Radioactivity

Definition
• Spontaneous emission of radiation, either directly
from unstable atomic nuclei or as a consequence
of a nuclear reaction.
• The radiation, including alpha
particles, electrons, and gamma rays, emitted by
a radioactive substance.
• Radioactive contamination refers only to the
presence of the unintended or undesirable
radioactivity and gives no indication of the
magnitude of hazard involved.

Units
Curie (Ci)–A unit of
radioactivity, equal to the amount of
a radioactive isotope that decays at
the rate of 3.7 × 1010 disintegrations
per second
SI unit is Bacquerel (Bq)- One Bq is
defined as the activity of a quantity
of radioactive material in which
one nucleus decays per second.
• The Bq unit is therefore equivalent to
an inverse second, s−1.
• 1 becquerel = 2.703x10-11 Ci.

Based on the magnitude of radiation exposures the
radiation dose is divided into 2 parts:
RAD (absorbed dose)-the amount of energy
deposited in the unit mass in human tissue or other
media.
• rad is replaced by SI unit gray
• 1 gray = 100 rad.
REM (biological dose)- This dose reflects the fact that
the biological damage caused by a particle depends
not only on the total energy deposited but also on
the rate of energy loss per unit distance traversed by
the particle.
• rem is expressed in SI system as sievert (Sv)
• 1 Sv = 100 rem

Sources of contamination
• Radioactive contamination is typically the result
of a spill or accident during the production or use
of radionuclides (radioisotopes), an unstable
nucleus which has excessive energy.
• Less typically, nuclear fallout is the distribution of
radioactive contamination by a nuclear explosion.
• The amount of radioactive material released in an
accident is called the source term.

Origin of Cosmic rays
• The term "cosmic rays" was coined by Robert Millikan who proved they were
extraterrestrial in origin, and not produced by atmospheric electricity.
• He believed that cosmic rays were high-energy photons with some secondary electrons
produced by Compton scattering of gamma rays.
• During the decade from 1927 to 1937, it was seen that the primary cosmic rays were
mostly positively charged particles, and the secondary radiation observed at ground
level was composed primarily of a "soft component" of electrons and photons and a
"hard component" of penetrating particles, muons.
• The muon was initially believed to be the unstable particle. Experiments proved that
the muon decays with a mean life of 2.2 microseconds into an electron and two
neutrons, but that it does not interact strongly with nuclei.
• The mystery was solved by the discovery in 1947 of the pion, which is produced
directly in high-energy nuclear interactions. It decays into a muon and one neutrino
with a mean life of 26 nanoseconds.
• The pion→muon→electron decay sequence was observed directly in a microscopic
examination of particle tracks in a special kind of photographic plate called a nuclear
emulsion that had been exposed to cosmic rays at a high-altitude mountain station.
• In 1948, observations with nuclear emulsions carried by balloons to near the top of the
atmosphere by Gottlieb and Van Allen showed that the primary cosmic particles are
mostly with some helium nuclei (alpha particles) and a small fraction heavier nuclei.

Radiation of cosmic origin
• Cosmic rays are energetic charged subatomic particles,
originating from outer space. They may produce secondary
particles that penetrate Earth's atmosphere and surface.
• About 89% of cosmic rays are simple protons or hydrogen
nuclei, 10% are helium nuclei or alpha particles, and 1%
are heavier elements. These nuclei constitute 99% of the
cosmic rays. Solitary electrons (much like beta particles,
although their ultimate source is unknown) constitute
much of the remaining 1%.
• Cosmic rays can have energies of over 1020 eV, far higher
than the 1012 to 1013 eV that Terrestial particle accelerators
can produce.
• Cosmic rays may broadly be divided into two categories,
primary and secondary.

 Primary cosmic rays
• The cosmic rays that arise in extrasolar astrophysical sources are primary cosmic rays;
these primary cosmic rays can interact with interstellar matter to create secondary
cosmic rays.
• The Sun also emits low energy cosmic rays associated with solar flares.
• The exact composition of primary cosmic rays, outside the Earth's atmosphere, is
dependent on which part of the energy spectrum is observed.
• Almost 90% of all the incoming cosmic rays are protons, about 9% are helium nuclei
(alpha particles) and nearly 1% are electrons.
• The ratio of hydrogen to helium nuclei (28% helium by mass) is about the same as the
primordial elemental abundance ratio of these elements (24% by mass He) in the
universe.
 Secondary cosmic rays
• Secondary cosmic rays consist of the other nuclei which are not abundant nuclear
synthesis end products, or products of the Big Bang, primarily lithium, beryllium, and
boron.
• These light nuclei appear in cosmic rays in much greater abundance (about 1:100
particles) than in solar atmospheres, where their abundance is about 10−7 that of helium.
• When the heavy nuclei components of cosmic rays, namely the carbon and oxygen
nuclei, collide with interstellar matter, they break up into lighter nuclei (in a process
termed cosmic ray spallation) - lithium, beryllium and boron.

Effects of Cosmic rays
 Changes in atmospheric chemistry
 Cosmic rays ionize the nitrogen and oxygen molecules in the atmosphere, which leads to a number of
chemical reactions.
 One of the reactions results in ozone depletion.
 The magnitude of damage, however, is very small compared to the depletion caused by CFCs.
 Role in ambient radiation
 Cosmic rays constitute a fraction of the annual radiation exposure of human beings on the Earth.
 For example, the average annual radiation exposure in Australia is 0.3 mSv due to cosmic rays, out of a
total of 2.3 mSv.
 Effect on electronics
 Cosmic rays have sufficient energy to alter the states of elements in electronic integrated circuit, causing
transient errors to occur, such as corrupted data in electronic memory devices, or incorrect performance
of CPUs.
 This has been a problem in extremely high-altitude electronics, such as in satellites, but with transistors
becoming smaller and smaller, this is becoming an increasing concern in ground-level electronics as well.
 Studies by IBM in the 1990s suggest that computers typically experience about one cosmic-ray-induced
error per 256 megabytes of RAM per month.
 To alleviate this problem, the Intel Corporation has proposed a cosmic ray detector that could be
integrated into future high-density microprocessors, allowing the processor to repeat the last command
following a cosmic-ray event.
 Cosmic rays are suspected as a possible cause of an in-flight incident in 2008 where an Airbus twice
plunged hundreds of feet after an unexplained malfunction in its flight control system. Many passengers
and crew members were injured, some seriously.

Significance to space travel
 Galactic cosmic rays are one of the most
important barriers standing in the way of plans
for interplanetary travel by crewed spacecraft.
 Cosmic Rays also place a threat to electronics
placed aboard outgoing probes.
 In 2010, a malfunction aboard the Voyager 2
space probe was credited to a single flipped
bit, probably caused by a cosmic ray.
Role in lightning
 Cosmic rays have been implicated in the
triggering of electrical breakdown in lightning.

Mechanism of Radiation action
The action pathway of radiation to the
human body can visualized in two ways:
one is direct action and the other one is
an indirect action.
The direct action is DNA breakage. DNA
has essential information to make body.
The damaged DNA would cause apoptosis
(cell death) and mutation of cells and
increase a risk of diseases.
The indirect action is generation of
radical oxygen in the human body.
We are influenced by radiation not only
through environment exposure but also
through breathing air and eating food.
The DNA base damage mediated by
radical oxygen would disturb normal cell
growth and cause a functional decline of
the body.

Normal cellular metabolism is source of
endogenous reactive oxygen species (ROS), and is
these cellular processes are largely responsible for
the background levels of oxidative DNA damage
detected in normal tissue.
ROS may also be generated by ionizing or
ultraviolet radiation.
In the same way, exogenous chemicals may
metabolise in cell with subsequent production of
electrons that can be transferred to molecular
oxygen and finally producing superoxide anion (a
free radical denoted as O2•-).
Dismutation of the superoxide anion generates
the hydrogen peroxide inside the cells and tissues
and these together with the complex interaction
with other ROS (such as the reactive hydroxyl
radical) can damage cellular biomolecules, such as
DNA, leading to modification and potentially
serious consequences for the cell if the DNA
damage is not repaired.
One such DNA oxidation product is 8-
hydroxydeoxyguanosine (8-OH-dG).

Radiation Effects
• Every living creature on earth contains significant quantities of carbon-14 and most
(including humans) contain significant quantities of potassium-40.
• These tiny levels of radiation are not any more harmful than sunlight, but just as
excessive quantities of sunlight can be dangerous, so too can excessive levels of
radiation.
• Radiation effects shows two types of Poisoning according to the exposure obtained:
Acute Radiation Poisoning
Chronic Radiation Poisoning

• Acute radiation syndrome (ARS) also known as radiation poisoning, radiation
sickness or radiation toxicity, is a constellation of health effects which occur within
several months of exposure to high amounts of ionizing radiation.
• The term generally refers to acute problems rather than ones that develop after a
prolonged period.
• The onset and type of symptoms that develop depends on the dose of radiation
exposure.
• Relatively smaller doses result in gastrointestinal effects such as nausea and
vomiting and symptoms related to falling blood counts such as infection and
bleeding.
• Relatively larger doses can result in neurological effects and rapid death.
• Treatment of acute radiation syndrome is generally supportive with blood
transfusions and antibiotics.

• Chronic radiation syndrome has been reported
among workers in the Soviet nuclear program
due to long term exposures to radiation levels
lower than what is required to induce acute
sickness.
• It may manifest with low blood cell counts and
neurological problems.
• Radiation exposure can also increase the
probability of developing some other diseases,
mainly different types of cancers.

Effects of Radiation on body
1) Hair
• The losing of hair quickly and in clumps occurs with radiation exposure at 200 rems or higher.
2) Brain
• Since brain cells do not reproduce, they won't be damaged directly unless the exposure is 5,000 rems or
greater. Like the heart, radiation kills nerve cells and small blood vessels, and can cause seizures and
immediate death.
3) Thyroid
• The certain body parts are more specifically affected by exposure to different types of radiation sources.
The thyroid gland is susceptible to radioactive iodine. In sufficient amounts, radioactive iodine can destroy
all or part of the thyroid. By taking potassium iodide, one can reduce the effects of exposure.
4) Blood System
• When a person is exposed to around 100 rems, the blood's lymphocyte cell count will be reduced, leaving
the victim more susceptible to infection. This is often refered to as mild radiation sickness. Early symptoms
of radiation sickness mimic those of flu and may go unnoticed unless a blood count is done.According to
data from Hiroshima and Nagaski, show that symptoms may persist for up to 10 years and may also have
an increased long-term risk for leukemia and lymphoma.
5) Heart
• Intense exposure to radioactive material at 1,000 to 5,000 rems would do immediate damage to small
blood vessels and probably cause heart failure and death directly.
(6) Gastrointestinal Tract
• Radiation damage to the intestinal tract lining will cause nausea, bloody vomiting and diarrhea. This is
occurs when the victim's exposure is 200 rems or more. The radiation will begin to destroy the cells in the
body that divide rapidly. These including blood, GI tract, reproductive and hair cells, and harms their DNA
and RNA of surviving cells.
(7) Reproductive Tract
• Because reproductive tract cells divide rapidly, these areas of the body can be damaged at rem levels as
low as 200. Long-term, some radiation sickness victims will become sterile.

Medical Treatment
• There is currently no effective medical treatment available
for potentially fatal radiation doses.
• The case of the Japanese boy mentioned above illustrates
an important fact about radiation sickness. The boy had
probably received a dose of 450 rems or more, yet his
symptoms were about the same as those of a person who
received about 300 rems.(EXAMPLE OF HIROSHIMA AND
NAGASAKI DISASTER)
• Medical science has no way of telling the difference
between people who have received fatal doses and will die
despite all efforts and others who received less radiation
and can be saved.
• Treatment for the ones that can be saved includes blood
transfusions and bone-marrow transplants.
• Bone-marrow transplants rejuvenate the supply of white
blood cells which was affected by the radiation.

Major Radiation Exposure in Real Life Events
Hiroshima and Nagasaki
• Many people at Hiroshima and Nagasaki died not directly from the actual explosion, but from the radiation released as a result of
the explosion. For example, a fourteen-year-old boy was admitted to a Hiroshima hospital two days after the explosion, suffering
from a high fever and nausea. Nine days later his hair began to fall out. His supply of white blood cells dropped lower and lower.
On the seventeenth day he began to bleed from his nose, and on the twenty-first day he died.
• At Hiroshima and Nagasaki, the few surviving doctors observed symptoms of radiation sickness for the first time. Within seven to
ten days after the A-bomb explosion, people began to die in swift succession. They died of the burns that covered their bodies and
of acute atomic disease. Innumerable people who had been burnt turned a mulberry color, like worms, and died...
• Doctors and nurses had no idea of how their own bodies had been affected by radioactivity. Dr. Akizuki wrote, "All of us suffered
from diarrhea and a discharge of blood from the gums, but we kept this to ourselves. Each of us thought: tomorrow it might be me...
We became stricken with fear of the future." Dr. Akizuki survived, as did several hundred thousand others in or near Hiroshima and
Nagasaki.
• The survivors have suffered physically from cataracts, leukemia and other cancers, malformed offspring, and premature aging, and
also emotionally, from social discrimination. Within a few months of the nuclear explosions, leukemia began to appear among the
survivors at an abnormally high rate. Some leukemia victims were fetuses within their mothers' wombs when exposed to radiation.
One child who was born two days after the Hiroshima explosion eventually died of acute leukemia at the age of eighteen. The
number of leukemia cases has declined with time, but the incidence of lung cancer, thyroid cancer, breast cancer, and cancers of
other organs has increased among the survivors.
Three Mile Island
• On a Wednesday morning, maintenance workers cleaning sludge from a small pipe blocked the flow of water in the main feedwater
system of a reactor at Three Mile Island near Harrisburg, Pennsylvania. The sift foreman heard "loud, thunderous noises, like a
couple of freight trains," coming. Since the reactor was still producing heat, it heated the blocked cooling water around its core hot
enough to create enough pressure to have popped a relief valve. Some 220 gallons of water per minute began flowing out of the
reactor vessel. Within five minutes after the main feedwater system failed, the reactor, deprived of all normal and emergency
sources of cooling water, and no longer able to use its enormous energy to generate electricity, gradually started to tear itself apart.
• The loss of coolant at the reactor continued for some 16 hours. Abort a third of the core melted down. Radioactive water flowed
through the stuck relief valve into an auxiliary building, where it pooled on the floor. Radioactive gas was released into the
atmosphere. An estimated 140,000 people were evacuated from the area. It took a month to stabilize the malfunctioning unit and
safely shut it down. The reactor was a total loss and the cleanup required years of repair and hundreds of millions of dollars.
• No one was reported injured and the little radiation that leaked out was quickly dispersed. Although this accident did cost lots of
money and time, no one was hurt.

Chernobyl
• A far more serious accident occured at Chernobyl, in what was then still the Soviet
Union. At the time of the accident, the Chernobyl nuclear power station consisted
of four operating 1,000 megawatt power reactors. Without question, the accident
at Chernobyl was the result of a fatal combination of ignorance and complacency.
• Although the problem at Chernobyl was relatively complex, it can basically be
summarized as a mismanaged electrical engineering experiment which resulted in
the reactor exploding. The explosion was chemical, driven by gases and steam
generated by the core runaway, not by nuclear reactions. Flames, sparks, and
chunks of burning material were flying into the air above the unit. These were red-
hot pieces of nuclear fuel and graphite. About 50 tons of nuclear fuel evaporated
and were released by the explosion into the atmosphere. In addition, about 70
tons were ejected sideways from the periphery of the core. Some 50 tons of
nuclear fuel and 800 tons of reactor graphite remained in the reactor vault, where
it formed a pit reminiscent of a volcanic crater as the graphite still in the reactor
had turned up completely in a few days after the explosion.
• The resulting radioactive release was equivalent to ten Hiroshimas. In fact, since
the Hiroshima bomb was air-burst--no part of the fireball touched the ground--the
Chernobyl release polluted the countryside much more than ten Hiroshimas would
have done. Many people died from the explosion and even more from the effects
of the radiation later. Still today, people are dying from the radiation caused by the
Chernobyl accident. The estimated total number of deaths will be 16,000.

Radioactivity

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