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The measurement of the radon concentration in the environment and the methods of reducing its density in the indoors.

INTRODUCTION

Radon is considered as one of the main radioactive materials in nature and as most important factor of human exposure. In general, radon exists in air, water and soil as gas. The amount of this gas in the nature depends on geographical position and underground resources of those regions. In the regions that natural deposits of uranium and radium exist or in any way their water and soil of those regions have these materials, this gas will be found in that region more abundant. 55% of exposure per person per year is due to this radioactive gas. 11% exposure resulted from internal exposure because of consuming foods and beverages (foods and beverages also naturally contain some radioactive materials), 8% due to cosmic exposure, 6% due to exposure from earth and 18% due to artificial exposure (including imaging with X -ray by using radiopharmaceuticals in the nuclear medicine and ...). That total annual exposure per person from these resources is about 3.6 msv. Radon is the only production of radium cleave that regarding to the presence of radium in the uranium cleave chain, this gas is present in the decay chain of uranium. Radon is a radioactive material with half-life 8.3 days, which itself emits an alpha particle and converts to PO-218, a radioactive material with 3-minute half-life. This material will convert to Pb-214 which is a radioactive material with 26.8-minute half-life, by irradiating alpha particle.

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As it can be seen in the radon decay chain, number of alpha particles emitted in this chain is high and given that alpha particle considered as one of the most dangerous particles resulted from decays so this gas can be considered as one of the dangerous radioactive gases. Three elements polonium, lead and bismuth which are resulted from consecutive decomposition of radon and have radiation properties, are called radon daughter. These elements are as solid in macroscopic quantities and when they are formed in air they will attach to the dust particles quickly and when we breathe they enter our longs along with air and stick to its surface. These elements emit high-energy alpha particles that their radiation will damage the trachea cells, which can eventually cause lung cancer.

Methodology:

Radon emission in a volume of air is determined easily and quickly with a radon monitor and a steam cap. Radon emission quantities is defined based on the observing increase in quantity of related radon with gas volume that is obtained in a specified time. Radon is as gas and it escapes from sands and sediments overlying bedrock and some tools have been made to facilitate the digging for the detection of radon present in soil and after digging trenches in the soil by alpha spectrometry (monitor), Research package and syringe are used, if necessary. If radon is soluble in water, for measuring the radon in the water, nothing doesn't require except a radon monitor and a degassing vessel. The radon soluble in the water sample will degassed by air bubble blowing dish. The degassing Vessel should be connected to radon monitor to create a closed air loop.

All available detectors measure directly the concentration of radon and its daughters. The basis of all these devices is to suction the air by pump and to trap the radon on the special filters which are located in the air path. Radon accumulated on these filters are counted by special detectors for counting alpha (ionization chambers) and will measure radon.

If radon is as dissolved in water, for measuring its value, radon monitor and a degassing vessel is need, the radon dissolved in water sample degassed by degassing vessel. The degassing vessel should be connected to radon monitor to create a closed air loop. Radon is a gas and will escape from sands and sediments covering bedrock that some tools were made which facilitate the digging for detecting radon in soil.

First by a special syringe, 100cc water samples will be injected into the degassing vessel which is a glass cylindrical and then the completely isolated system will be startup by turning on the pump.

The second vessel which is called security vessel is located in the circuit for this reason (Because of avoiding) to avoid penetration of any water and moisture into the pump, the pump will suction for 10 minutes with flow 3.0lit/min that during this process, due to air circulation in a closed circuit and its passing through a glass filter, by micro suction total radon will removed from sample. radon rotating in the air trap in the ionization chamber during passing through the machine. this is done by special filters for absorbing radon inside the counter machine and the alpha particles emitted from it are counted by ionization chamber in counter machine. The pump will be turn off after 10 minutes and the system will leave to itself for 20 minutes in order to the radon reaching to it minimum equilibrium with its daughters. after this period, radon concentration in the water will be measure by software of analyzer and its quantity will be calculate based on error. Temperature and humidity of environment are effective in calculating the radon concentration which these parameters are considered in computing. After any measurement, the system should be empty from radon to be prepare for next samples measurements. Sampling period should not be longer than two hours, otherwise radon diffuses through the walls of the tube. Thus the radon trapped in ionization chamber and the whole system must be empty which is done by using active charcoal. active charcoal can absorb the radon because of its chemical structure and make the system free from it. there are different devices for measuring radon in environment, that the most common are Ramon2.2, Rad 7,RTM1688, Alphaguard that are detectors RAD 7 made by Durridge Company, USA and Alphaguard by Genitron Instruments, Germany.

The measurement by radon digital monitor is among other methods for determining radon quantity that is done during a short time. The measurement process of RTM1688 is such that at first, radon monitor is switched with an external pump connected with an internal pump to measure the radon activated concentration in the closed air. Then steam cap with height h on the surface is examined. Its position should be fixed suitable to enter pressure on the cover of surface and to enter a weight on the cap horizontal. In addition, an additional seal (like silicon paste, sticky tape or solid materials in case of field measurements) is recommended. After that, entrance and exit of monitor are connected with two entries of steam cap via PVC tube. In this method, a closed circuit is obtained through flowing air. Time t from beginning with minimum concentration level ([C.sub.1] quantum) up to maximum level of radon activated concentration ([C.sub.2] quantum) is measured and by measuring [C.sub.diff]=C2-C1 and using h, t, the radon emission calculation can be obtained based on [E=C.sub.diff]*h/t. In some cases, stone, brick and cement contain trace amounts of radium that emit radon inside the homes and other buildings, the air pressure inside the home is lower than pressure in soil around the house foundation so the building act like a vacuum and causing penetration of radon through cracks, pores and any penetration ways to the building and therefore the cracks of buildings floor should be watertight, meanwhile by increasing the water temperature, the adsorption will decrease and so the radon level will be decreased. Device Rad7 is a system composed of an alpha detector that is located in a Hemisphere chamber, a nuclear electronic system embedded that allow Rad7 to detect the alpha particle. The air contaminated with radon is pumping into the chamber by internal air pump that embedded in the system. This air can be supplied from water sample that is placed in test glass 40ml and 250ml by filter (NYLON 0.45) and dehumidifiers CaSo4. For measuring well water, Rad7 is mounted on well, the well water enter lateral part of powdering device by piping such that it doesn't have any contact with air and so the radon soluble in water will release into the chamber. This gas by pump, after dehumidifies enters the device Rad7 and counted. This device is more accurate than others.

The methods of reducing radon in the building:

Before any action, the level of radon in the building, its origin and its penetration way should be determined. The measurement of radon in the building air is an easy task. Most common and simplest way is to place the radon tracking films in at least two rooms for at least 2 months in a cold season. If the resource of radon is construction materials, the solution is to increase the ventilation and covering the radon-producing materials with impenetrable materials. If radon enters from the below of foundation and or around of the ground, as a first action, the air ventilation level should be increased and then its entrance should be blocked. The resistant layers against radon penetration are: sheet (layer), adhesive tape, sealant, adhesive paste, and seamers. In general, whenever the building is in ground level and its floor is in contact with soil, the probability of radon penetration is more. In this regard, floor, foundation, joints, cracks, the radon penetration ways and wells must be degassed very well.

RESULT AND DISCUSSION

To measure the radon emission, device RTM1688-2 is most recommended solution. Its unit1 presents sensitivity higher than 3 cpm (KBq/[m.sup.3]) that only 130 ml is obtained from a small internal volume. Although sensitivity of RTM2100 is lower 1/5 cpm(KBq/[m.sup.3]) probability it occurs in high humidity and the internal volume is about 3 times more (ml370) RTM1688 is most suitable solution for measuring radon of soil. Today the permissible level of radon in drinking water is determined 100Bq/l, but in the refinery that isn't prepare for consuming it can be maximum 1000Bq/l. WHO suggested the 100Bq/[m.sup.3] as permissible level n residential buildings while it is determined as 200 Bq/[M.sup.3] for in fresh air.

Conclusion:

It concluded from this paper that the aim of making these devices is first to measure the radon concentration for a long time and at timed intervals in the different regions and second to use these devices in determining the active faults, discovering underground aquifers and uranium deposits regarding radon concentration changes and now one of the aims of scientists is to measure the radon concentration for predicting earthquake.

ARTICLE INFO

Article history:

Received 11 February 2014

Received in revised form 25 February 2014

Accepted 20 April 2014

Available online 15 May 2014

REFERENCE

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(1) Sara khoshghalb, (2) Sahar khoshghalb, (3) Nazanin Khosravi, (4) Iman Chaharmahali

(1,2,3,4) Department of Agricultural Management ,college of Agriculture, Borujerd Science and Research Branch, Islamic Azad University, Borujerd, Iran.

Corresponding Author: Iman Chaharmahali, Department of Agricultural Management, college of Agriculture, Borujerd Science and Research Branch, Islamic Azad University, Borujerd, Iran.

E-mail: iman_4mahali@yahoo.com

Table I: Specific data of radon measurements devices

Method                   Type            Field area   Volume

Alpha scintillation      Instantaneous   Gas/water    0.11-3.01
  detectors
Alpha track-etch         Integrated      Gas          456ml
  detectors
Electret ion chambers    Integrated      Gas          50ml-960ml
Barasol detectors        Continuous      Gas          590ml
Clipperton detectors     Continuous      Water        590ml
Radon/thoron monitors    Continuous      Gas/water    0.271

Method                   Sensitivity               Time period

Alpha scintillation      0.8-16cph/Bq [m.sup.-3]   1-5min
  detectors
Alpha track-etch         0.03-0.09 tracks          1-2 weeks
  detectors                [cm.sup.-2]/
                           kBq [m.sup.-3]h
Electret ion chambers    3 Bq [m.sup.-3]h-1.05     2-40 days
                           kBq[m.sup.-3]h
Barasol detectors        0.02 pulses [h.sup.-1]    15-240 min
                           /Bq [m.sup.-3]
Clipperton detectors     1cph/362 Bq [m.sup.-3]    1 min-48h
Radon/thoron monitors    0.01cpm/Bq [m.sup.-3]     1min-24h
                                                   (standard 6min)
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Article Details
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Author:Khoshghalb, Sara; Khoshghalb, Sahar; Khosravi, Nazanin; Chaharmahali, Iman
Publication:Advances in Environmental Biology
Article Type:Report
Geographic Code:7IRAN
Date:Apr 15, 2014
Words:2522
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