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The alpha particle was discovered and named in 1899 by an English scientist, Ernest Rutherford while working with uranium . Rutherford and his co-workers used alpha particles in experiments to probe the structure of atoms in thin metallic foil. From 1909 to 1911 this work achieved the first concept of the atom: a tiny planetary system with negative charged particles, electron, orbiting around a positively charged nucleus, via the use of the Rutherford-Bohr planetary model of the atom (2).
Alpha particles, denoted by the Greek alphabet a , is made up of two protons and two neutrons bound together into a particle (which is identical to a helium nucleus) (3). The alpha particle is a form of ionizing radiation and is one of the most common kinds of radiation. Alpha particles consist of a helium nucleus, having two neutrons and two protons, without electrons, resulting in a net positive charge (4). This particle is relatively heavy, high in energy and has a velocity in air of about one-twentieth the speed of light, according to the energy of the individual particle (5).
Alpha particles have the most destructive form of radiation because of their relatively high mass, however their penetration is fairly low.(6). Alpha particles have such a low penetration force that they are able to be stopped by few centimeters of air, by the skin or even by a piece of paper, presenting little danger unless swallowed (7).
The beta particle was discovered by Henri Becquerel in the late 19th century (8). In 1900, Becquerel showed that the beta particles were identical to electrons, which had been recently discovered by Joseph John Thompson (9)
The beta particle is denoted as + while the ordinary beta particle is - . It is a high-speed electron or position released from a degenerating radioactive nucleus. Beta particles have medium-energy and low mass therefore they are considered one of the least damaging types of radiation but they are still a significant health hazard (10). Even though beta particles have the same properties as electrons, they have a greater energy than the typical electrons orbiting the nucleus. Beta particles are not naturally radioactive but they can cause damage, break chemical bonds and create ions and damage tissue (11).
Bata particles have an electrical charge of 1 and their speed depends on how much energy they have. The beta particle s excess energy, in the form of speed, causes harm to living cells and when transferred, this energy can break chemical bonds and form ions (12).
In 1900 Paul Villard, a French chemist and physicist, discovered gamma radiation while studying radiation emitted from radium (13).
A gamma ray may be described as a packet of electromagnetic energy known as a photon . Gamma photons (gamma rays) are considered the photons with the most energy in the electromagnetic spectrum and they are emitted from the nucleus of certain radioactive, and consequently unstable, atoms. Gamma rays have approximately 10,000 times as much energy as the photons in the visible range of the electromagnetic spectrum These rays have neither mass nor electrical charge and, therefore, they consist of pure electromagnetic energy . The radiation from these rays is an extremely high-energy ionizing radiation (14).
The gamma rays, denoted as ? , are electromagnetic radiation of high frequency and have high energy, hence they are able to travel at the speed of light and can cover large distances i.e. hundreds to thousands of meters, in the air before their energy decreases. Gamma rays, unlike alpha particles, are able to pass through different types of materials, as well as human tissue. Materials which are very dense, like lead, are usually used for shielding which either slow down or stop penetration of gamma rays (15). Gamma rays can become a health hazards when being absorbed by living tissue because they are a form of ionizing radiation
In the elements, their nuclei undergo experience some of the stress in the atom and undergo radioactive decay order to release some of the "stress . At a certain point, the nucleus of an atom gets too large to sustain all of those protons and neutrons. The atom then relieves the stress and radioactive decay occurs (17).
When radioactive elements undergo various types of radioactive decay, until a stable atomic nucleus arises as a daughter product (18), and also when the sequence of alpha and beta decay until they finally become stable isotopes, they form lead.
As seen in the example provided in the Table, all of the natural series terminate with isotopes of lead, i.e., lead-206, lead-207, and lead-208. Secondly, all of these are stable isotopes of the element and no further radioactive emission therefore takes place (19).
Half-life is the period of time it takes for a substance to undergo decay to diminish by half, or the time it takes for one-half of the sample to decay (20). It is the time needed to transform one half of a reactant into product. This term is usually applied to radioactive decay whereby the reactant is the parent isotope and the product is the daughter isotope (21). The original name given to half-life was half-life period in the 1950 s (22). In order to prevent the chemical from remaining permanently within the norm a decay rate may be set. This sets a length of time over which the quantity of the chemical will slowly decrease towards zero (23).
Half-lives are usually used to describe undergoing exponential decay, for example radioactive decay, where the half-life remains constant during the whole life of the decay. The half-life can also be defined for non-exponential decay processes then in these cases the half-life varies throughout the decay process. The converse of half-life is doubling time (24).
The chemical half-life gene is used to define the rate of decay for all the chemicals inside their norm. Every chemical will have a value which ranges from 0 up to 255, this represents the quantity of substance within the norm (25).
Table 2. Half-life of the some substances
In 1949 radiocarbon dating was developed by Willard Libby and his team at the University of Chicago. He was then awarded the Nobel Prize in chemistry in 1960 for his discovery. His first demonstration to prove radiocarbon dating was done when Libby correctly calculated the age of wood belonging to a royal barge from ancient Egypt for which the age and provenance was previously established from historical records. Consequently, carbon dating was developed by a group of scientists led by Libby. He introduced the Libby half-life which was the carbon-14 half-life of 5568 30 years. Later a more accurate figure was introduced, the Cambridge half-life , of 5730 40 years (28).
Carbon dating, or radiocarbon dating, is a radiometric dating method that makes use of the naturally occurring radioisotope carbon-14 (14C) to calculate the age of carbonaceous matter up to approximately 58,000 to 62,000 years of age (29). Carbon dating is a technique of radioactive dating which applies only to once-live matter and assumed to be in a state of equilibrium with the atmosphere, absorbing carbon dioxide from the surrounding air for photosynthesis (30). The low activity of the carbon-14 restricts age estimation to the order of 50,000 years by these counting methods. Presumably these may be extended to 100,000 years via accelerator techniques for determining the carbon-14 concentration.(31). Cosmic ray protons bombard nuclei in the upper atmosphere, resulting in neutrons which consequently blast nitrogen, the main component of the atmosphere. The neutron bombardment results in the radioactive isotope carbon-14. The radioactive carbon-14 joins oxygen to produce carbon dioxide and is included into the cycle of living matter (32).
The most common use of radiocarbon dating is for determining the age of organic remains found at archaeological digs. When plants, during photosynthesis, add carbon dioxide into organic material, they incorporate a quantity of 14C which matches the level of isotopes in the atmosphere. Then, as plants die or are consumed by organisms i.e. humans, the 14C fraction of the organic material decreases at a fixed exponential rate due to the radioactive decay of 14C. The remaining 14C fraction of the decayed plant is compared to that expected from atmospheric 14C. This comparison enables the age of the sample to be determined (33).
The carbon-14 forms at a constant rate, therefore by calculating the radioactive emissions from the once-living materials and comparing this activity with the equilibrium level of living things, a measurement of the time elapsed may be determined (34).
A Geiger Counter, also known as Geiger-M ller Counter, is a particle detector that measures ionizing radiation and is also used to detect if objects emit nuclear radiation.
It is an inert gas-filled tube which briefly conducts electricity when a particle or photon of radiation makes the gas conductive. Usually helium, neon or argon with halogens are added. Then the tube amplifies this conduction by a cascade effect and outputs a current pulse, which is then often displayed by a needle or lamp and/or audible clicks.
Some Geiger Counters can be used to detect gamma radiation because the density of the gas in the apparatus is usually low, allowing most high energy gamma photons to pass through undetected. The sensitivity can be lower for high energy gamma radiation because lower energy photons are easier to detect, and are better absorbed by the detector. Gamma photons interact with the walls producing high-energy electrons which are then detected. Even though a sodium iodide scintillation counter is a better device for detecting gamma rays, Geiger detectors are still more favourable due to their low cost and robustness.
A variation of the Geiger tube is used to measure neutrons. This is when the boron trifluoride and a plastic moderator is used to slow the neutrons inside the detector. This creates an alpha particle inside the detector and thus neutrons can be counted (35).
Nuclear fission is the splitting up of atom (36) into two or more smaller nuclei plus some by-products (37), these may include free neutrons with a lighter nuclei, which can eventually become photons in the form of gamma rays (38). The strong nuclear force binding energy causes the fission to release substantial amounts of energy (39).
This nuclear fission can occur when a nucleus of a heavy atom captures a neutron or can even happen spontaneously. The nuclear fission splits into several smaller fragments, these fragments, or also called fission products, are equal to half the original mass. The remaining mass has been converted into energy according, to Einstein's equation.(40).
Nuclear fission products are radioactive and take a long time to disintegrate, causing nuclear waste problems. This has lead to debates on whether to use nuclear fission as an energy source due to the nuclear waste accumulation. Nuclear fission produces energy for nuclear power stations and nuclear bombs because certain substances called nuclear fuels undergo fission when struck by free neutrons and in turn generate neutrons when they break apart. This causes a self-sustaining sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon (41).
Critical mass may be defined as the smallest mass of a fissionable material that will sustain a nuclear chain reaction at a constant level (42) or support a self-sustaining nuclear chain.(43). It is also considered as the amount of a substance that is required for a nuclear chain reaction to commence (44).
Critical mass could also be seen as when fission events occur in the mass of fissile material, neutrons are released. Some neutrons are captured and lead to fission, while others escape the mass or are absorbed by some other kind of nucleus. If the expected number of neutrons , which triggers new fissions, is less than one, a nuclear chain reaction may occur causing it s size to decrease. This is known as criticality. Though, if the expected number of neutrons is greater than one, the chain reaction will increase exponentially and the configuration is called a critical mass (45).
Nuclear fission occurs when a massive atom is split into two or more smaller ones, while nuclear fusion is the fusing or joining of two or more lighter (or smaller) atoms into a larger one (46). In simple terms, nuclear fission splits a massive element into fragments and resulting in the release of energy in the process. While nuclear fusion refers to the joining of two light elements resulting in the formation of a massive element with the releasing of energy in the process (47). Nuclear fission reactions don t normally occur in nature, unlike nuclear fusion which occurs in stars, such as the sun.
A further difference is that nuclear fission requires substances to have their critical mass and high-speed neutrons in order to occur, while for nuclear fusion, high density and temperature environment is required. The nuclear fusion produces few radioactive particles compared to nuclear fission where many highly radioactive particles are produced.
The energy ratios between fusion and fission is also different because energy released during nuclear fusion is three to four times higher than energy released during fission. Energy released by nuclear fission is a million times higher than energy released during chemical reactions. This is due because nuclear fission requires little energy to split two atoms, compared to nuclear fusion whereby extreme amounts of energy is needed to bring two or more protons close enough so that nuclear forces can overcome their electrostatic repulsion (48).
Nuclear reactors are large machines used to control nuclear chain reactions while at the same time release heat at a controlled rate. If an uncontrolled nuclear reaction occurs in a nuclear reactor, it can potentially result in extensive contamination of water and air with radioactivity for hundreds of kilometres around the perimeter (49). Nuclear fusion is much more difficult to achieve than nuclear fission, which is what current nuclear power technology is based on. Secondly, it is difficult to produce a sustainable and stable nuclear fusion reaction and then also produce a reaction that has a larger output than input. If this were possible, it would provide the earth with unlimited technology because then the energy output would be similar to that of a star (50).
Thirdly, even though fusion reactors don t have the fission product waste disposal problem of fission reactors, fusion reactors generate large number of fast neutrons, leading to large quantities of radioactive by-products (51).
In summary nuclear fission is more controllable than nuclear fusion; fission is easier to create and sustain than fusion and fusion generates large quantities of radioactive by-products despite not having the fission product waste disposal issues (52).
The atomic bomb is usually heavier than the critical mass. The radioactive materials in the bomb are kept apart and are less than the critical mass until they collide into each other (53). When nuclear fusion begins, only one neutron is released and is free to strike an atom of U-238, this then gives rise to three more neutrons. These three neutrons strike another three atoms of U-238 and this releases three more neutrons from each atom, making a total of nine neutrons. This process is slowly initiated and it explains why the atom bomb does not blast off immediately (54).
Another method could be to collect enough plutonium inside the bomb, and if thick enough, the neutrons can t escape without hitting another nucleus, commencing the chain reaction. Then by inserting special neutron-absorbing matter in between the portions of plutonium it can control the rate at which the chain reaction proceeds, producing a 'slow burn' instead of the explosion (55).
Cadmium or boron rods are suspended between the fuel rods to control the fission reaction. The rods are raised or lowered to check the reaction by absorbing the right number of neutrons. They are known as control rods . When the control rods are inserted completely into the fuel, i.e., inside the reactor, all the neutrons are absorbed and the reaction can not start.
The control rods are raised slowly until they have absorbed the correct number of neutrons, leaving behind just the sufficient number of neutrons to sustain the chain reaction. The reactor has attained criticality when these rods have absorb two neutrons leaving behind one neutron to bring about further fission reaction. Now the number of atoms getting fissioned in one second is constant which means that energy is generated at a constant rate (56
The two Japanese cities which were bombed during World War II were Hiroshima and Nagasaki. On the 6th August 1945, the United States dropped an atomic bomb on Hiroshima, Japan. This atomic bomb was equivalent of 20,000 tons of TNT, killing tens of thousands of civilians (57). Then on the 15th August 1945, three days later to the previous attack, the United States dropped a second bomb on Nagasaki, Japan. Eventually ending World War II after Japan surrendered in 1945
When these atomic bombs exploded they caused short and long term effects. Within the first two to four months of the bombings, the acute effects killed 90,000 166,000 people in Hiroshima and 60,000 80,000 in Nagasaki. Most of these deaths occurred on the first day. Hiroshima s Health Department suspected that of the people who died on the day of the explosion 60% died from flash or flame burns, 30% from falling debris and 10% from other causes. During the following months after the bombs 20-30% died from flash burns or effect of burns, 15-20% died from radiation sickness, and 50-60% died from other injuries and illnesses. Since the bombings 231 people, who were under observation, died from leukaemia and 334 people died from cancer due to the exposure to radiation released by the bombs. In both cities, most of the dead were civilians (60).
In an atomic bomb, the energy source is a mass of radioactive matter like uranium or plutonium. This matter is extremely unstable due to the atom s nuclear being ready to fall apart or decay at the slightest nudge, and explode by releasing unneeded energy and extra neutrons. In the following diagram, the plutonium (B in Diagram 1) is given that nudge by the outer casing of TNT (A in Diagram 1), which explodes all around it.(1)
In comparison, the hydrogen bomb not only releases much more energy, through the process of 'nuclear fusion', but it is not triggered by TNT, rather it is triggered by an atomic bomb (61).
The central core (B in Diagram 2) is a mass consisting of atoms which are both isotopes of hydrogen, namely deuterium and tritium. These are both hydrogen bombs made up of extra neutrons in each nucleus. Small atomic bombs are placed around the outside, this causes the deuterium and tritium to be squeezed into a very dense mass. This process is called nuclear fusion, and it releases great quantities of energy. As the core of the bomb explodes, it causes the bomb casing (C in Diagram 2), consisting of uranium, to undergo fission, producing even more energy. Overall, an atomic bomb sets off a fusion bomb, which in turn triggers another atomic bomb creating a hydrogen bomb (62)
In summary, the differences between the atomic bomb and the hydrogen bomb are that the atom bombs work on the principle of atomic fission (splitting the atomic nucleus), while hydrogen bombs work on the principle of atomic fusion (combining atomic nuclei). Secondly, the hydrogen bomb is hundreds or thousands of times more powerful than the atom bomb and the hydrogen bomb uses an atom bomb as a trigger (63). Thirdly, the hydrogen bomb leaves behind no radiation and the activation energy is tremendous. Whilst in comparison the atomic bomb leaves behind massive after effects and requires a significant less amount of energy to occur (64).
There are many health hazards caused by radiation. In the atomic bomb the radioactive materials which decay spontaneously produce ionising radiation which remove electrons from atoms or break chemical bonds. Ionising radiation can damaged any living tissues in the human body in a unique manner. Then the body attempts to repair the damaged tissue, sometimes the damage cannot be repaired or is too severe or widespread to be repaired. Also, mistakes made in the natural repair process can lead to cancerous cells.
Being exposed to radiation causes different kinds of health effects. Generally, the duration and amount of radiation exposure affects the type or severity of health effects. There are two main categories of health effects: stochastic and non-stochastic.
Stochastic effects are usually associated with long-term, low-level (chronic) exposure to radiation. The greater levels of exposure to radiation increases the probability for these health effects to occur but do not influence the severity or type of the effect. Cancer is regarded as the primary health effect from radiation exposure because cancer is the uncontrolled growth of cells. This occurs when there is damage occurring at cellular or molecular level allowing for the uncontrolled growth of cells i.e. cancer.
Other effects occur because radiation can change the DNA that controls cell repair and replacement resulting in the perfect copy of the original cell. This is called mutation and can be teratogenic or genetic. The first, teratogenic mutations are caused by exposure of the fetus in the uterus and affects only the woman who was exposed. The second, genetic mutations are passed on to the baby.
While non-stochastic effects occur when there is exposure to high levels of radiation and effects become more severe as the exposure increases. These short-term, high-level exposure is known as 'acute' exposure. Conversely to cancer, health effects from 'acute' exposure to radiation usually appear immediately. These effects include radiation sickness and burns. Radiation sickness or 'radiation poisoning , causes premature aging or even death within two months if over exposed. The symptoms of radiation sickness include: nausea, weakness, hair loss, skin burns or diminished organ function (65).
Radiation is used in cancer treatment to cure cancer whilst maintaining acceptable function and cosmetics. Radiation can also be used alone or combined with chemotherapy and/or surgery. Radiation is recommended when the patient needs it to dull the pain after the spread of the tumor or until it is most beneficial for the patient's comfort. Radiation therapy can also be used in the treatment for various skin cancers, nasal cavity, cancer of the mouth, brain tumors, pharynx and larynx, gynaecological, prostate cancers and lung cancers. Radiation therapy plays an important role in conjunction with surgery and/or chemotherapy in breast cancer, bladder cancer, bowel cancer, leukemia and lymphomas, Hodgkin's disease, thyroid cancer and childhood cancers (66).
Radiation therapy destroys cells, either directly or indirectly by interfering with cell reproduction through the use of high-energy X-rays, electron beams or radioactive isotopes. This is when a radiated cell tries to divide and reproduce itself, it fails to do so and dies in the attempt. Usually normal or healthy cells can repair better the effects caused by radiation than malignant or abnormal cells, therefore normal cells can recover better from exposure to radiation and survive where as the malignant cells die. If radiation is applied in the correct region and in the correct amounts then the cancer dies and the patient is well again because normal or healthy tissue can survive. If not all cancer cells are killed then the cancer may reproduce and further radiation may needed but in lesser quantities because the normal tissues are less able to withstand the effects of further radiation.
Even though there is evidence of radiation exposure during medical x-ray procedures, the benefits of having an x-ray for a patient presenting some medical symptom outweigh the risk of the radiation affecting the person. The x-rays are known as ionizing radiation which means that the radiation is of a high enough energy to break chemical bonds and therefore has the potential to be harmful to living organisms. When these bonds are broken there is, unfortunately, the potential to cause damage to cell nuclei.
However, this same situation makes x-rays as effective as cancer treatment in the form of radiation therapy. Another benefit is that x-rays allow people to see the structure of internal organs and bones and evaluate without the need for surgery. The radiation know to occur during an x-ray is believed to be low and harmful effects are directly proportional to the amount or dose the patient endures (67).
A radioactive tracer, or radioactive label , is a substance containing a radioisotope and a radioactive atom to allow for quick and easy detection and measurement.. A radioisotope can be defined as an isotope that has an unstable nucleus and that can stabilize itself by spontaneously emitting energy and particles. They were initially invented by Quinn Hanson and later developed by George de Hevesy to measure the speed of chemical processes and used to track the movement of a substance through a natural system such as a cell or a tissue (68).
The simplest radioactive tracer studies show the tagging or labeling of a biological entity with a radioactive isotope (radioisotope). The entity is then tracked by following the radiation from the isotope. Mostly in biological tracer experiments, the radio-isotope is placed into the system and it s radiation is measured with the use of the Geiger-M ller Counters or scintillation detectors. Extremely low-intensity or soft radiations can then be detected through the use of photographic film.(69)
The radioactive tracer is relied on heavily by the medical profession for direct radiation fields and radioactive isotopes in identifying and treating diseases and are also used to test new drugs and conduct research into cures for disease.(70)
Radioactive materials consist of radionuclides and radioactive isotopes. A radionuclide is any type of radioactive material, including elements and the isotopes of elements . An isotope of an element is a particular atomic "version" of it. Radionuclides are used in more than 11 million nuclear medicine procedures every year in the United States. Examples of radioactive tracers in medical procedures are bone scans that can detect the spread of cancer six to eighteen months sooner than X-rays and kidney scans are much more sensitive than X-rays or ultrasound in fully evaluating kidney function (70). They also are used in 100 million laboratory tests on body fluid and tissue specimens. (Isotopes are atoms of the same element with different atomic structures.)
Radioactive tracers are used mainly for kidney and bone scans,. Radioactive isotopes and radioactively labelled molecules are used as tracers to identify abnormal bodily processes. Once the patient is injected with a radioactive element pictures of the internal workings of the organ are taken by a special camera