1. Transmittance Measurements of VUV Light as a Function of Water Vapor and Oxygen Concentrations
PHENIX Experiment, Brookhaven National Laboratory
June - July 2004
G. Karagiorgi**, B. Azmoun*, C. Woody*, M. Hohlmann**
*Brookhaven National Laboratory
**Florida Institute of Technology
Hello, my name is….
I am going to be talking about ….
This was a study performed for the PHENIX experiment at BNL
and it was performed over this last summer by myself, B. Azmoun and…
Florida Academy of Sciences 69th Annual Meeting
Tampa, FL
March 18, 2005

2. Purpose of Study: Reference for the Hadron Blind Detector
(HBD), which is going
to be employed at the
PHENIX experiment at
the Relativistic Heavy
Ion Collider (RHIC)
facility, at Brookhaven
National Laboratory.
The purpose of the study was to provide a reference for optimum operation conditions for the HBD detector, which is a gas Cherenkov detector.
This detector is currently under construction and it is going to be employed… by the end of year 2005
Reference:
Georgia Karagiorgi, FAS 2005

3. Introduction: Gas Cherenkov Detectors
Detection of Cherenkov light
v > c/n in medium (refraction index n)
β = c/v
cosφ=1/nβ
Reference:
A gas Cherenkov detector is a detector which is based on detection of Cherenkov light.
Cherenkov light is produced when an energetic particle travels through a medium (here, gas) at a speed that is faster than the speed of light in the medium. It is basically the same effect as a sonic boom, which occurs when an object travels in air faster than the speed of sound in the medium.
The HBD detected the cherenkov light that is produced by lepton pairs and it falls. This light is in the violet-ultra violet region of the light spectrum.
Factors that
HBD  Violet – Ultraviolet (VUV) light detection
Georgia Karagiorgi, FAS 2005

4. Introduction: Gas Cherenkov Detectors:
VUV Transmittance factors:
Gas Type ( radiator, transparent to desired λ )
Out-gassing ( vessel material )
Contaminant particles ( N2 , O2 , H2O vapor )
Georgia Karagiorgi, FAS 2005

5. Study: Transmittance of VUV light as a function of H2O vapor and O2 concentrations
Reference for water and oxygen levels that can be tolerated within such a detector before any significant fraction of VUV light is lost
% Transmittance of VUV light in Ar gas
vs.
H2O [ppm]
% Transmittance of VUV light in Ar gas
vs.
O2 [ppm]
This specific study was intended to act as a reference for water and oxygen levels that can be tolerated within such a detector before any significant fraction of VUV light is lost.
%T = (Flux out / Flux in)*100%
Georgia Karagiorgi, FAS 2005

6. Method: Experimental Setup
sample i
vacuum
Reference:
Georgia Karagiorgi, FAS 2005

7. Theory: Theoretical Transmittance
I(x) = Io e -μx
I(x=L) = Ioe –σNL
I(x=L) = Ioe –σpNL
I(x) : flux after the beam has traversed
a distance x trough the absorber
Io : initial flux
μ : attenuation coefficient
N : particle density (particles per
cubic cm)
L : total length through which the
VUV beam travels
σ : interaction cross section
Interaction cross section, [Mbarn] Vs wavelength [Angstroms] for H2O
Reference: A.N. Zaidel’ and E.Ya. Shreider, Vacuum Ultraviolet
Spectroscopy. Ann Arbor-Humphrey Publishers; Ann Arbor, London 1970
Attenuation coefficient, µ [cm-1] Vs wavelength [Angstroms] for O2
I(x) is the flux after the beam has traversed a distance x trough the absorber
I0 is the initial flux
Μ is the attenuation coefficient
N is the particle density (particles per cubic cm)
L is the total length through which the VUV beam travels
Σ is he interaction cross section
Reference: A.N. Zaidel’ and E.Ya. Shreider, Vacuum Ultraviolet
Spectroscopy. Ann Arbor-Humphrey Publishers; Ann Arbor, London 1970
Georgia Karagiorgi, FAS 2005

8. Results: Transmittance in H2O vapor
Plot 1: Transmittance spectra as a function of H2O levels
Interaction cross section, [Mbarn] Vs wavelength [Angstroms] for H2O
Reference: A.N. Zaidel’ and E.Ya. Shreider, Vacuum Ultraviolet Spectroscopy. Ann Arbor-
Humphrey Publishers; Ann Arbor, London 1970
Georgia Karagiorgi, FAS 2005

9. Results: Transmittance in H2O vapor
Plot 2: Transmittance Angstroms Vs H2O levels, compared to the expected transmittance--calculated from the interaction cross Angstrom, extracted from the theoretical data for attenuation coefficient.
Georgia Karagiorgi, FAS 2005

10. Results: Transmittance in O2
Plot 3 Transmittance spectra as a function of O2 levels
Attenuation coefficient, µ [cm-1] Vs wavelength [Angstroms] for O2
Reference: A.N. Zaidel’ and E.Ya. Shreider, Vacuum Ultraviolet Spectroscopy. Ann Arbor-
Humphrey Publishers; Ann Arbor, London 1970
Georgia Karagiorgi, FAS 2005

11. Results: Transmittance in O2
Plot 4: Transmittance Angstroms Vs O2 levels, compared to the expected transmittance--calculated from the attenuation Angstroms, extracted from the theoretical data for attenuation coefficient.
Georgia Karagiorgi, FAS 2005

12. Conclusions In agreement to previous experimental data
Provided reference for tolerable contaminant levels for
efficient operation of the HBD detector
Determined the necessity for good sealing
Georgia Karagiorgi, FAS 2005

13. References
A. N. Zaidel and E. Ya. Shreider. Vacuum Ultraviolet Spectroscopy. Ann Arbor Humphrey Publishers; Ann Arbor, London; 1970.
B. Azmoun, G. Karagiorgi and C. Woody. Transmittance as a function of water and oxygen levels in the VUV regime. September, 2004.
Georgia Karagiorgi, FAS 2005