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Salman Bin AbdulAziz University

Faculty of Science and

Humanitarian Studies

Physics Department

Radon Gas

Nature, Measurement, and

Hazards

Submitted by

Abdullah Akhatany Adel Elfifi Raied Abdou Elesserie

Advisor

Dr. Ahmed M. Maghraby

1436 H

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Abstract

Radon is the only radioactive gas which can be found widely distributed in

nature. In this work, there is a review on the nature of radon gas, isotopes of

radon and sources of radon in nature, its possible hazards, and a brief

account on measurements techniques. Radon also may possess some

beneficial uses in mining and earthquake prediction; some of these

applications were highlighted within the scope of this review. Radon levels in

Alkharj city were evaluated in a recent study, levels of different areas within

Alkharj were presented in this review. It is of much importance to increase

public awareness about radon because of its serious impacts on human life.

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Contents

Subject Page

Abstract 2

Contents 3

Chapter one (Introduction) 4

Chapter two (Radon Sources) 9

Chapter three (Radon Hazards and applications) 18

Chapter four (Radon measurements) 26

Conclusion 40

References 41

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Chapter One

Introduction 1.1. Radon gas discovery:

In 1899 Pierre and Marie Curie reported about the emanation of a gas

from radium, however, Radon was discovered by Fredrich E. Dorn in Halle,

Germany in 1900 where he had described this gas as a radium emanation

because it rises up from the element radium, and thus it is the fifth radioactive

lement discovered after Uranium, Thorium, Radium, and Polonium. Later on,

William Ramsay and Robert Gray isolated the gas and named it (Niton).

Rutherford also noticed emanation of a radioactive gas from some thorium

compounds and this gas was named later “Thorium Emanation”, similarly,

Andres-Louis Debierne observed such gas from Actinium and called it

“Actinium Emanation”.

Several names were suggested for these three gases, the most famous were in

1920 they were named Radon (Rn), Thoron (Tn), and Actinon (An), these

names were accepted by the International Union of Pure and Applied

Chemistry (IUPAC) in 1923. Later, when isotopes were numbered and were

given the names of the most stable isotopes, the three discovered gases were

named according to the most stable isotope (Radon), while thoron was

renamed as 220

Rn, and action was renamed 219

Rn.

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1.2. Physical Properties of Radon:

Radon is an odorless, colorless, and tasteless gas, hence, merely

human senses cannot detect it. Radon gas density is 9.73 kg/m3 at standard

temperature and pressure (STP) which is about 8 times the density of air at

sea level (1.217). Radon which is of atomic number (86) is one of the densest

gases at STP, and is the densest noble gas. Its melting point is 202 K (-71 oC)

and its boiling point is 211.5 K (-61.7 oC). When cooled below its freezing

point, Radon emits a brilliant radioluminescence that turns from yellow to

orange-red as the temperature decreases. Radon is moderately soluble in

water and is more soluble in organic liquids than water.

1.3. Isotopes of Radon:

Since its first discovery in 1900, 39 Radon isotopes were

discovered ranging from 193

Rn to 231

Rn. Although there is no stable isotope

for Rn, the most stable one is 222

Rn which is the decay product of 226

Ra,

within the uranium series where it is of the longest half-life (3.82 day) and

this is the isotope we usually refer to when talking about Radon.

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Table (1) presents the known isotopes of Radon gas indicating their historic

names, half life time, the isotopic mass (in atomic mass unit, u), decay mode

and the daughter product of each.

Table (1): Isotopes of Radon and some of their physical properties.

Nuclide

Symbol

Historic

Name Isotopic mass (u)

Half-life

Decay

Mode(s)

Daughter

Isotope(s)

195

Rn

195.00544(5) 6 ms

195mRn

6 ms

196Rn

196.002115(16)

4.7(11) ms α

192Po

[4.4(+13-9) ms] β+ (rare)

196At

197Rn

197.00158(7)

66(16) ms α 193

Po

[65(+25-14) ms] β+ (rare)

197At

197mRn

21(5) ms α 193

Po

[19(+8-4) ms] β+ (rare)

197At

198Rn

197.998679(14) 65(3) ms

α (99%) 194

Po

β+ (1%)

198At

199Rn

198.99837(7) 620(30) ms

α (94%) 195

Po

β+ (6%)

199At

199mRn

320(20) ms

α (97%) 195

Po

β+ (3%)

199At

200Rn

199.995699(14) 0.96(3) s

α (98%) 196

Po

β+ (2%)

200At

201Rn

200.99563(8) 7.0(4) s

α (80%) 197

Po

β+ (20%)

201At

201mRn

3.8(1) s

α (90%) 197

Po

β+ (10%)

201At

IT (<1%)

201Rn

202Rn

201.993263(19) 9.94(18) s

α (85%) 198

Po

β+ (15%)

202At

203Rn

202.993387(25) 44.2(16) s

α (66%) 199

Po

β+ (34%)

203At

203mRn

26.7(5) s

α (80%) 199

Po

β+ (20%)

203At

204Rn

203.991429(16) 1.17(18) min

α (73%) 200

Po

β+ (27%)

204At

205Rn

204.99172(5) 170(4) s

β+ (77%)

205At

α (23%) 201

Po 206

Rn

205.990214(16) 5.67(17) min α (62%) 202

Po

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β+ (38%)

206At

207Rn

206.990734(28) 9.25(17) min

β+ (79%)

207At

α (21%) 203

Po 207m

Rn

181(18) µs

208Rn

207.989642(12) 24.35(14) min

α (62%) 204

Po

β+ (38%)

208At

209Rn

208.990415(21) 28.5(10) min

β+ (83%)

209At

α (17%) 205

Po 209m1

Rn

13.4(13) µs

209m2Rn

3.0(3) µs

210Rn

209.989696(9) 2.4(1) h

α (96%) 206

Po

β+ (4%)

210At

210m1Rn

644(40) ns

210m2

Rn

1.06(5) µs

210m3Rn

1.04(7) µs

211Rn

210.990601(7) 14.6(2) h

α (72.6%) 207

Po

β+ (27.4%)

211At

212Rn

211.990704(3) 23.9(12) min

α 208

Po

β+β

+ (rare)

212Po

213Rn

212.993883(6) 19.5(1) ms α

209Po

214Rn

213.995363(10) 0.27(2) µs

α 210

Po

β+β

+ (rare)

214Po

214mRn

245(30) ns

215

Rn

214.998745(8) 2.30(10) µs α 211

Po 216

Rn

216.000274(8) 45(5) µs α 212

Po 217

Rn

217.003928(5) 0.54(5) ms α 213

Po 218

Rn

218.0056013(25) 35(5) ms α 214

Po

219Rn

Actinon

219.0094802(27) 3.96(1) s α 215

Po Actinium

emanation

220Rn

Thoron

220.0113940(24) 55.6(1) s

α 216

Po

Thorium

emanation β

-β

- (rare)

220Ra

221Rn

221.015537(6) 25.7(5) min

β- (78%)

221Fr

α (22%) 217

Po

222Rn

Radon[n 5]

222.0175777(25) 3.8235(3) d α 218

Po

Radium emanation

Emanation

Emanon

Niton 223

Rn

223.02179(32)# 24.3(4) min β-

223Fr

224Rn

224.02409(32)# 107(3) min β

-

224Fr

225Rn

225.02844(32)# 4.66(4) min β

-

225Fr

226Rn

226.03089(43)# 7.4(1) min β

-

226Fr

227Rn

227.03541(45)# 20.8(7) s β

-

227Fr

228Rn

228.03799(44)# 65(2) s β

-

228Fr

229Rn

229.0426536(141) 12 s

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Chapter Two

Radon Sources 2.1. Decay chains:

Most radioactive isotopes do not decay directly to a stable product, instead

they follow a long or a short series of transformations through which emission of

radiation occur before reaching the stable isotope, and such transformations are

called decay chains. The most common decay families (or decay chains) are

thorium series, uranium series (sometimes called radium series), actinium series,

and neptunium series.

Figure (1) represents the four series indicating the decay mode, daughter, half life

time.

From these figures, it was found 222

Rn isotope which is the most stable one is a

decay product of radium, 226

Ra within the Uranium series (Uranium -238). On the

other hand, the most stable Radon isotope in Thorium series is 220

Rn which

sometimes called ‘thoron’, its half life time is 55.6 s, while in Actinium series, the

most stable Radon isotope is 219

Rn and is called action with half life time of about

3.96 s. in Neptunium series, no significant Radon isotope can be noticed although

the presence of traces of 217

Rn (http://www.wikipedia.org).

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(a) (b)

(c) (d)

Figure (1): the most comon four decay chains, a: Thorium series , b: Uranium (Radium) series, c: Neptonium series, and d: Actinium series.

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2.2. Radon progenies:

222Rn belongs to the radium and uranium-238 decay chain, and has a

half-life of 3.8235 days. Its four first products (excluding marginal decay schemes)

are very short-lived, meaning that the corresponding disintegrations are indicative

of the initial radon distribution. Its decay goes through the following sequence:

222

Rn, 3.8 days, alpha decaying to 218

Po, 3.10 minutes, alpha

decaying to 214

Pb, 26.8 minutes, beta decaying to 214

Bi, 19.9

minutes, beta decaying to 214

Po, 0.1643 ms, alpha decaying to

210Pb, which has a much longer half-life of 22.3 years, beta

decaying to 210

Bi, 5.013 days, beta decaying to 210

Po, 138.376

days, alpha decaying to 206

Pb, stable.

Radon progeny measurements can improve dose estimates based on radon gas

measurements alone (http://www.wikipedia.org).

2.3. Radon in Environment:

Radon as a natural gas can be found in soil and rocks, and because it has no

color, taste, nor smell it cannot be noticed by human unless some detector is being

used. Ground water can contain Radon, also lakes, ponds etc. Radon can exist also

in caves, mines. Concentration of Radon gas in environment varies from location to

another and depends on several factors, such as the structure of the bedrock at this

location, wind speed, ventilation, porosity of the ground and sub-ground layers, etc.

Rainwater may contain a certain amount of Radon and some of its progenies. It is

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believed that Radon concentration in rainwater occurs during thunderstorms,

estimates of the raindrop age could be obtained by evaluating the abundance of

radioisotopes of Radon short lived decay progenies in rainwater. Figure (2)

represents the ratio of Radon compared to other sources of radiation.

Figure (2): Radon comprises 55 % of the total radiation sources on the earth, blue represents the

natural radiation, sources and yellow represents the artificial radiation source.

2.4. Radon in gas and oil industry:

Residues from the oil and gas industry often contain radium and its

daughters. The sulfate scale from wells of oil or gas can be very rich with

radium. Often, water coming out of of oil field is very rich in strontium, barium,

and radium. Hence it is not surprising to find Radon in water, oil, and natural

gas coming out from the wells, all contain Radon which decays to solid

radioisotopes and forms internal layers in pipework, in the oil processing plants,

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region of propane is the most contaminated area as the boiling point of propane

similar to that of Radon.

2.5. Radon in mines and caves:

In general, hard rock mining is a dangerous routine where the

possibility of emanation of Radon gas increases, however, the certain and

proved danger is the uranium mining where highly radioactive product

daughters are releases including Radon gas. Now, legislation ensures the level of

Radon in the air of mines by the use of proper ventilation, allowing limited time

exposure of miners and compensation. The unit of exposure to Radon gas

(Working level month, WLM) is derived from the miners work bearing

permitted level in one month (equivalent to 170 hours), more about this unit will

be discussed in a following chapter. In some mines, Radon level can reach 400 –

700 kBq/m3.

2.5. Radon and indoor environment:

Radon was discovered accidentally in dwellings in 1984 where one of

workers in Limerick nuclear power plant in Pennsylvania has notice the high

readings of his Geiger counter in his house, while authorities spent long time

searching for the nuclear plant source, they discovered that the source was

highly increased level of Radon in his basement.

2.5.1. Sources of indoor Radon:

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Although variations in Radon levels in dwellings, depending on the type,

ventilation rates, insulations, and other factors, sources of Radon in dwellings

can be summarized briefly in the following points:

2.5.1.1. Soil:

It is the main source of Radon in highly elevated indoor radon levels, the soil

surrounding the dwelling where it comprises about 64 % of indoor Radon

sources. Gas flow through the soil depends on the soil type, gas concentration,

and the sub-slab pressure. One of good practices in this issue is to depressurize

the flowing gas and applying proper insulations.

2.5.1.2. Water:

Since radium is widely distributed in the earth's crust, and it could be

found in minerals that come in contact with groundwater. Subsequently, Radon,

which is soluble in water, is found in groundwater, in some cases, significant

concentrations have been observed.

Use and heating of water containing dissolved Radon and/or radium containing

water results in the release of Radon into indoor air.

2.5.1.3. Outdoor air:

The outdoor air concentration of Radon forms the minimum value of the

indoor Radon concentration, to which other sources may add. Outdoor radon

concentrations have been observed to vary seasonally, diurnally, and according

to the geographical location, altitude. There are daily variations for example

ground floors are the highest in early morning hours when atmosphere is stable

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and the lowest in midafternoon as the air temperature varies fast, similar

seasonal variations were noticed. Annual average concentrations at 1-2 meters

above the ground was found to be within the range (0.6 – 28 Bq.m-3

).

2.5.1.4. Building materials:

As radium is widely distributed within the earth crust, it exists in all building

materials on the earth in trace amounts including rocks, gypsum, phosphate slag,

even woods taken from plants were planted in radium rich areas, etc.

2.5.1.5. Natural gas:

Similar to the case of the groundwater, natural gas can accumulate Radon

from surrounding rocks and deposited layers and mixed with it during gas

formation. Almost Radon decays during the transfer of natural gas through

pipes, at the outlet; it is almost decay products can be found. Figure (3)

represents the percentage pie chart contribution of the most important Radon

sources in the indoor environment. Also Figure (4) represents pathways of

Radon to indoors.

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Figure (3): Different sources contributing in Radon concentrations inside dwellings.

Figure (4): Pathways of radon to indoor environment.

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2.5.2. Reduction of Radon in indoor environment:

If radon level in a house is higher than 4 pCi/L (equivalent to about 148

Bq/m3) then acting on the lowering Radon concentration is recommended by the

Environmental Protection Agency (EPA), USA. There are some techniques for

the reduction of Radon level in indoor environments including but not limited

to: sealing all cracks, openings, and other possible pathways to the dwellings,

implementing system of vents and fans for sub-slab depressurization of Radon

indoors, design of this system may vary according to several factors such as

dwelling type, design, building materials. Increasing smart ventilation

possibilities may help in reduction of Radon level indoors.

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Chapter Three

Radon Hazards and Applications 3.1. History:

First description of Radon effect was described in 1530 by Paracelsus as

‘wasting disease of miners’ of unknown cause, afterthought Agricola described

the mountain disease and recommended ventilation for reducing it, later in 1879

that disease was named as lung cancer by Herting and Hesse from Germany.

Significant excess lung cancer deaths were identified within uranium miners

during 1940s and 1950s. Extensive studies were performed in order to estimate

the relation between the incidence probabilities of lung cancer versus Radon

concentrations. However, 2000-6000 Bq/m3 for about 10 years for uranium

miners were enough to show increased frequency of lung cancer.

3.2. Epidemiological studies of lung cancer and Radon:

Health hazards from Radon do not come directly from the gas itself, but due

to the decay products formed, if the gas inhaled, Radon decays inside the air

passages of the lung resulting in the deposition of polonium and lead on nearest

tissues. Lung cancer risk is associated to Radon exposure, and the risk of

malignancy incidence in smokers increases ten folds than that in non-smokers,

however, this ratio increases to twenty folds for heavy smokers. Lung cancer

occurs in multiple histopathological patterns, the most common types of lung

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cancer are squamous cell carcinoma, adenocarcinoma, small cell carcinoma, and

large cell carcinoma. The increase of risk in smokers might be attributed to the

possible interaction of Radon progenies with tobacco ingredients smoke; in

addition, particles of smoke may hold decay products of Radon increasing the

possibilities of re-inhalation of such products and in the same time increases the

risk for passively exposed nonsmoking persons.

3.2.1. Studies on miners:

Several studies concerning the relation between the lung cancer incidence

and mining revealed the strong non-linear proportional relationship; most of risk

was estimated in uranium mines, however, other mines of Iron, Magnetite,

Fluorspar, Zinc-lead, Tin, and Niobium. The exposure-response relationship

over a wide range was presented up to 10,000 WLM (Working Level Month,

details of this unit will be presented in the following chapter). Non-linear

response at high concentration values of Radon was attributed to the killing of

the exposed cell by alpha particles, in addition, after leaving the mines

associated risk decreases.

3.2.2. Studies on general population:

In general public, death due to Radon is the main cause in several places in

the world, Figure (5) represents the annual mortality causes in USA in one year,

the Figure clarifies that Radon exposure (leading to about 21,000 deaths per

year) is much a leading cause compared to drowning, drunk driving, etc.

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Figure (5): A histogram representing main factors leading to death in one year, USA.

Although it is difficult to investigate the exposure to Radon in dwellings due to

the variations in life style even within the same region, category, or family,

several studies were performed and modelled for confirming the response-

exposure relationship. In on study in Sweden, in a rural area and it was proved

that people who live in a stone houses were assumed to be most exposed and

those who live in wooden houses are least exposed. Other studies were

performed considering age, sex, and smoking were performed.

3.2.3. Studies on Animals:

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Animal studies enable intentional exposure of experimental animals to

different Radon levels with different exposure planning considering several

factors in the study which cannot be controlled in cases of human exposure to

Radon.

In a study using Swiss albino rats, rats received Radon doses in the range (13.01

– 65.05) WLM, cytogenetic effects due to inhalation of Radon clarified the

formation of different type of chromosomal aberrations where chromosome and

chromatin breaks dominates in bone marrow mitotic cells.

3.2.4. Risk assessment:

United Nations Scientific Committee on the Effects of Atomic Radiation

(UNSCARE) recommended the limit of 9 nSv (corresponding to 1 Bq h/m3),

while living permanently (8760 h per year) in a high level Radon area (1000

Bq/m3) resulting in receiving about 80 mSv. Several models were proposed for

estimating risks from Radon such as UNSCARE, ICRP65 (produced by the

International Committee of Radiation Protection), and BEIR VI model which

was produced by the National Academy of Science (NAS, USA) which is the

most sophisticated model considering sexual differences, smoking habits, age,

and time elapsed since exposure. According to BEIR VI model, the absolute risk

of lung cancer for age of 75 at normal Radon concentrations of 0, 100, and 400

Bq/m3 would be about 0.4%, 0.5%, and 0.7%, respectively, for lifelong

nonsmokers, and about 25 times greater (10%, 12%, and 16%) for smokers.

3.2.5. Other health effects:

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Radon impacts on human health is not limited to the risk of lung cancer,

other organs/systems might be affected: lung cancer at other sites, nonmalignant

respiratory diseases, renal diseases, and fertility. Because it is difficult to

correlate these effects to over exposure to Radon experimental animals were

used to provide evidences. Radon itself can be absorbed by blood but it can not

result in a significant dose to nonpulmonary tissues, however, radon decay

products deliver their alpha energy to the pulmonary tissues and even can be

translocate from the lungs causing adverse effects at distant sites. Few studies

related the incidence of skin cancer to radon exposure, others reported the

induction of stomach cancer.

3.3. Applications of Radon:

There are several benefits of Radon gas; these benefits can be summarized in

the following points:

3.3.1. Earthquake prediction:

Real-time monitoring of Radon was found to give signs prior to

earthquakes. Some movements and strain change within or beneath the earth

crust prior or during earthquakes lead to enhance emanation of Radon in soil gas

and groundwater. It is believed that the Radon is released from cavities and

cracks as earth’s crust is strained prior to the sudden slip of the earthquakes.

Figure (6) represents a typical station structure used for radon measurements in

soil, and Figure (7) represents a chart of radon concentration close to Marmara,

turkey before some seismic activities (Hussein, A. S. 2008).

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3.3.2. Geothermal energy may be defined as the natural heat of earth trapped

close to the earth’s surface to be extracted. Geothermal energy might be related

to volcanic activities where some signs may refer to which such as hot springs,

vapors or high Radon levels which indicates the possible existence of a

geothermal energy sources underneath the earth’s surface (Hussein, A. S. 2008).

3.3.3. Radon in medicine:

The stimulation of DNA repair was observed upon radon exposure,

similar DNA repair was noticed in lymphocytes of people living in increased

radon concentrations. Therapy uses of radon may involve the intake of radon gas

either through inhalation or by transcutaneous resorption of radon dissolved in

water. Most of the radon is subsequently discharged through exhalation, but a

small amount remains in the body as radioactive radon progeny, which are

physiologically active through their continued decay. In USA, radon therapy can

be obtained only by inhalation in four old mines near the small towns of Boulder

and Basin, Montana. In Europe, radon therapy is available in multiple forms,

including baths, steam, and inhalation in curative tunnels and mines. Spas

evidently containing radon have been used with success for hundreds of years

for special illnesses mainly in the pain therapy of chronic rheumatic illnesses

(Barbra E. Erickson, 2007). There should be a balance about how much the

radon impacts or damages the tissue, so that any radon spa treatments should be

given by a medical practitioner.

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Figure (6): A station of collecting radon as an indicator of earthquakes (Hussein, A. S. 2008).

Figure (7): Record of radon concentration close to the active tectonic fault in Marmara

region of Turkey before several seismic activities.

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3.3.4. Geological and atmospheric studies:

The physical characteristics of radon make it a reliable indicator of the air

mass which is in contact with earth. Simulation of radon transport is currently

one of the best tools for the evaluation of transport schemes in regional and

global models. Measurements of radon concentration in the "soil gas' and in

ground water can yield a information regarding the subsurface geological

features and the presence of mineral and oil and gas reserves.

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Chapter Four

Measurements of Radon 4.1. Measurement Unit:

SI unit of radon concentration is (Bq/m3) which represents the activity unit

(Bq) in one cube meter, however, the unit for radon decay product exposure rate

is called (working level month, WLM) and can be defined as Any combination

of short-lived radon decay products in one liter of air that will result in the

ultimate emission of 130,000 MeV of potential alpha energy, WLM equal to one

WL for 170 hours and is approximately equal to the total alpha energy released

from the short-lived decay products in equilibrium with 100 pCi of Rn-222 per

liter of air (Niren L. Nagda, 1994).

4.2. Equilibrium Factor:

This factor can be defined as “Ratio of the activity of all the short-lived

radon daughters to the activity of the parent radon gas”; radon daughter

activities are usually less than the radon activity.

The equilibrium factor F is a very important parameter to calculate the dose

equivalent from radon and its daughters.

(1)

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Where Ci stands for the ith radon daughter. At secular equilibrium (F=1) which

means that the concentration of all daughters have the same value of

concentrations equal to the radon concentration. In this case all daughters

present in air and do not deposit on the surface of the container or escape from

it. Otherwise, F deviates from unity and 3700 Bq/m-3

of radon gas do not give

the total potential α-energy of 1.3 X 105 MeV and hence the number of WL

decrease by the factor F,

(2)

4.3. Techniques of measurements:

4.3.1 Active Techniques

Active dosimeters are instruments for measuring the concentration in

real time where air is usually pumped through a filter. The active methods are

practically useful for short-term measurements and for detailed investigation of

individual dwelling. These dosimeters can be classified into three techniques

(Ionization, Scintillation and Spectroscopy techniques) that will be discussed in

the following sections.

4.3.1.1 Ionization technique

Ionization chamber is the widely used radiation measurement

technique applied to radon determination by sampling it from atmosphere. This

based on the phenomena that when a charged particle (like alpha particle from

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radon ) passes through a gaseous chamber containing a cathode and a collector

anode it leaves large number of ion pairs along its trajectory. The electrons drift

with very large velocity toward the anode and the positive ions drift toward the

cathode forming the ionization current. This current produces a potential drop

across the resistor in the electronic circuit, which is detected and amplified

electronically.

4.3.1.2 Scintillation technique

The tiny light flashes produced by Alpha-particles fitting the phosphor

are collected by a photo-multiplier tube. The photo-multiplier tube translate the

light into an electrical signal which is proportional to the number of incident

alpha particles. Scintillation depends mainly on the length of the counting

period. It improves slightly by the volume of the flask. Lucas cell is one of the

oldest and more reliable techniques, which is based on the scintillation

phenomena.

The equipment in general is a glass vessel internally covered with a scintillating

material such as ZnS. The multiplicity of design and conception is very large.

Shape, size, voltage, external polarized grid, type of amplifying set up, field

strength, etc , are amongst parameters that are found to change from one model

to another. Figure (8) represents a schematic diagram for one of possible designs

of radon monitors.

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Figure (8): Schematic diagram of a radon monitor.

4.3.1.3 Spectroscopy technique

Indirect radon determination can be achieved by spectroscopic

technique. Alpha spectrometer is more generally the so called Alpha gross

counting. This method is sensitive to the presence of long lived thoron

daughters, which can be corrected by taking more counts and solving a set of

linear equations. Many hours are required to complete the measurements.

Gamma-spectroscopy allows discrimination between products of Uranium and

Thorium series, which is based on the interaction of Gamma-rays with matter.

The more complex advantage method is the “combined Alpha and Beta particles

spectroscopy” in which the counting of Beta particles from 214

pb and 214

Bi in

scintillator along with Alpha particles spectroscopy with a surface barrier

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detector determines the three daughters concentration during a single count

period.

4.3.2 Passive Technique

Passive dosimeter is an instrument for measuring the radon

concentration, where air diffuses to the detector or radiation falls naturally on it.

Passive monitors are of two types: real time and time integrating. Real time

monitors are designed to measure varying radon concentration, usually on an

hourly basis, while the time-integrating monitors yield a single value

representing the average concentration during the exposure period.

With one exception, passive monitors for the detection of 222

Rn are based on the

measurements of the gas and its short-lived daughter products alone. The

passive technique can be used for long periods of monitoring, usually several

months, and the recorded events constitute an integration of the Alpha particle

decays, which have occurred over the full monitoring period. This technique

includes also an intermediate case, which is the adsorption of radon on charcoal

canisters where integration periods of several days are used and the activity is

counted before the decay of 222

Rn, with a half-life of 3.8 days, has progressed so

far (IAEA 2012).

4.3.2.1 Solid State nuclear track detector (SSNTD)

Any detectable Alpha particle produces a single trail of damage in

solid state nuclear track detector SSNTD which turns into a narrow channel after

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chemical enlargement to be visible under the microscope. SSNTDs exhibit

different sensitivities to the energy of the Alpha particles emitted by radon. A

concentration as low as 1 pci/l can be assessed by SSNTD exposed to this

concentration for one month. SSNTDs mostly are cellulose ester (nitrate (LR) or

acetate (CN) ) and polycarbonate like bis-phenol-A polycarbonate (Lexan and

Macrofol), polyallyldiglecol carbonate (CR-39), polyethylene, polyvenile

chloridepoly, phenoxide, polyamide and Amber. SSNTDs are insensitive to Beta

and Gamma rays which can’t produce any etchable track but it can be used to

increase the sensitivity and the etching speed. The most drawbacks in the use of

SSNTDs are that they only integrate the record flux of particles and therefore

don’t produce time dependent response. This shortcoming is overcome by

moving the detector step by step by means of an electrical motor, where each

part of the detector strip was irradiated to radon atmosphere for a certain time

period.

SSNTDs have a specific nature led to rapid applications in a wide variety of

fields and have the following advantages:

1. The simplicity of use and of construction compared with Cloud, Bubble and

Spark chambers and even nuclear emulsion.

2. The durability, which makes them particularly valuable for the remote use.

3. Do not need power supply and therefore low in cost.

4. Robustness with minute dimension enables them to use in personal dosimeter.

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5. Can be retaining their record after read-out, where their records are stable

when subjected to light or high doses of X-rays, Beta particles, UV radiation,

etc. Figure (10) clarifies tracks of alpha particles in CR-39 (IAEA 2012).

Figure (9): Set-up for measuring radon indoors using SSNTD, (IAEA 2012).

Figure (10): Alpha particles tracks in CR-39.

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4.3.2.2 Thermoluminescence detector (TLD).

When an ionizing particle travels within a crystal it ejects some

electrons from their normal position into the conduction band, leaving a hole in

the valence band. The electrons are then trapped into defects of the crystal and

stored there in a very stable position. If, later on, the crystal is heated, the energy

given to the electrons allow them to escape from their traps. They then

recombine with the hole in the valence band, or with recombination centers, by

means of a radiative process: light is emitted which is proportional to the

number of electrons ejected by the incident radiation and hence is proportional

to the concentration or the dose to be determined.

An electrically charged plate is placed at a short distances from the TLD to let

radon daughters deposited on it and decay, this producing energy storage in the

TLD. After a proper exposure to radon rich atmosphere, the TLD is recovered

and ‘read’ in a TLD apparatus. This apparatus is a tiny oven where the

temperature is raised under a very well controlled rate (Niren L. Nagda, 1994).

The amount of light emitted by the TLD falls on the photo-cathode of a photo-

multiplier and is converted into an electrical signal. Each peak of the recorded

spectra corresponding to a particular trap. The amplitude and / or the peak area

is proportional to the irradiation dose. By this technique radon levels as low as

0.02 pCi /l can be measured for sampling carried on over one-week with air

drawn at a rate of one liter per minute.

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4.3.2.3 Activated charcoal

Adsorption technique is a radon measurement system based upon the

adsorption of the gas on an adsorbing medium, such as charcoal. The trapped

daughters 214

Bi and 214

Pb can be measured from its Gamma activity.

Adsorption technique employs a plastic Can containing a few grams of activated

charcoal covered with a lid. During the exposure, the lid of the Can is opened

and left in a place for few days (from 4 to 12 days). After exposure the lid is

closed and counting its Gamma activity by means of a NaI scintillation counter.

After a proper calibration of NaI counter, one can determine the radon

concentration from the decay activity curves (Niren L. Nagda, 1994).

It has been found that the amount of adsorbed radon depends on the relative

humidity and the calibration depends on the amount of adsorbed water, water

vapor can be removed by adding a desiccant. The charcoal canister can be

reused with almost zero back ground if it is ‘rinsed’ in an atmosphere of 100

liters of air (kept at about 100 oC). The advantage of such device is the

simplicity of construction and better reproducibility. The exposure of Charcoal

for one week gives better accuracy than the exposure of SSNTD for the same

time period i.e. it can measure a concentration of 1 pCi/l if it is exposed to this

concentration for one week (Niren L. Nagda, 1994).

4.3.2.4 Electret detector

An electret is a piece of dielectric material that exhibit an almost

permanent electrical charge if it is otherwise perturbed. This charge produces a

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strong electrostatic field, which is able to collect ions of opposite sign and then

the total charge of the electret decreases. An electret radon monitor is basically

made of steel can, on the inside top of which the electret dosimeter is fixed. At

the bottom of the Can a small inlet allows the radon gas to enter the assembly

through a filter. Decaying away, radon producing ionizing particles that in turn

produce ions within the volume of the device. Such ions are collected and

change the total charge of the electret, where the surface potential is measured.

After a proper calibration, the electret dosimeter can deliver a dose response

curve. The sensitivity and the dynamic range of the detector depend on the

volume of the device chamber and on the thickness of the sensitive material

(Niren L. Nagda,. 1994).

Figure (11): Electret ion chamber (Niren L. Nagda, 1994).

4.4. Radon in Alkharj:

Indoor radon levels and the annual effective dose are measured in Al-kharj

city, Saudi Arabia dwellings using CR-39 detector. The dwellings were

classified according to their types (schools, homes and working area). The

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influence of some factors like height and ventilation conditions on indoor radon

levels, equilibrium factor and radon effective doses were studied. Can and bare

method was used for determine the equilibrium factor between radon and its

daughters. The average radon concentration varies from 76 ± 38 Bq m3 in work

places to 114 ± 41 Bq m3 in homes. About 77% of the studied dwellings give

radon concentration in the range from50 to 150 Bqm3. The overall weighted

mean of radon level is equal to 94 ± 41 Bq m3 which is about 2.5 times the

global average. The equilibrium factor has a wide range from 0.1 to 0.6 with

overall weighted average equal to 0.308 ± 0.13. The variety of living style,

constructed materials and ventilation rates are responsible for this wide range

and subsequently the obtained high uncertainty (42%). Homes showed larger

annual effective dose (3.186 ± 0.75 mSv) than other dwellings which locate in

the range of the recommended action level but about three times the global

average. The result shows that the ventilation condition is the major but not the

only factor affects the results. Poor ventilated dwellings showed the maximum

annual effective dose on the other hand the number of floor has insignificant

difference (Ahmed M. Maghraby et al., 2014).

Numbers of tracks recorded, Do, for the filtered detector were converted into the

corresponding radon concentration levels, Co, using the following equation:

tK

DC

T

o

o

(3)

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Where t is the exposure time in days and KT is the CR-39 detector calibration

factor for radon measurements. KT was determined by exposing the detector

itself to a standard radon concentration in a radon chamber. Calibration factor

for the used cup dimension was equal to 0.2 0.02 track cm-2

per Bq m-3

d.

Can and bare method is a widely used passive method for evaluation of the

equilibrium factor F. (Planinic et al., 1997) derived many equations of F as a

function of the track-density ratios D/Do, where D and Do are the track density

of bare and diffusion (filtered) detectors respectively, one of the suitable

functions takes the following form:

53.05.0

oD

DF (4)

This equation applies within certain conditions where 1.2 < D/Do< 3. This

function gives no comment about the used diffusion chamber dimension,

although measurement of the indoor radon level is of much importance as

radiation doses received by the human population due to the inhalation of radon

and its progeny constitute more than 50% of total doses from natural radioactive

sources (UNSCEAR, 2000). Different cup dimensions gives different values of

Do (Abo-Elmagd et al., 2006) which affects the value of D/Do, For this reason,

high uncertainty was expected in the measured values of ‘F’ using diffusion

chambers with different dimensions.

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For this reason, the following equation for F as a function of D/Do and V/A (cup

volume to internal area) was derived and takes the following form (Abo-Elmagd

and Soliman, 2009):

277.026.0)(15.0

oD

D

AVF (5)

Equation 5 is valid for CR-39 with a critical angle equal to 20o equipped in a

diffusion chamber satisfies the following conditions:

The radii r 3.5 cm.

The height h 10 cm.

0.4 cm ≤ V/A 1.3 cm.

The following table represents radon levels values obtained through radon

survey in Alkharj:

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Table (1): The measured parameters for different quarters in Al-Kharj city (Ahmed M.

Maghraby et al., 2014).

Quarter Radon concentration

Bqm-3

WLM/year

Annual effective dose

(mSv)

Meshrif 85±37 0.166±0.07 0.743±0.63

Ghernata 126±19 0.214±0.08 1.359±0.50

Alyamama 113±37 0.664±0.45 3.895±2.57

Alsulimaneya 117±55 0.469±0.20 2.797±1.17

Alshoa'ba 105±2 0.843±0.06 4.895±0.36

Alsalam 112±38 0.390±0.41 2.348±2.34

Alsahna 74±36 0.143±0.06 0.907±0.39

Alrayan 144±122 0.290±0.22 1.811±1.35

Alnahda 110±42 0.287±0.21 1.757±1.18

Almontazah 138±47 0.321±0.12 1.982±0.74

Almansoura 106±54 0.266±0.10 1.632±0.64

Alkhuzamy 121±59 0.499±0.32 2.969±1.85

Aljamaa 115±61 0.422±0.48 2.528±2.816

Aldelam 115±69 0.350±.19 2.116±1.18

Alazizeya 89±18 0.441±0.16 2.600±0.89

alandalus 57±20 0.204±0.09 1.225±0.45

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Conclusion Radon gas is the most abundant natural radioactive materials. Radon

possesses serious hazards to human health where it is considered as the second

cause of lung cancer, this is in addition to other health impacts. Indoor radon

may be of several sources, air, water, soil, building materials, mitigation of

indoor radon is important for high radon levels. Radon can be used for

earthquake prediction, geological explorations and uranium mining, and other

useful applications. Measurements of radon and its daughters can be performed

either by active or passive techniques, however, the most usable technique is

registration of alpha tracks because of its accuracy, efficiency, and low cost.

Radon levels in Alkharj city are very high compared to the international average

which reflects the abundance of the bedrock in Alkharj with uranium. It is

recommended to increase awareness in Alkharj about radon hazards and

mitigation procedures.

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References

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between radon and its short-lived products using CR-39 detector. Isotopes and Radiation

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Abo-Elmagd, M., Metwally, S. M., Elmongy, S. A., Salama, E., & El-Fiki, S. A. (2006).

External and internal exposure to natural radiation inside ancient Egyptian tombs in

Saqqara. Radiation Measurements, 41(2), 197-200.

Ahmed M. Maghraby, K. Alzimami, M. Abo-Elmagd. (2014). Estimation of the

residential radon levels and the population annual effective dose in dwellings of Al-kharj,

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