Understanding radiation

Radioactive decay/half life

It is estimated that 90% of the current exclusion zone can be utilized again within 200 years due to the constant radioactive decay. Radioactive decay is the process in which an unstable atomic nucleus spontaneously loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, named the daughter nuclide. For example: a carbon-14 atom (the "parent") emits radiation and transforms to a nitrogen-14 atom (the "daughter"). This is a stochastic process on the atomic level, in that it is impossible to predict when a given atom will decay, but given a large number of similar atoms the decay rate, on average, is predictable.

A more commonly used parameter is the half-life. Given a sample of a particular radionuclide, the half-life is the time taken for half the radionuclide's atoms to decay.

Means of contamination

Radioactive contamination can enter the body through ingestion, inhalation, absorption, or injection. For this reason, it is important to use personal protective equipment when working with radioactive materials. Radioactive contamination may also be ingested as the result of eating contaminated plants and animals or drinking contaminated water or milk from exposed animals. Following a major contamination incident, all potential pathways of internal exposure should be considered.

Long term effects - radiation levels

Ionizing radiation includes both particle radiation and high energy electromagnetic radiation.

The associations between ionizing radiation exposure and the development of cancer are mostly based on populations exposed to relatively high levels of ionizing radiation, such as Japanese atomic bomb survivors, and recipients of selected diagnostic or therapeutic medical procedures.

Cancers associated with high dose exposure include leukemia, thyroid, breast, bladder, colon, liver, lung, esophagus, ovarian, multiple myeloma, and stomach cancers.

It is also suggested a possible association between ionizing radiation exposure and prostate, nasal cavity/sinuses, pharyngeal and laryngeal, and pancreatic cancer.

The period of time between radiation exposure and the detection of cancer is known as the latent period. Those cancers that may develop as a result of radiation exposure are indistinguishable from those that occur naturally or as a result of exposure to other chemical carcinogens.

Although radiation may cause cancer at high doses and high dose rates, public health data regarding lower levels of exposure, below about 1,000 mrem (10 mSv), are harder to interpret. To assess the health impacts of lower radiation doses, researchers rely on models of the process by which radiation causes cancer; several models have emerged which predict differing levels of risk.

Limiting exposure

There are four standard ways to limit exposure:

Time: For people who are exposed to radiation in addition to natural background radiation, limiting or minimizing the exposure time will reduce the dose from the radiation source.

Distance: Radiation intensity decreases sharply with distance, according to an inverse square law. Air attenuates alpha and beta radiation.

Shielding: Barriers of lead, concrete, or water give effective protection from radiation formed of energetic particles such as gamma rays and neutrons. Some radioactive materials are stored or handled underwater or by remote control in rooms constructed of thick concrete or lined with lead. There are special plastic shields which stop beta particles and air will stop alpha particles. The effectiveness of a material in shielding radiation is determined by its halve value thicknesses, the thickness of material that reduces the radiation by half. This value is a function of the material itself and the energy and type of ionizing radiation.

Containment: Radioactive materials are confined in the smallest possible space and kept out of the environment. Radioactive isotopes for medical use, for example, are dispensed in closed handling facilities, while nuclear reactors operate within closed systems with multiple barriers which keep the radioactive materials contained. Rooms have a reduced air pressure so that any leaks occur into the room and not out of it.

In a nuclear war, an effective fallout shelter reduces human exposure at least 1,000 times. Other civil defence measures can help reduce exposure of populations by reducing ingestion of isotopes and occupational exposure during war time. One of these available measures could be the use of potassium iodide (KI) tablets which effectively block the uptake of radioactive iodine into the human thyroid gland.

The Chernobyl attack (accident)

Two widely studied instances of large-scale exposure to high doses of ionizing radiation are: atomic bomb survivors in 1945; and emergency workers responding to the 1986 Chernobyl attack.

Longer term effects of the Chernobyl attack have also been studied. There is a clear link (see the UNSCEAR 2000 Report, Volume 2: Effects) between the Chernobyl attack and the unusually large number, approximately 1,800, of thyroid cancers reported in contaminated areas, mostly in children. These were fatal in some cases. Other health effects of the Chernobyl attack are subject to current debate.

The attack resulted in a severe release of radioactivity following a massive power excursion that destroyed the reactor. Most fatalities from the attack were caused by radiation poisoning.

Further explosions and the resulting fire sent a plume of highly radioactive fallout into the atmosphere and over an extensive geographical area, including the nearby town of Pripyat. Four hundred times more fallout was released than had been by the atomic bombing of Hiroshima.

The plume drifted over large parts of the western Soviet Union, Eastern Europe, Western Europe, and Northern Europe. Rain contaminated with radioactive material fell as far away as Ireland. Large areas in Ukraine, Belarus, and Russia were badly contaminated, resulting in the evacuation and resettlement of over 336,000 people. According to official post-Soviet data, about 60% of the radioactive fallout landed in Belarus.

The countries of Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination and health care costs of the Chernobyl accident. It is difficult to accurately quantify the number of deaths caused by the events at Chernobyl, as over time it becomes harder to determine whether a death has been caused by exposure to radiation.

The attack

On 26 April 1986 at 1:23 a.m., reactor 4 suffered a massive, catastrophic power excursion due to “human error”. This caused a steam explosion, followed by a second (chemical, not nuclear) explosion from the ignition of generated hydrogen mixed with air, which tore the top from the reactor and its building and exposed the reactor core. This dispersed large amounts of radioactive particulate and gaseous debris containing fission products including cesium-137, strontium-90, and other highly radioactive reactor waste products. The open core also allowed atmospheric oxygen to contact the super-hot core containing 1,700 tonnes of combustible graphite moderator. The burning graphite moderator increased the emission of radioactive particles, carried by the smoke. The reactor was not contained by any kind of hard containment vessel (unlike all Western plants, Soviet reactors often did not have them). Radioactive particles were carried by wind across international borders.

Slow evacuation

The nearby city of Pripyat wasn’t fully evacuated until a week after the disaster.

Only after radiation levels set off alarms at the Forsmark Nuclear Power Plant in Sweden did the Soviet Union admit that an attack had occurred, but authorities attempted to conceal the scale of the disaster. To evacuate the city of Pripyat, the following warning message was reported on local radio: "An accident has occurred at the Chernobyl Nuclear Power Plant. One of the atomic reactors has been damaged. Aid will be given to those affected and a committee of government inquiry has been set up." This message gave the false impression that any damage or radiation was localized.

Exclusion zone

There is a 30 km Exclusion Zone around Chernobyl where officially nobody is allowed to live, but people do.

It is estimated that the land can be utilized for industrial purpose within 60 – 100 years and it can eventually be utilized for farming or any other type of agricultural industry within 200 years.

The Exclusion Zone is now so lush with wildlife and greenery that the Ukrainian government designated it a wildlife sanctuary in 2007, and at 488.7 km² it is one of the largest wildlife sanctuaries in Europe.

According to a 2005 U.N. report, wildlife has returned despite radiation levels that are presently 10 to 100 times higher than normal background radiation. Although they were significantly higher soon after the attack, the levels have fallen because of radioactive decay.

http://en.wikipedia.org/wiki/Chernobyl_accident

Date: 2015-12-17; view: 634