Improved performance in synthetic diamond neutron detectors: Application to boron neutron capture therapy S. Almaviva a , Marco Marinelli a , E. Milani a,Ã , G. Prestopino a , A. Tucciarone a , C. Verona a , G. Verona-Rinati a , M. Angelone b , M. Pillon b a INFN–Dipartimento di Ingegneria Meccanica, Universit  a di Roma ‘‘Tor Vergata’’, Via del Politecnico 1, I-00133 Roma, Italy b Associazione EURATOM-ENEA sulla Fusione, Via E. Fermi 45, I-00044 Frascati (Roma), Italy article info Available online 8 August 2009 Keywords: Diamond Detector Dosimetry BNCT abstract An improved thermal and fast neutrons detector is obtained, modifying a recently proposed multilayered homoepitaxial Chemical Vapor Deposition (CVD) diamond detector (M. Marinelli, et al., Appl. Phys. Lett. 89 (2006) 143509), where a 6 LiF layer deposited on the sensing layer was used to convert thermal neutrons into charged particles. By sandwiching this layer between two CVD diamond detectors connected in parallel, a better signal-to-background separation is achieved. This allows to use 10 B as converting element, so to realize a detector suitable for Boron Neutron Capture Therapy dosimetry. Also, the doubled detector volume enhances the sensitivity to fast neutrons. & 2009 Elsevier B.V. All rights reserved. 1. Introduction Neutron detection is obviously a necessity in fusion or fission nuclear reactors. All traditionally used neutron detectors such as fission chambers, gas counters, silicon detectors, etc. have some weakness (e.g. large size, use of fissile materials, lack of radiation or temperature hardness, inability to perform spectroscopic measurements). In addition, a severe problem comes from their high sensitivity to g-rays, which are often emitted by neutron sources. This leads to a high background level in the pulse height amplitude (PHA) spectra obtained from the detector, resulting in inaccurate evaluation of the neutron flux. Diamond-based detectors minimize this problem because of the low Z of carbon atoms, thus providing good signal-to-background discrimination. Recently, a detector based on a multilayer structure in which the sensing element is a homoepitaxial Chemical Vapour Deposi- tion (CVD) diamond film capable to overcome all the above limitations has been proposed and realized [1]. Good performance was demonstrated (100% charge collection efficiency, about 1% energy resolution) and a very high fabrication reproducibility was achieved. The neutron radiation hardness was tested up to 2 Â 10 14 n/cm 2 with 14 MeV neutrons [2]. The device working principle and detection physics have also been thoroughly investigated [3]. An important application of thermal neutron detectors is for monitoring the dose delivered in Boron Neutron Capture Therapy (BNCT) treatments. BNCT is a new and very promising radio- therapy technique [4,5] in which a boron containing contrast liquid is injected in the region to be treated. Boron is preferentially absorbed by cancer cells, so that upon thermal neutron bombard- ment the short-range products of the 10 B(n,a) 7 Li nuclear reaction selectively destroy cancerous tissues. However, a yet unsolved problem in BNCT is the accurate experimental evaluation of the delivered dose. A detector exclusively measuring that part of the neutron beam interacting with the boron containing contrast liquid is necessary. Diamond- based detectors using a boron containing conversion layer are the ideal solution. We will show in the following, however, that simply substituting the LiF layer in the device described in Ref. [1] with a boron containing one would not do, an appropriate geometry modification being essential for the proposed applica- tion. In this paper we report on a modified geometry of the device proposed in Ref. [1], which allows to significantly improve the detector performance while maintaining its advantages. In particular, a much better separation of the neutron-related peaks from the background is obtained, further decreasing the back- ground signal disturbance. In addition, quite interestingly, combining the new device geometry with a boron containing converting layer results in a detector, which can be used as a dose monitor for BNCT. 2. Detector design The basic element of the present detector is the device proposed in Ref. [1] and sketched in Fig. 1a. Commercial high- pressure high-temperature (HPHT) single crystal diamonds 4 Â 4 Â 0.4 mm 3 in size were used as substrates, on which a ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A 0168-9002/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2009.08.016 Ã Corresponding author. Tel.: +390672597228. E-mail address: milani@ing.uniroma2.it (E. Milani). Nuclear Instruments and Methods in Physics Research A 612 (2010) 580–582