Radiation Protection Dosimetry (2020), pp. 1–11 doi:10.

1093/rpd/ncaa107

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EFFECT OF WORKING CONDITIONS AND NATURAL
RADIOACTIVITY LEVELS ON OCCUPATIONAL DOSES
TO WORKERS OF AN OLD MANGANESE MINE
Mohamed H. E. Monged *
Department of Siting and Environment, Egyptian Nuclear and Radiological Regulatory Authority
(ENRRA), Nasr City, Cairo 11762, Egypt

*Corresponding author: [email protected]

Received 3 July 2020; revised 3 July 2020; editorial decision 17 July 2020; accepted 17 July 2020

The aim of this work was to use RESRAD-Build model to predict the resulting external and internal radiological doses
received by the workers of manganese mine located in Southern Sinai. In order to achieve that goal, measurement of the
activity concentrations of natural radionuclides in rock samples collected from the inside gallery of such mine, using hyper
pure germanium (HPGe) detector. Radon gas concentrations were also measured. The average activity concentrations of 238 U,
226 Ra, 232 Th, 40 K and 210 Pb in rock samples were 207.3, 155.5, 59.7, 304.5 and 119.3 Bq kg–1 , respectively. The average radon
activity concentration was 1254.6 Bqm−3 , which is equivalent to 0.135 WL. The radon concentration increases further as going
deep inside the mine up to 6238 Bqm−3 . RESRAD-Build model occupational effective dose equivalent (EDE) received by the
workers, from natural radionuclides, dominated by 222 Rn emanated from the parent nuclide 226 Ra.There was good agreement
between the occupational annual EDE calculated from the measured rock samples and that predicted by modeling, with estimated
values of 83.8 and 82.1 mSvy−1 , respectively. This radiological dose assessment indicated the predominance of internal pathways
owing to radon decay products, in both cases (measured and modeled). The occupational radiological dose from the inhalation of
radon and radon decay products resulted in a high lung cancer risk based on the current measurements and ventilation conditions
within the mine.

INTRODUCTION parking facilities, underground facilities for water

treatment and distribution, caves, former mines open
Radon is a radioactive, colorless, odorless and to the public and spas. In such workplaces, there
chemically inert gas that is formed by the decay of are many interfaces through which there may be
uranium in different environmental matrices. Radon substantial entry of radon into the air, and there may
emits alpha particles when undergoes radioactive be practical limitations on the amount of ventilation
decay, with a half-life of about 3.82 days. It decays that can be provided. In some underground mines,
also to short-living decay progenies of metallic including some in which the 226 Ra concentrations
nature, e.g.218 Po, 214 Pb, 214 Bi, 214 Po, 210 Bi and 210 Pb. in the rock are not significantly elevated, high
These short-lived decay products are reactive and concentrations of radon arise from the entry of
hold electric charge that enables them to attach to radon via groundwater and its subsequent release
flying dust particles in air. These aerosols can easily into the mine’s atmosphere. Other situation can be
be inhaled into the lung and settle in pulmonary met in underground facilities for water treatment and
mucosa. The deposited radionuclides disintegrate distribution(3) . Operations of mines may generate or
and consequently damage cells within the respiratory change pathways that enhance exposure to radon and
tract. Previous studies have proved that long-term its decay products. Preventive actions and mitigating
exposure to the α-emitting radon daughters increases measures can be applied in order to control such
the risk of lung cancer(1–2) . Inhalation of radon exposure scenarios. However, the source of radon
is categorized as the second cause of lung cancer, cannot be changed, and thus the source will exist
after smoking, as estimated by the EPA. Radon gas when such control measures have to be applied((4) .
concentrations can rise to harmful concentrations in The values of radon precursor concentrations
indoor air which can be due to its continuous decay in rocks or soil adjacent to or inside the mine, or
of uranium, as well as its tendency to stratification their mean value, should be specified to perform
and in case of degraded ventilation(2) . a dose assessment. The mechanism of radon and
The highest concentrations of radon tend to occur precursor emanations as well as movement through
in underground workplaces. Such workplaces include soil, rocks, pores and underground water should
underground mines, tunnels, basement storage and be analyzed with attention. The phenomenon of

© The Author(s) 2020. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
 M. H. E. MONGED
radon migration through soils is not well-known, radioactive materials. In this work, we will employ it

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because of the complicated interaction between soil as a tool to assess the radiological doses to workers of
characteristics (porosity, permeability, temperature, a mine (the building). Natural radioactivity contents
humidity), atmospheric parameters (such as wind, of mine’s rocks are considered as the radioactive
precipitation, etc.) and geological factors. The gas contamination of that building. Such assessment
can easily escape from aqueous to gaseous phase, and will consider the long-term exposure for 30 years of
then be transported by diffusion and convection in exposure of workers. Doses from different exposure
the water and through the soil pores. This can happen pathways and its relation to the ventilation rates will
when the air is not fully saturated and the pores are also be assessed.
interconnected(2) .
Concentrations of radon are reported to vary from
20 to more than 20 000 Bq m–3 in workplaces in caves MATERIALS AND METHODS
and underground mines open to the public(3) and
Description of mine and rock samples collection
from ∼200 to 7000 Bq m–3 in workplaces in tunnels(3) .
Much higher values have been found in some operat- The studied mine is located in Um Bogma and is
ing underground mines; particularly uranium mines. considered one of the significant mines to produce
Kenawy et al.(5) estimated radon gas concentration several economic minerals like iron, manganese, cop-
in four (closed) uranium exploration mines in the per and zinc. This mine is a cylindrical tunnel of
eastern desert of Egypt. The estimated concentrations ∼2.25 m wide on average (2–2.5 m) and is a∼950 m
vary considerably between summer and winter with long. It is located in the south west of Sinai Peninsula
higher concentrations during summer. The average ∼80 km from the Red Sea. In the mine, 36 rock
concentrations during summer within that uranium samples were collected from the walls and floors of
mines ranged between 19.4 and 36.6 kBq m–3 , while the mine, each three samples were mixed thoroughly
that averages during winter ranged between 8.3 and to give one representative samples with a total of
22.3 kBq m–3(5) . According to ICRP recommends a 12 representative collected along the main gallery of
reference level for radon exposure in indoor work- the mine and up to depth of more than 200 m from
places: 1000 Bq m–3 . Monitoring of potential concen- the mine’s entrance. Samples collection and radon
trations of radon and absorbed doses are necessary measurement have been done when the mine was not
to assure whether dose constraints can be respected in operation. No sources of ventilation were installed;
or not(4) . consequently, the lack of oxygen, in addition to the
The Phanerozoic (covers 541 million years to humidity inside the mine, made the accessibility of the
present) sediments cover uncomfortably the basement mine and working conditions unhealthy.
rocks and cover 90% of the whole Egyptian territory. The samples were collected in a uniform way at
Older Paleozoic rocks crop out near the basement depths 0–10 cm from the surface. The samples were
contacts in the Western Desert and in Sinai, but they homogenized and dried at 105◦ C, sieving through
underline of younger sediments toward North and 2 mm mesh size and then weighted and transferred
West. In Sinai, the part is mostly sandstone usually to 100 mL beakers and stored for 1 month to insure
ferruginous and manganiferous in Um Bogma(6) . that secular equilibrium between 226 Ra and its decay
The economic deposits of manganese ores occur progenies is obtained. The samples were then mea-
in Egypt in two main locations, one of which is Um sured with gamma-ray spectrometry based on hyper
Bogma in Central Western Sinai(7–8) . In Um Bogma pure germanium (HPGe) detector.
formation, manganese found as lenses and lensoidal
bodies with different geometries within Carbonifer-
Gamma spectrometric analysis
ous sediments. The ore shows sudden contact with
dolomitic rocks and reflects stratified form(9) . Mart Dry samples were minced, pulverized and homoge-
and Sass(10) classified the ore into two facies; one of nized. Then, they were packed and sealed in polyethy-
which is dolomite facies while the other is silty facies lene plastic container of 100 cc capacity. Activity
and they are inclined to shallow marine environmen- concentrations of 238 U (226 Ra), 232 Th (228 Ra) and40 K
tal deposition of the ore. in Bqkg−1 dry weight were measured using a gamma-
The aim of this work is to estimate the radiological ray spectrometer based on hyper pure germanium
dose received by workers of an Egyptian mine (HPGe) detector of 40% relative efficiency, 1.92 keV
through the measurement of radioactivity content resolution for 1332 keV gamma-ray line of 60 Co. The
of rock samples from the inner walls of the mine detector was coupled with multi-channels analyzer
in addition to the radon gas concentrations inside (16 k channels) and GENIE 2000 software. Point
the mine. The RESRAD-Build computer code is sources of 137 Cs (661.6 keV) and 60 Co (1172 and
a pathway analysis model designed to evaluate the 1332.3 keV) were used for the spectrometer energy
potential radiological dose incurred by an individual calibration. The minimum acquisition time was 22 h
who works or lives in a building contaminated with to reduce the statistical as well as area calculation

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 EFFECT OF WORKING CONDITIONS AND NRL OF AN OLD MM
errors. The IAEA reference material RGU-1 was used reference materials (kg) respectively, while Ns and

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for the spectrometer efficiency calibration in the same N ref are the net counts per second of the sample and
geometry as that of the sample measurements(24) . reference materials (cps) respectively. This equation
Every sample was counted for 80 000 s under was useful in avoiding the self-attenuation due to the
the same counting geometry of the standard source. sample matrix, especially for the low energy photons
The activity concentrations of 226 Ra and 232 Th in of 46.5 and 63.3 keV when calculating the activity
each sample can be estimated indirectly, via several concentrations of 210 Pb and 238 U, respectively, keep-
gamma-ray lines from their decay products with the ing in mind that the densities values of the samples
assumption of secular equilibrium. The gamma-ray and the reference materials were approximate.
lines (emission probability) at 295.2 keV (19.2%) and
351.9 keV (37.1%) from 214 Pb, and 609.3 keV (46.1%),
Radon gas and progeny measurement
1120.3 keV (15%) and 1764.5 keV (15.4%) from
214
Bi were used to assess the 226 Ra activities. Also, Radon progeny concentrations were measured apply-
the 232 Th activities were estimated using gamma-ray ing the Rolle method(11) . Air samples were collected
lines at and 583.19 keV (30.9%) from 208 Tl, 338.4 keV for 5 min at a flow rate between 3 and 3.5 L min–1
(12%) and 911.2 keV (29%) from 228 Ac and 238.6 keV on Millipore (type SM and diameter of 2.5 cm) filter
(43.6%) from 212 Pb. The 40 K activity was determined paper, alpha counting after a delay of ∼7.5 min.
directly by measurement of the single gamma line The filter papers were counted using an RAD-200
at 1460.8 keV (10.67%). 238 U activity concentrations Radon daughter detector (EDA Instrument Inc.) sys-
measured through its energy lines of 63.3 keV (3.8%) tem which incorporating a scintillation tray coated
and 1001.0 (0.83%), while 210 Pb measured via its with silver activated zinc sulfide. The counting effi-
energy line 46.5 keV (4.1%). A background spectrum ciency of the scintillation detector was determined by
241
due to naturally occurring radionuclides in the Am standard source. The radon progeny concen-
environment around the detector was subtracted from tration, expressed as working level (WL), was calcu-
each spectrum sample. The activity concentration lated using the following relation(3, 11, 20) :
A(E) in Bqkg−1 of the radionuclides found in the
samples was calculated using the following relation: C
WL = (4)
Cf .V .t.ε
(nT − n0 )
A= (1)
εmI γ T where C is the alpha net count, ε is the detection effi-
 ciency, V is the sampled volume in L, t is the sampling
(nT + n0 ) time in minutes and Cf is a conversion factor, which
σA = (2)
T(nT − n0 )2 may be approximated by 212 for sampling periods of
1–20 min(11) .
where A and δA are the activity and its associated
uncertainty, respectively. While nT and n0 are the
counting rates of the sample and background, respec- Calculation of radiological parameters
tively. The efficiency ε is derived from the standard Radiation internal and external absorbed dose rates
IAEA reference materials (IAEA-RGU-1) and val- (Din , Dex ), total annual effective dose (AEDtot ) were
idated by different certified reference materials and calculated according to the relevant formula in
T is the instrumental measurement time of the sam- Table 1.
ple, respectively. I γ represents the gamma energy line
intensity, while m represents the sample mass in kg.
The uncertainty originated from counting statistics RESRAD-Build model
and was represented as one standard deviation (1σ ). The RESRAD-Build code can be used to assess the
The obtained net counts per second corresponding dose received by an individual who stay for a certain
to the photopeak energy of a specific radionuclide in period of in an underground mine. It has been devel-
the reference materials and samples were substituted oped by Department of Energy (DOE) to calculate
into Equation (3) as given in the expression(25) : the radiological doses resulting from human activities
in buildings contaminated with radioactive material
MRef × Ns (RESidual RADioactivity in BUILDings)(2, 12, 13) .
Cs = × CRef (3) According to the code, the building can contains up to
Ms × NRef three compartments, and sources up to four geome-
tries (point, line, area and volume sources), 10 sources
where C s and C ref are the activity concentrations of and 10 receptors can be modeled. Between source
the sample and reference materials (Bq.kg−1 ), respec- and receptor, a certain amount of shielding material
tively. Ms and M ref are the mass of the sample and can be interposed, composed of up to eight different

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 M. H. E. MONGED
Table 1. Calculation formula of radiation absorbed and effective doses from natural radionuclides and radon gas and its decay

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products.

Radiological parameters Formula Reference

External absorbed dose rate (nGyh−1 ) Dex (nGyh−1 ) = 0.462 Cu + 0.604 CTh + 0.042CK (12)
Internal absorbed dose rate (nGyh−1 ) Din (nGyh−1 ) = 0.92 Cu + 1.1 CTh + 0.081CK (12)
Annual external effective dose rate (mSvy−1 ) AEDex = Dex (nGyh−1 ) × T × 0.7 SvGy−1 × 106 (12,21)
Annual internal effective dose rate (mSvy−1 ) AEDin = Din (nGyh−1 ) × T × 0.7 SvGy−1 × 106 (12,21)
Annual internal effective dose from Radon AEARn = C Rn × T × 2.08 × 10−5 × 103 × DCF (14)
and its progenies (mSvy−1 )
Total annual effective dose rate (mSvy−1 ) AEDtot = AEDex + AEDin + AEDRn

Where CRa , CTh and CK are the radioactivity concentrations in Bqkg−1 of 238 U, 232 Th and 40 K, respectively. T is the
annual working time of 2000 h, 0.7 SvGy−1 is the dose conversion factor for external gamma irradiation. C Rn is the radon
concentration in WL (1 WL = 2.08 × 10−5 J m−3 ) and DCF of 3 mSv mJ–1 h m−3 is used based on a 1.2 m3 h–1 breath
rate for reference person(14) .

materials. The transport of radioactive material from

one compartment to the adjacent is depending on
some factors: the presence of radioactive dust and
airborne materials, air exchange between the com-
partments outside atmosphere, deposition and resus-
pension, gathering and radioactive decay. Receptor’s
characteristics can be used to model different scenar-
ios of individuals spending a period of time inside
the contaminated building; their internal exposure
is calculated assuming homogenous air within the
compartments; while external exposure is calculated
considering the presence of a shielding material, its
characteristics and geometry. Exposure scenario rep-
resents the potential uses of the contaminated build-
ing, and different exposure scenarios are composed
by different combinations of site, occupation and
receptor parameters. The dose received as a result Figure 1. The activity concentrations of radon gas (Bq m–3 )
of building occupation is related to the building’s and natural radionuclides of 40 K, 210 Pb, 226 Ra, 232 Th and
use, to its conditions, position, size, dimensions and 238 U in (Bq kg–1 ) of the rock samples of the mine.
contaminating radionuclides.
RESRAD-Build considers three external exposure
pathways including exposure directly from the source;
from materials deposited on the floor; and due to air samples were analyzed. The samples were ordered,
submersion. In addition to four internal pathways so that they follow the location along the interior
which are inhalation of airborne radioactive particu- of the considered mine. The ranges of the activity
lates; inhalation of aerosol indoor radon progeny; concentrations of the radionuclides 238 U, 226 Ra, 232 Th,
40
direct ingestion of radioactive material from the K and 210 Pb were (67.6–330), (68.2–272.3), (37.1–
source and ingestion of materials deposited on the 82.6), (169.9.0–530.3) and (25.3–258.7) Bqkg−1 ,
surfaces of the building. RESRAD-Build evaluates respectively. The average activity concentrations were
the external radiation doses as the effective dose 207.3 ± 12.5, 155.5 ± 9, 59.7 ± 4.1, 304.5 ± 8.3 and
equivalent (EDE), and the internal exposure as the 119.3 ± 4.5 Bqkg−1 , respectively, as given in Table 2
committed EDE (CEDE). The sum of the external and presented in Figure 1. The activity concentra-
and internal doses represents the total EDE (TEDE). tions of sample No. 3 have the highest concentrations
of 238 U and 226 Ra, the parent radionuclides of 222 Rn,
which is the main contributor of EDE to workers in
the mine’s environment.
RESULTS AND DISCUSSIONS
In each underground building, there could be
The activity concentrations of the radionuclides radioprotection problems, and such situations should
238
U, 226 Ra, 232 Th, 40 K and 210 Pb in the collected be controlled. The radiological dose parameters

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 EFFECT OF WORKING CONDITIONS AND NRL OF AN OLD MM
Table 2. Activity concentrations (Bq kg–1 ) of radionuclides 226 Ra, 232 Th, 238 U, 40 K, 210 Pb and Rn gas concentration

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(Bq m–3 ).

226 Ra 232 Th 238 U 40 K 210 Pb Rn (Bq m–3 ) Rn (WL)

1 68.2 ± 4.2 45.8 ± 3.9 120.7 ± 8.0 320.7 ± 7.4 41.7 ± 2.1 17.3 1.85E-03
2 75.9 ± 7.9 39 ± 3.2 67.7 ± 5.6 220.5 ± 6.1 25.3 ± 1.3 21.6 2.31E-03
3 208.1 ± 13.5 64.8 ± 5.1 305 ± 18.3 530.3 ± 13.6 74 ± 3.2 14.4 1.54E-03
4 272.3 ± 15.1 58.4 ± 4.0 330 ± 16.7 380.2 ± 9.7 125.8 ± 4.3 179.6 1.92E-02
5 271.8 ± 18.8 65.1 ± 4.9 290.6 ± 16.1 398.8 ± 10.2 155.2 ± 5.7 196.4 2.10E-02
6 99.3 ± 5.2 76.7 ± 4.5 295.3 ± 17.4 279.1 ± 6.7 104.4 ± 4.0 149.6 1.60E-02
7 200.4 ± 12.7 58.8 ± 2.9 205.2 ± 12.9 243.6 ± 7.8 115.2 ± 4.5 113.2 1.21E-02
8 85.1 ± 3.7 37.1 ± 3.1 67.6 ± 5.1 172.5 ± 5.5 94.9 ± 3.7 168.3 1.80E-02
9 113.7 ± 6.6 54 ± 3.8 235.7 ± 12.4 169.9 ± 4.3 136.6 ± 4.9 292.7 3.13E-02
10 108.8 ± 6.2 67.9 ± 3.9 145.1 ± 9.8 270.1 ± 7.4 125.3 ± 3.9 2609.4 2.79E-01
11 242.2 ± 9.3 82.6 ± 5.6 230.4 ± 14.5 405.0 ± 12.0 258.7 ± 8.1 5079.12 5.45E-01
12 119.8 ± 4.8 66.4 ± 3.2 194.7 ± 13.3 262.6 ± 8.2 174 ± 6.8 6238.13 6.67E-01
Mean 155.5 ± 9.0 59.7 ± 4.1 207.3 ± 12.5 304.5 ± 8.3 119.3 ± 4.5 1256.7 1.35E-01
STD 77.89 13.97 91.03 106.97 61.67 2190.72 2.30E-01
CV% 0.50 0.23 0.44 0.35 0.52 174 174

like absorbed dose rates, external, internal and near the entrance of the mine and maximum value of
total effective dose rate from radon and natural 83.65 mSv y–1 . The average AEDRn is 16.8 mSv y–1
radionuclides derived from mine’s soil were calculated which is the result of the average radon concentration
according to formula in Table 1 and are illustrated of 1256.6 (0.135 WL) Bq m–3 . AEDRn was calculated
in Figure 2 and Table 3. It is clear from Figure 2A assuming 2000 annual working hours and an equilib-
that the internal pathway is dominant over external rium factor of 0.4 (because of the very low ventilation
one because of the high concentrations of Rn gas conditions inside the mine), and a reference worker
inside the mine and the presence of its ancestor with an average breathing rate of 1.2 m3 h−1(14) .
isotopes of radium with appreciable concentrations The total AEDtot for the workers of the mine
(Figures 1 and 2B). The average radon concentration ranged from 0.58 to 83.8 mSvy−1 with an annual
is 1254.6 Bqm−3 , which is equivalent to 0.135 WL. average of 17.4 mSvy−1 as presented in Figure 2B.
The lowest radon concentrations were observed The great variability of AEDtot was measured by the
near the mine’s entrance, with activity concentration relative standard deviation or so-called coefficient of
of 14.4 Bqm−3 and the concentration increases variation (CV%). The CV of AEDtot was 169% which
further as going deeper inside the mine up to 6238 is due to the great variability of Rn concentrations
Bqm−3 at 210 m (Figure 1). Higher concentrations throughout the mine (CV% = 174), since radon
of radon gas are expected deeper in the mine. The gas and its decay products is the main contributor
maximum radon concentration is more than six of the AEDtot . Rn gas concentration was increased
times higher than the ICRP recommended reference further inside the mine because of its accumulation by
level for radon exposure in indoor workplaces of convection and diffusion, while other radionuclides
1000 Bq m–3(26) . (226 Ra, 232 Th and 40 K) depends on its spatial
The average external absorbed dose (Dex ) rate in distribution in the rocks of the mine with much
air at 1 m from the ground surface was 116.4 nGyh−1 lower CV (50, 23 and 35%, respectively; Tables 2
with range from 65.5 to 173.5 nGyh−1 . The resulting and 3).
external annual effective dose, AEDex , ranged from
0.1 to 0.24 with an average value of 0.16 mSv y–1 ,
assuming annual exposure of 2000 h for miners. The
internal absorbed dose (Din ) rate due to the inhalation Exposure scenario description
and ingestion of natural radionuclides of 226 Ra, 232 Th and RESRAD-Build calculations
and 40 K are calculated using the formula in Table 1 Dose assessments can be always thought to be an
and was ranged from 111 to 424.2 nGy h–1 , resulting iterative process. Dose assessment can be one of two
in an internal AEDin of an average of 0.41 mSv y–1 approaches; prospective doses are estimated for peo-
and a range of 0.16–0.59 mSv y–1 . Because of the very ple whose exposure has not yet occurred, while retro-
high concentrations of Rn gas accumulated inside the spective doses are generally estimated for groups that
mine, the AEDRn due to inhalation and ingestion of are known to have received exposure. The assessment
Rn and its decay products was very much higher than generally begins with more conservative assumptions
the other pathways, with a minimum value of 0.23 for sources, parameter values and habit data. The
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 M. H. E. MONGED
Table 3. Radiation absorbed dose rates and annual effective doses from external and internal pathways.

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Dex Din AEDex AEDin Radon AEDRn Total AEDtot
(nGyh–1) (nGyh–1) (mSvy–1) (mSvy–1) (mSvy–1) (mSvy–1)

1 71.36 177.48 0.10 0.25 0.23 0.58

2 66.07 111.04 0.09 0.16 0.29 0.54
3 152.11 402.28 0.21 0.56 0.19 0.97
4 168.95 424.18 0.24 0.59 2.40 3.23
5 173.42 395.59 0.24 0.55 2.62 3.42
6 101.63 405.37 0.14 0.57 2.00 2.71
7 131.83 289.41 0.18 0.41 1.51 2.10
8 65.49 114.30 0.09 0.16 2.25 2.50
9 89.87 321.00 0.13 0.45 3.91 4.48
10 99.93 229.01 0.14 0.32 34.82 35.28
11 173.49 348.17 0.24 0.49 68.02 68.75
12 103.09 290.51 0.14 0.41 83.24 83.79
Mean 116.44 292.36 0.16 0.41 16.79 17.36
STD 41.90 112.26 0.06 0.16 29.27 29.29
CV% 36 38 36 38 174 169

results from each iteration are used for determi-

nation, if more realistic information is needed,
particularly when the magnitude of the doses calcu-
lated approaches the dose constraint. Uncertainties
associated with estimation of dose may be taken
into account either deterministically by selecting
appropriated single values for parameters, or proba-
bilistically by incorporating distributions for param-
eter values. With either methodology, the aim is to
perform a sufficiently robust evaluation to support
judgments and decisions to be made on radiological
protection and to set compliance with law and limits
that have been set by regulator(1) . In that regard,
we thought that the application of RESRAD-Build
and the measured levels of natural radionuclides
(especially 226 Ra) can be useful tools to perform such
prospective dose assessment inside the mine to insure
radiological protect of the workers and to assure
compliance with dose limits.
The scheme of the mine is made considering 210-
m length, 210 × 2.25 m section, made of three com-
partments (mine), where the area of each compart-
ment in RESRAD-Build is 157.5 m2 (2.25 × 70 m).
The dose received by the receptor is influenced by
the source depth until it is almost 1 m, as observed
when making parameter calculations. Inside the first
and second compartments, there are three sources
and one receptor each, while four sources and one
receptor are in the third compartment. The sources
cover the entire internal surface of the compartment.
The 10 sources were input as the average activity
concentrations of the measured rock samples, i.e. con-
Figure 2. Absorbed dose rates (A), external, internal and tain homogeneous activity concentrations of radionu-
total effective dose rate from radon and natural radionu- clides. The receptor is surrounded by sources and
clides (B) derived from mine’s rock samples. it is at 1 m from the floor and in the middle of

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 EFFECT OF WORKING CONDITIONS AND NRL OF AN OLD MM
and dose conversion factor (mSv y−1 ) (Bq g−1 ),

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respectively.

Estimation of dose resulting from inhalation of radon

Calculation of the doses from radon and its decay
products requires different variables such as radon
concentration in the air, radon exhalation rate and
concentration of the radon daughters to be estimated.
Merged air quality model is used by the code to
estimate the radon dose and the concentration of the
radon progenies based on the air exchange between
the compartment and outdoor air. Furthermore,
radioactive decay and ingrowth were also estimated.
The indoor radon concentration (C Rn ) is calculated
Figure 3. Display of the designed three compartments with
by Equation (6)(15) :
10 radiation sources and one 3 receptors representing the
mine. P × CRa × λ × ρ × A × d
CRn = (6)
V (λ + λv )
each compartment, as shown in Figure 3. External air
enters the building only through the opening of the where P and C Ra are the radon emanation fraction
first compartment through ‘Venturi effect,’ where the and activity concentration of radium in the building
blown wind transfers radon gas deeper in the mine materials (Bqkg−1 ), respectively. λ and λv are the
by convection causing Rn accumulation inside the radon decay constant (0.007 h−1 ) and air exchange
mine(23) . rate (h−1 ) respectively. ρ is the density of the materials
The general situation inside the mine is charac- mine walls (kg m−3 ), d is the thickness of the wall
terized by considerable degradation in air ventilation layer of the mine, A and V are the mine area (m2 )
within short distances. The measured radon concen- and the inner volume of the mine (m3 ), respectively.
trations were used to validate the results of the mod- The assessment of the long-term radiological risks in
eled scenario. One limitation in the RESRAD-Build the present study considers an average worker lifetime
is that it can model only 10 sources; however, in this of 50 years and the dose library used was the Interna-
scenario, we need to model 12 sources to surround tional Commission on Radiological Protection 72(22) ,
the 3 receptors from four directions. For that reason, and details of the input data are presented in Table 4.
we double the EDE values from sources 3 in the first The necessary parameters required for the dose
compartment and source 6 in the second one as seen assessment due to inhalation of radon and radon
in Figure 3. progeny are emanation fraction, ventilation rate,
effective radon diffusivity, porosity and density of
source materials. The radon diffusivity, porosity and
External dose within the mine
density used in this study are 2 × 10−5 m2 s−1 , 0.15 and
In RESRAD-Build computer code, the model is 2400 kg m−3 , respectively. Furthermore, no shielding
designed based on semi-infinite slab source and was considered in this study because there is no
corrections for geometric factors. The model employs barrier between the receptor and the walls of the
the dose-conversion coefficients of external exposure mine. Ventilation rate or air exchange rate represents
to photons emitted by radionuclides distributed in the the total volume of the air in the mine exchanged by
soil. To obtain dose coefficients of any shape, depth, the outside air per hour.
cover and size, the model assumed that sources are The radon emanation fraction is a unitless
infinite in lateral extent; it also accounts for area parameter ranging in value from 0 to 1. Values
and shape. The total external dose (Dex ) is calculated approaching 0 indicate that the majority of the radon
according to Equation (5)(15) : is retained in the matrix of the material and is not
being released to the pore space. An emanation
fraction approaching 1 indicates that most of the
Dex = OF × Ci × DCF × GF (5)
generated radon is being released to the pore spaces
inside the contaminated material. The values of the
where OF and GF are the indoor occupancy factor radon emanation fraction have been measured mostly
and geometrical factor, respectively, for the infinite for soils. Experimental measurements conducted
area, source thickness and position. Ci and DCF are by various investigators have been reported in
the activity concentration of the radionuclide (Bq g−1 ) Nazaroff et al.(16) ; they show variations in the radon

7
 M. H. E. MONGED
emanation fraction ranging from 0.02 to 0.72, with

ICRP 72 (Adult)
1.125 × 105 × 1
1.125 × 175 × 1

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average values ranging from 0.12 to 0.30. The radon

1.125 × 35 × 1
emanation fraction varies with total porosity and the

28.8 m3 d−1
volumetric water content. More pore space (larger
pore size) in a sample increases the likelihood of the
Value radon recoil terminating outside of a soil grain. An

1
increased water content also increases the probability
of a radon recoil terminating in a pore space because

Receptor/miner
Breathing rate
Time fraction
of the damping effect of the water on the radon

Dose library
parameters

Number of
receptors progression(17) . Since the total porosity of manganese
Receptor

location
ore (pyrolusite MnO2 and Hematite) measured by
Fahim et al.(18) = 0.18 which is higher than the
default value in the RESRAD-Build (0.1), and the
moderately humid air in the region of the mine which

2.25 × 2.25 × 70
could enhance radon emanation. For that reasons, the
5 × 10−7 s−1

value of 0.3 for emanation fraction was used instead

0.01 m s−1

0.001 h−1

of default emanation fraction value of 0.2.

For the calculation of doses following inhalation
Value

of radon and radon progeny in underground mines

and in buildings, in most circumstances, the ICRP
Mines’ exchange rate

recommends a dose coefficient of 3 mSv per mJ h

Deposition velocity

Resuspension rate

m−3 (∼10 mSv WLM−1 ). The Commission considers

Room dimension
Mine parameters
Table 4. RESRAD-Build input parameters.

this dose coefficient to be applicable to the major-

ity of circumstances with no adjustment for aerosol
characteristics(14) . In Publication 103, the ICRP con-
sidered that the internationally established value of
1000 Bq m–3 (10 mSv) might be used globally ref-
erence level for applying occupational radiological
protection requirements(19) .
226 Ra = 155.5,
232 Th = 61.8,

The total EDE for worker of the mine who works

Rn = 1256.6
40 K = 304.5
Walls, floor

for 2000 h per year is 31.7, 44.7 and 82.1 mSvy−1 at the
and ceiling

(Bq m–3 )

time of assessment for the receptors 1, 2 and 3, respec-

0 g h−1
Value

tively, as shown in Table 5. It is clear from Table 3

0.1
10

that radon and its daughter’s pathway accounts for

93.51% of the TEDE of receptor 1, while that con-
concentrations (Bq kg–1 )

tribution decease to 67.47% for the sake of inhala-

Location of the sources

tion pathway (31.93%) of the TEDE of receptor 2.

Number of sources
Source parameters

The situation is reversed in case of receptor 3, where

Direct ingestion

the contribution from inhalation pathway becomes

Radionuclides

the predominant one. The value of the TEDE is

Air fraction

inversely proportional to the air exchange rate with

the outer environment as well as the predominant
exposure pathway. This can be taken in consideration
in the radiation protection measures for protecting
the workers. The average TEDE for a worker occu-
0.23 (2000 h y–1 )

pying the position of the three receptors during a

working period is therefore 52.83 mSvy−1 . The worst
25 550 days

0–70 years

case scenario is a worker expending all his working

period in the third compartment, where the TEDE
Value

is 82.1 mSvy−1 . Those predicted doses are in accor-

129

dance with that doses experimentally measured from

radon gas and other natural radionuclides of the
(occupancy factor)
Exposure duration

Number of rooms
Time parameters

Time integration

rocks samples from the mine (Table 5). These com-

Indoor fraction

parisons showed a good agreement between the doses

calculation

from external and internal effective doses of both

Times for

modeled scenario and measured samples. Especially,

at the end of the mine where the highest concentration
of Rn gas was found, keeping in mind that inhalation

8
 EFFECT OF WORKING CONDITIONS AND NRL OF AN OLD MM
Table 5. EDE from different exposure pathways for the workers of the mine.

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Receptor External Deposition Immersion Inhalation Radon Ingestion Total

1 2.05E-01 1.52E-04 2.54E-06 1.84E+00 2.96E+01 1.07E-02 3.17E+01

2 1.91E-01 9.05E-04 1.51E-05 1.43E+01 3.02E+01 7.57E-02 4.47E+01
3 1.98E-01 3.11E-03 5.18E-05 5.14E+01 3.02E+01 2.68E-01 8.21E+01
3a 0.21 81.87 82.1
Measuredb 0.16 (0.1–0.24) 83.65 83.8

a Receptor 3 internal and external pathways for comparison with measured doses at the end of the mine.
b Measured at sampling site #12, the last sampling site in the mine.

Table 6. Relative contribution of different pathways in the TEDE.

Receptor External Deposition Immersion Inhalation Radon Ingestion

Pathway contribution %
1 0.65 Nila Nil 5.81 93.51 0.03
2 0.43 Nil Nil 31.93 67.47 0.17
3 0.24 Nil Nil 62.67 36.75 0.33
3b 0.25 99.7599.75
Measured 0.19 99.81

a Nil = negligible contribution.

b Receptor 3 internal and external pathways for comparison with measured doses at the end of the mine.

of radon and its decay products contributing more risk (ILCR) for the mine workers is calculated using
than 99.5% of the total effective dose in both cases Equation (7):
(measurement and modeling; Table 6).
The results of the three compartment scenario  
ILCR = Exposure WLM or J h m−3 × Rf (7)
were compared with one compartment scenario with
limited ventilation conditions and it gave approxi-
mately similar results. However, the three compart- where Rf is the nominal probability coefficient for
ment scenario seemed more realistic, since the TEDE radon- and radon-progeny-induced lung cancer (1.4
is homogeneous and independent on the receptor × 10−4 per mJ h m−3 or 5 × 10−4 per WLM).
position in the one room compartment, because the Therefore, the probability of induced lung cancer
air quality model assumes that the air is homoge- from inhalation of radon and its progenies is 3.8 ×
neously mixed in the compartment, which is different 10−3 in the worst case where the worker spends all his
from the measured radon concentrations profile that working time in the position of receptor 3. It means
increasing significantly with distance to the inside of that the estimated lung cancer attributable to radon
the mine. is ∼4/1000 worker annually according to the current
Taking into consideration that the detriment- radon levels and limited ventilation conditions of the
adjusted nominal risk coefficient for lung cancer is mine. Furthermore, working for 30 years will intro-
1.4 × 10−4 per mJ h m−3 (5 × 10−4 per WLM)(14) . duce 11.5% of lung cancers among mine workers that
The use of that risk coefficient was based on the are very high probability which impose the use of
review of the ICRP of a more recent epidemiological ventilation and radiological safety measures.
data resulting from lower level of exposure in mines The variations of the ventilation rate with effective
for a mixed group of smokers and non-smokers. In dose were studied and the results are presented in
addition, assuming annual work of 2000 h and an Figure 4. The ventilation rate of 0.8 h−1 reduces the
equilibrium factor of 0.4 between radon and its decay annual effective dose of the worker inside the mine
products, and a reference worker with an average below 2 mSvy−1 . To reach the annual limit of radi-
breathing rate of 1.2 m3 h−1 will result in a TEDE ation exposure for public and visitors (1 mSvy−1 ),
of 82.1 mSvy−1 for receptor 3. The TEDE of 82.1 the ventilation rate could be maintained at 2.5 h−1 .
mSvy−1 is equivalent to 7.7 WLM or 27.3 mJ h m−3 . The reduction of effective dose inside the mine to
Therefore, the probability of induced lung cancer lower levels (ALARA) requires extra efforts, taking

9
 M. H. E. MONGED
author also would like to thank Prof. Dr Hanan

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Diab from the Nuclear and Radiological Regulatory
Authority for her appreciated efforts during the sam-
ples measurement and analysis. The author would
like to thank Prof. Dr Abd Alla Alshamy from the
Nuclear Materials Authority for his great role in the
samples collection and measurement of radon gas
concentrations.

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11