# Activity Evaluation Methodology for the Disposed Medical Linear Accelerators
###### Abstract  
For the medical linear accelerators (linac) that utilize more than 10 MV of photon energy, components inside the linac head become radiocative during the 10-15-year operating cycle. Prior to disposal, radioactive waste must be evaluated for activity, and the same procedure should be followed for medical linacs. In the Republic of Korea, regulation and methodology for the radioactivity evaluation for the medical linac is not established yet. In this study, we employed gamma spectroscopy and a survey meter for evaluating the radioactivity of medical linac components. The components of the Siemens linac considered in this study were classified after decommissioning, and dose rates were measured to up to a 5 cm distance from the component surfaces by using a survey meter. Radionuclides from components were detected using an in situ HPGe detector. Based on the type of radionuclides and dose rate, we estimated the radioactivity of the components. We studied the feasibility of the methodology for disposing of radioactive components by using the in situ HPGe detector.  
radioactive waste; disposed linear accelerators; radioactivity; in situ HPGe detectors; gamma spectroscopy +
Footnote †: journal: Medical Linear Accelerators  
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Medical linacs are disposed of after an average of 10-15 years of usage. The internal components of the linac head become radioactive through neutron activation. Radionuclide identification and radioactivity evaluation must adhere to the clearance levels stipulated in the Nuclear Safety Act, Article 107, Paragraph 1, prior to the decommissioning of the disposal of linac components [1; 4; 5]. As the components of the linac head vary in shape and size and are manufactured using manufacture-specific compounds, identifying the component- and manufacturer-specific radionuclide information is important. However, as the majority of the components are composed of scrap metal, either melting or cutting them is impractical. Moreover, certified reference material (CRM) is used to correct the activity; however, its density is similar to that of water (1 g/cm\({}^{3}\)), and it is limited to correcting the radioactivity of the metal.  
Following the work by [PERSON] et al., various in situ measurement techniques and detectors have been proposed for radiological characterization in radiological installations under decommissioning and dismantling processes [6]. For waste studies, gamma (\(\gamma\))-ray spectrometry is the recommended technique as the non-destructive assay. The NaI(Tl) detector does not require cooling and is more cost effective and easier to handle in small sizes compared to the HPGe detector [7]. However, among the \(\gamma\)-spectrometry detectors, the high-purity germanium (HPGe) detector has the best energy resolution (\(\sim\)0.15% @ 662 keV) compared with other detectors, such as NaI(Tl) detector (\(\sim\)7% @ 662 keV), BGO (Bi4 Ge3O12) detector (\(\sim\)10% @ 662 keV), LaBr3(Ce) detector (\(\sim\)3% @ 662 keV), and CZT detector (\(\sim\)2.5% @ 662 keV) [6; 7]. For the radioactivity evaluation of each component mixed with various materials, the use of an HPGe detector with high sensitivity and high resolution [8; 9; 10] is considered appropriate.  
In this study, we developed a method for initial radioactivity evaluation by using a portable HPGe detector at the decommissioning site and studied the feasibility of the proposed method. After decommissioning the linac, its components were classified, and the radionuclides were identified using in situ gamma spectroscopy. We conducted the spectroscopy using a portable HPGe detector and an in situ objective counting system (ISOCSTM, Mirion Technologies (Canberra) Inc., Meriden, CT, USA) [11]. After the reference radionuclides were acquired, we estimated the activity (Bq/g) using the dose rate measured by the survey meter.