An Evaluation of Radon Reference Levels and Radon Measurement ...
Monitoring of different radiation exposure pathways...Units in radon (RnDP) measurement Working...
Transcript of Monitoring of different radiation exposure pathways...Units in radon (RnDP) measurement Working...
Monitoring of different radiation exposure
pathways
National Institute for NBC Protection (SÚJCHBO, v.v.i.)
Eliska Fialova, Petr PS Otahal
InterregionalWorkshop on Case Study of Conventional Uranium
Production from Exploration to Closure
14 – 18 October 2019
IAEA Technical Cooperation Project INT2019
Legislative framework
Czech legacy require measurement and determination of effective dose at
workplaces (Atomic law and it´s implementing regulation)
Czech State Office for Nuclear Safety (SONS) – many activities in the field of
radiation protection (among other) aimed to the protection of health and
environment against an unfavourable effect of ionizing radiation - supervision of
whole process
SONS control and regulate the using of nuclear energy and ionizing radiation
PERMISSION for all these activities
Recommendation of SONS for some special activities (for the concrete
permission) – free available
SUJCHBO:
Ensure the service of personal dosimetry for uranium miners
Ensure the service of measuring and determining of effective dose of workers
(„Radon“ and „NORM“ workplaces)
Type of measured workplaces
Activities regarding
uranium mining
(GEAM)
Remaining after
uranium mining
(SUL, HAMR)
„Rn“ workplaces
Workplaces with the possibility of
higher exposition to radon
„NORM“ workplacesWorkplaces with the possibility of
higher exposition to natural sources
of radiation
Potential exposure pathways
Long-lived RN αinhalation
Thoron (220Rn) inhalation
Radon (222Rn) inhalation
Skin contaminationsurface irradiation
Gammaexternal irradiation
Radon and RnDP
Radionuclide Half-lifeMajor radiation alpha energies
(MeV)
222Rn 3.82 d 5.49
218Po 3.05 min 6.00
214Pb 26.8 min -
214Bi 19.7 min -
214Po 164 µs 7.69
Units in radon (RnDP) measurement
Potential alpha energy The total alpha energy ultimately emitted during the decay of 222Rn progeny through
its decay chain, up to (but not including) 210Pb. The term potential then refers to the
fact that a given atoms (222Rn) has a potential to produce a certain amount of energy, if
it decays through the rest of the decay chain. It could be released in the lung if an atom
underwent the entire decay series after depositing in the lung.
Potential alpha energy concentration (PAEC) It is a sum of all the potential alpha energy in a volume of air, divided by the volume of
that air
A common unit is J·m-3. The conventional unit and the one often used for potential
alpha energy concentration is MeV·l-1. (1 MeV = 1.6 x 10-13 J)
Any atom of 218Po (one of the radon decay products – RnDP) emits during its decays
to long lived radionuclide (210Pb) two alphas of total energy of 13.2 MeV. The product
of this energy and concentration of 218Po in air therefore represent potential energy
deposited in lungs if breathing a unit of volume.
Units in radon (RnDP) measurement
Equilibrium equivalent activity concentration (EEC) In most situations the equilibrium between the parent radon isotope and the
progeny does not exist, and a single quantity is needed to describe the activity
concentration for such a non-equilibrium collection of atoms. The symbol is EEC
(Bq·m-3).
EEC presents the activity concentration of the parent that would have to exist in
complete equilibrium with the progeny if the short-lived progeny had the same
potential alpha energy concentration (J·m-3) as in the non-equilibrium mixture.
Equilibrium factor F The equilibrium factor is the ration of equilibrium equivalent activity
concentration Ceq and the radon activity concentration CRn.
F = Ceq/CRn
Units in radon (RnDP) measurement
Working level (WL) is the historical unit of potential alpha energy concentration.
1 WL was originally defined as the concentration of potential alpha energy
associated with the radon rogeny in equilibrium with 100 pCi·l-1 (3700 Bq·l-1).
1WL = 20.8 x 10-3 μJ·m-3
Working Level Month (WLM) is the cumulative exposure to an individual from breathing an atmosphere, at
concentration of 1 WL of radon progeny, over a time period of 1 working month
(170 working hours). 1WLM = 3.54 mJ∙h∙m-3.
WLM is not an SI unit, but it is important to undestand the historical publications
(Epidemiological studies).
Recapitulation of units
Intake
Exposition
Concentration
Bq, 1 MeV = 1.6 x 10-13 J
Bq·h/m3, J·h/m3,WLM
Bq/m3, J/m3, MeV/l, WL
WL –Working Level
1.3 x 105 MeV/m3 = 20.8 µJ/m3
WLM – RnDP exposition of PAEC 3.54 mJ·h·m-3
ICRP – 137, basic assumption for effective
dose calculation
• The working month has 170 hours
• The working year has 2000 hours
• The worker respiratory rate is 1.2 m3/h
Conversion coefficient – ICRP 137
MeasurementOld approach
[mSv/year]
New approach
[mSv/year]
Gama 0,85 [uSv/h] 1,7 1,7
RnDP 130 [Bq.m-3] 2,1 4,4
Rad. dust 0,12 [Bq.m-3] 3,1 1,8
Total effective dose 6,9 8
Uranium mine
Example of different contribution to the total
effective dose depends on a different coefficient
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
351 335 332 329 324 321 122 302 299 290 282 268
Eff
ecti
ve d
ose
(mSv
)
Uranium mine 2016
alfa
gama
Rn
E
Example of different contribution to the total
effective dose depends on a different coefficient
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
94 90 97 91 87 87 74 90 86 93 82 85
Eff
ecti
ve d
ose
(mSv
)
Uranium mine 2018
alfa
gama
Rn
E
Personal dosimetry
Sampling head of ALGADE
Completed head Decompleted head
Assessment of personal dosimeters
TLD type MCP-N (LiF: Mg,Cu,P) + Harshaw 3500
Membrane filter + alfa-beta automat / PSDA
KODAK LR 115 + microscop
H Effective dose (mSv)
Eext Effective dose from external gamma irradiation
Eint,Rn
Contribution to the effective dose from internal irradiation caused by inhalation
of RnDP (derived limit in the Czech Republic is 17 mJ/year)
Eint,dl.alfa
Contribution to the effective dose from internal irradiation caused by inhalation
of long-lived radionuclides emitted alpha radiation of uran-radium decay series
(derived limit in the Czech Republic is 3200 Bq/year)
Effective dose calculation (personal dosimeter)
H = Eext + Eint,Rn + Eint,long alfa
Effective dose calculation(workplace monitoring)
E Effective dose per year (mSv)
āv,Rn
Measured average of radon activity
concentration at workplace (Bq/m3)
T Duration of worker´s stay at workplace (h)
RamaRn
EECRadon gas
concentration
Detection efficiency [m] 0.0122 ± 0.0004 0.0062 ± 0.0003
Measuring range [MBqhm-3] 0.04 – 100 0.08 – 160
MDV [MBqhm-3] 0.015 0.027
Optimal measuring period 2 – 14 month 2 – 14 month
RAMARN is a Solid-State Nuclear
Track Detector (SSNTD) placed in a
diffusion chamber. It consists of a
plastic chamber which has a conically
cylindrical shape and about 0.5 l of
inner volume. Radon gas diffuses
into the chamber during the whole
exposure period. The plastic box
serves as a barrier for RnDP.
Thanks for your attention!