- 18 - Evaluation of Hazard from Internal Emitters The use of the word "hazard" to denote radioactivity in a biological sample, regardless of kind or amount, is questionable and therefore is used here with reservation. "Hazard" implies a risk or danger, which may or may not be correct depending upon the point of view. One point of view is that all ionizing radiations are damaging and, therefore, a hazard exists even from one ionizing event. The other point of view is that there can be some repair of the damage caused by ionizing radiations, thus, if the radiation dose does not result in an observable change, hazard does not exist. point of view, In other words, a from this latter there is a threshold level of radiation below which there is no net effect. A threshold level of ionizing radiation is more generally accepted for effects upon somatic tissue rather than upon genetic tissue. There is reliable evidence which demonstrates that the biological effect upon somatic tissues of two equal doses of radiation administered over unequal periods of time is less for the dose at the longer exposure. These results have been interpreted to mean that some repair has taken place and that tor very low levels of exposure,