Post on 15-Nov-2018
Physikalisch-Technische Bundesanstalt
erenkov counting and
liquid scintillation counting of 36Cl
Karsten Kossert, Ole Nhle
Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
and Agustn Grau Carles
Instituto de Fsica Fundamental (CSIC), Madrid, Spain
LSC 2010, Advances in Liquid Scintillation Spectrometry,
Paris, 6-10 September 2010
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
Motivation
The application of a new TDCR-erenkov technique for the
activity determination of 36Cl revealed discrepancies with liquid
scintillation counting.
This discrepancy indicates errors in the computation of the beta
emission spectrum.
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
The TDCR-erenkov method
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
BasicsCharged particles produce erenkov light when traveling in a
transparent dielectric medium with v>c/n
Electrons: m0 = 511 keV/c2 v/c=>1/n
At threshold: =1/n
in keV
21
1/ 511 1
=
+ E
2
th1
1511 1
(1 )
= n
E
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
Basics
in keV
0
100
200
300
400
500
600
700
1,0 1,2 1,4 1,6 1,8 2,0
refractive index n
Eth
in
ke
V
2
th1
1511 1
(1 )
= n
E
water:
n = 1.333
Eth = 261.6 keV
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
BasicsCherenkov light emission has a directional character (not isotropic)
1cos =
n
water:
n = 1.333
max = 41.40
5
10
15
20
25
30
35
40
0 500 1000 1500 2000 2500 3000 3500
Energy in keV
i
n
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
Basics
According to the Frank and Tamm theory the number of photons
per unit path is given by
- FS is the fine structure constant- n is the refractive index of the medium (here non-dispersive)
- =v/c- 1 and 2 are the lower and upper limit of the wavelength region
FS 2 2
1 2
d 1 1 12 1
d
=
k
x n
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
A new TDCR-Cherenkov technique
Number of photons is computed by numerical (Romberg)
integration
where
The electron stopping powers dE/dX
are taken from the ESTAR database
(NIST)
FS 2 2
1 2
d 1 1 12 1
d
=
k
x n
th
d 1( ) d
d d / d=
E
E
kk E E
x E X
0 500 1000 1500 2000 2500 3000 3500 4000
in keVE
0
100
200
300
400
500
600
700
(
)k
E
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
A new TDCR-Cherenkov technique
- Assumption: The number of created photoelectrons follows the
Poisson statistics, i.e. we can apply a free parameter model.
( )( )( )0
31 2
th
( )( ) ( )
T ( ) 1 e 1 e 1 e d =
E
qk Eqk E qk E
E
N E E
( )( )
( )( ) ( )( )
( )( )( )
0
1 2
th
3 31 2
31 2
( ) ( )
D
( ) ( )( ) ( )
( )( ) ( )
( ) 1 e 1 e
1 e 1 e 1 e 1 e
2 1 e 1 e 1 e d
=
+ +
E
qk E qk E
E
qk E qk Eqk E qk E
qk Eqk E qk E
N E
E
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
A new TDCR-Cherenkov technique
The anisotropy is described with only one parameter :
For =1/3 the formulas are similar to the TDCR formulas for LS.
( )( )( )0
31 2
th
( ) )( ) ( )
T ( ) 1 e 1 e 1 e d =
E
qk Eqk E qk E
E
N E E
( )( )
( )( ) ( )( )
( )( )( )
0
1 2
th
3 31 2
31 2
( ) ( )
D
( ) ( )( ) ( )
( ) )( ) ( )
( ) 1 e 1 e
1 e 1 e 1 e 1 e
2 1 e 1 e 1 e d
=
+ +
E
qk E qk E
E
qk E qk Eqk E qk E
qk Eqk E qk E
N E
E
1 = 23
(1 )2
= 33
1 (1 )2
=
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
A new TDCR-Cherenkov technique
-1.080.1327-2.530.13070.134100.3830204Tl
0.290.88340.230.88290.880830.9277106Rh
0.180.77100.030.76990.769660.874590Y
0.030.5930-0.330.59090.592850.763089Sr
0.070.6878-0.210.68580.687250.793132P
(E ) (x=0.655)(=0.41)
(D,calc-D,exp)/ D,exp in %D,calc
(D,calc-D,exp)/ D,exp in %D,calcD,expTDCRNuclide
K. Kossert, Applied Radiation and Isotopes 68 (2010) 1116-1120
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
A new TDCR-Cherenkov technique
The new method works excellent for several beta emitters,
but
calculations for 36Cl yield discrepancies up to 10%.
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
A new TDCR-Cherenkov technique
The method was extended and
improved:
- Wavelength-dependent PMT response
curves are taken into account
- Wavelength-dependent refractive
index (dispersion) is taken into
account
- PMT asymmetries are taken into
account (3 free parameters and
Downhill Simplex algorithm)
But: discrepancies for 36Cl remained.
100 200 300 400 500 600 700
wavelength in nm
0.01
0.1
1
10
quan
tum
eff
icie
ncy
in %
HAMAMATSU R331-05, 2"HAMAMATSU R331, 2"BURLE 8850, 2"
200 300 400 500 600 700
in nm
1.32
1.33
1.34
1.35
1.36
1.37
1.38
1.39
1.4
1.41
1.42
1.43
1.44
1.45
1.46
1.47
1.48
refr
acti
ve
index
of
wat
er
Fit used in this workEq. 1 from Thormahlen et al.
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
36Cl beta spectrum
Beta transition is 2nd
forbidden (non-unique) Decay scheme from DDEP:www.nucleide.org
N(W)dW = AW(W2-1)1/2(W0-W)2F(Z,W) C(W) dW
A=g2/23); W is the total electron energy in units of the rest mass; W0 is the maximum
value for W; F(Z,W) is the Fermi function taking into account distortion due to nuclear
charge; C(W) is the shape factor function
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
36Cl beta spectrum
Determination of 36Cl beta spectrum:
Reich and Schpferling, 1974 4-Si(Li) spectrometer
Sadler and Behrens, 1993 theory
Grau Malonda and Grau Carles, 1998 shape-factor derived from
Sadler and Behrens
Grau Carles, 2005 LS cutoff energy yield method
Rotzinger et al., 2008 cryogenic magnetic calorimeters
This work derived from exp. data of
Rotzinger et al.
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
36Cl beta spectrum
0 100 200 300 400 500 600 700
Energy in keV
0
0.01
0.02
0.03
pro
bab
ilit
y i
n a
rbit
rary
un
its
Fit of exp. data from Rotzinger et al. (2008)
Grau Carles (2005)
Grau Malonda and Grau Carles (1998)
36Cl shape-factor function as determined in this work using
experimental data: C(W)=1-1.326W+0.6328W2
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
LS sample composition: 15 mL Ultima GoldTM + 1 mL water, glass
vials, quenching agent: Nitromethane
erenkov samples: 12 mL HCl (1 mol/L) in PE vials
Preparation by difference weighing of a pycnometer with traceable
balances
Experimental details
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
Reference activity was determined by means of LS counting using
CIEMAT/NIST efficiency tracing and TDCR.
Efficiency was computed with MICELLE2 using
kB = 0.0075 cm/MeV.
LS measurements
Counters:
- Wallac 1414
- TriCarb 2800
- TDCR system of PTB
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
For TDCR, efficiency reduction
is necessary.
Results:
CN: 9.029(27) kBqg-1
TDCR: 9.047(27) kBqg-1
LS measurements
-1.00
-0.75
-0.50
-0.25
0.00
0.25
0.50
0.75
1.00
0.225 0.250 0.275 0.300 0.325 0.350 0.375 0.400
tracer
(ai-a
mean)/
am
ean i
n %
a)
-1.00
-0.75
-0.50
-0.25
0.00
0.25
0.50
0.75
1.00
0.275 0.300 0.325 0.350 0.375 0.400 0.425 0.450 0.475
tracer
(ai-a
mean)/
am
ean i
n %
b)
-1.00
-0.75
-0.50
-0.25
0.00
0.25
0.50
0.75
1.00
0.982 0.983 0.984 0.985 0.986 0.987 0.988 0.989 0.990
TDCR
(ai-a
mean)/
am
ean i
n %
c)
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
Standard uncertainty components for LS counting
LS measurements
0.290.30Square root of the sum of quadratic components
0.010.01Decay correction
0.100.10PMT asymmetry
--0.02Quenching indicator (SQP(E), tSIE)
0.010.01Ionization quenching
0.250.25Decay data (endpoint energy and beta shape-factor function)
0.010.013H activity/TDCR value and fit
0.050.05Radionuclide impurities (none detected)
0.050.05Adsorption
0.010.01Time of measurements (starting time and duration (life-time))
0.030.03Background
0.030.10Dead time
0.020.02Weighing
0.010.02Standard deviation of the mean (samples:5 (4 for TDCR);
repetition per sample for each counter: 8)
TDCRCIEMAT/
NIST
u(a)/a in %
Component
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
Alburger et al. (1986) measured 36Cl and 32Si/32P with an end-
window gas-flow proportional counter.
Seasonal fluctuations of the decay-corrected counting rates in the
order of 310-3 were observed with a maximum in February and
minimum in August.
Jenkins et al. (2009) developed a contentious explanation:
A correlation between the decay constant and the Earth-Sun distance
(corresponds to a change of the solar neutrino flux).
Our LS-TDCR measurements were started in Dec. 2009 and some
repetitions were made in summer 2010 to detect potential seasonal
effects.
Seasonal effects?
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
Deviation between the Dec. and the July measurements: about (2.32.5)10-4.
We can exclude seasonal variations of the decay rate of 36Cl in the stated
order. The measurements will be continued.
Seasonal effects?
-0.0233(246)9.04939.04989.0472Mean
-0.0169(259)9.0502(4)9.0482(25)9.0486(23)5
-0.0238(205)9.0483(7)9.0498(28)9.0461(17)4
-0.0253(170)9.0481(7)9.0470(25)9.0459(14)3
-0.0272(351)9.0507(14)9.0543(27)9.0482(29)2
Deviation (a1-
a3)/a
1in %
a3
in kBqg-1a2
in kBqg-1a1
in kBqg-1Sample
No.
Comparison
(Dec. July)
6-12 July 2010
measurement
14-16 June
2010
measurement
10-14 Dec.
2009
measurement
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
Reasonable agreement is obtained with the new shape-factor function.
Theoretical prediction from Sadler and Behrens (1993) can be ruled out.
erenkov counting results of 36Cl
D, , calc
D, , calc
D, , calc
-3.840.2010-6.320.2036-6.490.2032Grau Carles
(2005)
1-1.167W
+0.884W2
10.010.23917.350.23337.190.2330
Grau Malonda
and Grau Carles
(1998)
1-1.875W
+1.375W2
0.160.2177-2.260.2124-2.400.2121
This work (with
exp. data from
Rotzinger et al.
(2008))
1-1.326W
+0.6328W2
x in %x in %x in %
=1.0, n=1.341, dispersion for
water
=1.07, n=1.331, dispersion for
water
=1.11, n=1.341, no dispersion
ReferenceShape factor
C(W)
D, , calc D, , exp D, , exp( ) /x =
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
Summary
A new shape-factor function was derived for 36Cl.
The results of LS measurements and TDCR-erenkov counting are in
reasonable agreement when using the new shape-factor function.
This confirms the results from Rotzinger et al. (2008).
From our LS-TDCR data we find no evidence for a correlation of the
decay rate and the Earth-Sun distance.
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
Outlook
Potential application of the new TDCR-erenkov method:
- measurement of radionuclides for nuclear medicine (e.g. 32P, 89Sr, 90Y)
- measurements in environmental radioactivity (e.g. 210Pb, Sr isotopes)
- due to the large sensitivity on shape-factors the method can provide
useful information on beta spectra (as shown for 36Cl)
- preliminary tests indicate that the method can also be applied
with the new Hidex-TDCR counter
- further effects must be investigated, e.g. bremsstrahlung and direct
interaction of electrons with PMTs (see e.g., full MC approach
from Bobin et al. (2010))
The recent extensions and improvements as well as a computer
program will be published soon.
Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl
Thank you for your attention