ONLY - Oxygen Nitrogen Light Yield
Since 1998 IASF-Palermo groups are deeply involved in experimental activities of support
for Astroparticle Research from space and in particular in those activities related to the
EUSO will explore the Extreme Energy Cosmic Rays (EECR) component in the region
above 1019 eV,
using the Earth's atmosphere as a scintillating giant absorber. EUSO will detect EECRs from space
by looking, in the Earth's night sky, at the streak of UV fluorescence
light produced when the particles interact with the Earth's atmosphere.
In this framework, laboratory experiments have been identified as propaedeutic
experimental supporting activities to know fundamental information concerning the UV fluorescence yield.
Laboratory measurements of UV fluorescence yield at low energy (22 KeV), using the X-ray facility
LAX located in Palermo,
have been performed in 1998-2000 with the ONLY (Oxygen Nitrogen
Light Yield) experiment, whereas the possibility of measurements
at higher energies, of basic importance for the project, is presently under discussion
within the EUSO collaboration.
The ONLY Experiment
The ONLY experiment refers to measurements of UV light yield obtained in pure dry air and,
for comparison, in pure Nitrogen, using an intense flux of X-ray photons at the LAX facility in Palermo.
The UV fluorescence radiation from air results, almost entirely, from electronic transition
from the first excited levels of the Nitrogen molecule or molecular ion to the ground level.
The radioactive emission from these electronic transitions is detected as very narrow lines
in the near UV band (mainly lines 337, 357 for Nitrogen molecule and 391 nm for molecular ion).
The apparatus of measurement
To measure the UV fluorescence yield it has chosen to use of the technique of the
counting of events seen by two photomultipliers operated in coincidence mode.
The apparatus of measurement consists of a cylindrical gas cell of ceramic closed at top
and bottom by quartz windows 5 mm thick. Two photomultipliers (EMI D319Q operated at 2 kV)
of 8 cm of diameters detect the UV light produced inside the cell.
To reduce the variations of the solid angle subtended by the photomultipliers at the point
production of the UV light, the X-ray photons are collimated inside the cell in an absorption
region of only 4 cm of length centered on the Pmts.
Schematics of the entire experimental set-up
Due to the low photoelectric cross section of air and the small absorption region,
it has been used the intense X-ray source of the X-ray Beam Facility at LAX in Palermo.
The X-ray generator is a "Seyfert" tube, with flux ranging from 1010
to 1012 photons sr-1 sec-1,
covering the energy range from few keV to 25 keV depending of the target material used
as anode in the tube.
It has been chosen the 22.1 keV fluorescence line of the Silver target with a trade-off
between as much UV photons as possible inside the cell and a minimum X-ray Compton diffusion.
As the fluorescence decay time of the excited Nitrogen molecules is about 50 nsec,
it has been chosen in the electronic chain a coincidence gate time of 500 nsec.
For the photomultipliers and the electronic chain, it has been used high gain settings
and low discrimination thresholds.
Following a statistical approach and measuring the coincidence rate of the X-ray events detected
via UV fluorescence photons, it has obtained the UV light yield.
The UV light yield measured with ONLY
The UV yield follows a proportional inverse law with the pressure (expected from kinetic theory)
both for air and for pure nitrogen. The value, for pure-air, range from 0.2% to 0.02% below
300 mbar of air pressure.
Now the IASF-Palermo, in collaboration with the EUSO groups, is willing to spend
its activity to develop and build an more complex experimental apparatus suitable to measure
the fluorescence Yield in the atmosphere, as produced by a particle beam (mainly electrons)
with energies in the range from about 1 MeV to several GeV, and to perform the connected measurements
in the suitable accelerator sites.
The scientific goal is to measure the fluorescence Yield in a gas simulating the Earth's atmosphere
as a function of a gas composition, temperature, pressure and humidity.
The measurements should mimic, in a controlled environmental situation,
the fluorescence Yield of a cosmic ray induced shower in atmosphere.
With different commitments and tasks, the following
IASF-Palermo personnel is part of the ONLY group:
Salvo Giarrusso (ONLY Respons.) |
Gaetano Agnetta |
Benedetto Biondo |
Filippo Celi |
Osvaldo Catalano |
Renato Di Raffaele ||
Gino Gugliotta |
Giovanni La Rosa |
Angelo Mangano |
Francesco Russo |
Bruno Sacco |
Paolo Scarsi |
Salvo.Giarrusso at iasf-palermo.inaf.it
"Laboratory measurements of Air UV fluorescence Light Yield induced by X-ray
S. Giarrusso, O. Catalano, F. Celi, G. Fazio, G. La Rosa, T. Schillaci,
Proc. 26th ICRC, D. Kieda, M. Salamon, B. Dingus, (Eds.),
Vol.5, 449, 1999
"AIRWATCH/OWL: Preliminary Results from Lab Measurements and from Ballon Background Observations",
S. Giarrusso, O. Catalano, F. Celi, G. La Rosa, J. Linsley, C. Maccarone, B. Sacco, L. Scarsi,
Proc. 19th Texas Symposium on 'Relativistic Astrophysics and Cosmology',
E. Aubourg, T. Montmerle, J. Paul, P. Peter, (Eds.), CD-ROM code 08/05, E627G, 1999
"AIRWATCH: air induced fluorescence by radiation: laboratory experiments" ,
S. Giarrusso, O. Catalano, F. Celi,
G. Fazio, G. La Rosa, G. Richiusa, T. Schillaci, G. Bonanno,
R. Cosentino, R. Di Benedetto, S. Scuderi,
Proc. SPIE'98 Conf., 3445, 460-469, 1998
"Air Fluorescence efficiency measurements for AIRWATCH based mission:
experimental set-up" ,
B. Biondo, O. Catalano, F. Celi, G. Fazio,
S. Giarrusso, G. La Rosa, A. Mangano, G. Bonanno,
R. Di Benedetto, S. Scuderi, G. Richiusa, A. Gregorio,
Proc. Workshop on 'Observing Giant Cosmic Ray Air Showers from Space',
J.F. Krizmanic, J. Ormes, R.E. Streitmatter, (Eds.), AIP-CP433, 361-366, 1998
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Last Modification: Monday, January 23 2012