The Muon Portal Project: A large area tracking detector for muon tomography Francesco Riggi Dept. of Physics and Astronomy, University of Catania, Italy On behalf of the Muon Portal Collaboration NN 2015 Conference, Catania, June 21-26, 2015 Catania, Villa Bellini

Presentation Overview Cosmic-rays and muon tomography The Muon Portal Project in Catania Construction and test of the detection modules Simulation and reconstruction algorithms Present status of the Project and outlook

The problem Containers: employed since 50 years as a standard way to transport goods by ships or trucks. Our (small) port in Catania: about container /year Estimated yearly traffic: 200 M containers Safety regulations demanding a better and fast way to inspect such containers, not possible by traditional techniques. Presently only about 1% inspected 2012 Data

Why Muon Tomography Secondary cosmic muons: highly penetrating radiations (even more than X-rays) “Natural” radiation, hence no additional dose delivered to users and goods Muon flux at sea level relatively large: 1 cm -2 min -1 Muonic interactions well understood Muon scattering strongly dependent on the Z of the material Each muon may contribute to determine the overall imaging result (contrary to muon absorption techniques ) Primary eV

Muon Tomography  L. Schultz IEEE NSS Conference Record (2006)

High-Z  a b Muon Tomography ● Muon tomograph: basically made by several detection planes, above and below the volume to be inspected ● Reconstruction of muon tracks allows to produce a 3D image ● Performance of the system are given in terms of - Sensitive area / volume to be inspected - Spatial and angular resolution - Time to scan a volume - Sensitivity & Efficiency to high-Z objects - Sensitivity to false positive - Discrimination between high-Z vs low & medium-Z

On-going Projects Several Projects worldwide interested in Muon Tomography INFN Padova (Italy) Los Alamos National Laboratory (USA) Florida Institute of Technology (Australia) Carleton University (Canada) Tsinghua University (China) Bristol University (UK) … (a non exhaustive list) Various detector prototypes built and tested Various detection techniques employed Drift chambers Drift tubes GEM MRPC …. Same technique also used for similar applications (nuclear waste, orphan sources,…)

The Muon Portal Project in Catania ● Basic architecture based on 8 physical detection planes (4 XY logical planes) segmented into 48 detection modules (1 m x 3m) ● Modules segmented into 100 strips of extruded scintillator with double WLS fibre readout ● High PDE, high fill-factor Silicon photomultipliers as readout sensors The Project in numbers: 30 km WLS optical fibers 15 km Scintillating strips 9600 Silicon Photomultiplier 18 m 2 Detection area 130 m 3 Overall volume 0.1° Tracking angle resolution O(10 7 ) Muons detected per day

Mechanical structure ● Mechanical structure under control with PLC ● Variable distance between detection planes ● Monitoring and storage of various parameters ● Sensors for alignment and alarms

Detection modules: 1 x 3 m sandwiches of 100 scintillator strips with 200 WLS fibers Readout by Silicon Photomultipliers at one end Detection modules

Various designs of extruded strips tested in the lab and simulated by GEANT4 Strip design d (cm) Threshold = 2 p.e. Threshold = 1 p.e. Distance from SiPM (cm)

Photosensor design Silicon PhotoMultipliers by STMicroelectronics as photosensors - Compactness - Cost-effective - Low voltages required - High Photon Detection Efficiency to light from WLS fibres - High Fill Factor - Several prototypes built, customized for this application

Photosensor testing ● Individual characterization of ~10 4 devices ● Breakdown voltage selection (100 mV bins)

Front-end readout and channel reduction Combining the information of two WLS fibres Reduction factor for module: 2√N (N number of channels per module) (8 planes) x (6 modules) x (100 x 2 WLS) = 9600 channels After channel reduction (8 planes) x (6 modules) x (2√100 ) = 960 channels

A lot of home-made work.. Construction of the detection modules

Tests of detection modules Test of detection modules with a trigger scintillator: ● Photoelectron yield ● Coincidence rate of single strips ● Mono and two-dimensional maps Uniformity along the modules

Tests of detection modules Light yield from the SiPM. 1 p.e. = 20 mV Measured coordinate along the 100 strips of a detection module, in coincidence with a trigger scintillator

Simulation procedures Full GEANT4 replica of the detector Cosmic muons modelled with realistic energy and angular distribution by CORSIKA air shower simulations Transport of optical photons fully simulated Reconstruction of hits and cluster in each plane Single muon tracks and e.m. showers taken into account After track reconstruction, tomographic images built by several methods (POCA, EM-EL, Clustering,…) Various scenarios considered

19 Simulated scenarios Large set of events simulated for each scenario, with realistic energy and angular distributions of muons 4 threat boxes (W, U, Pb and Sn) size 10x10x10 cm A “MUON” shape with letters of different materials (U, Fe, Pb, Al) As B, with a heavy scenario with washing machines elements (iron, concrete,..) surrounding the “MUON” shape

The POCA algorithm Simplest approach, fast and easy to implement Geometrical point of closest approach between incoming and outcoming tracks Spatial distribution of the scattering centres, weights given by some power of the scattering angle However: Neglects multiple scattering within the material Poor resolution images Critical behaviour for material located close to volume borders Several improvements may be implemented: - Density based clustering algorithms - Two points (2P) correlation analysis

Results from POCA Basic POCA methodAfter clustering algorithms

The EM-ML method Better statistical treatment of scattering processes by a log- likelihood method Volume to be inspected divided into voxels Scattering density defined for each voxel Iterative estimation with some stopping criterion

EM-ML results Slightly better results obtained However, optimal tuning of this algorithm is often required to cope with different scenarios. More sophisticated algorithms also implemented Usually, combination of several methods

Present status of the Project ● A large area muon tomograph currently under construction after extensive R&D phase ● Large number (10 4 ) of channels involved, with corresponding number of SiPM photosensors ● New solutions exploited for channel reduction, electronic readout and data acquisition ● Monitoring and image reconstruction with different algorithms and tools implemented ● Construction of 46 (of 48) modules achieved ● First plane (12 modules) already installed and tested ● End of construction and installation procedures expected by end 2015

The Muon Portal and cosmic ray physics Due to large area and tracking capabilities, it is also planned to employ the Muon Portal for studies in cosmic ray physics. A few possible items of interest: ● Study of multi-muon events and muon bundles in triggered showers ● Coincidence studies with external extensive air shower detectors ● Environmental monitoring of the cosmic ray flux (solar flares, …) ● Sky map overview and isotropy/anisotropy studies of low energy primaries

The Muon Portal and cosmic ray physics Trigger on air showers by 3-fold coincidences Muon bundles in the Portal

Outreach and dissemination activities Due to the nature of the Project, even outreach activities are believed to be important ● Public meetings and colloquia targeted to students, high-school and citizen people ● Posters, articles on local newspapers ● Stands during public events ● Construction of an exhibition box located in a public area for outreach activities

The partners Dept. Of Physics & Astronomy, University of Catania INAF, Astrophysical Observatory, Catania STMicroelectronics S.r.l. Catania Insirio SPA Meridionale Impianti Welding Technology