E. Leonora

A large area cosmic ray detector for the inspection of hidden high-Z materials inside containers

Traditional inspection methods are of limited use to detect the presence of fissile (U, Pu) samples inside containers. To overcome such limitations, prototypes of detection systems based on cosmic muon scattering from high-Z materials are being tested worldwide. This technique does not introduce additional radiation levels, and each event contributes to the tomographic image, since the scattering process is sensitive to the charge of the atomic nuclei being traversed. A new Project, started by the Muon Portal Collaboration, plans to build a large area muon detector able to reconstruct muon tracks with good spatial and angular resolution. Experimental tests of the individual detection modules are already in progress. The design and operational parameters of the muon portal under construction are here described, together with the preliminary simulation and test results. Due to the large acceptance of the detector for cosmic rays, coupled to the good angular reconstruction of the muon tracks, it is also planned to employ such detector for cosmic ray studies, complementing its detection capabilities with a set of trigger detectors located some distance apart, in order to measure multiple muon events associated to extensive air showers.

Search for hidden high-Z materials inside containers with the Muon Portal Project

The Muon Portal is a recently born project that plans to build a large area muon detector for a noninvasive inspection of shipping containers in the ports, searching for the presence of potential fissile (U, Pu) threats. The technique employed by the project is the well-known muon tomography, based on cosmic muon scattering from high-Z materials. The design and operational parameters of the muon portal under construction will be described in this paper, together with preliminary simulation and test results.

Strip detectors for a portal monitor application

A design for a new equipment for non intrusive inspection of containers in ports is described. The project involves the construction of a ~ 125 m3 cosmic muon-tracking detector, to measure the deflection of cosmic muons when traversing high-Z materials. The apparatus consists of four X-Y charged particle detector planes, two placed below and two above the container to be inspected. The detection planes are segmented into 300 cm long, 1 cm2 square plastic scintillating strips with embedded WLS fibers that transport the scintillation light to photo-sensors (SiPMs) at one end of the fiber. Detailed GEANT4 simulations have demonstrated the possibility of reconstructing a 3D image of the container volume in a reasonable amount of time, compatible with the requirements of a fast inspection technique.

Design of a large area tomograph to search for high-Z materials inside containers by cosmic muons

In recent years the need to have a better control of potentially dangerous materials across the borders has raised the opportunity to search for alternative detection techniques. In particular, to detect the presence of hidden high-Z materials inside containers, traditional techniques based on X-rays or neutron scattering are of limited use, and prototypes of detection systems based on cosmic muon scattering from high-Z materials are being tested worldwide to overcome these limitations. The use of this method is particularly suited to this aim, since it does not introduce additional radiation levels to the already existing natural dose. Since the technique is based on the scattering process of muons and not on their absorption, each event may in principle contribute to produce the tomographic image. A new Project has recently started by the Muon Portal Collaboration, which plans to build a large area muon detector, able to reconstruct muon tracks with good spatial and angular resolution. The design and operational parameters of the tomograph under construction are here described, together with preliminary simulation and test results of the individual detection modules. Due to the large acceptance of the detector for cosmic rays, coupled to the good angular reconstruction of the muon tracks, it is also planned to employ such detector in the future for cosmic ray studies, complementing its detection capabilities with a set of trigger detectors located some distance apart, in order to measure multiple muon events associated to extensive air showers.

Characterization technique of sub-millimeter scintillating fibers

The characterization of sub-millimeter scintillating optical fibers involves the measurement of the attenuation length, which is one of the main properties together with the yield and the trapping efficiency, given the use of these fibers in the design of particle detectors. Every technique considered allows for the optical coupling of the scintillating fibers to suitable photo sensors, at one or both ends. What essentially changes is the cause of scintillation light within the fibers, which comes from a UV laser or radioactive source. We have developed an alternative technique that is based on the use of cosmic rays as a uniform scintillation source. In this paper we present the results of this method compared to others obtained using standard ones.

Status and first results of the NEMO Phase-2 tower

In March 2013, the NEMO Phase 2 tower has been successfully installed in the Capo Passero site, at a depth of 3500 m and 80 km off from the southern coast of Sicily. The unfurled tower is 450 m high; it is composed of 8 mechanical floors, for a total amount of 32 PMTs and various instruments for environmental measurements. The tower positioning is achieved by an acoustic system. The tower is continuously acquiring and transmitting all the measured signals to shore. Data reduction is completely performed in the Portopalo shore station by a dedicated computing facility connected to the persistent storage system at LNS, in Catania. Results from the last 9 months of acquisition will be presented. In particular, the analyzed optical rates, showing stable and low baseline values, are compatible with the contribution mainly of 40K light emission, with a small percentage of light bursts due to bioluminescence. These features reveal the optimal nature of the Capo Passero abyssal site to host a km3-sized Neutrino Telescope.

Design and characterisation of a YAG(Ce) calorimeter for proton Computed Tomography application

The design and the characterization of a calorimeter system, aimed at measuring the residual energy in a proton Computed Tomography (pCT) apparatus, is described. The calorimeter has a 6 × 6 cm2 active area to fully cover the tracker area of the pCT system, being 10 cm thick it is able to stop up to 200 MeV protons and sustain 1 MHz particle rate (average rate on the whole area). The YAG(Ce) scintillator is promising for charged particle detection applications where high-count rate, good energy resolution and compact photodiode readout, not influenced by magnetic fields, are of importance. The aim of this work is to show data acquired with proton beam energy up to 175 MeV and to discuss the performances of this calorimeter.

Design of a muonic tomographic detector to scan travelling containers

The Muon Portal Project aims at the construction of a large volume detector to inspect the content of travelling containers for the identification of high-Z hidden materials (U, Pu or other fissile samples), exploiting the secondary cosmic-ray muon radiation. An image of these materials is achieved reconstructing the deviations of the muons from their original trajectories inside the detector volume, by means of two particle trackers, placed one below and one above the container. The scan is performed without adding any external radiation, in a few minutes and with a high spatial and angular resolution. The detector consists of 4800 scintillating strips with two wavelength shifting (WLS) fibers inside each strip, coupled to Silicon photomultipliers (SiPMs). A smart strategy for the read out system allows a considerable reduction of the number of the read-out channels. Actually, an intense measurement campaign is in progress to carefully characterize any single component of the detector. A prototype of one of the 48 detection modules (1 × 3 m2) is actually under construction. This paper presents the detector architecture and the preliminary results.

A Real-time, large area, high space resolution particle radiography system

In this paper we describe a new detection system for the high resolution measurement of the residual range of charged particles, designed and developed with the aim of achieving real-time data acquisition and large detection areas. A prototype of the residual range detector, with a sensitive area of about 4 × 4 cm2, consisting of a stack of sixty ribbons of scintillating fibers (Sci-Fi) has been designed and tested. Each layer is read-out by two wavelength shifter (WLS) fibers and a position sensitive photomultiplier (PSPM). The Bragg peak shape is calculated real-time by the time over a suitable threshold for each channel. The results of the measurements taken using the prototype and a 62 MeV proton beam and a comparison with the GEANT4 simulations of the detector are presented. The main concepts on which the prototype is based have been used to demonstrate the technique patented by the INFN. The next step will be to design and validate the final detector which will have 30 × 30 cm2 FOV and cover the 250 MeV proton range with about 150 micron range resolution. These performances are suitable for almost all medical imaging applications.

Development of a scintillation-fiber detector for real-time particle tracking

The prototype of the OFFSET (Optical Fiber Folded Scintillating Extended Tracker) tracker is presented. It exploits a novel system for particle tracking, designed to achieve real-time imaging, large detection areas, and a high spatial resolution especially suitable for use in medical diagnostics. The main results regarding the system architecture have been used as a demonstration of the technique which has been patented by the Istituto Nazionale di Fisica Nucleare (INFN). The prototype of this tracker, presented in this paper, has a 20 × 20 cm2 sensitive area, consisting of two crossed ribbons of 500 micron square scintillating fibers. The track position information is extracted in real time in an innovative way, using a reduced number of read-out channels to obtain very large detection area with moderate enough costs and complexity. The performance of the tracker was investigated using beta sources, cosmic rays, and a 62 MeV proton beam.