Chapter 8
Ionizing Radiation and Life
All the good experimental physicists I have known have had an
intense curiosity that no Keep Out sign could mute. Physicists
do, of course, show a healthy respect for High Voltage,
Radiation, and Liquid Hydrogen signs.
—Luis Alvarez
Summary Ionizing radiation includes all electromagnetic waves from ultraviolet
light to gamma rays, for the simple reason that the localized interaction of light with
matter is by photons with energy proportional to frequency. With frequencies below
ultraviolet light in the spectrum, the photons have insufficient energy to break typical
organic molecular bonds. Subatomic particles moving with high kinetic energy
can also be ionizing, and therefore potentially damaging to organic tissue. These
realizations make radiation dosimetry an important topic. On the positive side, mild
radiation facilitates genetic mutation, necessary for evolution, and strong radiation
can be used in therapy to purposely kill aberrant cells.
8.1 Detection of Ionizing Radiation
There are a wide variety of techniques for detecting ionizing radiation, corresponding to the various ways particles lose energy while traveling through materials,
including solids, liquids, and gases.
Each of the following schemes have found wide use in detecting ionizing
radiation:
• Photographic materials: Henri Becquerel discovered radioactivity by the effect
that uranium salts had on photographic film. The basic idea is this: Some
compounds form structures that are changed by exposure to light. A silver
bromide crystal is such a compound sensitive both to visible light and to light
of higher frequencies. An incoming photon converts a AgBr pair into native
silver and bromine. The silver atoms, with a large quadrupole moment from its dshell electrons, can migrate through the crystal with little activation energy (about
© Springer Nature Switzerland AG 2020
W. C. Parke, Biophysics, https://doi.org/10.1007/978-3-030-44146-3_8
279
Ionizing Radiation and Life
All the good experimental physicists I have known have had an
intense curiosity that no Keep Out sign could mute. Physicists
do, of course, show a healthy respect for High Voltage,
Radiation, and Liquid Hydrogen signs.
—Luis Alvarez
Summary Ionizing radiation includes all electromagnetic waves from ultraviolet
light to gamma rays, for the simple reason that the localized interaction of light with
matter is by photons with energy proportional to frequency. With frequencies below
ultraviolet light in the spectrum, the photons have insufficient energy to break typical
organic molecular bonds. Subatomic particles moving with high kinetic energy
can also be ionizing, and therefore potentially damaging to organic tissue. These
realizations make radiation dosimetry an important topic. On the positive side, mild
radiation facilitates genetic mutation, necessary for evolution, and strong radiation
can be used in therapy to purposely kill aberrant cells.
8.1 Detection of Ionizing Radiation
There are a wide variety of techniques for detecting ionizing radiation, corresponding to the various ways particles lose energy while traveling through materials,
including solids, liquids, and gases.
Each of the following schemes have found wide use in detecting ionizing
radiation:
• Photographic materials: Henri Becquerel discovered radioactivity by the effect
that uranium salts had on photographic film. The basic idea is this: Some
compounds form structures that are changed by exposure to light. A silver
bromide crystal is such a compound sensitive both to visible light and to light
of higher frequencies. An incoming photon converts a AgBr pair into native
silver and bromine. The silver atoms, with a large quadrupole moment from its dshell electrons, can migrate through the crystal with little activation energy (about
© Springer Nature Switzerland AG 2020
W. C. Parke, Biophysics, https://doi.org/10.1007/978-3-030-44146-3_8
279