The linear no-threshold model (LNT model) is a conservative model used in radiation protection to estimate the health effects from small radiation doses. According to the LNT model, radiation is always considered harmful with no safety threshold, and the sum of several very small exposures are considered to have the same biological risk as one larger exposure (linearity). .
LNT and Collective Dose
In case of collective dose, conservativeness of the LNT model has enormous consequences and the model is sometimes wrongly (perhaps intentionally) used to quantify the cancerous effect of collective doses of low-level radioactive contamination. A linear dose-effect curve makes it possible to use collective doses to calculate the detrimental effects to an irradiated population. Simply:
But what does it mean? If ten million people receives an effective dose of 0.1 µSv (an equivalent of eating one banana), then the collective dose will be S = 1 Sv. Does it mean there is 5.5% chance of developing cancer for one person due to eating bananas? Note that, for high doses one sievert represents a 5.5% chance of developing cancer. A number of organisations disagree with this result and with using the linear no-threshold model to estimate risk from environmental and occupational low-level radiation exposure. There is a question, whether the collective dose is meaningful at all.
The ICRP alone states:
“The collective effective dose quantity is an instrument for optimisation, for comparing radiological technologies and protection procedures, predominantly in the context of occupational exposure. Collective effective dose is not intended as a tool for epidemiological risk assessment, and it is inappropriate to use it in risk projections. The aggregation of very low individual doses over extended time periods is inappropriate, and in particular, the calculation of the number of cancer deaths based on collective effective doses from trivial individual doses should be avoided.”
Special Reference: ICRP, 2007. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann. ICRP 37 (2-4).