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Conversion factor and uncertainty estimation for quantification of towed gamma-ray detector measurements in Tohoku coastal waters

Conversion factor and uncertainty estimation for quantification of towed gamma-ray detector measurements in Tohoku coastal waters
Conversion factor and uncertainty estimation for quantification of towed gamma-ray detector measurements in Tohoku coastal waters
Factors to convert the count rate of a NaI(Tl) scintillation detector to the concentration of radioactive cesium in marine sediments are estimated for a towed gamma-ray detector system. The response of the detector against a unit concentration of radioactive cesium is calculated by Monte Carlo radiation transport simulation considering the vertical profile of radioactive material measured in core samples. The conversion factors are acquired by integrating the contribution of each layer and are normalized by the concentration in the surface sediment layer. At the same time, the uncertainty of the conversion factors are formulated and estimated. The combined standard uncertainty of the radioactive cesium concentration by the towed gamma-ray detector is around 25 percent. The values of uncertainty, often referred to as relative root mean squat errors in other works, between sediment core sampling measurements and towed detector measurements were 16 percent in the investigation made near the Abukuma River mouth and 5.2 percent in Sendai Bay, respectively.

Most of the uncertainty is due to interpolation of the conversion factors between core samples and uncertainty of the detector?s burial depth. The results of the towed measurements agree well with laboratory analysed sediment samples. Also, the concentrations of radioactive cesium at the intersection of each survey line are consistent. The consistency with sampling results and between different lines? transects demonstrate the availability and reproducibility of towed gamma-ray detector system.
0168-9002
111-121
Ohnishi, S.
01024033-2168-4330-80be-a840fb9c6043
Thornton, Blair
8293beb5-c083-47e3-b5f0-d9c3cee14be9
Kamada, S.
2c260678-0588-4fba-a4b1-b7c1ea7a5f69
Hirao, Y.
46382e99-b647-4cd4-889b-dab7229a326f
Ura, T.
d8977b89-c549-45da-8fd1-a288eae9407c
Odano, N.
3b043b04-7919-4815-8172-3c41eec5f1f7
Ohnishi, S.
01024033-2168-4330-80be-a840fb9c6043
Thornton, Blair
8293beb5-c083-47e3-b5f0-d9c3cee14be9
Kamada, S.
2c260678-0588-4fba-a4b1-b7c1ea7a5f69
Hirao, Y.
46382e99-b647-4cd4-889b-dab7229a326f
Ura, T.
d8977b89-c549-45da-8fd1-a288eae9407c
Odano, N.
3b043b04-7919-4815-8172-3c41eec5f1f7

Ohnishi, S., Thornton, Blair, Kamada, S., Hirao, Y., Ura, T. and Odano, N. (2016) Conversion factor and uncertainty estimation for quantification of towed gamma-ray detector measurements in Tohoku coastal waters. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 819, 111-121. (doi:10.1016/j.nima.2016.02.065).

Record type: Article

Abstract

Factors to convert the count rate of a NaI(Tl) scintillation detector to the concentration of radioactive cesium in marine sediments are estimated for a towed gamma-ray detector system. The response of the detector against a unit concentration of radioactive cesium is calculated by Monte Carlo radiation transport simulation considering the vertical profile of radioactive material measured in core samples. The conversion factors are acquired by integrating the contribution of each layer and are normalized by the concentration in the surface sediment layer. At the same time, the uncertainty of the conversion factors are formulated and estimated. The combined standard uncertainty of the radioactive cesium concentration by the towed gamma-ray detector is around 25 percent. The values of uncertainty, often referred to as relative root mean squat errors in other works, between sediment core sampling measurements and towed detector measurements were 16 percent in the investigation made near the Abukuma River mouth and 5.2 percent in Sendai Bay, respectively.

Most of the uncertainty is due to interpolation of the conversion factors between core samples and uncertainty of the detector?s burial depth. The results of the towed measurements agree well with laboratory analysed sediment samples. Also, the concentrations of radioactive cesium at the intersection of each survey line are consistent. The consistency with sampling results and between different lines? transects demonstrate the availability and reproducibility of towed gamma-ray detector system.

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More information

Accepted/In Press date: 22 February 2016
e-pub ahead of print date: 27 February 2016
Published date: 21 May 2016
Organisations: Civil Maritime & Env. Eng & Sci Unit, Fluid Structure Interactions Group

Identifiers

Local EPrints ID: 400005
URI: http://eprints.soton.ac.uk/id/eprint/400005
ISSN: 0168-9002
PURE UUID: 6e36b9bb-8526-4b33-863d-a361dbddfa48

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Date deposited: 06 Sep 2016 15:32
Last modified: 09 Jan 2022 04:53

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Contributors

Author: S. Ohnishi
Author: Blair Thornton
Author: S. Kamada
Author: Y. Hirao
Author: T. Ura
Author: N. Odano

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