Yuri Kamyshkov / University of Tennessee
Aqueous Scintillators Meeting
at Temple University, January 19, 2010
 Will talk about possible extension of Cherenkov radiation
detection due to absorption and re-emission of Cherenkov
light in wider wavelength range by the additives to water
 Will illustrate this mechanism with our work performed
for organic scintillator in KamLAND that resulted in LS
response non-linearity understanding measurement and
correction
 Will discuss our R&D plans for water studies
Cherenkov light emission
at threshold velocities
Cherenkov radiation
starts with UV photons
J.D. Jackson, Classical Electrodynamics
3-rd edition, page 638
;   n 2 
Cherenkov emission band
Red UV
PMT
sensitivity
range
for LS
0 ~ 100 nm
 1
d 2 N  2πα 
1
 2 1  2 2   2
dxd
λ  β n    
mostly UV
Cherenkov yield in Super-K
(simple estimate)
Say, for relat ivist ic muon wit h dE dx @ 2 MeV cm in wat er:
# of g per cm produced bet ween 300 and 600 nm
~ 347
[compare wit h 100 eV/ g in t ypical LS
~10,000 g / MeV ]
# of phot ons per MeV
wit h 40% phot ocat hode coverage
~ 175
~ 70
say, 25m pat h for 100m at t enuat ion len gt h e ~ 20% phot ocat hode back reflect ion
0.25
~ 54.5
~ 43.6
efficiency 90% averaged over t yp incidence angle
~ 15.3% P MT average quant um efficiency
~ 39.2
~ 6.0 p.e./ MeV
S-K report ed
~ 6.0 p.e./ MeV
S. Fukuda et al., NIM A 501 (2003) 418–462
index of refraction n
Refraction index and
absorption coefficient
for water from book of
J.D. Jackson (3-rd edition)
page 315
absorption coefficient [cm1]
 1 m
 1 mm
Water data are from Segelstein, D., 1981:
"The Complex Refractive Index of Water",
M.S. Thesis, University of Missouri, Kansas City
n
PMT Q.E.
Wavelength, nm
Refraction index of water
How Cherenkov photons with  < 300 nm can be detectable?
(Yield 70-600 nm)/(Yield 300-600 nm) ~ 7.5
Total energy of Cherenkov photons (for 70-600 nm)
is ~ 20 times higher that 400 nm photons
Common “wisdom” for organic scintillators:
 light yield is quenched for large dE/dx (Birks’ phenomenological law)
 therefore quenching is important for p, , C-ions ...
 but not for electrons ...
Non-linearity of e-m response is essential for
detectors

related to the purpose of such precision LS neutrino experiments
like KamLAND, Double Chooz, Borexino Daya Bay, NO A,
HanoHano, SNO+, LENA ...

e.g. for antineutrino detection  e  p  e  n
measured positron KE is almost equal to antineutrino energy
which is used for determination of oscillation parameters
Relative efficiency
for BC505 liquid
scintillator
Calibration with monoenergetic
radioactive  sources in KamLAND
arbitrary normalization
Strong
non-linearity!
Light yield in KamLAND ~ 270 spe/MeV with 1325 17”-PMTs (22% coverage)
~ 430 spe/MeV with + 554 20”-PMTs (34% coverage);
due to non-linearity L.Y. depends on the reference energy and might also
depend on other factors (verified by periodic source calibration).
Two possible mechanisms that can produce non-linearity:
(a) Birks’ quenching in scintillator
dL
dE dx

L
0
(b) Cherenkov light production
dx
1  k B  dE dx
within
of the PMT photocathode
Initial GEANT
simulations in KamLAND
with two parameters
reproducing non-linearity
measured with
Direct
Cherenkov
contribution
Reasonably
expected
GEANT
recommended
Birks’ constant
Region of
solar  in
KamLAND









will depend
on particular
mechanism
of non-linearity
Conversion of UV to detectable light in LS
Dodecane
80%
PPO
~1.5 g/L
Pseudocumene
20%
Energy transferred by emission and
re-absorption, and by molecular
collisions—Forster mechanism.
UV Cherenkov
incident
Detectable PPO
emission
1
PPO emission
Q.E. = 80% [Borexino]
Emission yield (A.U.)
0.8
0.6
Pseudocumene (PC) emission
Q.E. = 34% [Borexino]
Excitation transfer to PPO
via Forster mechanism
is high, say ~65%
0.4
0.2
0
200
300
400
500
Wavelength, nm
600
700
Mixture of n-dodecane and pseudocumene
Mixture of 80% dodecane + 20% benzene (neglect PPO)
2.2
n
__ Newton mixing
__ Lorents-Lorenz mixing
refractive index n
2
1.8
1.6
benzene (~ PC)
1.4
dodecane
Koseki
measurement
1.2
PMT
1
0
100
200
300
400
500
600
700
wavelength, nm
Mixing references: W. Heller, Physical Review vol. 68 (1945) 5-10;
R. Mehra, Proc. Indian Acad. Sci. (Chem. Sci.), vol. 115 (2003)147-154
2
Newton : nmix
 v1n12  v2 n22 , where vi is volume fraction
Lorentz - Lorenz :
2
nmix
1
n12  1
n22  1

v

v
1 2
2 2
2
nmix
2
n1  2
n2  2
Transmission of KamLAND LS components
10
Attenuation length, cm
10
10
10
10
10
10
10
10
10
10
5
4
3
Mineral oil 80%
2
1
PPO ~1.5 g/L
0
-1
-2
 100 m
-3
PC 20%
-4
-5
200
250
300
350
400
450
500
Wavelength, nm
550
600
650
700
UV LS re-emission flux calibration details
D2 lamp
Focusing elbow
Vacuum UV Monochromator
MgF2 window
Si-photodiode
(for flux calibration)
Manual
wavelength
control
Vacuum tube for
Si diode volume
Wavelength
reading
Electrometer for
current measurements
Turbo-molecular pump
Vacuum tube to
fore-pump
Calibrated Si-diode (IRD/US Company)
allows to measure photon beam
intensity (# photons/sec) at every
wavelength starting from 115 nm
No voltage bias is required
(internal output impedance
of the diode ~ 100 M)
LS chamber with PMT
LS/N2 OUT
MgF2 window
Hamamatsu
R329-02 PMT
Direct protocathode
coverage without
reflections is ~ 0.6% of 4
LS/N2 IN
The goal is to measure the re-emission efficiency C()
of UV photon (as produced by Cherenkov)
to the “scintillation” photon emitted by PPO in LS
meas
bkgr
light
PPO
   I PMT
   n   C   collection
I PMT
 QEPMT
 GPMT 1.6E 19
~ 22%
Measured
Measured
with calibrated
Si-diode
Measured
as (2.70.5)E+5
Combined
efficiency
Light collection efficiency can be studied by MC...
But C() for PPO in LS is known for 300 nm as 80-100%
(80% is Borexino number)
KamLAND LS re-emission probability
normalized to Q.E. of PPO: 80% (Borexino)
0.040
100
0.030
80
0.025
60
0.020
0.015
40
0.010
20
0.005
0.000
100
150
200
250
Wavelength, nm
300
0
350
Re-emission probability %
Combined efficiency
0.035
Combined eff
in 150+300 nm range
Liq. Scint, Liq. Scint
KamLAND LS refractive index (80% dodecane, 20% pseudocumene, 1.5 g/l PPO).
5
Old single-resonance fit
of Koseki measurements
n2 or epsilon
4
3
n2
2

1
Wavelengths where Cherenkov contributes
0
0
100
200
300
400
500
600
700
wavelength, nm
d 2 N 2z 2

dxd
2

1 
1   2 n 2  


Reemission increases the number
of Cherenkov photons detected at
1 MeV by factor of 3.7
Absorption lengths for LS components
10
10
Absorption length, cm
10
10
10
10
10
10
10
10
10
10
10
5
PSEUDOCUMENE 20%
200-310 nm Extinction (w ith extr. tails)
310-480 nm Borexino measurements
480-700 nm Reyleigh scattering
4
3
Total
2
MINERAL OIL 80%
280-700 nm averaged measurements
of Hatakeyama
1
PPO 1.52 g/L
200-330 nm Extinction
330-480 nm Borexino measurements
480-700 nm Reyleigh scattering
0
-1
-2
-3
-4
Absorption of
dodecane+PC mix
-5
 10 nm
-6
-7
0
100
200
300
400
500
600
700
Wavelength, nm
1
Tot

1
MO

1
 PC

1
 PPO
Study of electron response with Compton spectrometer
Compton spectrometer scheme
22
  source (11
Na)
Test sample
1.6
m
NaI
Eekin  E  E
me
me  E 1 cos  
Scattering angle variation
from 20 to 120 degrees.
NaI
Energy of recoil electron is
determined by scattered photon
angle and certain initial energy of
the incident photon
22Na
gamma source
0.511 MeV and 1.275 MeV
Electron energies: 29-300keV and
166.3-1000keV
Compton Spectrometer
1 mCi 22Na source
(511 and 1275 keV
lines) inside massive
lead collimator
LS test sample
r=2.5cm radius,
h=6.35 cm
quartz cylinder
NaI
VME DAQ system
NaI 13 cm
1.6 m arm
Data & Monte-Carlo
20 degrees MC
E, MeV(NaI)
ADC, channels(NaI)
20 degrees Data
1.275MeV
0.511MeV
1.275MeV
0.511MeV
double Compton
Scattering
double Compton
Scattering
Backscattering
in NaI
Backscattering
in NaI
ADC, channels(scintillator)
E, MeV(scintillator)
70 degrees Data+Monte-Carlo
Data
Monte-Carlo
Scintillator response to electrons
Systematic errors 0.5%
parameterization
0.997  0.168e 4.92 E ( MeV )
Oleg Perevozchikov, PhD thesis, UT 2009
GEANT simulations
Measured electron response is a ready product for electrons
in GEANT: integrates Birks and Cherenkov non-linearity effects.
For and positron simulation one needs n( ) and Birks’
coefficient.
Conversion of deposit
energy into p. e.
Evis = Edep(E)  m + NCh(E)
Calculated in GEANT,
Birks dependent
Calculated in GEANT
with reemission;
4.5% contribution
at 1 MeV
(or ~ 20 s.p.e. / MeV)
Best fit (Monte-Carlo)
Number of photons/MeV (scintillation)
N p.e./MeV best fit is
(609+110–80) p.e.
in agreement with
direct yield measurement
N p.e./MeV=643.5+/-3.8 p.e.
in Compton spectrometer
Fitted Birks value is
kB=(0.01072 +0.0012–0.0005)
g/(MeV∙cm2)
=0.138mm/MeV
Birks,g/MeV/cm2
GEANT recommended
kB =0.013g/(MeV∙cm2)
Comparison with and protons
in KamLAND
LS response for and protons calculated without parameters
compared with values measured in KamLAND
proton quenching measurements
KamLAND data(gammas)
UT MC(gammas)
UT Data(electrons)
UT MC(electrons)
proton quenching MC
How LS non-linearity would contribute in NOvA?
GEANT3 10 GeV muon in 6 cm liquid scintillator layer
(normal incidence; KamLAND LS non-linearity)
2 GeV electron in infinite size liquid scintillator volume
(KamLAND LS properties)
15% effect
dependent on
LS properties
(if neglected)
LS re-emission efficiency (PMT readout)
~ 5% PC
C() conversion efficiency
Combined Efficiency of
KamLAND LS ~ 20% PC
preliminary, no WLSF
New automatic UT vacuum monochromator
 In collaboration with UT chemists (Shawn Campagna, Mark Dadmun)
will identify photosensitive molecules with excitation range covering
70-300 nm; probably with 2-3 absorption and re-emission steps.
With final emission in the visible (detector) range.
 Components solubility in water, stability, concentration, composition,
removal of components, absorption competing with water, quantum
efficiency, and emission timing should be considered.
 For candidate components will measure and cross compare re-emission
efficiency with our UV monochromator (integrated detector response vs
Cherenkov ). Tune composition of components based on the measured
efficiency vs . Spectral composition of re-emitted light could be very
instructive for mechanism analysis (unfortunately, we are short of ~ $60K)
 After finding the optimized composition, test light amplification effect
with ~1 m3 cosmic muon water-Cherenkov detector that we have at UT.
Hope that amplification factor of 5-10 can be achieved.