Year : 2011 | Volume
: 34 | Issue : 1 | Page : 4--5
Novel fluorescent nuclear track detectors for use in neutron and heavy charged particle dosimetry
Bhuwan C Bhatt
Associate Editor, RPE Journal, C/o. Radiation Safety Systems Division, Bhabha Atomic Research Centre, Trombay, Mumbai - 400 085, Maharashtra, India
Bhuwan C Bhatt
Associate Editor, RPE Journal, C/o. Radiation Safety Systems Division, Bhabha Atomic Research Centre, Trombay, Mumbai - 400 085, Maharashtra
|How to cite this article:|
Bhatt BC. Novel fluorescent nuclear track detectors for use in neutron and heavy charged particle dosimetry.Radiat Prot Environ 2011;34:4-5
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Bhatt BC. Novel fluorescent nuclear track detectors for use in neutron and heavy charged particle dosimetry. Radiat Prot Environ [serial online] 2011 [cited 2020 Aug 7 ];34:4-5
Available from: http://www.rpe.org.in/text.asp?2011/34/1/4/93896
Precise measurements of neutrons and heavy charged particles (HCPs) remain one of the most challenging tasks in radiation dosimetry. Recently, Akselrod and co-workers have reported development of novel Al 2 O 3 :C,Mg fluorescent nuclear track detectors (FNTDs) for neutrons and HCPs. These detectors have demonstrated a promising performance for dosimetry of neutrons, protons, and other heavy charged particles (Akselrod et al, 2006). FNTD technology is based on a single crystal of aluminum oxide doped with carbon and magnesium (Al 2 O 3 :C,Mg) and has aggregate vacancy defects (denoted as F2 2+ (2Mg) - centers). Radiation-induced color centers in the new material have an absorption band at 620 nm and produce fluorescence at 750 nm with a high quantum yield and short fluorescence lifetime of 75 ns (Akselrod and Akselrod, 2006). Non-destructive readout (which is also termed as radiophotoluminescent (RPL) readout) of FNTD is performed using a confocal fluorescence microscope. Scanning of the three-dimensional distribution of HCP permits reconstruction of particle trajectories through the crystal and linear energy transfer (LET) can be determined as a function of distance along the trajectory based on the fluorescence intensity. Like plastic nuclear track detectors (PNTDs), FNTD is a passive integrating type of detector. But unlike PNTDs, Al 2 O 3 :C,Mg is also sensitive to low LET radiation including secondary electrons resulting from interactions of photons with the crystal. FNTDs show a low LET threshold of about 0.4 keV/μm, with no saturation at LET in water as high as 1800 keV/μm. As is well known, CR-39 PNDTs possess sensitivity to radiation with LET above 5 keV/μm and can register tracks from charged particles of LET between ~5 and ~1500 keV/μm. Thus, the major advantages of Al 2 O 3 :C,Mg FNTD over the conventionally used CR-39 PNTD include superior spatial resolution, wider range of LET sensitivity, no light sensitivity, thermal fading or signal build-up, and no need for post-irradiation chemical processing of the detectors (as needed for CR-39 PNTDs). FNTDs are reusable as erasure of radiation-induced fluorescence signal and complete restoration of initial low level of fluorescence takes place at annealing temperatures around 680 o C.
Al 2 O 3 :C and Al 2 O 3 :C,Mg are nearly insensitive to neutrons. Therefore, neutron converter installed in front of the detector is necessary for getting neutron response (Sykora et al., 2007, 2008). Neutron radiation is usually accompanied by gamma radiation, and a high contribution of gamma to radiation-induced fluorescence signal might be a problem for neutron detection. Dose dependence of FNTDs has been studied and reported (Sykora and Akselrod, 2010) in the track counting mode and in the newly developed image power mode behind polyethylene (PE) and polytetrafluoroethylene (PTFE). The dose response in the track counting mode is reported to be linear in the range 0.2-300 mSv. The image power processing method extends the linear dose response range by two orders of magnitude as it accounts for overlapping tracks making saturation dose of FNTDs more than 1000 times larger than CR-39. It is reported that it is possible to separate neutron to gamma doses at ratios down to 1:3 in terms of dose equivalent. For gamma photons, the low limit of detection is reported to be 5 mGy with good potential for improvement (Akselrod and Sykora, 2011). Recently, Rodriguez et al. (2011) have reported that intensities of thermoluminescence (TL) and optically stimulated luminescence (OSL) signals of Al 2 O 3 :C,Mg samples are comparable to those of regular carbon-doped aluminum oxide (Al 2 O 3 :C). Therefore, OSL from Al 2 O 3 :C,Mg detector can also be used for determining gamma dose component. However, this aspect has not been addressed by the authors in their recently published papers. It is also stated that a compact table-top FNTD instrument for automatic detector processing is under development by Landauer, Inc. For further information on FNTD technology, the reader may refer the original articles by the authors. This development is likely to have positive impact in the field of neutron and heavy charged particle dosimetry.
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