Toxic Pollution 153
Beta (β) particles are electrons that result from the fission of a neutron into
a proton and an electron, or positrons (positively charged electrons) that result
from the fission of a proton into a neutron and a positron. They are emitted by
radioactive nuclei at speeds equal to 30–99% of the speed of light. Their penetrating power varies as a function of velocity, but in general it is much greater
than that of alpha particles. Beta particles emitted e.g. by the radio active
isotopes Iodine-131, Strontium-90 and Cesium-137 have a kinetic energy of
emission much higher than that required for them to penetrate human skin
(Figure 7.2), and those emitted by Tritium-3 have a lower one. A sheet of aluminium a few millimetres thick is generally capable of stopping beta radiation.
Gamma (γ) radiation is electromagnetic and is transmitted at the speed of
light. It is similar to X (Roentgen) radiation but has shorter wavelengths and
therefore greater energy and penetrating power. It travels great distances in
the air (Figure 7.2), from tens to hundreds or even more meters. To stop it, a
lead wall a few centimetres thick or a concrete wall around one meter thick
is needed.
The following units are used to measure emitted or absorbed radioactive radiation:
• One Curie (Ci) is the radioactive radiation emitted by radioactive
material that undergoes 37 billion nuclear transformations per second
(the transformation rate of 1 gram of Radium-226). The submultiple
units millicurie (mCi), microcurie (μCi), nanocurie (nCi) and picocurie
(pCi) are used, each of which is one-thousandth of the previous one.
• The Becquerel (Bq) is equal to one nuclear transformation per second,
therefore 1 Bq = 27 pCi.
• The rad (Roentgen-absorbtion-dose) is equal to an energy absorption
of 100 ergs per gram of irradiated material.
• The rem (rad-equivalent-man) is also a unit of energy absorption,
which takes into account its biological effects as a function of the
type of radiation and its distribution in the human body. It is the dose
that has the biological effects of 1 rad of x-rays and is determined by
multiplying rad by a quality factor QF. A unit usually used for smaller
doses is the millirem (mrem), i.e. one one-thousandth of a rem.
There is a great variety of natural and artificial isotopes with unstable
nuclei that emit radioactive radiation. Isotopes decay due to emission, with
a decay rate that decreases exponentially as a function of time. Complete
disappearance of the isotope requires a theoretically infinite time. In practice, many isotopes quickly lose practically all their mass and consequently
their ability to emit radioactive radiation. It is noted, however, that the
radioactivity-induced transformation of the nuclei of an isotope creates in
some cases new radioactive nuclei, i.e. a different element, which can emit
radioactive radiation with different characteristics.
Beta (β) particles are electrons that result from the fission of a neutron into
a proton and an electron, or positrons (positively charged electrons) that result
from the fission of a proton into a neutron and a positron. They are emitted by
radioactive nuclei at speeds equal to 30–99% of the speed of light. Their penetrating power varies as a function of velocity, but in general it is much greater
than that of alpha particles. Beta particles emitted e.g. by the radio active
isotopes Iodine-131, Strontium-90 and Cesium-137 have a kinetic energy of
emission much higher than that required for them to penetrate human skin
(Figure 7.2), and those emitted by Tritium-3 have a lower one. A sheet of aluminium a few millimetres thick is generally capable of stopping beta radiation.
Gamma (γ) radiation is electromagnetic and is transmitted at the speed of
light. It is similar to X (Roentgen) radiation but has shorter wavelengths and
therefore greater energy and penetrating power. It travels great distances in
the air (Figure 7.2), from tens to hundreds or even more meters. To stop it, a
lead wall a few centimetres thick or a concrete wall around one meter thick
is needed.
The following units are used to measure emitted or absorbed radioactive radiation:
• One Curie (Ci) is the radioactive radiation emitted by radioactive
material that undergoes 37 billion nuclear transformations per second
(the transformation rate of 1 gram of Radium-226). The submultiple
units millicurie (mCi), microcurie (μCi), nanocurie (nCi) and picocurie
(pCi) are used, each of which is one-thousandth of the previous one.
• The Becquerel (Bq) is equal to one nuclear transformation per second,
therefore 1 Bq = 27 pCi.
• The rad (Roentgen-absorbtion-dose) is equal to an energy absorption
of 100 ergs per gram of irradiated material.
• The rem (rad-equivalent-man) is also a unit of energy absorption,
which takes into account its biological effects as a function of the
type of radiation and its distribution in the human body. It is the dose
that has the biological effects of 1 rad of x-rays and is determined by
multiplying rad by a quality factor QF. A unit usually used for smaller
doses is the millirem (mrem), i.e. one one-thousandth of a rem.
There is a great variety of natural and artificial isotopes with unstable
nuclei that emit radioactive radiation. Isotopes decay due to emission, with
a decay rate that decreases exponentially as a function of time. Complete
disappearance of the isotope requires a theoretically infinite time. In practice, many isotopes quickly lose practically all their mass and consequently
their ability to emit radioactive radiation. It is noted, however, that the
radioactivity-induced transformation of the nuclei of an isotope creates in
some cases new radioactive nuclei, i.e. a different element, which can emit
radioactive radiation with different characteristics.