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 actionThe 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 body1) 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.