detectors around charged particle accelerator workplaces ... and the Tandem Van der Graaf linear accelerator of the Centro Nacional de Aceleradores (CNA).
Poster HP-15
Neutron personal dose equivalent measurements using PADC detectors around charged particle accelerator workplaces O. Ortega-Gelabert1, M. Romero-Expósito1, B. Fernández2, J. García-López2,3, M.C. Jiménez-Ramos2, J. Praena2, C. Domingo1 1Grup
15th-19th September 2014 Kobe, Japan
de Recerca en Radiacions Ionitzants (GRRI), Departament de Física. Universitat Autònoma de Barcelona. E-08193 Bellaterra. Spain 2Centro Nacional de Aceleradores (U. Sevilla, CSIC, Junta de Andalucía), 41092, Sevilla, Spain. 3Departamento Física Atómica, Molecular y Nuclear, Universidad de Sevilla, 41012, Sevilla, Spain.
Abstract This work reports the use of Poly-Allyl-Diglycol-Carbonate (PADC) based neutron dosimeters for the evaluation of personal dose equivalent Hp(10) in workplaces, namely, the cyclotron and the Tandem Van der Graaf linear accelerator of the Centro Nacional de Aceleradores (CNA) in Seville (Spain). Several PADC neutron dosimeters from the UAB group were distributed in selected locations around the particle accelerators, inside and outside the irradiation rooms with the purpose of evaluating the neutron ambient dose equivalent around the accelerators, especially in places where workers are expected to stay.
1.- Introduction
4.- Measurement points
In particle accelerators, a parasitic neutron field is produced due to nuclear interactions of the beam particles with the elements of the accelerator, such as collimators and bending magnets, as well as with the shielding material and walls. Therefore, from the point of view of radiological protection, it is worth to evaluate the neutron personal dose equivalent around the accelerator, especially in places where workers are expected to stay. A measurement campaign using the UAB PADC-based dosimeters was performed in June 2014 around the cyclotron and the tandem Van der Graaf accelerators of the Centro Nacional de Aceleradores (CNA) in Seville, Spain, as part of a wider collaboration work in the field of neutron detection. The present work reports on the results obtained.
• Cyclotron:
2.- The UAB PADC-based neutron dosimeter The following figure displays the actual configuration of the UAB PADC-based neutron dosimeter [1]: Incident neutrons Polyethylene (3mm) Makrofol (300 µm) Nylon (100 µm) PADC (1mm) Methacrylate (5mm)
• Tandem:
Once irradiated, the PADC plates re electrochemically etched following our standard 3-step procedure [2], choosing KOH 6M as etching solution in the front side of the PADC sheets and a low concentration KOH 0.25M solution to close the electric circuit in their back side. The electrochemical etching process is automatically controlled with a specifically designed software application using Labview, through a computer-controlled multifunction DAQ system (National Instruments, model USB-6341) and a high-speed high-voltage power amplifier (Trek, model 10/10b-HS).
Digitised images of the etched PADC plates were obtained using a commercial photographic scanner (Canon, model 700f) with high optical resolution (up to 9600 x 9600 dpi). The scanned area covers a minimum of 0.4 cm x 0.4 cm. A software application (“ContaTracks”) to perform track counting was developed using MATLAB. This application is specifically designed to be able to separate and count adequately overlapping tracks. We have not observed saturation for track densities up to 15000 tracks/cm2.
5.- Results 3.- Calibration and validation The combination of the dosimeter’s structure with the electrochemical etching technique used makes it sensitive to a wide neutron energy range. Its response had already been validated experimentally up to 20 MeV with ISO sources and realistic neutron fields as specified by the ISO standards, as well as in quasi-monoenergetic neutron beams at the Institute for Reference Materials and Measurements from the European Joint Research Center JRC-IRMM (Gëel, Belgium) Van der Graaf accelerator. As neutron spectra at the points of measurement are expected to have a relevant evaporation component around 1 MeV, we have applied the calibration factor evaluated for the ISO Am-Be source from reference [3] in order to assign personal dose equivalents from track density measurements,
The minimum detectable dose equivalent was evaluated using the Currie equation for the detection limit and was found to be 0.025 mSv. Cyclotron
Tandem
References: [1] García, M.J., Amgarou, K., Domingo, C., Fernández, F. 2005. Neutron response study of two CR-39 personal dosemeters with air and Nylon converters. Radiat. Meas, 40, 607-611. [2] Bouassoule T. Contribución a la Dosimetría de Neutrones por Detectores Sólidos de Trazas. Ph.D. thesis (in Spanish), Universitat Autònoma de Barcelona (1998). [3] Domingo, C., de-San-Pedro, M., García-Fusté, M., Romero, M.T., Amgarou, K., 2013, Estimation of the response function of a PADC based neutron dosimeter in terms of fluence and Hp(10). Radiat. Meas., 50, 82-86
