Application of the three photomultiplier liquid ...
Transcript of Application of the three photomultiplier liquid ...
ApplicationApplication ofof thethe threethree photomultiplierphotomultiplierliquidliquid spectrometerspectrometer HIDEX 300SL HIDEX 300SL
for for radiocarbonradiocarbon datingdatingMarek Krąpiec1,2, Adam Michczyński3, Adam Walanus1
1 Faculty of Geology, Geophysics and Environmental Protection, AGH-University of Science andTechnology, Al. Mickiewicza 30, 30-059 Kraków, Poland2 Laboratory of Absolute Dating, Cianowice 225, 32-043 Skała, Poland3 Gliwice Radiocarbon Laboratory, GADAM Centre of Excellence, Institute of Physics, SilesianUniversity of Technology, Krzywoustego 2, 44-100 Gliwice, Poland
adamwalanus.pl [email protected] www.c14.pl
50eV 156eV
14C
T1/2 = 5730 years biosphere: 226 Bq/kgC = 13 dpm/gC
-> T=25 ka -> 13*2-25/5.73 = 0.63 dpm/gC
-> counting time = 2 days -> 1800 d/gC
Poissonian error = 18001/2/1800 = 2.3%
Medieval sample: 1260-1390 AD -> 14 h -> 10000 d/gC -> 1%
0.36% -> ± 30 years
Venu
sof
Bras
sem
pouy
Two Multichannel Analysers, each with 1024 channels
• Quench correction via three methods:
1. TDCR – Triple to double coincidence ratio2. Using a known quench curve
3. An external standard (Eu-152; ~ 440 kBq)
• Alpha / Beta separation based on pulse length discrim.
• Automatic Luminescence Reduction
HIDEX 300SL
Width: 520 mm Height: 685 mmDepth: 630 mm Weight: 130 kg
Threephotomultipliertubes
TDCR Triple to double coincidence ratio
The TDCR method is an absolute activity measurement method specially developed for pure beta-and pure EC-emitters activity determination, in which the detection efficiency is calculated from a physical and statistical model of the photon distribution emitted by the scintillating source.Source: Laboratoire National Henri Becquerel
Sample - BFm =
StandardModern - B
14C dating –
relative activity measurement:
0.80
0.60
0.80
0.60
Effic
ienc
y
Effic
ienc
y
Sample - BFm =
StandardModern - BSample - B
<< 1Sample
14C dating – old samples are close to background:
2
3
Empty vial
No 14C sample
Amount of impurity (chlorophorm drops)
Stan
dard
ized
valu
eB double(cpm)
B triple
TDCR 14C
TDCR
14C
14C age calibration
S = 501% of modern 14C
<- 0 yr BP Before Present
<- 1500 yr BP
<- 3000 yr BP
30 kyr BP
14C lower (and upper) discriminationlevel, choosen to obtain good S/N ratio
(factor of merit FOM=s/b1/2, maximum determinable age),
and to obtain the correct age ->
Two samples ofslightly different purity
Standards, one pure and sixwith the quencing agent (chlorophorm) added
Model: sigmoid
Sigmoid function: y=1-1/(1+e-x)
y=b+a*(1-1/(1+exp(-(x-xH)/xd)))
a
b
Xd - slope
xH
s = linear interpolant between s1 and s2
<- 6, 4, 2, 0
Av = -0.34 ± 0.27 yr, p=0.10; StDev of norm. = 1.24 ± 0.15, p=0.055;
Shapiro Wilk normality test: p=0.25
14C
dend
ro–
14C
mea
sure
d(y
r)