Improving the NAA laboratory pneumatic transfer system for using Tehran research reactor H. Khalafi * , F. Rahmani Radiation Applications Research School, Nuclear Science and Technology Research Institute, Atomic Energy Organization of Iran, North Kargar Avenue, Tehran, Iran article info Article history: Received 15 October 2007 Received in revised form 12 June 2008 Accepted 22 June 2008 Available online 21 August 2008 abstract Neutron activation analysis (NAA) is a precise multi-elemental method which performs well for qualita- tive and quantitative analyses. This method has been applied to the laboratory of Radiation Applications Research School (RARS) at University of Tehran. The new pneumatic transfer system (Rabbit) has been designed and constructed for transferring samples, in particular short half-life samples, to Tehran Research Reactor (TRR) core for NAA. With this system samples were transferred and returned to/from the reactor as fast as possible in both automatic and manual modes. This system has two distinct paths for sending and receiving with transfer time of 30 s to the reactor core and 36 s from the irradiation posi- tion to the counting station in NAA laboratory which is about 700 m from the laboratory. Experiment and calculation have been carried out for calibration of the neutron flux and spectrum. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Although advanced nuclear analytical methods have been developed in the past two decades, classical (n, c) reactor neutron activation analysis (RNAA) is still preserving its role as a ‘‘work- horse” for vast amounts of analytical work. Combined with com- puterized high resolution gamma-ray spectrometry, RNAA offers the mostly nondestructive, multi-element routine analysis needed in such areas as environmental monitoring, geochemistry, medi- cine and technological processes. Among its favorable characteris- tics, negligible matrix effects, excellent selectivity and high sensitivity are worth mentioning (Alfassi, 1994; Baranyai et al., 2006; IAEA-TECDOC, 2001; Tsoulfanidis, 1983). RARS working field is in the area of irradiation research and applications. One of these activity fields is NAA on environmental and industrial samples. In this method, samples are analyzed for element identification and their quantity determination. More recently our research are con- centrated on the environmental issues (soil, water, plant analysis), industrial analysis (concrete, ore) and semiconductor industry. In this study the new pneumatic transfer system was designed and tested for short-lived radioactive elements. The core of Tehran Research Reactor (TRR) has been used as a neutron source for NAA. Until 1993, TRR had been in operation with high enriched uranium (HEU) fuels IAEA-TECDOC, 2001 and with an old manual pneumatic transfer system in which samples were transferred to the reactor core manually. Methods for improving the systems and related equipment for analyzing short-lived decaying elements were then studied. This study in- cludes the design of a new automatic control system for transfer- ring (sample shooting) as well as determination of neutron flux and spectrum at irradiation locations. One aspect which should be considered is that there is an approximately 700 m distance be- tween the NAA laboratory and TRR core, which makes the mea- surement of short-lived decaying elements difficult. The new pneumatic system was designed for transferring and returning samples, in short periods of time, from NAA laboratory to the reac- tor by an automatic control system. The new rabbit control system has the capability of introducing all the needed times and data through hardware to a computer file. The system can be pro- grammed up to 24 h for shooting samples one after another. In addition, opening and closing times of the solenoid valves and sen- sor responses in the path of the rabbit are recorded in a computer file. In the old system, samples were transferred to a shielded loading station, however, in the new system, if it is desired, after separation of standard and samples, samples could be passed one-by-one in front of the detector for Gamma spectroscopy. Four sensors are used in the path of samples between NAA laboratory and TRR core. Some experiments and calculations were carried out to determine the neutron flux and the spectrum at irradiation positions as well as the main spectroscopy parameters. 2. Material and methods TRR is used as a neutron source for NAA in our laboratory. TRR is a 5MW pool-type research reactor. Six beam tubes, one thermal column and two rabbit tubes are available around the TRR core for irradiation purposes. (Fig. 1) shows the typical core configura- tion and (Fig. 2) demonstrates the location of the beam and rabbit tubes around the core (AEOI, 1989). Two similar pneumatic tubes 0306-4549/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.anucene.2008.06.003 * Corresponding author. Tel.: +98 21 88221222; fax: +98 21 88221219. E-mail address: hkhalafi@aeoi.org.ir (H. Khalafi). Annals of Nuclear Energy 35 (2008) 2019–2023 Contents lists available at ScienceDirect Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene