604 Chapter 11. Dosimetry and Radiation Protection
11.1.ADoseandDoseRate
Radiation causes damage to the medium it passes through by depositing energy to
the medium. This damage can beacuteif a high level of dose is delivered in a short
period of time. In such a case the dose delivered per unit time is so high that the
material does not get enough time to repair the damage. In literature, this kind
of dose is sometimes referred to as theinstantaneous dose. However, this notion
is somewhat misleading. The acute damage always depends on the time integrated
energy deposited by the radiation. If the energy deposition time is shorter than the
repair mechanisms, acute damage can occur. Hence the safe practice is to usedose
anddose rateto refer to the integrated energy deposited and the energy deposited
per unit time respectively. Note thatintegrateddose rate simply refers to dose.
Having warned the reader, in this book wherever the term high instantaneous
dose is mentioned it will refer to high dose delivered in a short period of time. The
following three cases give examples of the damage caused by various amounts of
doses.
Very high dose rate, such as 500rem/sreceived due to a neutron burst near a
reactor core.Low dose received over a long period of time. For example, 20mrem/sreceived
by a radiation worker for 5 days would exceed the 5000remlimit set by most
organizations.Very high dose rate received for an extended period of time. This serious
scenario can lead to fatality.The termdosimetryhas traditionally been mostly used to refer to the measure-
ment of dose. However modern dosimetry includes the measurement of dose rate
as well. The mathematical definitions of these terms will be presented later in the
chapter.
11.2QuantitiesRelatedtoDosimetry
11.2.ARadiationExposureandDose..................
Radiation is capable of causing damage to both living and nonliving things through
different processes. It is natural to think that the severity of such a damage would
depend on the amount of radiation absorbed by the material. This is true for the
case of acute radiation effects. The severity of the stochastic effects, on the other
hand, does not depend on the intensity of the radiation. One such effect is the
mutation of cells, where even low levels of radiation can cause permanent damage.
In this case the amount of radiation can only increase the probability of initiation of
the damage, such as cancer, but not its severity. Many organizations keep track of
thefatal cancer risk factorof their radiation workers by computing the integrated
dose they have received during the time period. Apart from cancer, exposure to
high radiation can also cause severe skin burns and tissue damage. In medicine,
radiation dose calculations are routinely performed to minimize the harmful effects
of radiation.