environmental radioactivity studies at ned-ntua
TRANSCRIPT
Environmental radioactivity studies
at NED-NTUA
Marios Anagnostakis
Nuclear Engineering Department, National Technical University of Athens,
15780 Athens, GREECE
[email protected] http://nuclear.ntua.gr
Outline
� History of environmental radioactivity studies at NED-
NTUA
� Equipment and techniques used, Q/A protocols applied
� Research today at NED-NTUA and future plans
History of environmental radioactivity
studies at NED-NTUA
Chernobyl fallout mapping
� A total of 1242 samples of 1cm thick surface soil were collected all over
Greece during the period from May to November 1986.
� The sampling covered the most populated areas of the mainland
(~92300km2).
� In several cases repetitive samplings were conducted at the same location,
either simultaneously or at a later period, resulting several hundred samples.
� A total of ten Chernobyl fallout radionuclides (137Cs, 134Cs, 125Sb, 106Ru, 144Ce,110mAg, 54Mn, 95Zr, 103Ru and 141Ce) were determined and mapped
� At several sites a second 1cm thick soil layer sample, at the depth of 10cm
was also collected in the period 1986-1992 in order to study the vertical
migration of 137Cs.
� Three natural radionuclides existing in the soil (226Ra, 232Th and 40K) were also
determined and mapped.
Chernobyl fallout mapping
Natural radioactivity mapping
Determination of radionuclides emitting low
energy photons
� The analysis of the existing samples and
not only for radionuclides emitting low-
energy photons was the next step
� Need for a Low energy photon detector
(LEGe)
� Need for self absorption correction of
photons within the sample
� Permitted the accurate determination
and mapping of radionuclides such as 210Pb, 234Th (238U) and 241Am
Mapping of 238U and 210Pb
Dose rate due to terrestrial gamma radiation
from natural radionuclides
� Knowledge of the distribution of
the main natural radionuclides
(226Ra, 232Th and 40K) in Greek
surface soil allowed the
estimation of the gamma ray
dose rate due to the natural
radionuclides of terrestrial
origin.
� This dose rate was
experimentally verified.
Lead-210 in soil is of particular importance for
many reasons
� It is produced from 226Ra existing in the soil
(supported 210Pb)
� It is produced in the air from the decay of 222Rn exhaling from the ground
(unsupported 210Pb)
� It has a characteristic vertical profile which
can be used to study the transport of
surface soil associated with erosion and
sedimentation
� As all radionuclides deposited in the ground
it presents a size fraction in the soil
210Pb in soil
Equipment and techniques used, Q/A
protocols applied
Analytical techniques available at NED-NTUA
� High resolution gamma spectrometry (It is the workhorse of radioactivity measurements at NED-NTUA)
� Radon measurements (radon indoors measurements, exhalation measurements from the ground and materials, radon in water)
� Alpha spectrometry
� Liquid scintillation
� Total α-β measurements
� Neutron activation analysis
� X-ray fluorescence
The gamma spectroscopic analysis isperformed using for detector systemsof NED-NTUA:
� HPGe (34% rel ef., 1.78keV at 1322keV)
� LEGe (2000 mm2 active area, fwhm=341eV at 5.9keV).
� XtRa (104.5% rel. eff., fwhm=1003eV at 122keV)XtRa-CSS)
� HPGe (40% rel. ef.)
Gamma spectrometry
1 0 0 1 0 0 0
1 E -3
0 .0 1
0 .1 G e o m e try V o lu m e 2 8 2 c m3
M a te r ia l : 4 M H C l
D e te c t o r 2 : G e r m a n iu m D e te c t o r (G e )
D e te c to r 1 : G e r m a n iu m L ith iu m D e t e c to r ( G e L i)
Eff
icie
ncy
D e t e c to r 4 : E x t r a R a n g e G e r m a n iu m D e te c to r (X tR a )
D e te c t o r 3 : L o w E n e r g y D e te c t o r (L E G e )
E n e rg y ( k e V )
� The XtRa detector is coupled to a Compton Suppression System for background reduction and improvement of detection limits
� This result to the reduction of measurement uncertainty in environmental samples and permits the analysis of low volume samples (10-20cm3) with good accuracy
Gamma spectrometry
0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0
0
1 0 0 0
2 0 0 0
3 0 0 0
4 0 0 0
5 0 0 0
6 0 0 0
Πλήθος καταγραφόμενων παλμών
Ε ν έ ρ γ ε ια (k e V )
φ ω τ ο κ ο ρ υ φ ή 1 3 7
C s
σ τ α 6 6 1 .6 2 k e V
In-situ gamma spectrometry
In situ measurements using a BEGe detector
Soil vertical profile - sampling
� Easy to sample when soil is hard
� Soil profile may be disturbed
� Extraction of soil not very easy
� Power supply is required
� Depth profiles are determined by sampling with a core sampler.
� For good depth resolution (~1 cm) the amount of sample collected per slice is low
(~45cm3).
� The amount of sample may be further reduced due to the presence of stones, etc.
� Collecting multiple samples is time and labor intensive.
Small sample geometries
are essential!
Soil vertical profile sampling
Soil and sediments samplings and in–
situ measurements
� 24 hours air-drying
� Sieving with a sieving machine for
20 mins
� Weighing
� Moisture content measurement
� Sealing with silicon
� Painting with epoxy resin
Soil sample preparation
I2
u1
Slide 19
I2 You should also add the volume and if possible the dimensions of each geometry and not just the nameIason, 18-May-18
u1 this slide should be previously put. First you sieve the material, and then you prepare the samples. user, 24-May-18
QA/QCNED-NTUA is
� A member of the IAEA ALMERA Network and for more than two decades
participates 1-2 times per year in radioactivity measurements Proficiency
Tests and Intercomparison Exercises
� A member of the International Committee for Radionuclide Metrology
(ICRM) and participates in the Gamma Spectrometry Working Group
Intercomparison Exercises and publications
Research today at NED-NTUA
and future plans
Geometry optimization for 210Pb
determinationMean
Radius
(cm)
Height
(cm)
Volume
(cm3)
A 1.25 1.73 9.1
B 1.61 1.70 14.5
C 1.69 2.73 24.6
D 1.41 1.99 12.6
E 2.59 1.20 24.1
F 2.65 1.34 27.6
G 2.40 1.89 34.1
H 2.85 0.64 17.9
I* 3.57 1.00 40.0
J* 3.75 2.20 97.2
Size fractionation of radionuclides in the soil
Uranium series radionuclides vertical distribution
234Th (238U)
� Activity is more or less constant with depth
226Ra
� Equilibrium with 234Th close to the surface
� Significant disruption of equilibrium between the three radionuclide in the deep soil
210Pb
� Significant decrease with depth, close to equilibrium with 226Ra
0
10
20
30
40
50
60
70
80
90
100
110
120
130
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Ac
tivit
y c
on
ce
tra
tio
n(B
q/k
g)
depth (cm)
URANIUM SERIES RADIONUCLIDES
Pb-210
Th-234
Ra-226
Slide 24
I3 maybe you should add : "...at this point"Iason, 18-May-18
210Pb
� Decreasing activity concentration in larger particles. A significant amount of the 210Pb detected in the surface soil comes from the atmosphere, as a decay product of atmospheric 222Rn (unsupported 210Pb).
226Ra
� Disruption of radioactive equilibrium between 234Th and 226Ra, indicating that 226Ra is not produced locally by the decay of 238U, but is brought in the area, probably with the water.
Uranium series radionuclides size fractionation
Sampling of radioactive aerosols
� High volume air sampler F&J DH-50810E
� Glass fiber 8x10” FP810M air filter
� Air sampling from 2h to 10 days depending on the
application
� Total air volume up to 20000m3
� Analysis for the determination of 210Pb, 7Be, 22Na
Future plans
� The techniques which have been developed and tested over the years for
the analysis of environmental samples in the ground and the air have proven
to provide very good quality results, in terms of type A and type B
uncertainty as well as detection limits, even for small sample volumes.
� Therefore, it is believed that techniques and models (like MODERN) which
are based on the use of natural or artificial radionuclides like 210Pb, 137Cs,7Be, 22Na as tracers of environmental processes (sedimentation, erosion, air
masses transport etc) may be easily applied at NED-NTUA in the future to
provide reliable results.