## 2 Material and Methods  
Field studies were carried out in the territory of the Chidvinskaya pipe, which is part of the Chidvinsko-Izhmozersky field of the Arkhangelsk diamondiferous province (NW Russia, Figure 1). The Chidvinsko-Izhmozersky field is located 30 km northeast of the city of Arkhangelsk and includes six kimberlite pipes, forming a 20 km-long chain stretching along the ore-controlling fault with a north-northeast direction [42; 43]. The Chidvinskaya pipe is the largest and most studied pipe in the Chidvinsko-Izhmozersky field. The dimensions of the pipe are \(1810\times 580\) m. In projection, the pipe has an irregular dumbbell shape. The rocks hosting the Chidvinskaya pipe are sandstones with siltstone interlayers of Ediacaran sedimentary rocks, represented by a mixture of siltstones, mudstones, and sandstones. The overlying layer is represented by Quaternary deposits, which consist mainly of sands, peat and pebbles. The average thickness of the overlying Quaternary deposits is 9.4 m. In the northern part of the pipe, the thickness of the overlying sediments decreases to 1.5 m. Among the known pipes of the Arkhangelsk diamondiferous province, the Chidvinskaya pipe has the smallest thickness of overlying sediments [44], which is important for radiometric field studies.  
The body of the pipe consists of pyroclastic kimberlite, tuffs, and volcaniclastic kimberlite, the formation time of which has been dated to the Upper Devonian-Middle Carboniferous D\({}_{3}\)-C\({}_{2}\). The contacts between diattreme and the hosting sediments are clearly visible. The thickness of the contact zone exceeds 10 m. The Chidvinskaya pipe has a low diamond content and is currently of no commercial importance. However, this could be attributed to the small amounts of sampling which might give a low level of reliability in the estimates of the diamond content of the pipe [44]. Currently, additional exploration of the pipe is planned to clarify its diamond reserves [45].  
Radiometric field studies in the area of the Chidvinskaya pipe were carried out along a network of profiles crossing the pipe in the NW-SE direction. The distance between the measurement points varied depending on the specific landscape situation, but did not exceed 100 m. A total of 118 points were selected. At each point of measurement in the field, radon radiation and soil gas permeability were determined. Specialists of the Laboratory of Environmental Radiology of the Laverov Federal Center for Integrated Arctic Research (Arkhangelsk city, Russia) applied the emanation method to determine the radon radiation, using the radon radiometer \"Alpharad plus\" (Manufacturer-\"NTM\" Protection, Moscow city, Russia). Gas permeability was determined using the RADON-JOK system (Manufacturer-RADON v.o.s. corporation, Prague, Czech Republic).  
The calculation of radon transport along three profiles (kimberlite pipe, country rocks, sandstones with siltstone interlayers of Ediacaran sedimentary rocks) was made on the basis of the radon diffusion model under homogeneous and single-layer conditions. The layout of the profiles is shown in Figure 2. For this, we used the previously measured radiation and physical parameters of the host rocks and kimberlite [23].  
Figure 1: Location map of the Chidvinskaya pipe and the location of the profiles for calculating the vertical transport of radon.