s. bricola, a. menegolli , m. prata, m.c. prata, g.l. raselli, m. rossella, c. vignoli infn and...

S. Bricola, S. Bricola, A. MenegolliA. Menegolli, M. Prata, M.C. Prata, G.L. Raselli,, M. Prata, M.C. Prata, G.L. Raselli,M. Rossella, C. VignoliM. Rossella, C. Vignoli

INFN and University of Pavia - Via Bassi, 6 – 27100 Pavia – ItalyINFN and University of Pavia - Via Bassi, 6 – 27100 Pavia – Italy

Noble-gas liquid detectors: measurementNoble-gas liquid detectors: measurementof light diffusion and reflectivity on of light diffusion and reflectivity on

commonly adopted inner surface materialscommonly adopted inner surface materials

IPRD06 - 5/10/06 Siena - A. MenegolliIPRD06 - 5/10/06 Siena - A. Menegolli

Outline

Introduction Purposes Experimental set-up Results Future measurements


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Anode wire planes

Liquid Argon T=87 K

Drift field = 500 V/cm

ETL 9357FLA PMT

Cathode plane

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Noble-gas liquids, such as xenonxenon and argonargon, have been recently proposedas light scintillatorslight scintillators in some experiments dedicated to neutrino physics and dark matter research.

Introduction

Scintillation light is emittedin the VUV spectrum:

(LAr) = 128 nm(LAr) = 128 nm

(LXe) = 178 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


PurposesMaterials 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.

AluminumAluminum::detector detector structurestructure

Stainless Stainless steelsteel::

detector detector structurestructure

PeekPeek::insulatorinsulator

TeflonTeflon::insulatorinsulator


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-upVUV (115 nm ÷ 400 nm) VUV (115 nm ÷ 400 nm)

deuterium lamp (Hamatsu deuterium lamp (Hamatsu L7293L7293 ), with monochromator ), with monochromator

filter (filter ( ~ 172 nm) ~ 172 nm)

Frame for sample placementFrame for sample placement

Hamatsu R7311 PMT (QE Hamatsu R7311 PMT (QE ~ 35% at ~ 35% at = 172 nm = 172 nm

R = 17 cm


VUV source: - Hamatsu L7293 deuterium lamp with emission range 115 nm ÷ 400 nm;115 nm ÷ 400 nm; - MgF- MgF2 2 window;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 - monochromatic filter to select ~ 172 nm (FWHM ~ 24 nm); ~ 172 nm (FWHM ~ 24 nm); - lense to collimate the beam (- lense to collimate the beam ( = 8 mm) = 8 mm)


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 Measurements were carried out after having inserted all after having inserted all instruments inside a vacuum instruments inside a vacuum chamberchamber

Detector: - Hamamatsu R7311 PMT, QE ~ Detector: - Hamamatsu R7311 PMT, QE ~ 35% at 172 nm, photocathode: 35% at 172 nm, photocathode: Cs-Te; Cs-Te; - detector window: MgF- detector window: MgF22 - active area = - active area = 4 mm x 5 mm 4 mm x 5 mm


Results

A preliminary measurement with a mirror of known reflectivity Rmir = 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:

QEJN

)106.1( 19

J = current (in Ampere) J = current (in Ampere) QE = PMT Quantum Efficiency (~ 0.35)QE = PMT Quantum Efficiency (~ 0.35)

mirlamp RQE

JN 1)106.1(

)()( 19,

By integrating over all solid angle, the total number of photons emitted per second by the lamp was evaluated:

NNtottot = 2.4 x 10 = 2.4 x 101010 ph/s ph/s


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:

NNtottot = 1.37 x 10 = 1.37 x 101010 ph/s ( ph/s (57% of the light emitted by the lamp57% of the light emitted by the lamp))


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:

NNrefref = 0.33 x 10 = 0.33 x 101010 ph/s; N ph/s; Ndifdif = 1.35 x 10 = 1.35 x 101010 ph/s ph/s

NNrefref = 1.68 x 10 = 1.68 x 101010 ph/s ( ph/s (70% of the light emitted by the lamp70% of the light emitted by the lamp))


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:

NNrefref = 0.75 x 10 = 0.75 x 101010 ph/s; N ph/s; Ndifdif = 0.85 x 10 = 0.85 x 101010 ph/s ph/s

NNrefref = 1.60 x 10 = 1.60 x 101010 ph/s ( ph/s (67% of the light emitted by the lamp67% of the light emitted by the lamp))


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)


Resume

Reflective Reflective componentcomponent Diffusive componentDiffusive component

Emitted Emitted lightlight

Absorbed Absorbed lightlight

Emitted Emitted lightlight FWHMFWHM EmittedEmitted

lightlight FWHM FWHM

Stainless Stainless steelsteel 57%57% 4°4° 57%57% 43%43%

AluminumAluminum 14%14% 26°26° 56%56% 58°58° 70%70% 30%30%

PeekPeek 31%31% 28°28° 36%36% 37°37° 67%67% 33%33%

TeflonTeflon 30°30°


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:

s. bricola, a. menegolli , m. prata, m.c. prata, g.l. raselli, m. rossella, c. vignoli infn and...

Documents

emitted light

vuv scintillation light

nm lense

nm fwhm

detector window

detector structurepeek

measurementof light

detector inner surfaces