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Calibration facility for portable gamma-ray spectrometers

Straz pod Ralskem, Czech Republic

size of the room: 22.4 x 12 m

Ground surface standards

Cylindrical concrete pads, diameter 1.9 m, thickness 0.62 m
(zero standard from silicious sand: size 2 x 2 m, thickness 0.8 m)
Density: 1.8 g/cm3
Density of the sand in the zero standard: 1.58 g/cm3
Geometrical correction is 1/0.934 = 1.071 for the detector height 6.3 cm (centre of the NaI(Tl) 76 x 76 mm scintillation crystal)

Effective concentrations of elements K, U and Th in calibration pads from precise gamma spectrometry, including change of environment between original and new placement

Calibration pad

% K

ppm U

ppm Th

K - pad PK

15.33

2.4

2.1

U - pad PU

0.24

29.2

2.4

Th - pad PTh

0.29

5.1

94.6

Background - pad P0

0.02

0.3

0.9

Besides the spectrometry calibration, the surface standards can be used for simple test of the total gamma radiometers.

Well logging standards:

Cylindrical concrete standards, diameter 1.4 m, height 1.2 m
Density of concrete: 1.8 g/cm3
The potassium standard is from powdery kalium chloride fertiliser (technical KCl) with density 1.15 g/cm3.
The zero standard from silicious sand: size 1.5 x 1.5 m, height 1.8 m, density of the sand 1.58 g/cm3.

Pipe: Aluminum, outer diameter 90 mm, inner diameter 80 mm

Average concentrations of elements K, U and Th in well logging standards from laboratory analyses in the year 1975

Calibration cylinder

% K

ppm U

ppm Th

K - cylinder KK

46.2

0.2

0.5

U - cylinder KU

0.3

1200

26

Th - cylinder KTh

0.3

61

1630

blank standard K0

0.02

0.3

0.9

Apparent effective concentrations of elements K, U and Th in well logging standards after the international intercalibration (IAEA) in the years 1989 and 2018 including pipe attenuation Al 90/80 for spectrometry tool (the higher values in brackets on the right side would be indicated after remove of pipes)

Calibration cylinder

depth [m]

% K

ppm U

ppm Th

K - cylinder KK

0.5 - 0.7

40 (42)

0.2

0.5

U - cylinder KU

0.5

0.3

1287 (1344)

25 (26)

0.6

1323 (1381)

0.7

1239 (1293)

Th - cylinder KTh

0.5

0.3

59 (61)

1529 (1586)

0.6

1445 (1498)

0.7

1441 (1494)

blank standard K0

0.8 - 1.0

0.02

0.3

0.9

Higher pipe attenuation for small energies causes for total counts the apparent concentrations 1.066-times smaller as the values in brackets.

the potassium well logging standard KK after the move from Bratkovice to Straz pod Ralskem

Layered well logging model:

Cylindrical concrete rings, diameter 0.9 m, height of one ring 0.1 m
Density of concrete: 1.8 g/cm3
Count: 18
Concentration: U 5 - 1155 ppm, Th 3 - 2135 ppm
Pipe: Aluminium, outer diameter 90 mm, inner diameter 80 mm

the well logging layered model KV

Concentration of elements K, U and Th in the rings of the layered model KV

ring

% K

ppm U

ppm Th

KVN 1

< 0.4

5

3

KVN 2

< 0.4

7

3

KVN 3

< 0.4

8

4

KVN 4

< 0.4

6

6

KVN 5

< 0.4

6

3

KVN 6

< 0.4

7

3

KVN 7

< 0.4

7

3

KVN 8

< 0.4

12

3

KVTh 10 '0,05%'

< 0.5

40

673

KVTh 11 '0,05%'

< 0.4

30

468

KVTh 12 '0,20%'

 

73

2135

KVTh 13 '0,20%'

 

82

2097

*KVU 14 '0,03%'

 

288

35

KVU 15 '0,03%'

 

281

37

KVU 16 '0,10%'

 

982

83

*KVU 17 '0,10%'

 

1054

68

KVUTh 18 '0,10/0,20'

 

1142

2040

KVUTh 19 '0,10/0,20'

 

1155

1988

(* The rings KVU 14 and KVU 17 were broken in several tiles. Now they are functional only in the configuration with other rings.)

The response of the 10 cm anomaly layer from two different
total gamma probes

Calculation of the reverse filter for automatic interpretation
excel list