international rich-workshop of the cbm experiment at fair
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International RICH-Workshop of the CBM Experiment at FAIR Gesellschaft für Schwerionenforschung Darmstadt, GERMANY March 6 - 7 2006 . Radiator Gases { s m a l l r e f r a c t i v e i n d i c e s } Olav Ullaland (PH, CERN) . ?. 330 10 -6 < n -1 < 360 10 -6. - PowerPoint PPT PresentationTRANSCRIPT
International RICH-Workshop of the CBM Experiment at FAIR
Gesellschaft für SchwerionenforschungDarmstadt, GERMANY
March 6 - 72006
Radiator Gases {small refractive indices}
Olav Ullaland (PH, CERN)
The requirements
th 38,
good UV transmittance,
long radiation length ideal: non inflammable, chemically passive gas
potential problem: fluorescence of N2? CH4/CO2 could be used as quenching gas in mixture
?22
11
th
n
330 10-6 < n-1 < 360 10-6
If n-1 « 1
CH4 [from Air Liquide ]Major hazard : Fire and High PressureToxicity: Simple AsphyxiantFlammability limits in air (STP conditions) : 5.0-15.0 vol%[CERN rules: LEL(%): 4.4 UEL(%):16.9]Odour : None
Tci values (%) for CH4 N2 9.9CO2 22.45He 11.86Ne 9.2Ar 6.15SF6 50.4CF4 33.4R134a 11.98
Data from:J.V. Jelly, Čerenkov Radiation and its ApplicationV.P. Zrelov, Čerenkov Radiation in High Energy Physics IIDuPont Freon Technical Bulletins B-32, 32A
and the answer is:
Journal of the Optical Society of America 59(1969)863at 0 oC and 760 torr
Anything wrong with dry air?
Cheap!Abundant!
Non flammable!~Correct refractive index!
Eigenshaften der Materie in Ihren Aggregatzustanden, 8. Teil Opische Konstanten, 1962
22
CO
22
Ar
24
5
O
22
N
C 0 torr 760air dry 6
10.80
068681.00003.0
82.73
050854.00093.0
003755.0275.2010496.5
12095.0
36.74
053191.07809.0
10)1(
2
2
2
o
n
+ 18 ppm Ne, 5.2 He, 1.5 CH4, 1.14 Kr, 0.5 N2O, 0.5 H2, 0.4 O3, 0.086 Xe
0.1
1
10
100
1000
100 125 150 175 200
Wavelength (nm)
Abs
orpt
ion
(/cm
/bar
) .
Water
Oxygen
CO2
The (possible) drawback:The transparency of a fluid is
defined by:where t is the path length in cm, f = f() is the absorption coefficient and p is the pressure in bar.
pfteT
K. Watanabe et al., Absorption Coefficients of Several Atmospheric Gases, AFCRC Technical Report No. 53-23, 1953
From:G. R. Cook and B. K. Ching, The Journal of Chemical Physics 43(1965)1794-1797R. Abjean et al., NIM A292(1990)593-594H.E. Watson and K.L. Ramaswamy, Proc. R. Soc. London, A156(1936)144Eigenshaften der Materie in Ihren Aggregatzustanden, 8. Teil Opische Konstanten, 1962
CO2 start absorbing around 180 nm.CF4 around 110 nm.N2, Ar, Ne .... transparent well below 150 nm.
With a little bit of mixing of CF4 and Ne:Setting (n-1) 106 = 350 at 400 nmgives a mixing ratio of CF4:Ne = 67:33
22
6
10.61
091553.010)1(
nWell described by:
at 0 oC and 760 torr
‘The Dutch Chemist’, c 1780s. Copper engraving by J Boydell after a painting by J Stein.
We can do the same with CF4 and He:Setting (n-1) 106 = 350 at 400 nmgives a mixing ratio of CF4:He = 695:305
22
6
45.61
09050.010)1(
nWell described by:
at 0 oC and 760 torr
http://www.levity.com/alchemy/cab_min1.html
Do a little comparison:
density X0 X0
g/l g/cm2 cmHe 0.178 94.32 5.3 105 at 0 oC and 1013 hPaNe 1.25 37.99 3.0 104 CF4 3.92 33.6 8.6 103
air 3.0 104 at 20 oC and 1013 hPa
Radiation length, X0, for a 1 m radiatorCF4/Ne 1.05 %CF4/He 1.14air 0.33
In addition:He and vacuum photo tubes no good
If using a binary (or more) gas mixturechose gases which are easy to separate. Or use and discard.
•Boiling point•Size
The gases considered have all very low boiling point.
Rather strong correlation between refractive index and size
Kinetic Diameter (A)
0.01
0.1
1
10
100
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
Kinetic diameter (A)
Sel
ectiv
ity r
elat
ive
to N
2 .
CO2
O2
ArN2
CF4 C4F10
UBE Industries, Specialty Chemicals and Products Division, High Purity Chemicals Business Unit, Ube Europe GmbH, Duseldorf, Germany.
Selectivity measurement with different types of membranes.
0.01
0.1
1
10
100
2 2.5 3 3.5 4 4.5 5 5.5 6
Kinetic diameter (A)
Sele
ctiv
ity r
elat
ive
to N
2
.
He
NeCO2
O2Ar
N2
CF4C4F10
0.01
0.1
1
10
100
2 2.5 3 3.5 4 4.5 5 5.5 6
Kinetic diameter (A)
Sele
ctiv
ity r
elat
ive
to N
2 .
He
Ne
CO2
O2Ar
N2
CF4
C4F10
NeoMechscomposite hollow fibre
GT-0212-0025-50308
Generon hollow fibre membrane Model B210
It is therefore (fairly) easy to separate He or Ne from CF4
Some reasons why NOT having quantum efficiency below ~190 nm.
•Air contamination (O2, H2O and CO2) levels of a few ppm.•Trace contamination of the main radiator gas to levels approaching ppb•Outgassing properties of the main structures to space requirements•Perfect gas flow pattern•Chromatic aberration is important•Rayleigh scattering starts to be important•Expensive optical windows•Photon detector entrance window in contact with the radiator
or high quality atmosphere in the photon detector enclosure
6.5 eV
C2H2
C6H6
What some CnHm traces can do to you (and your photons).
CnH2n+2
CnH2n
The fate of a photon after 8 m with 10 ppm O2
The (apparent) radiator length will therefore change as function of wavelength.
Two extremes.1 m N2 as radiator
#photons/m 13 detected CsI up to ~8 eV
RMSMaPMT = 0.43 mradRMSCsI = 0.45 mrad
What about scintillation and fluorescent?
Example:Ar 130 nmKr 150 nmXe 175 nm 2 time constants: from a few ns to 1 µs.CF4 >120 nm 20% [3% + 9% - 6%] of Xe
>180 nm 45% [3% +17% -13%] of Xe NIM 361(1995)543
As it is non-directional, it will (normally) not influence the pattern recognition algorithm.
To watch: Cherenkov signal photons to background hits.
(10-19 cm2) = 3303914 A
(10-19 cm2) = 934278 A
Perhaps evident, but still:
n=Fn: photons emitted/cm3
F: proton flux: cross section for excitation: molecular density
In additionn dE/dx
Spectra induced by 200 keV proton impact in nitrogen.Phys.Rev.123(1961)2084
Relative light yield:Xe:Kr:Ar:Ne:He=1.0:0.52:0.16:0.043:0.33
Conclusion
Gases with low refractive index
are not (really) different from gases with high refractive index
If you want to move down a little, neon is a good gasIf you want to move up a little, CF4 is a good gas
If you are nearly right with air, use air, but remove the water and the dust. {There will always be somebody who ask if you have included Mie's theory in the simulation.}