Download A. Menegolli

Noble-gas liquid detectors: measurement
of light diffusion and reflectivity on
commonly adopted inner surface materials
S. Bricola, A. Menegolli, M. Prata, M.C. Prata, G.L. Raselli,
M. Rossella, C. Vignoli
INFN and University of Pavia - Via Bassi, 6 – 27100 Pavia – Italy
Outline
 Introduction
 Purposes
 Experimental set-up
 Results
 Future measurements
IPRD06 - 5/10/06 Siena - A. Menegolli
Introduction
Noble-gas liquids, such as xenon and argon, have been recently proposed
as light scintillators in some experiments dedicated to neutrino physics
and dark matter research.
ICARUS T600 detector
m
Cathode plane
Drift field = 500 V/cm
Liquid Argon
T=87 K
Anode wire planes
in the VUV spectrum:
l (LAr) = 128 nm
l (LXe) = 178 nm
eee-
E
Scintillation light is emitted
E
eeeeETL 9357FLA PMT
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:
Stainless
steel:
detector
structure
detector
structure
Peek:
Teflon:
insulator
insulator
IPRD06 - 5/10/06 Siena - A. Menegolli
Experimental set-up
The samples used for these measurements were taken from the materials
used in a real experimental set-up (ICARUS T600)
VUV (115 nm ÷ 400 nm) deuterium
lamp (Hamatsu L7293 ), with
filter (l ~
The goal is to extract the optical propertiesmonochromator
of each sample exposed
to172
a nm)
~ monochromatic VUV light of known intensity : absorption, diffusion and
reflectivity
Hamatsu R7311 PMT (QE ~
35% at l = 172 nm
Frame for sample placement
IPRD06 - 5/10/06 Siena - A. Menegolli
VUV source: - Hamatsu L7293 deuterium lamp
with emission range 115 nm ÷ 400 nm;
- MgF2 window;
- long nose type to be put inside a vacuum chamber;
- monochromatic filter to select l ~ 172 nm (FWHM ~ 24 nm);
- lense to collimate the beam (f = 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:
Detector: - Hamamatsu R7311 PMT, QE ~
35% at 172 nm, photocathode: Cs-Te;
- detector window: MgF2
- active area = 4 mm x 5 mm
q
Measurements were carried out after
having inserted all instruments inside
a vacuum chamber
IPRD06 - 5/10/06 Siena - A. Menegolli
Results
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:
N 
J
(1.6 1019 )  QE
J = current (in Ampere)
QE = PMT Quantum Efficiency (~ 0.35)
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 q:
N  ,lamp (q ) 
J (q )
1

(1.6 10 19 )  QE Rmir
By integrating over all solid angle, the
total number of photons emitted per
second by the lamp was evaluated:
Ntot = 2.4 x 1010 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:
Ntot = 1.37 x 1010 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:
Nref = 0.33 x 1010 ph/s; Ndif = 1.35 x 1010 ph/s
Nref = 1.68 x 1010 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:
Nref = 0.75 x 1010 ph/s; Ndif = 0.85 x 1010 ph/s
Nref = 1.60 x 1010 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
light
Emitted
light
FWHM
Emitted
light
Absorbed
light
57%
43%
FWHM
Stainless
steel
57%
4°
Aluminum
14%
26°
56%
58°
70%
30%
Peek
31%
28°
36%
37°
67%
33%
Teflon
30°
IPRD06 - 5/10/06 Siena - A. Menegolli
Future measurements
The following measurements on all four materials are foreseen to be carried
out in the next future:
- @ 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 on a cold finger
IPRD06 - 5/10/06 Siena - A. Menegolli
IPRD06 - 5/10/06 Siena - A. Menegolli