Different potential systematic
uncertainties involved in 210Pb dating
method
Begy R.-Cs.1,2 , Reizer E. 1, Forray F.-L. 3, Simon H. 1, Gabor A.-I. 1,2,
1Babeş-Bolyai
University, Faculty of Environmental Science and Engineering, 30 Fântânele Street,
400294, Cluj-Napoca, Romania;
2INCDO-INOE 2000, Research Institute for Analytical Instrumentation, ICIA Cluj-Napoca, Romania
3Babeş-Bolyai University, Faculty of Geology, M. Koganiceanu Street nr.1 , Cluj-Napoca, Romania;
This work is financially supported by PN-II-RU-TE-2012-3-0351 project
About us
• Nuclear spectrometry laboratory from “BabesBolyai” University (Faculty of Environmental
Science and Engineering)
• Team: Begy R.-Cs.(Phd. head), Simon H. (Phd
stud.), Reizer E.(Msc. Stud.), Vasilache D. (Phd
stud.), Kelemen Sz. (Res. asist)
• Facilities: two HpGe gamma spectrometer (GEM
and GMX type) 8 alpha chamber with 900 mm2
PIPS detector, scintillations cell for Rn and Ra
measurements etc.
• Task: Pb-210 dating(Starts in 2005 for first time in
Romania (in our laboratory)) and Monitoring of
Environmental radioactivity (NORM, TENORM)
Aims of this study
For Pb-210 dating
Determination of Pb-210
• Alpha spectrometry (chemical preparation)
To analyze the effect of the undisolved (insoluble)
materials especially for silicates found in the sediments
Estimate the uncertainty caused by the silicates
Improved the chemical separation process
• Gamma spectrometry
To analyze the variation of the mass attenuation in sediment
layers (compared with IAEA reference material)
Establish a correction for the self attenuation effect
Study Area
Name
Location
Type
1.Buhăescu
47°35’18,52″N
24°38’ 35,56″E
GLACIAL
2.Știol
47°35’ 08,97″N
24°48’ 59,50″E
GLACIAL
3.Muced
47°34’26,63″N
24°32’41,64″E
GLACIAL
4.Saint Anna
46°07’66″É
25°53’14,52″K
VOLCANIC
45° 07' 49,30'' N
29° 23' 38.80''
DELTAIC
5.Iacob
Alpha spectrometry
• The total 210Pb can be determine by measuring its daughter
isotope 210Po ( one of the most precise method)
is generally based on various acids leachings procedures.
Negative effect
1.
Leaching with mineral
acids, partial digestion
without HF
Lose of Po-210
Positive effect
Just HCl and H2 O2
EPA -David N.Edgington, 1975
digestion totality of sediment
samples using HF
Negative effect
2.
Wojciech Tylmann, 2013
Rolf Aalto, 2012
Begy et al. 2015
Positive effect
Less time
consuming (max 1
day)
•quick contamination of
teflon disches
•their difficult decontaminations
•their costly prices
•Most time consuming
•(1 week)
Getting the total
amount of Po from
sample
Materials and Methods 1
(EPA -David N.Edgington, 1975)
• Application of the first method, and the
residual was digested in Teflon dishes in
presents of HF, HNO3 until total dissolution.
• Total activity represent the activity measured
in first and second step together
• Chemical processes was yielded by adding Po209 as tracer
• Measurements with PIPS detector alphaspectrometric system
• Total time consumption is 1 day
Control of measurements
1.Results of Leaching with mineral acids,
partial digestion without HF
Total Activity of
sed. (Bq/kg)
Activity of
silicate content
(Bq/kg)
Activity of 226Ra
Știol
Buhăescu
Muced
Iacob
St Anne
57260
2727400
33029
20030
16120
915
(16%)
22618
(9%)
-
609
(30%)
787
(45%)
554
60%
765
33%
-
202
33%
504
64%
The uncertainty of the value are represented in 2σ confidence interval
Undissolved
silicate content
(mass)
25%
36%
-
48%
22%
2. Total digestion of sediment
samples using HF (Wojciech Tylmann, 2013 Rolf Aalto, 2012 Begy
et al. 2015)
Activity in
residuals
(Bq/kg)
Teflon dish
contamination
%
UDL
UDL
-
UDL
UDL
20
46
-
35
22
UDL – Under Detection Limit that in our case is 3 mBq
Improvement for avoid the using of Teflon:
The sample is place first in a single use plastic glass with 2.5 ml HF and 3 ml of HNO3 for two
days.
After, 2 ml of 0.8 mol boric acid is added and replaced in Erlenmeyer glasses with 10 ml of HNO3
and placed on a hot plate at 90 ˚C .
Evaporation at almost dryness
10ml HNO3
Evaporation
10 ml HCl
Evaporation
10 ml HCl
Evaporation
Adding H2O2 and three times distilled Water
Deposition on a Stainless Steel disc at 0.4-0.9 pH fixed with HCl on 82 ˚C
Mineralogy of the residuals 1
• The samples mineral composition were identified using powder X-ray
diffraction (XRD) analysis with a Bruker D8 Advance powder
diffractometer using Bragg-Brentano geometry.
• The samples from Muced, Buhăescu and Știol Lakes contain quartz with
undulatory extinction typical for metamorphic rocks. Besides quartz,
muscovite and feldspar where identified by x-ray diffraction Other
minerals identified by polarised optical microscopy, besides those
identified by x-ray diffraction, are amphiboles and chlorite.
• Sediments accumulated in St. Anna Lake consist of minerals originated for
the alteration of volcanic rocks (dacite). The dominant minerals identified
by X-ray diffraction are feldspar and quartz The quartz is of nonundulatory type, typical for magmatic rocks. Small quantities of
amphibole, pyroxene, biotite where identified by polarised optical
microscopy.
• Jacob lake samples have predominantly quartz with undulatory
extinction, muscovite, and rare feldspars, pyroxene and amphiboles.
Mineralogy of the residuals 2
Power X-ray diffraction patterns for sediments from
Buhaiescu Lake, St. Anna Lake. Identified minerals are: MSmuscovite, Pl-plagioclase and Qtz-quartz
Resulted Uncertainties
Lakes
Difference
in
Effect
of
Ages(y)
silicates
%
to 210Pb Difference
in
dating
method Dates
%
uncertainties in
210Pb dating
method (%)
uncertainties in 210Pb
dating method with
silicates effect
Știol
Buhăescu Muced
Iacob
St Anne
-5,9
(max 21)
-11
(max 17)
2,05
(max 8,6)
-1,03
(max 8,3)
-
0,78
(max 4,5)
0,54
(max 3,4)
-
7
12
-
5
19
19%
20%
-
26%
36%
0,2
0,45
(max 3,11) (max 1,3)
Gamma spectrometry
• The main problem is regarding to the matrix
effect, the self attenuation in the sample
• Three possibilities:
– Computing software for self attenuation corrections
(monte-carlo simulation)
– Analytical techniques for density correction (empirical
equations)
– Simple determination of the self attenuation
coefficient and recalculate the peak intensity (very
important in relative method )
Unfortunately it must to be apply for each analyzed
sediment layer
Self attenuation coefficient in sediment
column
Empirical approach
I    y
geom 

  det geom absprobabs ap

1 1
 x 

arctg 

4 2
Rr
absprob  e
  m x
I    geom  det  y      r  x  e
2
a    y    r  det  
2
h
I  a  x  geom  e bx
0
  m x
b   m  
 e  bh  b  h  b  h  2   2  2 
1  1  e  bh  b  h  1 
1
 

 
I  
2
3
4
b
b
 2 R  r  


 24  e bh  b 4 h 4  4b 3 h 3  12b 2 h 2  24bh  24
1


6 R  r  
b5
 


Correction by recalculation the peak
intensity trough mass attenuation
correction
Before Correction
After Correction
Conclusions
• Leaching with just mineral acids (HCl and H2O2) can result
residue of 22-48% depending on the origin of the sediments
• The remaining activity of 210Pb(210Po) in the undisolved
material can vary in the range of 9-45%
• The remaining residual activity found in sediments which have
predominantly quartz or are originating from volcanic rocks
• Second digestion procedure was developed, in this case the
residue was negligible and the remaining activity was under
the detection limit
• The highest uncertainty is produced in case of volcanic rocks,
total error can reach 30%
• In gamma spectrometric measurements the matrix effect is
very important to correct, the simplest way being with the
determination of the mass attenuation coefficient for each
sediment layer
This work is financially supported by PN-II-RU-TE-2012-3-0351 project,
Radionuclides as tracers of the anthropic influence on the Danube Delta
sedimentary processes
National project, initiated by the Romanian Guverment
Thank you for attention