R.Novotnya*, S. F. Burachasd, W. Döringa, V. Dormenevb, Y. M. Goncharenkoc, M. S. Ippolitovd, A. Hofstaettere, M. Korzhikb,
V. Mankod, Y. M. Melnickd, O. Missevitchb,V. V. Mochalovc, V. Ryazantsevc, P. A. Semenovc, G. Tamulaitisf, A. V. Uzunianc,
A. Vasilievd, A. N. Vasilievc and for the PANDA collaboration
aII. Physics Institute, University Giessen, Heinrich-Buff-Ring 16, 35392 Giessen, Germany
bINP, Belarus State University, 11 Bobruiskaya, 220030 Minsk, Belarusc Institute for High Energy Physics, Protvino, Russia
dR.RC Kurchatov Institute, Moscow, RussiaeI. Physics Institute, University Giessen, Heinrich-Buff-Ring 16, 35392 Giessen, Germany
fVilnius University, Vilnius, Lithuania
Radiation hardness and recovery processes of PWO crystals
at –25oC
SCINT 07 R.Novotny 1SCINT 07 R.Novotny 1
• high resolution calorimetry with PWO CMS – HYCAL – DVCS – ALICE - PANDA• the experimental facility at IHEP• experimental results• interpretation
decay kinetics – defects - impurities• consequences, further experiments and outlook
SCINT 07 R.Novotny 2
SCINT 07 R.Novotny 3
• high resolution calorimetry with PWO
+ fast and very dense scintillator: <10ns Xo=0.9cm
+ radiation hard @RT: CMS-ECAL
- low light yield: medium-energy application
improvement of the photon statistics by:• increase of light output PWO-II• operation well below room temperature
0 200 400 600 800 10000
20
40
60
80
100
LY
/ p
.e./M
eV
integration gate / ns
-25oC
-10oC
-0oC+10oC+25oC
photon energy / MeV
/ E
%
excellent energy resolutionachievable at low temperatures
envisaged operation at T = -25oC
PHOS (PHOton Spectrometer) 17920 PWO channels (22x22x180mm3)
study of initial phase of HI collision: via direct photons, high pT ,
PHOS @ALICE LHC EMC @PANDA - FAIR
20000 PWO channels (20x20x200mm3)
hadron physics with anti-protons
SCINT 07 R.Novotny 4
no permanent damage due to defect formation activation due to proton induced reactions reduction of optical transmission
can be handled by monitoring
dose:1013 protonsEp = 90 MeV@ KVI, Groningen
wavelength / nm
tran
smis
sion
/ %
both experiments can expect a lower radiation dose
SCINT 07 R.Novotny 5
all tests of radiation hardness have been so far performed at RT
• the experimental facility at IHEP Protvino
schematic layout
SCINT 07 R.Novotny 6
SCINT 07 R.Novotny 7
cooling machine
-source
crystal container
coolingmachine
crystal container
SCINT 07 R.Novotny 8
Bq105dt
dN 12
137Cs-
source
dose rateprofile /a.u.
air PWO
the samples to be tested
irradiation time / h
rela
t. P
M-c
urr
ent
dose rate 20rad/h
LY(-20oC)/LY(+20oC)
sam
ple
s
SCINT 07 R.Novotny 9
the typical behavior
• @RT small tranmission loss fast saturation• @ T=-23oC increase of light yield no saturation due to
slow recovery
similar behavior at lowerdose rate of 2rad/h (upper limit @PANDA)
SCINT 07 R.Novotny 10
recovery after irradiation
time / h
tran
smit
tan
ce @
455n
m /
a.u
.
at low temperatures no improvement of the transmittance with time
SCINT 07 R.Novotny 11
irradiation of PWO-II crystalslig
ht
yiel
d /
pe/
MeV
integration gate / ns
-25oC
0oC
+25oC
time / h
PM
T o
utp
ut
/ a.u
.
2 rad/h 20 rad/h
+20 C -25 C
PWO-II - 28
PWO-II - 30
SCINT 07 R.Novotny 12
recovery process at +20C
recovery process at -25C
time / h
PM
T o
utp
ut
/ a.u
irradiation of PWO-II crystals
SCINT 07 R.Novotny 13
Crystal ID
LY* @ RT [p.e./MeV]
ratio, DC@-25C/ DC@+20C
signal loss (%) after 310 h of irradiation
@ 2 rad/h &-25C
DC Blue LED Red LED
3 19.1 3.4 50 19 9
27 19.5 3.4 20 7 1
28 19.6 3.4 19 5 1
29 17.8 3.4 36 13 6
30 19.8 3.5 32 10 3
37 21.1 3.3 29 8 3
* LY – light yield measured by RINC, Minsk
irradiation of PWO-II crystals
SCINT 07 R.Novotny 14
crystal #94 (large)
crystal #136 (small)
irradiation of PWO crystals of CMS-type:different concentration of dopants
dose rate 2rad/h @ -25oC
scintillation signal
time / h
rela
tive
PM
res
pon
se
blue LED signal
SCINT 07 R.Novotny 15
interpretations and (?) solutions
wavelength / nm
tran
smit
tan
ce /
%
@RT
R.-Y. Zhu et al, IEEE Trans. on Nucl. Scí. (2004)
ind
uced
abs
orpt
ion
/ m
-1
irradiation time / min
M.Korzhik et al.
SCINT 07 R.Novotny 16
time / s
k /
k0
long release times: V.Dormenev, M.Korzhik et al.
• analysis of TSL data up to 230K delivers no slow time constantsat –10oC or –25oC
• center @580meV (observed in pure PWO) should be suppressed by La/Y doping
• deep trap @700meV (Frenkel defect)
• induced absorption @400nm• release time ~ 2.8h @RT• release time = 125h @ -10oC
= 808h @ -25oC
operation of the calorimeter at –10oC not sufficient
SCINT 07 R.Novotny 17
SCINT 07 R.Novotny 18
origin of slow recovery processes S. Burachas et al.
results are related to radiation induced structural changes in inclusions of variable valency tungstate oxide complexes WO3-x
due to re-arrangement of oxygen ions.
S.Burachas et al., J. Crystal Growth 293(2006)62
the changes proceed slower at reduced temperatures
thermal energy insufficient for recovery
recovery after fast neutron irradiation
1,2: b/a red.annealing1´,2´: b/a n-irradiation
induced absorption of PWO after irradiation: 20krad (60Co) @ RT
350 400 450 500 5500,0
0,2
0,4
0,6
0,8
1,0
Lumi
nesce
nce i
ntens
ity (no
rmaliz
ed)
Wavelength (nm)
Excitation 325 nmT
Meas 250 K
exc.@325nmT=250K
• Mo as a contributor to the optical absorption induced in PWO (A.Hofstaetter et al.)
SCINT 07 R.Novotny 19
Hofstaetter, R. Oeder, A. Scharmann, et al.phys. stat. sol. (b) 89, 375 (1978)
thermoluminescence of PbWO4/PbMoO4 mixed crystals
SCINT 07 R.Novotny 20
crystals were irradiated with 50keV x-rays
temperature of maximum thermal decaydepends strongly on the Mo-content.
34Mo
responsible trap: MoO4 tetrahedron
identification via EPR
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ESR measurements identify the complex in PWO-II crystals
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optical absorption due to (MoO4)3- ?
difference in optical absorption of CaWO4:Pb: • irradiation with x-rays @T = 77 K• subsequent annealing
M. Böhm, R. Grasser et al.,J. de Physique C6, 508 (1980)
SCINT 07 R.Novotny 23
is it relevant for PWO-II crystals?
SCINT 07 R.Novotny 24
energy / eV
opti
cal a
bso
rpti
on
Emax=2.35eVFWHM=0.8eV
wavelength / nm
PbW(1-x)O4/PbMoxO4, x=0.001
0
20
40
60
80
100
120
140
180 200 220 240 260 280 300
Temperature, K
TL
, a.u
.
Experimental data
Sum of the 3 peaks
1st peak
2nd peak
3rd peak
SCINT 07 R.Novotny 25
in contrast: evaluations of the TSL-parameters in the temperaturerange between 180K and 300K by Korzhik et al. lead
to trap-lifetimes of 4 < < 250s @ 248K
• consequences, further experiments and outlook 1/3
• optimum experimental resolution and stabilization (constant term)will rely on very sophisticated monitoring
probably not!
• online bleaching
SCINT 07 R.Novotny 26
bleaching wavelength / nm
ES
R in
ten
sity
/ a.
u.
• consequences, further experiments and outlook 2/3
• more conclusive investigations
irradiation of PWO crystal @ -25oC with1.2MeV photons (60Co) @GI
andmeasurement of optical transmission
of the cooled crystal @ -25oC
• modification of doping or further reduction of impurities (Mo?)
SCINT 07 R.Novotny 27
• consequences, further experiments and outlook 3/3
• operation at higher temperature: test performed at T= 0oC !
central detector3x3 matrix
ring of neighbors E=40.9MeV
/E = 9.5%
energy / a.u.
cou
nts
3x3 matrix of PWO-II crystals20x20x200mm3
readout with LAAPDs
0 , 0
1 , 0
2 , 0
3 , 0
4 , 0
5 , 0
6 , 0
7 , 0
8 , 0
9 , 0
1 0 , 0
0 , 0 0 , 1 0 , 2 0 , 3 0 , 4 0 , 5 0 , 6 0 , 7
p h o t o n e n e r g y / G e V
/ E = 2 . 4 6 % @ E = 1 G e V
14.2)GeV/Eln(22.2GeV/E
21.1
E
p h o t o n e n e r g y / G e V
/ E
[%
]
SCINT 07 R.Novotny 28
+20○C
-25○C
2 rad/h 20 rad/hPMT anode signals under different modes of crystal irradiation by 137Cs gamma-source
irradiation of PWO-II crystals
Recovery process at +20C
Recovery process at -25C
irradiation of PWO-II crystals
VB
CB
0
-0.25
-0.5
-0.75
-1
eV
-4.1
(WO4)3-
(WO4)3- -SE3+
(MoO4)3-
Pb+ -VO
325 nm