In March 2002, the IAEA’s Board of Governors approved a Safety Requirements publication entitled Preparedness and Response for a Nuclear or Radiological Emergency [22]. This publication established the requirements for achieving an adequate level of preparedness and response for a nuclear or radiological emergency in any Member State. Amongst other things, the publication specifies requirements for emergencies involving a dangerous source. The Requirements define a dangerous source as one “that could, if not under control, give rise to exposure sufficient to cause severe deterministic effects”. The Requirements then go on to define a severe deterministic effect as one that “is fatal or life threatening or results in a permanent injury that decreases the quality of life”.

The operational definition of a dangerous source is known as the D value. The D value is that quantity of radioactive material, which, if uncontrolled, could result in the death of an exposed individual or a permanent injury that decreases that person’s quality of life.

For the purposes of determining D values, the exposure scenarios that were used fall into two groups: one for material that has not been dispersed and one for material that has been dispersed.

Different numerical values are provided for each of these groups:

• The D1 value is the activity of a radionuclide in a source that, if uncontrolled but not dispersed (i. e. it remains encapsulated), might result in an emergency that could reasonably be expected to cause severe deterministic health effects.

• The D2 value is the activity of a radionuclide in a source that if uncontrolled and dispersed might result in an emergency that could reasonably be expected to cause severe deterministic health effects.

• The D value is the lowest value of the Dj and D2 values for a radionuclide.

For pure beta emitters D1 values do not apply in this actual radiotracer application. For gamma tracers, both D1 and D2 values apply. The quantities (activity) of radionuclides typically used in interwell tracer examinations are evaluated against their recommended D values.