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Radon and Thoron Activity Measurements in Marble Tiles Using RAD 7 Detector
2
By: Areej Asim & Hanan AlSubaie
Radon and Thoron Activity Measurements in Marble Tiles Using RAD 7 Detector
Supervisor: Prof. Ibrahim F. Al-Hamarneh
December, 2019
Introduction
Outline:
1
Introduction.
Theoretical Background.
2
RAD7 .
Outline
3
Results & Discussion.
4
5
Conclusions & Suggestions.
Introduction:
- Why Radon?
- What are the health effects?
- Why marble?
Theoretical Background:
Theoretical Background
Radiation:
Radiation
Radiation is energy emitted from unstable nuclei in the form of electromagnetic waves or stream of particles.
Non-ionizing radiation
Non-ionizing radiation:
cannot ionize matter because its energy is lower than the ionization potential of matter.
Examples:
visible light, infrared, radio waves, microwaves, sunlight.
Applications:
global positioning systems, cellular phones, television stations, AM and FM radio.
Ionizing radiation
Ionizing radiation:
ionizing radiation can ionize matter either directly or indirectly because its energy exceeds the ionization potential of matter.
Types of Ionizing radiation:
Indirectly ionizing
photons (gamma & X-rays) and neutrons.
Directly ionizing
electron, proton, alpha particles.
Radon:
Radon
Natural Decay Series
Natural Decay Series:
U-238 and Th-232 decay chains
Radon gas Characteristics
Radon gas Characteristics:
- Nobel gas with atomic number 86.
- Density of 9.73 kg/m3 at STP.
- Colorless, Odorless and Tasteless gas.
Radon isotopes
Radon isotopes:
- Rn-222: the most stable isotope with half- life 3.82 d.
- Rn-220: the second most abundant isotope with half-life 55.6 sec.
- Rn-219: have very short half-life 3.96 sec.
Radon hazards
- SI unit Bq/m3 or pCi/L.
- Guideline level according to(WHO) is 200 Bq/m3 corresponding to an annual dose of 10 mSv.
- The danger lies in the daughters of radon.
- The second leading cause of lung cancer is for smokers and the first for non-smokers.
health effects
Marble Stone
Marble Stone
Most of natural stones contain considerable concentrations of natural radioactive materials.
Marble is a metamorphic rock that primarily composed of the crystalline form of mineral calcite (CaCO3) or dolomite (MgCO3).
Widely used in dwellings for external cladding of walls and floors as well as for interior and exterior decorative purposes is natural building decorative.
Radon Detectors
Radon Detectors:
There are several methods available to measure radon concentration in air. These methods are classified under several ways such as active and passive devices, short (AC & LS) term, long (Alpha Track detection system) term and continuous measuring.
Radon Detectors
Sampling:
Five different types of natural marble are collected randomly from local market, were packed in plastic bags and labeled at the point of collection.
At the laboratory, the tiles were pulverized to fine powder, and dried in a furnace to remove moisture. After sieving and weighing, the obtained powder of each sample were transferred to RAD7 chamber for radon and thoron measurements.
The elemental composition has been determined by (XRF) & (ICP-MS).
Sampling
RAD7:
RAD7 is a radon in air detector made by “DURRIDGE”.
It is capable of measuring the concentrations of both radon and thoron in air simultaneously by detecting the energy of the alpha particles emitted by the progenies of radon (Po-218 and Po-214) and thoron (Po-216, Po-212 and Bi-212).
RAD7
The RAD 7 radon detector.
The schematic of the RAD 7 setup and sample chamber
RAD 7 alpha spectrum showing Po-218 in window A and Po-214 in window C.
Results & Discussion:
Results & Discussion.
Elemental Composition of Marble Samples
Mass density (g/cm3) and elemental composition (% by weight) of the five marbles.
Radon and Thoron Concentrations in Marble Samples:
Radon and Thoron Concentrations in Marble Samples
The radon concentrations vary in a narrow range from 11.43 +/- 1.35 Bq/m3 to 13.42 +/- 1.54 Bq/m3 with an average radon concentration of 12.27 Bq/m3.
The thoron concentrations are ranged from 0.26 +/- 0.06 Bq/m3 to 0.72 +/- 0.17 Bq/m3 with an average thoron concentration of 0.41 Bq/m3.
Annual effective dose
Radon and thoron activity concentrations (Bq/m3) in marble tiles.
Annual effective dose:
According to the UNSCEAR report, annual effective dose E (mSv/y) to the public from Rn-222 and its progeny is estimated using the following equation:
E = C * F * H * T * D = 0.31 mSv/y
where:
C Rn-222 concentration (Bq/m3)
F equilibrium factor (0.4)
H occupancy factor (0.8)
T hours in a year (8760 h/y)
D dose conversion factor (9.0 * 10-6 mSv Bq/m3 h)
The indoor radon and thoron concentrations in the investigated marbles were varied from 11.43 and 0.26 to 13.42 and 0.72 Bq/m3, respectively, with average indoor radon and thoron concentrations of 12.27 Bq/m3 and 0.41 Bq/m3, respectively.
Conclusions& Suggestions:
Conclusions& Suggestions
Variations in radon and thoron concentrations were lie in narrow ranges and these variations were attributed to differences in the elemental composition of the tiles and the environment from which the stone are coming from.
The effective annual dose due to radon exposure from marble tiles in Riyadh city dwellings and workplaces was calculated to be 0.31 mSv/y.
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The observed level of indoor radon concentration due to the use of marble tiles in floor and wall cladding in Riyadh city is within the permissible level as set by monitoring agencies.
The health hazards related to the radon emanated from these tiles are expected to be negligible. Therefore, occupants of these dwellings are relatively safe.
Based on the results obtained, the radon concentration in the five types of marble was found to be in the order:
Travertine > Nacarado > Botticino > Tala Maroon > Najran Rawn.
The sample Najran Rawn marble that was produced locally is the preferable one to use for external cladding of floors and walls in comparison with the other types as it has the lowest radon content.
The current study, presented new data on radon and thoron concentrations of natural marble stone. Hopefully, assessing these parameters would provide information for the management and use of marble in building aspects.
As there are few data on indoor radon and thoron concentrations of marble used in Saudi Arabia, this study can be considered as one of the first studies that aims to form a baseline data for further studies.
Finally, it is recommended to carry similar studies that include larger number of samples and different types of building materials in Riyadh city and other regions of Saudi Arabia.
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