Construction and characterization of the Central Neutron Detector for CLAS12

The Central Neutron Detector (CND) is part of the CLAS12 apparatus, at the Jefferson Lab, and it was primary designed to detect the recoil neutrons in Deeply Virtual Compton Scatterings events on neutrons (n-DVCS). This measurement is an important step to complete our understanding in the description of the structure of the nucleon in terms of Generalized Parton Distributions. In order to match the experiment requirements in terms of photon-neutron rejection the CND must provide good time properties. With the conclusion of the R&D phase, we defined the final design of the detector, which will make use of scintillator bars read-out with PMTs organized in a three layer barrel. The CND will count then 24 elements of 6 scintillators each optically coupled two-by-two with a U-turn light guide, for a total of 144 scintillators and PMTs. In this communication we will report on the status of the CND construction and characterization. In particular we will present the different steps necessary to assemble each block of the detector; we will discuss the outcomes on the tests performed to fully characterize each block in terms of time resolution, charge collection, light attenuation and velocity in the scintillators; finally we will show as well the mechanic structure designed to integrate the CND in the full apparatus

Temperature-Induced Aging Effect on Extruded Scintillators and Optical Fibers for the Pierre Auger Observatory Upgrade

In the framework of the Pierre Auger Observatory upgrade, which foresees the installation of scintillator-based surface detectors placed above the water-Cherenkov tanks, we studied the light yield and the effect of temperature cycling for different extruded scintillators/optical fibers configurations. In this paper we will report on the light yield of extruded scintillators read out with wavelength shifting optical fibers, optically coupled to a PMT. We tested many different geometries, different fibers qualities and diameters and different scintillators providers. Then, for a selected number of configurations, we tested the effect of temperature variations on the detector response, in a climatic chamber. In order to reproduce the thermic excursion that will affect the detectors installed in the field in Argentina (between -5°C to +40°C), we studied the scintillator response in the temperature range from -20°C to +70°C. We performed as well many temperature cycles between -20°C to +50°C to study the temperature-induced degradation on the detectors due to mechanical stress

Design and time properties of the Central Neutron Detector for CLAS12

The primary goal of the experiments using the CLAS12 detector at energies up to 12 GeV, at the Continuous Electron Beam Accelerator Facility at the Jefferson Laboratory, is the study of the structure of the nucleons in terms of the Generalized Parton Distributions. One of the necessary steps to complete our understanding in this field is the measure of the Deeply Virtual Compton Scattering on the neutron (n-DVCS) and so, to this aim, we are constructing a scintillator detector dedicated to the detection for the recoil neutron to be placed in the Central Detector system of the CLAS12 apparatus. To match the requirements of the experiment the Central Neutron Detector must provide good time properties in order to ensure good photon-rejection capabilities.In this communication we will report on the study and R&D of the Central Neutron Detector for CLAS12. In particular, we will describe the results on the tests that lead us to the final choice of the detector’s design and we will discuss the outcomes of the study on the time resolution properties of the prototype

Study of light yield for different configurations of plastic scintillators and wavelength shifting fibers

International audienceIn the effort of the AugerPrime scintillator surface detector R&D; activity, we investigated the performances of different extruded and cast plastic scintillators that were read out with wavelength-shifting (WLS) optical fibers and then coupled to a PMT. In particular we compared the light yield of eighteen scintillator/fiber configurations, obtained combining eight different scintillator bars with six fiber types, in order to investigate which was satisfying the AugerPrime specifications in terms of light production ( >12 photoelectrons per minimum ionizing particle). In this paper, we present the results of the study on different scintillator bar geometries, scintillator production techniques, and wavelength-shifting optical fiber types. We also propose an effective way to optically couple the fibers to the PMT entrance window

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances

Design and characterization of a single photoelectron calibration system for the NectarCAM camera of the medium-sized telescopes of the Cherenkov Telescope Array

International audienceIn this work, we describe the optical properties of the single photoelectron (SPE) calibration system designed for NectarCAM, a camera proposed for the Medium Sized Telescopes (MST) of the Cherenkov Telescope Array (CTA). One of the goals of the SPE system, as integral part of the NectarCAM camera, consists in measuring with high accuracy the gain of its photo-detection chain. The SPE system is based on a white painted screen where light pulses are injected through a fishtail light guide from a dedicated flasher. The screen – placed 15 mm away from the focal plane – is mounted on an XY motorization that allows movements over all the camera plane. This allows in-situ measurements of the SPE spectra via a complete scan of the 1855 photo-multiplier tubes (PMTs) of NectarCAM. This calibration process will enable the reduction of the systematic uncertainties on the energy reconstruction of γ -rays coming from distant astronomical sources and detected by CTA.We discuss the design of the screen used in the calibration system and we present its optical performances in terms of light homogeneity and timing of the signal

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances

Dip-coated screen for gain calibration and alignment of gamma-ray telescope mirrors

In this communication, we will present a dual-purpose calibration system of NectarCAM, a medium-size-telescope camera proposed for the Cherenkov Telescope Array (CTA). The device is based on a white diffuse-reflective screen mounted on an XY motorization to reach every location in the focal plane, including a parking position when not in use. The design of the system was led by the requirements to perform the mirror alignment and the study of the telescope Point Spread Function (PSF) on one side (A), and to calibrate the photodetection chains (one for each of the 1855 photomultiplier tubes) of the camera in single photoelectron mode on the other side (B). The main requirement for the calibration device consists in producing a high-reflective (> 90% between 450 nm and 700 nm) and diffusive (following Lambert's cosine law) surface for side A. The other side, B, should emit an homogeneous amount of light over the surface. To satisfy these requirements, we developed a unique screen made out of PMMA and coated with the BC-620 paint from Saint-Gobain. For single-photoelectron calibration purposes, light is produced by a pulsed light source and injected into the screen via a fishtail light guide. We studied the optimal screen shape, paint, and painting process. To do so, we produced several prototypes and compared the light output intensity over the screen surface. These studies led to the definition of a specific painting pattern that enhances the light emission uniformity over the final octagonal screen surface. After having briefly described the developed prototypes that led to the current calibration device, we will focus on the calibration system performances and will describe the dip-coating application process, which is an essential technique to achieve reliable and reproducible optical performances