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if you regularly visit the dentist chances are you've sat at least once for a set of dental
x-rays the procedure is usually straightforward first the dentist will drape a protective lead
vest over your chest and abdomen then place x-ray film in a plastic holder in your mouth
and the x-ray machine against the side of your head finally they will retreat behind a shielded
wall to activate the machine the actual exposure typically taking no more than one second but as
you are sitting there waiting for the process to end several questions may have crossed your mind
why if the x-rays are dangerous enough to warrant a lead vest is your head left unshielded and if a
simple lead vest is enough to block the x-rays why does the dentist need to hide behind a shielded
wall and how powerful are those x-rays anyway also how dangerous are they and just so much radiation
can the human body absorb without risking cancer or worse by now you're probably tired
of me telling you the answer these questions is is complicated but a lacid is complicated in order
to answer the question how much radiation is too much radiation we must first define what exactly
we mean by radiation in physics the term radiation typically refers to electromagnetic radiation that
is forms of energy which propagate by means of electric and magnetic fields electromagnetic
radiation lies on a spectrum with lower energy longer wavelength microwaves on one end and higher
energy shorter wavelength gamma rays on the other the visible spectrum that is the electromagnetic
wavelengths which are detectable by the human eye lie somewhere in the middle between 380
and 750 nanometers for our purposes however we're only interested in so-called ionizing radiation
that is electromagnetic waves with enough energy to ionize or strip electrons off atoms and damage
the dna of living cells this includes all the wavelengths past the visible spectrum that is
ultraviolet rays x-rays gamma rays with a boundary between non-ionizing and ionizing radiation
typically being defined as 124 nanometers thus despite the claims of certain conspiracy
theorists our cell phones and micro weapons cannot give us cancer as these devices operate
at energies too low to produce serious genetic damage still though plenty of other reasons not
to stick your head in a microwave okay another source of ionizing radiation is from high energy
subatomic particles the three types most commonly encountered being alpha particles beta particles
and neutrons both alpha and beta particles are produced by the natural decay of radioactive
elements like uranium the former being composed of two protons and two neutrons and the latter being
identical to electrons neutrons while occasionally produced by the spontaneous fission of radioactive
elements are typically encountered as a byproduct of nuclear fission chain reactions in reactors and
nuclear weapons occasionally other kinds of ionizing particles like protons are
also encountered at densities and energies high enough to damage living tissue for example in
scientific or medical particle accelerators but regardless of the type of ionizing radiation
encountered the mechanism of action is the same the radiation damages the dna within the exposed
cells resulting in one of two outcomes in most cases the cell detects the genetic damage and
either repairs it or undergoes a process known as apoptosis or cell suicide preventing the damaged
dna from being replicated thanks to these defense mechanisms the body can safely absorb mild doses
of radiation such as those produced by cosmic rays from space radioactive elements in the air
and medical x-rays however if the dose is large enough and enough cells are damaged at once
a nasty chain of symptoms known collectively as acute radiation syndrome or ars may result
first observed in survivors of the atomic bombings of hiroshima and nagasaki aeros typically presents
as severe nausea vomiting and abdominal pain skin directly exposed to radiation may initially redden
like a sunburn and later swell up depending on how deeply the radiation has penetrated into the
tissue from here the symptoms only get worse and may include weakness fatigue headache bloody vomit
and stools hair loss and cataracts the latter three resulting from severe damage to the cells of
the digestive tract hair follicles and lenses of the eye however around 24 hours following exposure
some victims may seem to spontaneously recover their symptoms appearing to disappear for several
days this is known as the walking ghost phase and results from certain tissues being more sensitive
to radiation than others cells undergoing rapid divisions such as those of the stomach sexual
organs and bone marrow were the most sensitive hence why one of the first symptoms of ars is
nausea and vomiting massive exposure to radiation causes the bone marrow to stop producing blood
cells resulting in a condition known as aplastic anemia this not only cripples the immune system
leaving the body vulnerable to infection but also significantly hinders the healing of burns cuts
and other injuries however the cells already in the blood which are less affected by radiation
remain in circulation for around a month and thus the immune system initially continues to
operate normally after a few days however these cells become depleted and the victim's condition
rapidly begins to deteriorate as organs shut down blood vessels collapse and tissues literally
liquefy the victim will experience delirium coma excruciating pain which even the most powerful
opioids cannot touch and inevitably death but even relatively mild doses of radiation can still have
serious health effects while in the vast majority of cases the combination of natural genetic
repair mechanisms and apoptosis prevents cells from propagating radiation damaged dna once in
a while a cell's dna becomes mutated in such a way that it starts dividing and multiplying out
of control a condition better known as cancer and since rapidly dividing sex cells are particularly
sensitive to radiation damage exposure of the gonads or a developing embryo to even
moderate amounts of radiation can result in birth defects but exactly how much radiation constitutes
a mild moderate or severe dose well this is where things get complicated for radiation exposure
is a stochastic process meaning it is highly probabilistic and there is no linear predictable
relationship between radiation exposure and negative health effects thus while it
is generally the case that a higher radiation dose will result in more severe health effects
there is no way of predicting the precise effects a particular dose will have on a particular person
this is true of all carcinogenic processes for example while smoking more cigarettes certainly
increases one's risk of cancer it is on one hand entirely possible for someone to smoke a pack a
day for 80 years and never develop cancer or on the other hand to smoke a single cigarette and
immediately develop cancer it is even possible that mild doses of radiation may actually be
beneficial by stimulating the body's dna repair mechanisms and effects known as radiation hormesis
and for more on that please check out our video the curious case of the widespread radioactive
apartment yet despite the complex unpredictable nature of radiation exposure health physicists
have nonetheless developed a complex system of units measurements and recommended doses in an
attempt to keep workers in nuclear power plants research laboratories medical imaging departments
and other high radiation environments safe and healthy so buckle up and take a deep
breath because yes there's going to be some maths involved radiation exposure is typically measured
in terms of energy absorbed by a given volume of mass or matter the first standard unit for
radiation exposure was the ronkan adopted in 1928 named after german physicist wilhelm rajkin the
discoverer of x-rays one rontgen was initially defined as the amount of ionizing radiation
capable of inducing one static column of electric charge in one cubic centimeter of dried air
but while an important milestone in quantifying radiation exposure the roncam was only applicable
to air and not other materials like human tissue thus in 1945 american medical physicist herbert
parker introduced the rontgen equivalent physical or rep equivalent to 93 ergs of energy absorbed by
one gram of matter in 1953 the rep was replaced by a new unit known as the rad initially defined in
the centimeter gram second or cgs system as 100 ergs of energy absorbed by one gram of matter
the rad is now defined in the system international or si system as 0.01 joules of energy per kilogram
of matter the rad itself was subsequently replaced in 1975 by a new si unit known as the grey named
after british nuclear physics pioneer lewis robert gray the gray is defined as one drool of energy
absorbed by one kilogram of matter while the gray is the de facto standard unit
of radiation absorption in much of the world certain laboratories and industries especially
in the united states still continue to use the rad and even sometimes the ronkin however both
the rad and the grey measure radiation absorption in any kind of material be it air water plastic
concrete or anything else and do not account for the particular effects of radiation on
human tissue as mentioned before certain tissues are more sensitive than others to radiation with
the gonad stomach and bone marrow being among the most sensitive and the brain skin and liver
among the least tissue damage also varies greatly depending on the type of radiation and the manner
in which it is absorbed for example x-rays and gamma rays can penetrate more deeply into
tissue that are proportionally less ionizing than neutrons protons and alpha particles conversely
while alpha particles can deposit large amounts of energy and inflict massive cellular damage
they are easily blocked by most tissues including the skin thus while alpha emitting materials like
uranium are relatively harmless outside of the human body if they are somehow absorbed into
the body they can become extremely dangerous this is especially true for elements like radium which
the body mistakes for calcium and incorporates into the bones allowing radiation to be deposited
directly into the marrow furthermore few instances of radiation exposure involve the victim absorbing
a full body dose meaning that in order to predict the effects of a particular dose with
any degree of accuracy it's necessary to account for both what type of radiation was absorbed and
where it was absorbed the first standard unit of radiation absorption was the wrong equivalent man
or rem and adaptation of the rep first introduced in 1947. however since 1979 the standard si
unit for biological radiation dose has been the sievert named after swedish medical physicist
rob siebert the subit is a measure of equivalent dose which is calculated by multiplying the
absorbed dose in grays by a pair of weighing factors accounting for the type of radiation
absorbed and the specific tissues affected for example the radiation weighing factors ranges from
1 for x-rays and gamma rays to 20 for alpha particles while the tissue weighing factor
ranges from 0.01 for the brain and skin to 0.12 for the bone marrow so let's say you're poking
around in dr bruce banner's laboratory one day and accidentally receive a one grade dose of gamma
rays spread 50 50 between your liver and colon to calculate your total equivalent dose you must
first multiply the absorbed dose by the radiation weigh-in factor the proportion absorbed by each
tissue and the weighing factor for each tissue in this case one grade by 0.5 grays by 1 for gamma
rays by 0.12 for the colon and one grade by 0.5 by 1 for gamma rays and 0.04 for the liver these
calculations give you the effective doses for each particular tissue which when added together yield
your total equivalent dose in this case 0.31 sieverts all right relax the maths is done but
what exactly does this number mean in practical terms onesie represents a 5.5 percent increase
in the probability of developing cancer over one's lifetime thus your little incident in dr banner's
lab would have made you 1.7 more likely to develop cancer or possibly turn you into the hulk this
relationship is based on the linear no threshold model which relates radiation exposure linearly to
cancer risk and assumes that there is no safe dose of radiation although as previously mentioned the
body is naturally able to handle small doses of natural background radiation the linear threshold
model ignores this and the potential effects of radiation hormesis out of a desire to set
conservative limits for acceptable radiation exposure to give an idea of what constitutes
a regular or acceptable radiation dose 98 nano sieverts is the equivalent to the so-called banana
equivalent dose the amount of radiation absorbed by eating a typical banana which contains small
quantities of the radioactive isotope 40 5 to 10 microsieverts is equivalent to a set
of dental x-rays 10 to 30 micro sieverts a full body ct scan 250 millisieverts the annual dose
for flight attendants who are exposed to more cosmic rays at high altitudes and one sievert
the maximum allowed radiation exposure for nasa astronauts over their entire career
exposure in radiation-intensive environments is typically measured using a dosimeter a
small badge-like device that continually monitors one's cumulative radiation dose that doses higher
than one see that the danger shifts sharply from cancer to acute radiation syndrome and rapid death
for example victims of the hiroshima and nagasaki atomic bombing standing 1.2 kilometers from ground
zero receive doses of around five sieverts while manhattan project scientist louis slaughten killed
by a plutonium bomb core accident in 1946 absorbed a massive dose of 21 sieverts and you can see
our video tickling the dragon's tail the horrible heart of a nuclear bomb for more on that based on
these and some other radiation accidents the upper limit for acute radiation exposure is typically
set at four to five sieverts a dose which has a 50 chance of killing the average person
within 30 days the maximum allowable annual dose for industrial workers in the united states is
considerably lower at only 0.05 sieverts however even a massive radiation dose is not necessarily
fatal if absorbed over a long period of time in may 1945 58 year old house painter albert stevens
who had been diagnosed with terminal stomach cancer was unknowingly injected with what should
have been a lethal dose of plutonium as part of a top-secret uc berkeley experiment as it turned out
to whether stevens did not have cancer but rather a benign stomach ulcer and despite the massive
amounts of plutonium in his system he suffered few ill effects and lived a further two decades
dying of heart disease in 1966 at the age of 79. over the intervening 21 years he had cumulatively
absorbed a whopping 65 sieverts of alpha radiation the highest dose that any human has been recorded
as surviving so going back to our original dental x-ray scenario we can start to answer
some of those burning questions the reason the dentist shields your body while leaving your head
unprotected is because the brain and other tissues in the head are significantly less sensitive to
radiation than those in the rest of the body like the gonads bone marrow and intestines
this is also why the dentist retreats behind a wall while taking the x-ray since the x-ray
machine is pressed right up against your head your absorbed dose will be highly concentrated
however if the dentist was standing in the same room they would receive that dose over
a greater percentage of their body exposing more sensitive organs to the radiation beam
as for how dangerous that beam is as previously noted the average equivalent dose from a set of
dental x-rays is around 5 to 10 micro sieverts meaning that you would need to receive more than
100 000 such x-rays to raise your chances of developing cancer by only 5.5 percent so while
ionizing radiation is everywhere and its effects on the body are complex and unpredictable unless
you work in a nuclear power plant medical imaging department or other similar environment you are
highly unlikely to be exposed to anywhere near a dangerous dose of radiation in fact you should
be far more concerned about gum disease which according to a five-year study conducted between
1993 and 1998 carries a 12 higher risk of early death so listen to your dentist start flossing
it might just save your life so i really hope you enjoyed today's video if you did please do
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