Hello and welcome to TranslatorsCafe.com channel. In this video we will talk about radiation.
We will discuss its sources and uses, devices for its measurement and the effects of radiation
on living creatures. We will talk in more detail about radiation
dose and radiation dose rate. There are many uses for ionizing radiation,
from energy generation to medical applications in a range of treatments, including treatments
of cancer patients. Here we will discuss how ionizing radiation affects human and other
biological material, with a focus on the rate at which the tissue is irradiated.
Radiation is a physical phenomenon of electromagnetic
waves or subatomic particles with high kinetic energies propagating through media. This media
could be either matter or vacuum. Radiation occurs in nature and is everywhere around
us, and we rely on it for our survival. For example without radiation we would not have
basic necessities for life such as light and heat. We would not have either mobile phones
or the Internet. In this video we will discuss a subset of
radiation, known as ionizing radiation, which is present in our environment. This radiation
causes the electrons to separate from atoms and molecules, thus ionizing them.
Ionizing radiation can be present in the environment
due to natural causes, or it could be artificially introduced into the environment by placing
radioactive substances there. Natural sources of radiation include solar and cosmic radiation,
some minerals, for example, granite as well as radiation of some radioactive materials,
such as uranium and even common bananas, which contain radioactive potassium isotope. We
mine some of these radioactive substances and use them as fuel or in medicine and in
some industries. Radioactive materials sometimes leak into the environment as a result of accidents.
Often this is a result of improper handling or inadequate safety regulations at the facilities
that work with radioactive materials. It is important to note that until recently
radiation was not considered dangerous and radioactive materials have been used historically
for their supposed health benefits as well as for their decorative properties. Uranium
glass is one example. It is glass with uranium oxide added to it. This glass fluoresces bright
green in ultraviolet light. The amount of uranium is usually very small and this glass
is considered safe, because it emits very low amounts of radiation. As such, it is even
used to make glasses, bowls, and other items for serving food and drink. It is valued for
its glow. Since solar light also has UV, uranium glass glows in sunlight as well, although
the glow is not as pronounced as with a black light.
As you saw, these uranium beads can be used to check working of Geiger counters. The beads
are available on eBay for a couple of bucks.
Let us consider some definitions first. Radiation
can be measured in many different ways, depending on whether we want to know the total amount
of radiation in the environment, the amount of radiation that affects biological tissue
and cells, the amount of radiation that was absorbed by the object or body, and so on.
Here we consider two ways of measuring radiation. The total amount of radiation that is in the
environment, per unit of time, is the total ionizing dose rate. The amount of radiation
absorbed by the body per a given unit of time is the absorbed dose rate. The absorbed dose
rate is calculated by using data for the total ionizing radiation dose rate, and the parameters
of the body, body part, or object being irradiated, including its mass, density, and volume.
The two values may be similar for materials that are highly absorbent, but this is often
not the case, as absorbency differs greatly for materials. For example, a sheet of lead
will absorb gamma radiation more readily than would a sheet of aluminum of the same thickness.
It is known that a high dose of radiation, also called an acute dose, causes health risks,
and the higher the dose the greater these risks. We also know that radiation does not
affect all cells equally. Cells that rapidly divide and cells that are not specialized
are affected the most. In particular, cells in embryos, as well as blood cells and reproductive
tissue are the most sensitive. Skin, bone, and muscle tissue are less sensitive, and
nerve cells are the least sensitive. Thus, if we have a higher dose acting upon less
sensitive tissue, it may be less damaging than a lower dose acting upon more sensitive
tissue. An interesting theory known as radiation hormesis
suggests that small doses of radiation may have an opposite effect and stimulate defence
mechanisms of the body. As a result it is suggested that this makes the organism healthier
than if this radiation was not present. It is important to note that this research is
in its developmental stages right now and that it is not known if this can be replicated
in real life, or if it will have the same effect on the human body as it does on laboratory
animals. It is hard to conduct this research on human subjects for ethical reasons.
Absorbed dose (also known as total ionizing dose, TID) is a measure of the energy deposited
in a medium by ionizing radiation per unit mass. The SI unit of measure is joules per
kilogram, which has a special name gray. The non-SI unit rad is also used.
The absorbed dose depends not only on the incident radiation but also on the absorbing
material: a soft X-ray beam may deposit four times more dose in bone than in air, or none
at all in a vacuum.
Equivalent dose, which represents the health
effect of ionising radiation on the human body is measured in sieverts.
To understand the difference between the dose and dose rate, consider the analogy of filling
up a kettle from a water tap. The volume of water in the kettle is the dose and the rate
of water flow measured in units of volume per units of time is the dose rate.
The dose rate is measured in sieverts per unit time, for example, microsieverts per
hour or millisieverts per year. Radiation is generally invisible and the only
way for humans to detect it is to use special measuring devices. Geiger counters are frequently
used to measure radiation. A Geiger counter has a tube where the ionizing radioactive
particles are counted. This count is then shown on the display in a range of units,
generally as the amount of radiation per a given amount of time, such as per hour. Geiger
counter instruments often make a clicking sound that indicates that a particle is emitted.
The sound is optional and the user can usually set it to clicks per a given number of particles
counted, for example one click per every 20 particles. It is also possible to disable
this function completely. In addition to Geiger counters, scintillation
counters and proportional counters are used because they allow to determine which type
of radiation is being measured more easily. Scintillation counters can detect alpha, beta,
and gamma radiation. They use a scintillator that converts the energy of the radioactive
particles into light, hence the name of the counter. The light, in turn, is converted
into an electrical signal in a sensitive photomultiplier and then measured. The area of detection is
larger than for the Geiger counter, which allows for more efficient detection.
Because of the very high energy capacity of ionizing radiation it ionizes particles such
as atoms and molecules within biological material. As a result of ionization, electrons are separated
from the atoms and the molecules, and the structure of these molecules and atoms changes.
This happens because ionization weakens or breaks chemical bonds. As a result, molecules
within cells and tissues become damaged or dysfunctional. Sometimes new bonds may be
created during this process. When the cells and tissue are thus affected
by radiation, there are several possible outcomes. In some cases the damage does not disrupt
the cell's functioning. In other situations the damage occurs but can be repaired. This
is a natural process in all living cells that occurs frequently, and if the radiation dose
or the dose rate is small, repair is possible. Another possibility is irreversible damage.
If the damage to cells is irreversible, they either function differently from their intended
mode, or stop functioning and die. When radiation thus affects vital cells and molecules, such
as molecules that oversee and control various processes in the cell, including proteins,
enzymes, DNA, and RNA, then radiation induced illnesses occur. Damage to cells may also
result in mutations, which cause genetically-related diseases in the offspring. These mutations
may also cause cells to divide abnormally fast, which is a precondition for cancer.
At present our knowledge of the effects of radiation and conditions which worsen these
effects is limited because we have a small set of data to work with. Much of the research
in this area relies on the case studies of the Hiroshima and Nagasaki bombing survivors
as well as survivors of nuclear disasters such as the Chernobyl disaster.
We should note that some of the research on the effects of radiation on the human body
was done between 1950-s and 1970-s in an extremely unethical and inhumane manner. The work that
we currently know of includes research in the facilities sanctioned by the military
of the US and the Soviet Union governments. Much of this research was done in areas around
the nuclear testing facilities, such as the Nevada Test Site in the USA, the testing grounds
on Novaya Zemlya (now a territory of Russia) and the Semipalatinsk Test Site (now in Kazakhstan).
Some studies were also carried out as part of military exercises, for example during
the Totskoye nuclear exercise (the territory is now part of Russia), and the Desert Rock
exercises in Nevada, USA. After detonating bombs that released radiation
researchers studied the effects of this radiation on the body.
Some unethical human experiments were also conducted on unconsenting individuals from
1946 and until the 1960-s in US hospitals. Thank you for watching! If you liked this
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