Bomb ¹⁴C and human radiation burden

Abstract

RADIOACTIVE fallout from nuclear weapon tests has resulted in a significant increase in mean radiation dose received by the world's population. While fission nuclides such as ¹³⁷Cs and ⁹⁰Sr are important sources of internal radioactivity, notable characteristics of artificial ¹⁴C production are (1) its long half-life (5,730±40yr¹), (2) easy access via the food chain to all key molecules of body tissue, and (3) relatively long residence times in both stratosphere and troposphere of four and eight years respectively² (cf. mean residence time of particulate nuclear debris in the troposphere ∼30 d^3a). Although ¹⁴C emits a low-energy β-particle (β_max=156keV), its ease of incorporation in genetic material and the associated implications have provoked concern among several eminent scientists over artificial production of this radionuclide, even prior to the major testing period^4–7. Recent data on levels of bomb ¹⁴C and residence times of carbon in the human body are now available⁸. Thus excess human radiation burdens from this radioisotope are evaluated in this article under the assumption that no radiation dose, however small, can be regarded as entirely harmless biologically. This assumption, albeit a major one, is still adopted for radiation hazard considerations in the absence of conclusive evidence otherwise.