Rapid nuclear event determination by caesium-137, stroncium-90 and

plutonium activity and atomic ratios T2.2-P16

A. Puzas*, D. Baltrūnas, B. Lukšienė, R. Gvozdaitė, A. Gudelis, R. Druteikienė, R. Davidonis, Š. Buivydas, V. Remeikis

Institute of Physics of Center for Physical Sciences and Technology, LITHUANIA *Andrius.Puzas@ftmc.lt

Problem

Global nuclear test fallout, the large

scale nuclear accidents at the Chernobyl

nuclear power plant (NPP) in 1986 and at the

Fukushima Daiichi NPP in 2011 caused a

widespread dispersion of technogenic

radionuclides all over the world. These events

have proven that radionuclides can reach

territories from the source even at a distance of

thousand kilometres under favourable

meteorological conditions and can be detected

by radionuclides “finger prints” which depend

on their source.

In this work a rapid comprehensive method

considering optimisation of man-hours of work,

materials and including activities such as

radiochemistry, alpha-, beta-, mass- and

gamma-spectrometry techniques combined

together for radionuclide determination and

assessment source is demonstrated.

Equipment

Four different techniques for

measurements of soil samples:

• alpha spectrometry - for plutonium-238 and

plutonium-239,240 determination,

• inductively coupled plasma mass

spectrometry (ICP-MS) - for plutonium-239

and plutonium-240,

• gamma-spectrometric system – for caesium-

137,

• beta counter – for strontium-90.

Conclusion

1. A one gamma spectrometer is not enough for more than three samples set rapid 137Cs determination as only a one sample is measured per time.

2. Alpha spectrometer can measure 8 samples simultaneously, thus, it is optimal to

measure 8 samples as a one sample set for rapid 238Pu, 239,240Pu determination.

3. ICP-MS technique lets to measure 239Pu, 240Pu isotopes significantly faster than

alpha spectrometry.

4. APEX IR sample introduction system for ICP-MS stabilizes plutonium isotopic

signals s by 67%, thus, shorter analysis time could be used.

5. According to 137Cs/90Sr, 137Cs/239,240Pu, 238Pu/239,240Pu and 240Pu/239Pu activity

and atomic ratios it was assessed that global fallout and Chernobyl accident

sources prevail.

6. It is shown that less than 48h (+24h for sampling) is enough for a rapid

radionuclides analysis.

Sample preparation &

measurement

Three soil samples set was taken.

Time used to collect samples and to start

samples preparation and measurement – 24 h.

Caesium-137: soil samples were prepared in

plastic containers of the standard geometry for

gamma spectrometry measurement. The

reference standards with radionuclides (57Co, 139Ce, 113Sn, 85Sr, 137Cs, 54Mn and 65Zn) free of

the coincidence-summing effects were used for

the efficiency calibration. The gamma

spectrometer was equipped with the HPGe

coaxial gamma-X-ray detector (GMX-series with

a 0.5 mm thickness Be window) made by Ortec

(USA). The relative efficiency of the detector

was 33 %, the energy resolution at 1332.5 keV

was 1.8 keV. All samples were counted for the

fixed time of 50,000 s. The detection limit for 137Cs is 0.185 Bq. Additionally, activity

concentration of 37Cs was measured in the

IAEA-TEL-2014-03 reference soil sample for

analytical quality control. Work total – 3 x 13

h of measurement = 36 h.

Strontium-90 was extracted by acid leaching of

ashed soil samples. We determined 90Sr using

methods based on 90Y separation from samples

by di-2-ethylhexylphosphoric acid (HDEHP)

extraction. The ashed soil samples were

dissolved in 1 mol/L HCL, and 90Y was extracted

with 10% HDEHP at pH 1.0–1.2. 90Y was back-

extracted with 3 mol/L HNO3 and precipitated as

a hydroxide. The chemical yield of 90Y was

determined using the known amount of inactive

Y. Y precipitates were suction filtered onto a

membrane filter. The precipitate and a filter were

dried at 60°C, weighed and placed in a copper

planchet for counting. Work total - (3 x 1.5

h) of preparation, 8 h of counting

simultaneously = 14 h.

Plutonium was extracted by acid leaching from

the soil matrix and purified using the anion-

exchange (Bio-Rad AG-1×8 100-200 mesh, Bio

Rad Company) method followed by the

extraction chromatography technique. Initially,

samples were dried at 500°C for 2h, then left for

12h in 700°C to burn organic part of soil. The

analytical procedure has been reported in [1].

Work total - 14h of drying and ashing, 3

x 1.5h preparation, 25h of alpha- and 1h

of ICP-MS measurements = 44.5 h.

Man-working hours in total – 94.5 h + 24 h

of sampling.

The analysis results

;

References:

1. A. Puzas et al. J Radioanal Nucl Chem (2015) 303:751–759.

A man-hour plan and timetable

hours 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

Caesium-137

Strontium-90

238Pu, 239,240Pu (alpha

spectrometry)

239Pu, 240Pu

(ICP-MS)

p.s. There should be +20% of time to be added for sample handling. preparation is done with alpha spectrometry together.

Fig. 1. Air mass trajectories from suspected nuclear event place modeled.

We assume an nuclear event registered by seismic stations that pointed out

to Kaliningrad district governed by Russian Federation (Fig. 1). Samples

collection begins right after 72h.

Three samples from undisturbed meadow soils were collected right under the trajectories

where the air masses with the possible plume traveled. The samples preparation started just

right after collecting them. The analysis results are presented in Table 1.

p.s. 137Cs/239+240Pu global fallout value for 2015 is 29±3, typical global fallout value of 240Pu/239Pu is 0.180.

Sample

Specific activity, Bq/kg 238Pu/239,240Pu

Specific activity, Bq/kg

239,240Pu 238Pu 90Sr 137Cs 240Pu/239Pu 137Cs/90Sr 137Cs/239+240

Pu

2` Dir. Vilkaviškis 0.13 0.007 0.05 1.9 6.1 0.194±0.009 3.2 46.9

9 Dir. Molėtai 0.2 0.007 0.04 2.7 5.6 0.194±0.009 2.1 28.0

10 Dir. Jurbarkas 0.14 0.035 0.24 3.5 5.8 0.189±0.013 1.7 41.4

Table 1. The analysis results.