S. Bricola, A. Menegolli, M. Prata, M.C. Prata, G.L. Raselli, M. Rossella, C. Vignoli INFN and University of Pavia - Via Bassi, 6 – Pavia – Italy Noble-gas liquid detectors: measurement of light diffusion and reflectivity on commonly adopted inner surface materials

IPRD06 - 5/10/06 Siena - A. Menegolli Outline  Introduction  Purposes  Experimental set-up  Results  Future measurements

IPRD06 - 5/10/06 Siena - A. Menegolli E  e-e-e-e- e-e-e-e- e-e-e-e- e-e-e-e- e-e-e-e- e-e-e-e- e-e-e-e- Anode wire planes Liquid Argon T=87 K Drift field = 500 V/cm ETL 9357FLA PMT Cathode plane E xenonargon Noble-gas liquids, such as xenon and argon, have been recently proposed light scintillators as light scintillators in some experiments dedicated to neutrino physics and dark matter research. Introduction Scintillation light is emitted in the VUV spectrum:  (LAr) = 128 nm  (LXe) = 178 nm ICARUS T600 detector The prompt (~ µs) photon emission is useful as it provides an absolute time measurement and a trigger for ionizing events occurring in Liquid Noble Gases

IPRD06 - 5/10/06 Siena - A. Menegolli Purposes Materials which compose detector inner surfaces can diffuse the VUV scintillation light the study of the optical properties of such materials in the VUV region is fundamental to provide inputs for MONTECARLO simulations of scintillation light. Aluminum: detector structure Stainless steel: detector structure Peek: insulator Teflon: insulator

IPRD06 - 5/10/06 Siena - A. Menegolli The samples used for these measurements were taken from the materials used in a real experimental set-up (ICARUS T600) The goal is to extract the optical properties of each sample exposed to a ~ monochromatic VUV light of known intensity : absorption, diffusion and reflectivity Experimental set-up VUV (115 nm ÷ 400 nm) deuterium lamp (Hamatsu L7293), with monochromator filter ( ~ 172 nm) VUV (115 nm ÷ 400 nm) deuterium lamp (Hamatsu L7293 ), with monochromator filter ( ~ 172 nm) Frame for sample placement Hamatsu R7311 PMT (QE ~ 35% at = 172 nm R = 17 cm

IPRD06 - 5/10/06 Siena - A. Menegolli VUV source: - Hamatsu L7293 deuterium lamp 115 nm ÷ 400 nm; with emission range 115 nm ÷ 400 nm; - MgF 2 window; - MgF 2 window; - long nose type to be put inside a vacuum chamber; - long nose type to be put inside a vacuum chamber; - monochromatic filter to select ~ 172 nm (FWHM ~ 24 nm); - monochromatic filter to select ~ 172 nm (FWHM ~ 24 nm); - lense to collimate the beam (  = 8 mm) - lense to collimate the beam (  = 8 mm)

IPRD06 - 5/10/06 Siena - A. Menegolli Sample : - the sample to be studied is placed on a frame in the center of the chamber; - the mechanical support of the sample has been verified to be exactly normal to the plane where the detector moves; - all measurements are performed with the sample placed at 45° with respect to the incident beam. Detector : the detector of the emitted light is placed on a stepping motor that allows to collect the light at several angles along the plane:  Measurements were carried out after having inserted all instruments inside a vacuum chamber Detector: - Hamamatsu R7311 PMT, QE ~ 35% at 172 nm, photocathode: Cs-Te; 35% at 172 nm, photocathode: Cs-Te; - detector window: MgF 2 - detector window: MgF 2 - active area = 4 mm x 5 mm - active area = 4 mm x 5 mm

IPRD06 - 5/10/06 Siena - A. Menegolli Results A preliminary measurement with a mirror of known reflectivity R mir = 0.76 placed on the frame at the center of the chamber allowed the evaluation of the total number of photons emitted per second by the lamp at angle  : From the PMT output the currents in the several positions along the plane of displacement of the PMT are available. From these, the number of photons collected per second can be extracted: J = current (in Ampere) QE = PMT Quantum Efficiency (~ 0.35) By integrating over all solid angle, the total number of photons emitted per second by the lamp was evaluated: N tot = 2.4 x ph/s

IPRD06 - 5/10/06 Siena - A. Menegolli 1. Stainless Steel Stainless steel presents a roughly all-reflective behavior, though the reflection is diffusive, with an opening angle ~ 4° (FWHM) The integration over the solid angle gives the total number of photons per second: N tot = 1.37 x ph/s (57% of the light emitted by the lamp)

IPRD06 - 5/10/06 Siena - A. Menegolli 2. Aluminum Aluminum presents both reflective and diffusive behavior; the two contributions were disentangled, so that it was possible to measure the opening angle of the diffusive reflection (~ 26° - FWHM) The integration over the solid angle gives the total number of photons per second: N ref = 0.33 x ph/s; N dif = 1.35 x ph/s N ref = 1.68 x ph/s (70% of the light emitted by the lamp)

IPRD06 - 5/10/06 Siena - A. Menegolli 2. Peek Peek presents both reflective and diffusive behavior; the two contributions were disentangled, so that it was possible to measure the opening angle of the diffusive reflection (~ 28° - FWHM) The integration over the solid angle gives the total number of photons per second: N ref = 0.75 x ph/s; N dif = 0.85 x ph/s N ref = 1.60 x ph/s (67% of the light emitted by the lamp)

IPRD06 - 5/10/06 Siena - A. Menegolli 4. Teflon Teflon also presents both reflective and diffusive behavior, but the diffusion now dominates; it is present a strong asymmetry going from -45° to +45°, maybe due to the shadow from the support of the sample; the two contributions could not properly have been disentangled, so that it was possible just to have an estimate of the opening angle of the diffusive reflection (~ 30° - FWHM)

IPRD06 - 5/10/06 Siena - A. Menegolli Resume Reflective component Diffusive component Emitted Emitted light lightAbsorbed Emitted FWHMEmitted FWHM Stainless steel 57% 4° 4°57%43% Aluminum14%26°56%58°70%30% Peek31%28°36%37°67%33% Teflon30°

IPRD06 - 5/10/06 Siena - A. Menegolli Future measurements 128 nm (LAr scintillation light wavelength); more other wavelengths, by using a vacuum monochromator; °; angles of incidence of the beam other than 45°; cryogenic temperatures, by mounting the sample cryogenic temperatures, by mounting the sample on a cold finger The following measurements on all four materials are foreseen to be carried out in the next future:

IPRD06 - 5/10/06 Siena - A. Menegolli