Diagnostic assessment to estimate and minimize neutron dose rates received by occupationally exposed individuals at cyclotron facilities L.C. Reina a,Ã , A.X. Silva b , J.C. Suita a , M.I.S. Souza a , A. Facure c , J.C.P. Silva a , J.A.D. Furlanetto a , W. Rebello d a Instituto de Engenharia Nuclear, Comiss ~ ao Nacional de Energia Nuclear, Caixa Postal 68550, Cidade Universita ´ria, CEP: 21941-906 Rio de Janeiro, Brazil b [PEN/COPPE–DNC/Escola Polite´cnica], Universidade Federal do Rio de Janeiro, Cidade Universita ´ria, CEP: 21945-970 Rio de Janeiro, Brazil c Comiss ~ ao Nacional de Energia Nuclear Rua General Severiano, 90-Botafogo, CEP: 22290-901 Rio de Janeiro, Brazil d Instituto Militar de Engenharia, Ministe´rio da Defesa Prac - a General Tibu ´rcio, 80-Praia Vermelha, CEP: 22290-270 Rio de Janeiro, Brazil article info Article history: Received 17 December 2008 Received in revised form 21 October 2009 Accepted 1 December 2009 Keywords: Radiation protection Neutron activation analysis Radiation shielding Computer simulation abstract Since 2003, radiopharmaceuticals for medical diagnostic purposes have been produced at the Instituto de Engenharia Nuclear, in Brazil, using two cyclotron accelerators – CV-28 and RDS111. As a result of the ever increasing production, a diagnostic assessment to reduce neutron dose rates received by occupationally exposed individuals during irradiation processes has been developed. The purpose of this work is to present this assessment, which is currently being applied to both the Fluorine and Iodine targets of CV-28 and RDS111 cyclotron accelerators. & 2009 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, Fluorine ( 18 F) and Iodine ( 123 I) have been widely used in nuclear medicine diagnostic tests. Both radionuclides are regularly produced in our cyclotron complex at the Instituto de Engenharia Nuclear (IEN), a unit of the Comiss ~ ao Nacional de Energia Nuclear (CNEN), Brazil. This complex comprises two cyclotron accelerators: the CV-28, by The Cyclotron Corporation and the RDS111, by CTI Cyclotron Systems Inc. The former is an old 1974 model whose manufacturer has already closed down. It has been used in the production of radionuclides since the late 1980s. The CV-28 cyclotron bombards three targets with a 24-MeV proton beam. The first target (KIPROS – Karlsruhe Iodine Production System), in which 123 I is produced, is composed of 124 Xe, the second target is H 2 18 O, producing 18 F and the third one is dedicated to research and is seldom used. The second cyclotron is a self- shielded 11-MeV machine, manufactured in the late 1990s, which is dedicated exclusively to the production of 18 F through the bombardment of two diametrically opposed H 2 18 O targets. The arrival of this second cyclotron in 2003 and the consequent increase in the production of radionuclides prompted the survey of neutron dose rates at certain locations within the cyclotron facilities so that measures could be taken in order to ensure the compliance of such doses to the ALARA principle. During target irradiation, there are some significant reactions which produce neutrons. Since the targets were designed to produce 18 F with maximum yield, 18 O(p,n) 18 F was considered as the main reaction. This main reaction accounts for the majority of neutrons produced. Moreover, the amount of neutrons produced depends on the nuclear reaction cross section. In our specific case, the energy range is 0–11 MeV at the RDS111 cyclotron, and 0–24 MeV (degraded to 19.2 MeV) at the CV-28 cyclotron. Even with the maximum energy of bombardment, 19.2 MeV for CV-28, the most significant neutron producing reaction is the (p,n) reaction which produces 18 F. Nevertheless, secondary reactions, like 18 O(p,pn) 17 O and 18 O(p,2n) 17 F, also produce neutrons. The first and the second reactions may occur at the CV-28 target. The 18 O(p,pn) 17 O reaction has a 8.49 MeV threshold energy (Prity- chenko and Sonzoogni, 2008) and the 18 O(p,2n) 18 F has a 12.2 MeV threshold energy (Pritychenko and Sonzoogni, 2008). It can be seen that the second reaction cannot occur at the RDS111, and even the first one can scarcely occur. The available data for (p,n) reaction in 18 O oxygen show a threshold energy 2.57 MeV (Pritychenko and Sonzoogni, 2008). A diagnostic assessment to minimize dose rates has been developed and is currently being applied with positive results. The steps leading to the development and implementation of this diagnostic assessment are presented in this work, along with some results. ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/apradiso Applied Radiation and Isotopes 0969-8043/$ - see front matter & 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2009.12.002 Ã Corresponding author. E-mail addresses: reina@ien.gov.br, lcreinasilva@gmail.com (L.C. Reina). Applied Radiation and Isotopes 68 (2010) 489–495