THE SIGNIFICANCE OF THORON (Rn-220) CONTRIBUTION TO NATURAL RADIATION DOSE IN MALAYSIA

Ismail Sulaiman; Khairuddin Mohamad Kontol; Faizal Azrin Abdul Razalim

Ismail Sulaiman
Khairuddin Mohamad Kontol
Faizal Azrin Abdul Razalim

Keywords: radon, thoron, indoor, outdoor, dose

Abstract

ABSTRACT

The objective of this study was to assess the significance of thoron contribution to the natural radiation dose in the environment. The indoor and outdoor radon/thoron (gas and progenies) concentrations in a few areas in Peninsular Malaysia, Sarawak and Sabah were measured based on active method using continuous radon/thoron gas and progeny monitors. Their respective concentrations and doses were compared. The mean indoor and outdoor radon gas concentrations were 23 Bq m^-3 and 17 Bq m'³ respectively while the mean indoor and outdoor thoron gas concentrations were 10 Bq m^-3 and 9 Bq m^-3respectively. The mean indoor and outdoor EEC (Rn) were 11.1 Bq m^-3 and 3.2 Bq m^-3respectively while the mean indoor and outdoor EEC (Tn) were 3.0 Bq m^-3 and 1.1 Bq m^-3respectively. Total annual effective dose (indoor and outdoor) from radon and thoron series were 0.9 mSv and 1.1 mSv respectively. Thoron contribution to the total annual effective dose was about 50%, indicating that radon and thoron are equally important in the assessment of natural radiation dose. Thus, the presence of thoron in the Malaysian environment cannot be simply ignored otherwise it will underestimate the dose receive by the people.

ABSTRAK

Objektif kajian ini adalah untuk menilai kepentingan sumbangan thoron kepada dos sinaran semula jadi di alam sekitar. Kepekatan radon / thoron (gas dan sepsis susulan) dalaman dan luaran di beberapa kawasan di Semenanjung Malaysia, Sarawak dan Sabah diukur berdasarkan kaedah aktif menggunakan radon / thoron berterusan dan monitor progeny. Kepekatan dan dos masing-masing telah dibandingkan. Mean konsentrasi gas radon dalaman dan luaran adalah 23 Bq m^-3 dan 17 Bq m^-3 masing-masing manakala kepekatan gas thoron dalaman dan luaran adalah 10 Bq m^-3 dan 9 Bq m^-3 masing-masing. EEC (Rn) dalaman dan luaran adalah 11.1 Bq m^-3 dan 3.2 Bq m^-3 masing-masing manakala EEC (Tn) dalaman dan luaran adalah 3.0 Bq m^-3 dan 1.1 Bq m^-3 masing-masing. Jumlah dos berkesan tahunan (dalaman dan luaran) dari siri radon dan thoron adalah 0.9 mSv dan 1.1 mSv masing-masing. Sumbangan Thoron kepada jumlah dos tahunan tahunan adalah kira-kira 50%, menunjukkan bahawa radon dan thoron adalah sama penting dalam penilaian dos sinaran semula jadi. Oleh itu, kehadiran thoron dalam persekitaran Malaysia tidak boleh diabaikan sebaliknya ia akan meremehkan dos yang diterima oleh orang awam.