Gamma dose rate detection and mapping using a drone-mounted Safecast sensor
Authors: Katreiner Hédi , Horváth Ákos , Vörös Fanni , Pál Márton , Tóth Szabolcs , Várhegyi András , Kovács Béla 
Published: March 2022

&lt;p&gt;After a nuclear accident in the Fukushima Dai-ichi reactor in 2011, huge amounts of radioactive material were released into the air. The contaminated area was first surveyed by a fleet of 15 vehicles equipped with GM tubes, followed by traditional airborne measurements. These methods were extremely time-consuming, expensive and enhanced the risk for human lives. After the disaster, a drone with a radiation sensor was sent to survey radiation levels using similar technology. This method speeded up the evaluation and did not risk human lives, but the measuring device was heavy and expensive. Since then, many research have been investigating how to perform a radiation survey task with less weight, more cheaply and yet effectively at different distance scales.&lt;/p&gt;&lt;p&gt;The aim of our research is to find out the optimized parameters to detect large radiation anomalies by a low-cost radiation sensor mounted on a drone. What are the best altitude, drone speed, integration time, for the most reliable description of the anomaly. What is the altitude dependence of the gamma dose at certain circumstances and how can we extend the measured radiation level values in 3 dimension?&lt;/p&gt;&lt;p&gt;A survey was carried out in the area of K&amp;#337;v&amp;#225;g&amp;#243;sz&amp;#337;l&amp;#337;s, not far from the city of P&amp;#233;cs (Hungary), where a uranium mine had been operating until 1997. The remediation has been succesfully completed, but according to the geological conditions of K&amp;#337;v&amp;#225;g&amp;#243;sz&amp;#337;l&amp;#337;s, anomalous radiation can be measured at few locations (U ore outcrops). The survey used a DJI Matrice 210 V2 RTK drone and a Japanese radiation measuring device, the Safecast bGeige Nano Kit. The Safecast bGeige Nano Kit uses a Geiger-M&amp;#252;ller counter, sunk to a depth of 1 cm to measure gamma radiation. It averages the number of impulses every 5 seconds and then calculates a 60s average from that (CPM). The device also includes a GPS unit, adds a time-stamp to the GPS data and writes it to an SD card. All of these are covered by a thick, waterproof polycarbonate housing, allowing only gamma radiation to enter the GM tube.&lt;/p&gt;&lt;p&gt;During the survey, this instrument was mounted on the drone and then flown at different altitudes; 5, 15 and 25 meters above the ground in uncovered terrain. The survey also included an elevation profile measurement of an anomaly, moving upwards every 10 metres up to 120 metres.&lt;/p&gt;&lt;p&gt;This low-cost device has been able to detect effectively larger anomalies. It can also be said that in an uncovered area, the device provides almost equal values up to a height of about 15 metres from the ground; above this altitude its reliability decreases.&lt;/p&gt;&lt;p&gt;BK is supported by the NRDI Fund of Hungary, Thematic Excellence Programme no. TKP2020-NKA-06 (National Challenges Subprogramme) funding scheme. FV is supported by EFOP-3.6.3-VEKOP-16-2017-00001: Talent Management in Autonomous Vehicle Control Technologies &amp;#8211; The Project is financed by the Hungarian Government and co-financed by the European Social Fund. The bGeigie device is supported by G&amp;#225;bor Garamhegyi and the G&amp;#225;bor D&amp;#233;nes School.&lt;/p&gt;