m3) and the measured value of the bed surface is up to 109.3 pCi/L (=4044 Bq/m3) have. Considering that the bed surface had an average of 100 pCi/L, the space average was 8 pCi/L, and the space concentration before put the bed in the room was 2 to 3 pCi/L (= 74 to 111 Bq/m3) It is confirmed that there is an increase in the concentration of the space, and the radiation emitted from the bed contributes about 5% to the concentration of about 4m2.
We measured the sample using a sodium iodide(NaI) scintillation detector. The left picture is the measurement of the bed sample from which the radioactivity,
is emitted and the right picture shows the measurement of the bed sample. As a result, it can be seen that a peak of 239 kev, one of the energy regions of Pb-212, a daughter nuclide of thoron, appears prominently. In the case of the NaI detector, the energy range can not be precisely selected, including 242 kev, one of the energy regions of Pb-214, a daughter nuclide of radon. To know exactly of emissions of Radon and Thoron, Use the Germanium detector.
Exposure Dose Assessment
In South Korea, it is recommended that the annual allowable radioactivity, excluding the radiation dose naturally exposed, should not exceed 1 mSv.
When there are seven types of bed products using monazite in the mattress cover or sponge being produced since 2010, it was confirmed that the annual exposure dose exceeded 1 milli sievert (mSv).
In South Korea, government agency has provided information on the annual exposure dose assessment to evaluate every bed model for this issue.
▶ Estimation of Annual Dose by Radon Concentration
ㅇ Radon Concentration(CRn) : Radon concentration in air (Bq/m3)
ㅇ Equilibrium Factor(F) : Effective amount of radon and short-life daughter nuclide in air
- Radon : 0.4 (The rate of attaching Radon daughter nuclides to aerosol in air.)
- Thoron : 0.04 (The rate of attaching Thoron daughter nuclides to aerosol in air.)
ㅇ Exposure Time(T) : Time to exposure to the radon concentration.
ㅇ Dose Conversion Factor(DCF) : In case of light activity(1.2 m3/h), Factors
needed to convert the concentration to the exposure dose based on the
respiratory rate.
- Radon : 20.4 x 10-6 mSv/(Bq•h/m3)
• 1 (WLM) = 6.37 x 105 Bq•h/m3 (Equilibrium equivalent Radon concentration)
• Dose Factor = 13 mSv/WLM
- Thoron : 120 x 10-6 mSv/(Bq•h/m3)
• 1 (WLM) = 4.68 x 104 Bq•h/m3 (Equilibrium equivalent Thoron concentration)
• Dose Factor = 5.6 mSv/WLM
▶ A Calculation that annual exposure dose by radon(Rn-222)(Bed)
ㅇ Scenario
- 10 Hour per day (3,650 Hour per day),
- Respiration rate in sleep: 37% of Light activity(1.2 m3/h).
▶ A Calculation that annual exposure dose by Thoron(Rn-220)
ㅇ Scenario : Same with Radon
Dispersal of Radon Emitting mattress
In South Korea, the government recalled the beds which are emitting radon. Using post offices with nationwide logistics network, the president took immediate action to recall them. The amount of mattresses that the post office will recall is estimated to be about 60,000-80,000. The recalled mattresses were piled up in some harbor yards until solutions were figured out. But this was countered by local residents, so South Korea is currently in the process of dismantling and incineration.
Conclusion
This issue occurring in Korea and Taiwan is because of lack of law and regulation of radioactive matter. The monazite minerals not only used in the bed. Almost all of the products that were advertised as anion-emitting products without being supplied with energy are emitted anions using minerals such as monazite. Such products include bracelets, necklaces, pillows, and even underwear. It is best to regulate the use of radioactive materials such as monazite in the country, and statistical and preemptive compensation should be made to the people who have suffered damage using these products.
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