86 J . A . Corbacho et al .: Radioprotection 2024 , 59 ( 2 ), 80 – 87
considering that these measurements take only 30 s , the result can be considered highly satisfactory .
Mapping is the final step in obtaining a comprehensive view of ambient dose equivalent rate levels in an area . Ordinary Kriging interpolation provides an optimal estimate based on observations and spatial relationships ( Mabit and Bernard , 2007 ), yielding more realistic results than inverse distance weighting interpolation . However , to obtain an adequate contour map using ordinary kriging , it is necessary to follow several steps that ensure it . First , it has been verified that the data distribution approximately follows a normal distribution . The histogram is shown in Figure 3B . Next , a variogram was performed to obtain the parameters of the spherical function that will be used to determine the ordinary kriging interpolation . The obtained variogram is shown in Figure 3C . The optimal interpolation parameters indicate a radius and anisotropy angle of 2 and 48 °, respectively . Furthermore , the optimal range has been 200 m . The ambient dose rate H *( 10 ) contour map was generated and is presented in Figure 3D .
The cross-correlation between the measured dose values and those estimated with the spherical function has been verified . Figure 3E displays this cross-correlation , where an adequate correspondence is observed across a wide range of dose rate values , with the exception of the higher dose values measured in the study area . However , it can be demonstrated that there are significant differences between estimated and measured values . These differences are also illustrated in the kriging deviation error map shown in Figure 3F . Ascanbe seen , the highest dose rate values are observed above the phosphate sludge ponds and in the phosphogypsum piles . Outside these areas , dose rate values range from 0.1 to 0.2 mSv / h , indicating surface contamination probably caused by former industrial activity with significant 238 Useries radionuclide content .
The measurements obtained by the Reuter Stokes ionisation chamber ( red dots and blue values ) align with the contour levels shown on the map .
4 Conclusions
A versatile radiation system was implemented on a rotarywing UAV to identify and quantify radioactive anomalies above the background . Calibration was performed for both point sources and extended sources .
Quantification of 137 Cs and 60 Co in low to medium activity scrap container from the José Cabrera nuclear power plant ( Spain ) was conducted . Results for point source measurements differed by 15 % from reference values , a satisfactory outcome .
Characterisation of the former industrial area “ El Hondón ” with elevated ambient dose equivalent rates was achieved using the drone . Four hundred 30 s measurements were taken . A comparison with a Reuter Stokes ionisation chamber showed differences of less than 16 %. A contour map of the ambient dose equivalent rate highlighted concentrated high doses over the phosphate sludge ponds .
The results demonstrate that radiological characterisation of a site using a system such as the one presented in this work can be carried out with sufficient sensitivity to enable an immediate response by the competent authorities .
Acknowledgements
We wish to thank the ENRESA Company for allowing us to carry out measurements at the decommissioned José Cabrera nuclear power plant ( Spain ). This paper is dedicated to the memory of Professor Antonio Baeza ( 1955 – 2022 ).
Funding
This work was supported by Project IB 16165 . Resolution of 24 May 2017 of the General Department for Science , Technology , and Innovation , aid to research projects in public I + D + i centres of the Autonomous Region of Extremadura .
Conflicts of Interest The authors declare that they have no conflict of interest .
Authors contributions
JA Corbacho : Conceptualization , manuscript writing , figure drafting . JM Caballero : Experimental , Investigation . JA Baeza : data collection .
Ethics approval Ethical approval was not required
Informed consent
This article does not contain any studies involving human subjects
References
Arnold J , Duval M , Falguères C , Bahain J , Demuro M . 2012 . Portable gamma spectrometry with cerium-doped lanthanum bromide scintillators : suitability assessments for luminescence and electron spin resonance dating applications . Radiat Meas 47 ( 1 ): 6 – 18 .
Baeza A , Corbacho JA . 2005 . Comparative analysis of the in and ex situ determination of environmental radiation and dosimetry levels . Radiat Prot Dosim 113 ( 1 ): 90 – 98 .
Baeza J , Valencia D , Baeza A . 2018 . Use of drones for remote management of the close measure of radioactivity sources . In IGARSS 2018 – 2018 IEEE International Geoscience and Remote Sensing Symposium 7914 – 7917 .
Beck HL , Gogolak C , DeCampo J . 1972 . In situ Ge ( Li ) and NaI ( T1 ) gamma-ray spectrometry ( No . HASL-258 ). CM-P 00066834 .
Bednář D , Otáhal P , Nemecek L , Gerslova E . 2021 . The analytical approach of Drone use in radiation monitoring . Radioprotection 56 ( 1 ): 61 – 67 .
Bevelacqua JJ . 2004 . Point source approximations in health physics . Radiat Prot Manag 21 ( 5 ): 9 – 13 .
Casanovas R , Prieto E , Salvadó M . 2016 . Calculation of the ambient dose equivalent H *( 10 ) from gamma-ray spectra obtained with scintillation detectors . Appl Radiat Isot 118 : 154 – 159 .
Chen C , Sinclair L , Fortin R , Coyle M , Samson C . 2020 . In-flight performance of the advanced radiation detector for UAV operations ( ARDUO ). Nucl Instrum Methods Phys Res Sect A 954 : 161609 .
CSN ( 2009 ). Informe de evaluación sobre la gestión de los residuos de los antiguos terrenos industriales “ El Hondón ” ( CSN / JEV / ARBM / GENERJ0609 / 512 ) Consejo de Seguridad Nuclear . ( In Spanish )