Radiation research priorities in the mineral sands industry

Mineral sands processing involves exposure to external and internal radiation sources. The level of exposure is associated with the production of monazite, which contains approximately 6% thorium by weight. External radiation levels may range from less than 1 µGy h-1 to 10 µGy h-1 in the general plant environment, to greater than 150 µGy h-1 in monazite storage areas. Internal radiation may also be significant since airborne gross alpha activity levels from less than 0.05 Bq m-3 to about 5 Bq m-3 are found. Recent estimates of radiation exposure indicate that approximately 15% of workers in the industry exceed 15 mSv y-1. A small percentage of workers are estimated to be receiving radiation doses approaching or exceeding the statutory 50 mSv y-1 limit. Whilst the majority of the radiation dose is contributed by inhaled radioactivity, recent reviews of ICRP models and data reveal that the assessment protocols and default values used in internal dose estimation may be overly conservative, possibly by more than an order of magnitude. The basis for present assessment procedures is briefly reviewed, as are the major areas of uncertainty in internal dose estimation protocols. Priorities for radiation research are suggested and the practicability of obtaining better estimates of internal radiation dose is discussed.