J. S. Bogard, J. I. Golzarri, G. Espinosa
Americium beryllium neutron source, track density imaging, CR-39 Nuclear Track, chemical etching process
|PUBLISHED DATE||August 6, 2018|
|PUBLISHER||The Author(s) 2018. This article is published with open access at www.chitkara.edu.in/publications.|
In neutron detection, the more common method is using electronic instrumentation associate with Bonner spheres, however, currently the Nuclear Tracks Methodology (NTM) is coming popular because of the simplicity, flexibility in size of the detector, no requirement for sophisticated instrumentation and installation, and low cost. In this work, a preliminary result of the dose calibration and track diameter distribution of Americium-Beryllium (241Am-Be) source using Nuclear Track Methodology is presented. As material detector, CR-39 polycarbonate, cut in 1.8 × 0.9 cm2 chips was chosen, and two step chemical etchings after neutron exposure was used to develop the tracks. The irradiations were made in environmental normal conditions, in the ORNL neutron calibration facilities. The CR-39 chips were placed in a phantom, with 3mm plastic (Lexan) sheet in between the source and detectors to increase the proton generation. The total track density and track diameter distribution was performing in a Counting and Analysis Digital Image System (CADIS), developed at the Institute of Physics of the University of Mexico UNAM. The results are compared with a standard survey instrument and energy reference spectra of the International Atomic Energy Agency (IAEA).
The neutron detection is not a simplest issue: a) first neutrons are indirectly ionizing radiation, they need to have an interaction with the mater to produce ionizing particles; b) very different reaction can be produced by the neutrons with the matter, as (n,a), (n,p) and (n,g), dealing with the detection of the reaction particle; c) the neutron energy distribution from epithelial to fast neutrons; d) the cross section for each particular reaction ; and e) the generation of strong field of betas, X-rays and g radiations [1-2]. All these considerations, plus some more experimental problems makes hard the neutron detection and very complicated to have a good accuracy in the characterization of neutron radiation fields. The most common detection method is the use of electronic instrumentation, but no mater this system will require the change of sphere of different materials and sizes. Since the introduction of CR-39 polycarbonate as detection material, other option for the neutron measurements is the use of the Nuclear Tracks Methodology (NTM). The main advantage of using NTM in fast neutron dosimetry and measurements is the insensitivity to photon and beta exposure, low energy threshold, no changes in a considerable variation of environmental conditions as temperature, humidity, barometric pressure and altitude, plus a wide range of neutrons energy and considerable low cost compared with the electronic systems [3-4]. In this work, a preliminary results of dose calibration, efficiency detection and diameter distribution for 241Am-Be neutron source, using CR-39 Nuclear Track Detectors (NTD) are present. In collaboration between the Oak Ridge National Laboratory, and Dosimetry Applications Project group (DAP) of the Physics Institute of the University of Mexico (UNAM), important results were found, providing a very promising basic experimental methodology for future developments on the neutron detection, neutron dosimetry and energy analysis.
|ISSN||Print : 2321-8649, Online : 2321-9289|
The neutron detection is not a simple procedure, the electronic detection system is sometimes the solution, but there are other options for neutron measurements; one is using the NTM and the NTD with polycarbonate materials as detectors. The detection efficiency is not to high then other detection systems, but the neutron flux can be measured with reasonable accurately if the detection efficiency is known. The NTD can be use as fast neutron dosimeters, with high confidence, the neutron spectra can be obtained, giving a fast energy distribution of the neutrons. These two methods can not compete, but they can be considered complementary using the attributes and characteristics of each one.