisely with suitable calibration preparations, but not so simply the efficiency ε _S (N _i ), which depends very sensitively on the sample density and the sample mass and therefore must always be applied conservatively. If, however, it is possible to prepare samples of each type such that ε _S (N _i ) and thus ε (N _i ) reliably assume one and the same characteristic value, ie become independent of the sample material, then the activity A (N _i ) of the nuclide can N _i in any samples from Betazählratenmessung be determined. Such a sample property may have the following theoretical Hin The attenuation of the beta radiation of a nuclide N _i is a function of the max. Energy of the beta radiation E _max (N _i ) and the shielding thickness d / cm / of the material with the density ρ / g / cm ³ /. The measuring sensitivity of the beta measurement ε (N _i ), which is a measure of the attenuation of the beta radiation, can therefore be written as a function of these two variables: ε (N i ) = μ i · e Max (N i ) · Ρ · d, where μ _{i is} a proportionality factor characteristic of each nuclide N _i . In addition to E _max (N _i ), the attenuation of the beta radiation thus not only determines the type of material, but rather the product ρ · d = f _m (f _m : shielding area weight in g / cm ² ). With the same screening surface weight f _m , ε (N _i ) is therefore independent of the type of sample material.

The central point of the patent claim is now to determine the measuring sensitivity ε (N _i ) for a given screening surface weight for each nuclide N _i . This can be done by measuring the beta count rate of a sample to which a calibration fluid of known activity has been added. If such a calibration liquid is not available, then ε (N _i ) must be calculated.

2.2 Calibration of the measuring procedures

2.2.1 Calibration of the beta radiation measurement

For each beta emitter N _i whose activity has been determined on the basis of its gamma radiation, the measurement sensitivity of the counter tube for the beta radiation ε (N _i ) in units of IPS / Bq is to be determined by calibration measurements. The measurement sensitivities ε (N _i ) for the artificial nuclides can be determined by calibration samples which are contaminated with solutions of the expected nuclides N _{i of} precisely defined activity. The calibration samples must exactly match the samples to be measured in their self-absorption behavior. The parameters determining the sample properties with regard to the attenuation of the beta radiation, the shielding effect area f _m / g / cm ² / and the grain size, must be identical. For a solid ground sample with a sample mass of 10 g (f _m = 33 mg / cm ² ) and a grain size <0.2 mm, the measurement sensitivities ε (N _i ) listed in Table 1a were used to determine the beta count rates by measurement (of Sr90 / Y90 and Cs137) or by calculation (natural activities).

• * durch Kalibrierpräparate ermittelte Messempfindlichkeiten
• ** theoretisch ermittelte und anhand von Umweltproben überprüfte Messempfindlichkeiten: siehe Tabelle 1b

Tabelle 1b: Vergleich berechneter und gemessener Betazählraten an 10-g-Proben, die frei von künstlichen Aktivitäten sind gemessene Netto-Betazählrate IPS berechnete Netto-Betazählrate* IPS Zählratendifferenz ΔZ IPS S04-676: Erdprobe 2,829 2,873 –0,044 S04-858: Bauschutt 0,775 0,792 –0,017 S04-982: Bauschutt 0,942 0,946 –0,004 S04-983: Erde-Kiesel 1,556 1,546 +0,010 S04-985: Erdprobe 2,955 2,912 +0,043 S04-986: Erdprobe 2,788 2,819 –0,031 S04-1027: Molekularsieb 0,493 0,497 –0,004

• * aus den gammaspektrometrisch gemessenen spezifischen Nuklidaktivitäten und ihren Beta-Messempfindlichkeiten ε(N_i) nach Tabelle 1a berechnet

For the beta emitters of the uranium and thorium family, the measurement sensitivities are to be estimated by comparing the beta energies with known measuring sensitivities of artificial nuclides. The error of this estimation is very small, since the beta count rates generated by the uranium and thorium daughter can be very well checked against environmental samples not contaminated with artificial nuclides (see Table 1b). Table 1a: Measurement sensitivities ε (N _i ) of artificial and natural nuclides in the measurement of the beta count rate of solid samples artificial nuclides * natural nuclides ** natural nuclides ** ε (Sr90 / Y90) = 0.28 IPS / Bq ε (K40) = 0.405 IPS / Bq ε (Bi 214) = 0.32 IPS / Bq ε (Cs 137) = 0.20 IPS / Bq ε (TI 208) = 0.45 IPS / Bq ε (Pb 214) = 0.38 IPS / Bq ε (Bi 210) = 0.44 IPS / Bq ε (Ac 228) = 0.36 IPS / Bq ε (Bi 212) = 0.25 IPS / Bq ε (Pa 234m) = 0.46 IPS / Bq ε (Pb 212) = 0.25 IPS / Bq ε (Th 234) = 0.04 IPS / Bq

• * Measurement sensitivities determined by calibration preparations
• ** Theoretically determined and verified environmental sensitivities: see Table 1b

Table 1b: Comparison of calculated and measured beta count rates on 10 g samples free of artificial activities measured net beta count IPS calculated net beta count * IPS Counting rate difference ΔZ IPS S04-676: Earth sample 2,829 2,873 -0.044 S04-858: rubble 0.775 0,792 -0.017 S04-982: rubble 0.942 0.946 -0,004 S04-983: Earth pebbles 1,556 1.546 +0.010 S04-985: Earth sample 2,955 2,912 +0.043 S04-986: Earth sample 2,788 2,819 -0.031 S04-1027: molecular sieve 0.493 0,497 -0,004

• * calculated from the gammaspektrometrisch measured specific nuclide activities and their beta-sensitivity ε (N _i ) according to Table 1a

2.2.2 Calibration of gamma-spectrometric Measurement

The Calibration of the gamma spectrometric measurement is a standardized one Nuclear measurement process, which is therefore not explained here.

2.3 Sample preparation

2.3.1 Sample preparation of solid samples

The Raw material of the sample to be measured (sample mass: at least 10 g) is to be dried and then ground immediately to a particle size <0.2 mm and to homogenize. Soft materials, such as rubber, PVC or other organic samples that can not be ground at room temperature, be for the grinding process cooled down to the temperature of liquid nitrogen. At Metals that are not be ground, the sampling is done by milling or grinding.

After sample conditioning, the sample must have reached a state that ensures that the gamma spectrometric and gage rate measurements used are the same as those used to calibrate these two gauges. As best reproducible in this regard, it has been found that for the gamma spectrometric measurement, a sample amount of about 1 liter and for Betazählratenmessung a sample amount of 10 g, which is evenly distributed over a measuring area of about 300 cm ² (shielding effect surface f _m = 33 mg / cm ² ).

2.3.2 Sample preparation of liquid samples

The Sample material is evaporated. The sample quantity is arbitrary. In dependence From the solids content of the raw material, the sample is after the evaporation process either in measurable form or it must be at high solids content according to chap. 2.3.1 will be further discussed.

2.4 Measurement and evaluation

2.4.1 Gamma spectrometric measurement

At the gamma-spectrometrically the sample becomes the activity of all detectable gamma emitters including from K 40 as well as the gamma emitters from the thorium and uranium family measured.

2.4.2 Beta radiation measurement

With a counter tube the gross count rate of the beta radiation n _b as well as the zero n _{0 is} determined for solid samples on a partial sample of 10 g from the prepared total sample.

at liquid Samples, this measurement is carried out on the residue of the evaporated sample.

2.5 Evaluation

The measured count rate n _{b of} the subsample in IPS is composed of the count rates of the different beta emitters: n b = n (Sr / Y90) + n 0 + n (N 1 ) + n (N 2 ) + n (N 3 ) + ... (1)

In this equation, n (Sr90 / Y90) are the count rate produced by Sr90 / Y90 in / IPS /, n _{0 is} the zero effect rate and n (N _1), n (N _2), n (N ₃₎ ... the Betazählraten in / IPS / the beta / gamma emitter N ₁ , N ₂ , N ₃ ....

The beta count rates of the beta / gamma emitters, based on the partial sample mass m used in the beta measurement, can be calculated from the determined measurement sensitivities ε (N _i ) - see Table 1a - and the determination of the specific beta / gamma emitter activity a (2.4.1). N _i ) in Bq / g as follows: n (N i ) = ε (N i )·at i ) · M / IPS /, (2)

The count rate n (Sr90 / Y90) generated by Sr90 / Y90 is calculated as Eq. (2) from Eq. (1) too n (Sr90 / Y90) = n b - n 0 - Σn (N i ) (3).

The Sr90 / Y90 activity of subsample A (Sr90 / Y90) is determined from the count rate n (Sr90 / Y90) and the measurement sensitivity ε (Sr90 / Y90) as follows: A (Sr90 / Y90) = n (Sr90 / Y90) ε (Sr90 / Y90) Bq (4).

The specific activity a (Sr90 / Y90) of the sample is given by Eq. (4) too a (Sr90 / Y90) = A (Sr90 / Y90) m Bq / g (5).

Since Sr90 and Y90 are in the activity equilibrium, the specific activity for the nuclide Sr90 is: a (Sr90) = a (Sr90 / Y90) 2 Bq / g (6).

2.6 Experimental Determination of Recognition and detection limit of the Sr90 activity measurement method

For the count rate difference ΔZ between the measured net beta count rate and the net beta count rate in Table 1b calculated from the gamma spectrometrically determined activity, theoretically ΔZ = 0. For the sample measurements listed in Table 1b, this is obviously the case for statistical safety. The standard deviation of the count rate difference is σ (ΔZ) = 0.031 IPS. From this standard deviation, the detection limit EG and detection limit NWG for the Sr90 / Y90 activity measurement can be determined on the assumption that there are no further non-gamma spectrometry detectable activities: EC (Sr90 / Y90) = 3 · σ (.DELTA.Z) ε (Sr90 / Y90) · m = 3 x 0.031 0.36 x 10 = 25.83 E-3 Bq / g or NWG (Sr90 / Y90) = 4.6 · σ (.DELTA.Z) ε (Sr90 / Y90) · m = 39.61 E-3 Bq / g or for the nuclide Sr90 alone: EG (Sr90) = 13.0 E-3 Bq / g, NWG (Sr90) = 19.81 E-3 Bq / g.

These Values are in agreement with the theoretically determined detection limit in chapter 3 Detection limit for the Sr90 / Y90 activity determination.

2.7 Additional comments on the measurement the count rate the beta radiation

In rare cases, samples also include the short-lived radionuclide Sr89 (T _1/2 = 50.5 d), a likewise pure beta emitter, such as Sr90. This nuclide theoretically can occur in nuclear fission in a maximum of a factor of 100 higher activity than Sr90. Because of its short half-life it does not accumulate to the same extent as Sr90 (T _1/2 = 28.64 a), so that in a reactor in operation, a Sr89 / Sr90 activity ratio of max. 10 sets. In decommissioned nuclear facilities, this nuclide no longer provides any relevant activity contribution even one year after the end of reactor operation. In environmental samples, there is generally no Sr89. Exceptions are environmental samples that are measured in the immediate vicinity of nuclear catastrophes such as in the case of Chernobyl or after nuclear tests in the atmosphere. In such extreme cases, the activity ratio is either known or it can be derived from the radioactive decay of Sr89 by a second beta radiation measurement about 3 days after the 1st measurement. Since the Sr89 / Sr90 activity ratio is constant in one compartment to be examined, one Sr89 activity measurement is sufficient for extrapolation to the other samples.

Pure gamma emitters (eg Cr51) or pure beta emitters with beta energies E _max <0.1 MeV like H3 need not be taken into account, because the counter tube used is insensitive to gamma radiation or to beta particles of this energy. The pure beta emitter C14 with a beta energy E _max <0.2 MeV is detected by the beta measurement. However, its beta radiation can easily be completely shielded by a foil without affecting the beta count rates of the other nuclides, whose beta energies are significantly higher.

In contrast to solid samples, for samples of aqueous origin it must be taken into account that the Sr90 daughter Y90 (T _1/2 = 64.1 h) is not in equilibrium with its mother. In such cases, the missing contribution of Y90 can be determined on the basis of a second beta radiation measurement approx. 2 to 3 days after the first measurement and taken into account in the final result.

3 Example 1: Sr90-free rubble sample (sample S04-858)

3.1 Measurement results of gamma spectrometry

It were not artificial Detected gamma emitter (detection limit <1 E-3 Bq / g).

• * Die Aktivität von Bi210 lässt sich aus der Aktivität seines (messbaren) Vorläufers Bi214 berechnen, sofern Aktivitätsgleichgewicht zwischen beiden Nukliden vorliegt
• ** Die Aktivität von Th234 lässt sich aus der Aktivität seiner Tochter Pa234m ableiten, mit der es im Aktivitätsgleichgewicht steht

The activity of the natural beta / gamma emitters is composed as follows: a (K 40): 1.30 E-1 Bq / g a (Bi 214): 7.91 E-3 Bq / g a (TI 208): 3.43 E-3 Bq / g a (Pb 214): 9.29 E-3 Bq / g a (Bi 210) *: 7.91 E-3 Bq / g a (Ac 228): 1.02 E-2 Bq / g a (Bi 212): 1.06 E-2 Bq / g a (Pa 234m): 1.29 E-2 Bq / g a (Pb 212): 1.08 E-2 Bq / g ** a (Th 234): 1.29 E-2 Bq / g

• * The activity of Bi210 can be calculated from the activity of its (measurable) precursor Bi214, provided there is activity balance between both nuclides
• ** The activity of Th234 can be deduced from the activity of its daughter Pa234m, with which it stands in the activity balance

3.2 Measurement results of beta count rate measurement

The mean gross count of 3 beta measurements of a sub-sample of 10 g of sample S04-858 is
n _b = 1.031 IPS during a total measurement time t _M = 2700 s.

The mean zero reflectance is n ₀ = 0.256 IPS with a total measurement time t ₀ = 2700 s.

evaluation

According to Eq. (3) applies: n (Sr90 / Y90) = n b - n 0 - n (nat.) (7), where n (nat.) are the calculated count rates of all gamma spectrometrically detected natural beta emitters. n (nat.) is composed of the beta counts of the beta daughters of the U and Th families and of the beta count rate of K 40. So it's true n (nat.) = Σn (N i (U, Th)) + n (K 40) (8).

Taking into account the relationships n (K40) = a (K40)) · ε (K40) and correspondingly for n ( _Ni (U, Th)) = a ( _Ni (U, Th)) · ε ( _Ni (U , Th)), where ε (N _i (U, Th)) can be taken from Table 1a, n (nat.) With the measurement results from Chap. 3.1 to be calculated n (nat.) = .792 IPS (8a).

According to Eq. (7) gives the count rate of the Sr90 / Y90 activity: n (Sr90 / Y90) = 1.031 - 0256 - 0.792 = - 0.017 IPS (9).

There the sample certainly not with artificial activity is the expected value for n (Sr90 / Y90) = 0.0 IPS. The Measurement result n (Sr90 / Y90) = -0.017 IPS deviates within the error range of the counting statistics and systematic Uncertainties of beta and gamma measurements slightly lower than expected.

3.4 Error Consideration

The standard deviation s (Sr90 / Y90) of the count rate n (Sr90 / Y90) for the 10 g sample is composed of the following 3 standard deviations:
s _nz for the count statistical error of the net count rate n (net) = n _b - n ₀ - n (nat.),
s _az for the count statistical error of the beta count rate n (nat.) due to the statistical error in the activity determination of the gamma emitters and
s _s for the systematic error, which arises in the determination of the measurement sensitivities of ε (N _i (U, Th)) and ε (K40).

For s (Sr90 / Y90), therefore, the equation holds

in der n₀ die Nulleffektrate, t₀ die Messzeit für die Nulleffektrate und t_M die Messzeit für die Bruttozählrate sind.The count statistical standard deviation s _{nzEG of} the net count rate for the measurement of beta radiation near the detection limit is generally described by the equation

where n _{0 is} the zero rate, t _{0 is} the measurement time for the zero rate, and t _{M is} the measurement time for the gross count rate.

Now we are not interested in the standard deviation of a net count n (total) - n ₀ = n (nat.), But the standard deviation for the net count near the Sr90 / Y90 detection limit n (total) - n ₀ - n (nat.) = n (Sr90 / Y90), so that

in denen a(N_i) und ε(N_i) die spezifische Aktivität bzw. die Messempfindlichkeit des Nuklids N_i bei der Betazählratenmessung darstellen und Δa(N_i) bzw. Δε(N_i) die entsprechenden Fehler dieser Messgrößen sind. Werden in die Gleichungen (11), (12) und (13) die oben ermittelten Werte eingesetzt, so ergibt sich mit den vereinfachend – aber nicht ungenau – angenommenen gleichen Fehlern Δa(N_i)/a(N_i) = 0,038 und Δε(N_i)/ε(N_i) = 0,04 für alle Nuklide: snzEG = ±√(0,256 + 0,792)·(1/2700 + 1/2700) = ±0,028 IPS (11a) saz = ±√(0,13·0,405·10·0,038)² + ... = ±0,020 IPS (12a) ss = ±√(0,13·10·0,405·0,04)² + ... = ±0,021 IPS (13a) For the errors in the activity measurements, based on a 10 g sample, the equations apply s az = ± √ Σ (a (Ni) 10 · ε · (Ni) · .DELTA.a (Ni) / a (Ni)) ² (12)

in which a (N _i ) and ε (N _i ) represent the specific activity or the measuring sensitivity of the nuclide N _i in the Betazählratenmessung and Δa (N _i ) or Δε (N _i ) are the corresponding error of these measures. If the values ascertained above are used in equations (11), (12) and (13), then the same errors Δa (N _i ) / a (N _i ) = 0.038 and Δε are assumed with the simplified - but not inaccurate - assumptions (N _i ) / ε (N _i ) = 0.04 for all nuclides: s nzEG = ± √ (0.256 + 0.792) · (1/2700 + 1/2700) = ± 0.028 IPS (11a) s az = ± √ (0.13 · 0.405 · 10 · 0.038) ² + ... = ± 0.020 IPS (12a) s s = ± √ (0.13 · 10 · 0.405 · 0.04) ² + ... = ± 0.021 IPS (13a)

• (Die theoretisch ermittelte Streuung ist in diesem Beispiel geringfügig höher als die aus der Messreihe in Tabelle 1b bestimmte von s(Sr90/Y90) = ± 0,031 IPS – siehe 2.6.)

In Eq. (10) gives the theoretical total error for the Sr90 / N90 activity measurement of sample S04-858 s (Sr90 / Y90) = ± √ 0.028² + 0.020² + 0.021² = ± 0.040 IPS.

• (The theoretically determined scattering in this example is slightly higher than that determined from the measurement series in Table 1b of s (Sr90 / Y90) = ± 0.031 IPS - see 2.6.)

The uncertainty u (Sr90) for the determination of the Sr90 specific activity a (Sr90) near the detection limit is calculated with the sample mass m = 10 g, the measuring sensitivity for the beta measurement of Sr90 / Y90 with ε (Sr90 / Y90) = 0.28 IPS / Bq and taking into account the activity balance between Sr90 and Y90 u (Sr90) = s (Sr90 / Y90) ε (Sr90) · 2 · m = ± 0.040 0.28 × 2 × 10 = ± 0.007 Bq / g (15).

The detection limit for the Sr90 determination is given by the total error u (Sr90) and a factor for the statistical reliability k _g = 3 (confidence interval> 99%) EG (Sr90) = k G · U (Sr90) = 3 · 0.007 = 0.021 Bq / g (16), and the detection limit with a statistical factor k _n = 4.6 NWG (Sr90) = k n · U (Sr90) = 4.6 · 0.007 = 0.032 Bq / g (17).

4 2nd example: With Cs137 and Sr90 / Y90 contaminated soil sample (sample S04-985)

4.1 Measurement results of gamma spectrometry

Measurement results in Bq / g: a (Ka40): 4.76 E-1 a (Bi214): 2.72 E-2 a (Tl208): 1.26 E-2 a (Pb214): 3.15 E-2 a (Bi210): 2.72 E-2 a (Ac228): 3.85 E-2 a (Bi212): 4.03 E-2 a (Pa234): 5.22 E-2 a (Pb212: 4.03 E-2 a (Th234): 5.22 E-2

This soil sample was contaminated with calibration solutions of Sr90 / Y90 and Cs137; specific activity:
a (Sr90 / Y90): 3.885 Bq / g
a (Cs137): 1.956 Bq / g

4.2 Measurement result of beta count rate measurement

The beta count rate of a subsample of 10 g mass increased
n _b = 1128 IPM = 18.21 IPS measured during a measurement time of t _M = 2700 s.

The nulleffektrate is n ₀ = 21.3 IPM = 0.350 IPS at a measurement time of t ₀ = 2700 s.

evaluation

According to Eq. (3) applies: n (Sr90 / Y90) = n b - n 0 - n (K40) - Σn (N i (U, Th)) - n (Cs137) = n b - n 0 - n (nat.) - n (Cs137)

After inserting the measured values taking into account the calculated beta count rate n (nat.) = 2.912 IPS (see sample S04-985 in Table 1b) and the measurement sensitivity for Cs137 of ε (Cs137) = 0.2 IPS / Bq from Table 1a, the Determine the beta count rate of the 10 g sample for Sr90 / Y90 as follows: n (Sr90 / Y90) = 18.21 - 0.350 - 2.912 - 0.2 · 1.956 · 10 = 14.95 - 3.912 = 11.04 IPS.

In compliance with Eqs. (4) and (5) gives specific activity for Sr90 / Y90 a (Sr90 / Y90) = 3.925 ± 0.093 Bq / g.

snZ = ±√(0,35 + 2,912 + 3,912)/2700 + 18,21/2700 = ±0,097 IPS (18a). It deviates only by 1.0% from the activity of the calibration solution at 3.885 Bq / g and is within the uncertainty of measurement u (Sr90) = ± 0.093 Bq / g, which is calculated as follows:
The measurement error s (Sr90 / Y90) is made up of the zählstatistischen error s _nZ the net count rate of the beta measurement n (net) = n _b - n ₀ - n (nat.) - n (Cs 137), the zählstatistischen error of the activity measurement the gamma emitter s _az and the systematic error of the measuring sensitivities for the beta measurement of the gamma emitter s _s . Unlike sample S04-858 in Example 1, the net count rate of the beta measurement is not close to the detection limit for a positive Sr90 / Y90 contribution, but the net count rate is formed exclusively by Sr90 / Y90. The standard deviation of the net counting rate is therefore too

s nZ = ± √ (0.35 + 2.912 + 3.912) / 2700 + 18.21 / 2700 = ± 0.097 IPS (18a).

For the standard deviations s _az and s _{s of} the measured gamma emitters, according to Eq. (12) and (13) with Δa (N _i ) / a (N _i ) = 0.038 and Δε (N _i ) / ε (N _i ) = 0.04 s az = ± √ (3.912 x 0.038) 2+ (0.476 x 0.405 x 10 x 0.038) 2 + ... = ± 0.166 IPS and ε s = ± √ (3.912 x 0.04) 2+ (0.476 x 0.405 x 10 x 0.04) 2 + ... = ± 0.17 IPS, so that as a total deviation s (Sr90 / Y90) = ± √ 0.097² + 0.166² + 0.174² = ± 0.26 IPS and as measurement uncertainty for this Sr90 / Y90 measurement u (Sr90 / Y90) = ± 0.26 0.28 x 10 = ± 0.093 Bq / g results.

5 Advantages of the invention

The new process requires no knowledge of chemical interrelations since the sample preparation only mechanically by drying and grinding happens and the activity measurements only require standard knowledge of Nuclear Metrology: The Sr90 activity of a Sample simply results from the difference of the measured beta count rate and the sum of the beta counts, after appropriate calibrations for each beta emitter from the gamma-spectrometric activity measurement let calculate.

Claims (1)

Simplified procedure for SR90 activity determination with the following process steps: - dry and grind raw sample material (particle size: <0.2 mm) - gamma spectrometric measurement of the sample material to determine the specific activity a _{β / γ} (N _i ) in Bq / g of beta / Gamma emitter - Unique determination of the measurement sensitivities ε (N _i ) for the nuclide mixture Sr90 / Y90 and for the remainder Beta-Strahler - For Beta Count Rate Measurement Sample material with a mass assignment of max. 40 mg / cm ² and the mass M evenly distributed on the measuring surface F _D - At the mass M on the measuring surface F _D the total beta counting rate n _n / IPS / measure - conversion of gamma spectrometrically measured specific activities a _{β / γ} (N _i ) in beta count rates n _{β / γ} (N _i ) according to n _{β / γ} (N _i ) = ε (N _i ) · a _{β / γ} (N _i ) · M - by taking the difference from the total beta count n _n and the sum of the beta count rates of the beta / gamma emitters Σn _{β / γ} (N _i ), the contribution of the beta count rate n (Sr90 / Y90) of Sr90 / Y90 - determination of the specific Sr90 activity a ( Sr90) in / Bq / g / according to n (Sr90 / Y90) / ε (Sr90 / Y90) * M * 2 = a (Sr90)