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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 Presentation

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Page 1: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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)

Page 2: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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

Page 3: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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:

Page 4: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

Journal of the Optical Society of America 59(1969)863at 0 oC and 760 torr

Page 5: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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

Page 6: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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

Page 7: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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.

Page 8: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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.

Page 9: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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

Page 10: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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

Page 11: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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)

Page 12: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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

Page 13: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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

Page 14: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

C2H2

C6H6

What some CnHm traces can do to you (and your photons).

CnH2n+2

CnH2n

Page 15: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

The fate of a photon after 8 m with 10 ppm O2

The (apparent) radiator length will therefore change as function of wavelength.

Page 16: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

Two extremes.1 m N2 as radiator

#photons/m 13 detected CsI up to ~8 eV

RMSMaPMT = 0.43 mradRMSCsI = 0.45 mrad

Page 17: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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

Page 18: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    
Page 19: International  RICH-Workshop of  the  CBM  Experiment  at  FAIR    

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.}