MEASUREMENT OF RE-EMISSIONOF CHERENKOV RADIATION

Yuri Kamyshkov / University of TennesseeAqueous 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

Outline

J.D. Jackson, Classical Electrodynamics3-rd edition, page 638

Cherenkov emission band

for LS 0 ~ 100 nm

PMT sensitivity

range

2 ; n

Cherenkov light emission

2222

2 1112

nβλπα

dxdNd mostly UV

Red UV

at threshold velocitiesCherenkov radiation starts with UV photons

Cherenkov yield in Super-K

Say, for relativistic muon with  2 in water:# of per cm produced between 300 and 600 nm [compare with 100 eV/ in typical LS ~10,000 / MeV ]

~ 347

# of photons per

dE dx MeV cmg

g g

@

0.25

MeV with 40% photocathode coverage say, 25m path for 100m attenuation len

~ 175~ 70~ 54.gth

~ 20% photocathode bac re5

k e-

~ 43.6~ 39.2

flection efficiency 90% averaged over typ incidence angle ~ 15.3% PMT average quantum efficiency

~ 6.0 p.e./ MeV

S-K reported ~ 6.0 p.e./ MeV

(simple estimate)

S. Fukuda et al., NIM A 501 (2003) 418–462

abso

rptio

n co

effici

ent

[cm

1]

inde

x of

refr

actio

n n

Refraction index and absorption coefficient for water from book of J.D. Jackson (3-rd edition)page 315

1 mm

1 m

PMT Q.E.

n

Wavelength, nm

Water data are from Segelstein, D., 1981: "The Complex Refractive Index of Water",M.S. Thesis, University of Missouri, Kansas City

Refraction index of water

(Yield 70-600 nm)/(Yield 300-600 nm) ~ 7.5

How Cherenkov photons with < 300 nm can be detectable?

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, NOA, HanoHano, SNO+, LENA ...

e.g. for antineutrino detection measured positron KE is almost equal to antineutrino energy which is used for determination of oscillation parameters

e p e n

Rela

tive

effici

ency

fo

r BC5

05 li

quid

sc

intil

lato

r

Calibration with monoenergetic radioactive sources in KamLAND

Strong non-linearity!

arbitrary normalization

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(b) Cherenkov light production within of the PMT photocathode dxdEk

dxdELdxdL

B

10

GEANT recommendedBirks’ constant

Direct Cherenkovcontribution

Reasonablyexpected

Initial GEANT simulations in KamLANDwith two parameters reproducing non-linearity measured with

Region of solar in KamLAND

will dependon particularmechanism of non-linearity

Energy transferred by emission and re-absorption, and by molecular collisions—Forster mechanism.

Detectable PPO emission UV Cherenkov

incident

Dodecane80%

Pseudocumene20%

PPO~1.5 g/L

200 300 400 500 600 700

Wavelength, nm

0

0.2

0.4

0.6

0.8

1

Em

issi

on y

ield

(A.U

.)

Pseudocumene (PC) emissionQ.E. = 34% [Borexino]Excitation transfer to PPO via Forster mechanism is high, say ~65%

PPO emissionQ.E. = 80% [Borexino]

Conversion of UV to detectable light in LS

0 100 200 300 400 500 600 700

wavelength, nm

1

1.2

1.4

1.6

1.8

2

2.2

refra

ctiv

e in

dex

n

benzene (~ PC)

dodecane

__ Newton mixing__ Lorents-Lorenz mixing

Kosekimeasurement

Mixture of 80% dodecane + 20% benzene (neglect PPO)

n

Mixture of n-dodecane and pseudocumene

Mixing references: W. Heller, Physical Review vol. 68 (1945) 5-10;R. Mehra, Proc. Indian Acad. Sci. (Chem. Sci.), vol. 115 (2003)147-154

21

21

21 : Lorenz-Lorentz

fraction volumeis where, :Newton

22

22

221

21

12

2

222

211

2

nnv

nnv

nn

vnvnvn

mix

mix

imix

PMT

200 250 300 350 400 450 500 550 600 650 700

Wavelength, nm

10-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

Atte

nuat

ion

leng

th, c

mTransmission of KamLAND LS components

Mineral oil 80%

PPO ~1.5 g/L

PC 20%

100 m

D2 lamp

Electrometer for current measurements

Wavelength reading

Focusing elbow

UV LS re-emission flux calibration details

Si-photodiode (for flux calibration)

Vacuum tube to fore-pump

MgF2 window

Vacuum UV Monochromator

Vacuum tube for Si diode volume

Manual wavelength control

Turbo-molecular 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

HamamatsuR329-02 PMT

LS/N2 OUT

LS/N2 IN

Direct protocathode coverage without reflections is ~ 0.6% of 4

MgF2 window

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

196.1 EGQECnII PMTPPOPMT

lightcollection

bkgrPMT

measPMT

Measured as (2.70.5)E+5

~ 22%

Measuredwith calibrated

Si-diode

Measured

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)

100 150 200 250 300 350

Wavelength, nm

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

Com

bine

d ef

ficie

ncy

0

20

40

60

80

100 Re-em

ission probability %

Combined effin 150+300 nm rangeLiq. Scint, Liq. Scint

KamLAND LS re-emission probability normalized to Q.E. of PPO: 80% (Borexino)

0 100 200 300 400 500 600 700

wavelength, nm

0

1

2

3

4

5

n2 o

r eps

ilon

n2

Old single-resonance fit of Koseki measurements

222

22 112n

zdxd

Nd

Wavelengths where Cherenkov contributes

KamLAND LS refractive index (80% dodecane, 20% pseudocumene, 1.5 g/l PPO).

Reemission increases the number of Cherenkov photons detected at

1 MeV by factor of 3.7

0 100 200 300 400 500 600 700

Wavelength, nm

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

Abs

orpt

ion

leng

th, c

m

PSEUDOCUMENE 20%200-310 nm Extinction (with extr. tails)310-480 nm Borexino measurements480-700 nm Reyleigh scattering

MINERAL OIL 80%280-700 nm averaged measurementsof Hatakeyama

PPO 1.52 g/L200-330 nm Extinction 330-480 nm Borexino measurements480-700 nm Reyleigh scattering

Absorption lengths for LS components

Absorption of dodecane+PC mix

Total

PPOPCMOTot 1111

10 nm

Study of electron response with Compton spectrometer

Energy of recoil electron is determined by scattered photon

angle and certain initial energy of the incident photon

cos1

EmmEEE

e

ekine 22Na gamma source

0.511 MeV and 1.275 MeV

Compton spectrometer scheme

)(2211Nasource

1.6

m

Test sampleNaI

NaI

NaI

Scattering angle variation from 20 to 120 degrees.

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 sampler=2.5cm radius,

h=6.35 cm quartz cylinder

NaI 13 cm1.6 m arm

NaI

VME DAQ system

Data & Monte-Carlo

Data

Monte-Carlo

70 degrees Data+Monte-Carlo

1.275MeV

0.511MeV

1.275MeV

0.511MeV

Backscattering in NaI

Backscattering in NaI

E, MeV(scintillator)

E, M

eV(N

aI)

ADC,

cha

nnel

s(N

aI)

ADC, channels(scintillator)

20 degrees Data 20 degrees MC

double ComptonScatteringdouble Compton

Scattering

Scintillator response to electrons

)(92.4168.0997.0 MeVEe parameterization

Systematic errors 0.5%

Oleg Perevozchikov, PhD thesis, UT 2009

GEANT simulations

Evis = Edep(E) m + NCh(E)

Calculated in GEANT, Birks dependent

Conversion of deposit energy into p. e.

Calculated in GEANT with reemission;

4.5% contributionat 1 MeV

(or ~ 20 s.p.e. / MeV)

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.

Best fit (Monte-Carlo)N

umbe

r of p

hoto

ns/M

eV (s

cinti

llatio

n)

Birks,g/MeV/cm2

N p.e./MeV best fit is (609+110

–80) p.e.

in agreement withdirect yield measurement

N p.e./MeV=643.5+/-3.8 p.e.in Compton spectrometer

GEANT recommendedkB =0.013g/(MeV cm2) ∙

Fitted Birks value is kB=(0.01072 +0.0012

–0.0005) g/(MeV cm∙ 2)

=0.138mm/MeV

Comparison with and protons in KamLAND

proton quenching measurements

proton quenching MC

KamLAND data(gammas)UT MC(gammas)UT Data(electrons)UT MC(electrons)

LS response for and protons calculated without parameters compared with values measured in KamLAND

GEANT3 10 GeV muon in 6 cm liquid scintillator layer (normal incidence; KamLAND LS non-linearity)

How LS non-linearity would contribute in NOvA?

2 GeV electron in infinite size liquid scintillator volume(KamLAND LS properties)

15% effect dependent on LS properties(if neglected)

C()

con

vers

ion

effici

ency

LS re-emission efficiency (PMT readout)

Combined Efficiency of KamLAND LS ~ 20% PC

preliminary, no WLSF

~ 5% PC

New automatic UT vacuum monochromator

Our R&D Plans

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.

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.