Radioactive Decay And Radiation Biology Essay


The symbol for the alpha particles is α. Alpha particles are positively charged particles which are emitted from radioactive substances. They have a mass which is equal to that of a helium atom as they have two protons and two neutrons. Alpha radiation consists of the nucleus known as "helium-4". This type of radiation is weak and can be stopped by clothes and even a sheet of paper as shown in Source A below. Ernest Rutherford discovered alpha radiation in 1899. [2] 

Beta particles

Beta particles are high-energy particles which move at the speed of light and are take the form of either electrons or positrons. The symbol given to beta particles is "β" and these particles are emitted from certain radioactive nuclei. Beta radiation is made up of electrons and some can be absorbed when passing through substances and the amount absorbed depends on the thickness of the substance. Beta radiation can be blocked by a sheet of aluminium as shown in Source A. Henri Becquerel discovered some form of unknown radiation which Ernest Rutherford later identified this radiation consisted of beta particles. [3] 

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Gamma rays

Gamma rays are a form of "electromagnetic radiation". These rays are represented by the symbol "γ" and they are emitted at an extremely high frequency (short wavelength). Gamma rays are considered to be a health hazard as they can do a large amount of damage to human tissue and because of this, gamma rays are often used in order to kill living organisms giving this process the name "irradiation". Source A shows how gamma rays can be absorbed and pass through dense substances. Gamma radiation was first discovered by Paul Villard (a French Chemist and physicist) in 1900 and then in 1903 Ernest Rutherford named Villard's new form of radiation "gamma rays". [4] 

Source A

This picture indicates how the different types of radiation react when they come into contact with different substance. Alpha radiation (α) is stopped by a piece of paper, beta radiation (β) is stopped by a piece of aliminium and gamma rays (γ) are eventually absorbed and can also pass through dense material A

question 1.png

Why do some isotopes of elements spontaneously undergo radioactive decay? (2)

The isotopes of elements spontaneously undergo radioactive decay because the atom can no longer maintain the amount of energy that has built up within the nucleus as a result of the number of protons and neutrons. The isotope therefore releases some of the energy and matter that has built up and this process is known as "radioactive decay". [5] 

The element is Lead. The process of alpha and beta decay is shown in the diagram below. [6] 

Source B

A radioactive series.

The rate at which radioactive decay occurs is given in half-life. Explain this term and give the half life of a few substances. (4)

The half-life of a substance is the time period during which activity of the particular radioactive substance "decreases by a factor of one-half."; half the nucleus of the radioactive substance disintegrates. [7] 

The half-life of certain radioactive elements [8] :

Sodium (24) - half-life = 15 hours Uranium (238) - half-life = 4.5 billion years

Iodine (103) - half-life = 8.07 days Radium (226) - half-life = 1 600 years

Cobalt (60) - half -life = 5.26 years

Carbon dating is used in archeology to date materials. Explain how Carbon dating works. (5)

Carbon dating is method used to determine estimates of the age of organic materials. Carbon has three isotopes which are known as "naturally occurring isotopes", however, only two of these three, C-12 and C-13, are stable. The third isotope, C-14, is said to be unstable and has a weak "beta decay" to another organic substance known as "nitrogen-14". This isotope has a half-life of around 5 730 years. After an organism dies, the carbon-14 inside it begins to decay (it is not replaced because the organism is dead). The process of carbon dating involves the scientist (archeologist) burning a small piece of the artifact in order to convert it into "carbon dioxide". A radiation counter is used to detect the electrons which C-14 gives off as it decays into nitrogen. Once the amount of C-14 is determined, it is compared to the amount of C-12 in order to establish the amount of radiocarbon which has decayed. Scientists are thus able to date the artifact in question. [9] 

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What is a Geiger Counter? (2)

A Geiger Counter is a tube which can detect and measure "ionizing radiation". When a particle of radiation enters into an "inert gas filled tube", the gas is able to briefly conduct electricity as the particle has made it a conductive substance. This conductivity is enhanced by the tube by means of a process known as the "cascade effect". The current causes a pulse to be outputted and this displayed by mean s of a needle or lamp or audible clicking sounds. [10] 

Source C

A needle point Geiger counter. 10File:Geiger counter.jpg

Nuclear fission and nuclear fusion


The fission reaction involves the bombarding of a nucleus of a radioactive isotope with neutrons. When this occurs the nucleas splits in two and it is this process which is known as nuclear fission. During a fission reaction fewer neutrons are required to begin the process than are produced as a result of the actual process. When a uranium-235 nucleus gains a single neutron it produces three neutrons which thus cause three more fission reactions. This releases nine neutrons which subsequently induce nine more fission reactions to take place, thus releasing twenty-seven neutrons and so on. The amount of uranium-235 is extremely small and therefore, only a few neutrons are captured by the nuclei and this means that the chain reaction in not sustained. [11] 

When the nucleus splits into smaller parts, free neutrons as well as lighter nuclei may be produced as a results, which may even produce photons which take the form of gamma rays. When a fission reactions takes place with "heavy elements" it is classified as an "exothermic reaction". This reaction can result in the release of large amounts of energy, including "electromagnetic" as well as "kinetic" energy. In order for a fission reaction to produce energy the "binding energy" of the formed elements must be higher that the "binding energy" of the element you started with. Nuclear fission is a form of "nuclear transmutation". [12] 

Source D

A diagram showing the beginning stages of the nuclear fission of the isotope uranium-235. (the orange 'blast' indicates the stage at which the nuclear fission occurs)Dnuclear fission of uranium.jpg

What is meant by the term 'critical mass'? (2)

The critical mass refers to the least amount of fissile material which is required in order to sustain a chain nuclear fission chain reaction. This mass is dependable on the nuclear properties and the elements density, shape, temperature as well as its surroundings. [13] 

The stars emit radiations due to nuclear fusion reactions. What is the difference between nuclear fusion and nuclear fission? (2)

Nuclear fusion is the formation of heavier nuclei from the combining of lighter nuclei, [14] whereas nuclear fission is the formation of light nuclei from the splitting of heavier nuclei. [15] Nuclear fusion is an endothermic reaction. This means that it requires energy, in this case in the form of heat, in order for the reaction to take place.14 Nuclear fission, however, is an exothermic reaction - meaning that it gives off energy, in the form of "electromagnetic" or "kinetic" energy. [16] 

Nuclear fusion is not used in nuclear reactors because scientists have not been able to establish a stable as well as sustainable fusion reaction. This means that they are unable to maintain the temperatures as well as the amounts of energy that are needed in order to sustain a fusion reaction. Another reason as to why fusion reactions have not been used is the fact that they require a large amount of energy to occur, but they release a smaller amount of energy. This means that the reaction has a greater "input" than it does "output" [17] another main problem is that scientists have not been able to create a machine which will hold the nuclear fusion reaction. At the temperature which is required for the reaction to occur, common material such as metal and plastic vaporize instantly. [18] 

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Source E

A Diagram to indicate an example of nuclear fusion EThe atom bomb

In a nuclear reactor the fission chain reaction if controlled. An uncontrolled fission reaction is the principle of the atom bomb. For this reaction to occur, the radioactive material must have a mass equal to or greater than the critical mass. How is the bomb constructed to ensure that it does not go off immediately? (3)

The two small pieces of uranium (the radioactive material required for the atomic bomb) are kept apart. They are then brought together by means of a chemical explosive. [19] When these fissionable materials (in this case uranium) are separate, they have a mass which is less than that of the critical mass. [20] When they are combined the mass is greater than that of the critical mass19 and they form a larger piece which is able to support a chain reaction (mentioned above in question 7) and this consequently results in an explosion. [21] 

Over which two Japanese cities were atom bombs dropped during World War II? (2)

Hiroshima and Nagasaki.

Approximately how many people were killed by these two bombs? (2)

In Hiroshima (bomb dropped on the 6th August 1945) the acute effects of the bomb killed between 90 000 - 166 000 people. In Nagasaki (bomb dropped on the 9th August 1945) the acute effects killed between 60 000 - 80 000. At least half of these deaths occurred on the first day and over the months following the bomb the death toll grew as a result of burns, radiation sickness and other severe injuries. [22] 

502px-Nagasakibomb.jpgFile:Atomic cloud over Hiroshima.jpg

Source G

The mushroom cloud over Nagasaki as a result of the dropping of the second atomic bomb22

Source F

The mushroom cloud over Hiroshima as a result of the dropping of the first atomic bomb22

Briefly explain how a hydrogen bomb works and how it differs from an atom bomb. (5)

A hydrogen bomb is also known as a thermonuclear bomb and it is a nuclear weapon. The energy the "H-bomb" requires is based on the energy acquired from the fusion of hydrogen nuclei into helium nuclei. The fusion typically involves the nuclei of the heavier isotopes of hydrogen known as "Deuterium" and "Tritium". "Deuterium" can be obtained from normal water as it is a naturally occurring isotope of hydrogen, "Tritium", however, is an artificial and radioactive isotope which can be formed in nuclear reactors. Because these nuclei are both positively charged, they naturally repel each other and the only way to get them close enough to each other to fuse into a helium nuclei is to heat them in extremely high temperatures. This temperature is acquired through the use of a fission reaction. The heat emitted when the fission bomb explodes (occasionally referred to as an atomic bomb) forces the two hydrogen nuclei to collide and thus fuse. This fusion emits massive amounts of energy.

An atomic bomb, however, does not require any other reaction to start it off. Once the radioactive material combine it sets off a series of reactions, thus resulting in a massive explosion. The atomic bomb is a fission reaction, whereas the hydrogen bomb is a fusion reaction which requires a fission reaction in order to set it off. [23] 

Source H

A diagram showing the fusion reaction between the two hydrogen molecules H

Radiation sickness

Radiation is extremely dangerous. There are a large number of ways in which radiation is harmful. Write a paragraph outlining the health hazards associated with radiation. (8)

Radiation can result in a sickness known as "radiation poisoning" or "radiation sickness". This type of sickness is a result of over exposure to the type of radiation which is known as "ionizing radiation" over a short period of time (it can, however, result occasionally from long term exposure). Radiation sickness can cause other illnesses to form such as cancer, tumors and internal bleeding. Exposure to radiation can also result in damage of the genetic material. This means that even if a victim shows no signs of radiation sickness, if he/she has children they may be physically or mentally deformed. [24] Exposure to gamma rays is also a health hazard as they kill living tissue and have been used in order to kill living organisms [25] . Direct exposure to "electromagnetic radiation" can result in severe burns (the same as those which would be caused inside a microwave) [26] . A recent study has shown that there may be health hazards with regard to cellular mobiles and the "electromagnetic radiation" they emit. These effects include damage in the blood-barrier and an increase in cancer risks as well as other illnesses. It must be stated, however, that scientists are still researching into these effects and as of yet they are not directly linking them with mobile radiation - studies are still being carried out. [27] Radiation treatment for illnesses such as cancer also has known side effect which include nausea, hair loss, a drop in white blood cell count and fatigue. [28] 

Despite its harmful side effects, radiation is used in many ways in medicine. Write short paragraphs on each of the following medical applications:

Cancer treatment


Radioactive tracers (10)

Cancer treatments

"Radiation therapy" is used in order to kill the cancer cells as well as to shrink tumors. Radiation therapy uses "ionizing radiation" in order to damage the genetic material making up the cancer cells and tumors this destroys the cells (killing the cancer cells) or injures them (causing tumors to shrink) and these cells are no longer able to undergo mitosis. Radiation damages the normal cells of the body as well, however, these cells are able to recover. There are different types of radiation therapies available and it depends on the size of the area which needs to be treated and how deep the treatment is required to reach. "Palliative Radiation Therapy" is a technique used in order to relieve pain from cancer in the bones or other parts of the body. "Prophylactic Radiation Therapy" is given in order to prevent the cancer from spreading and it does this by treating areas which do not show signs of cancer. [29] 


"X-radiation" is a form of "electromagnetic radiation". The wavelengths used are shorter than the wavelength of a UV ray and the process of x-rays was discovered by Wilhelm Conrad Röntgen. X-rays are used by radiologists for radiology because of their medical imagery. X-rays can detect certain defects in the skeleton such as deformities as well as breaks and can also be used to identify lung cancer and other diseases by means of a chest x-ray. Abdominal x-rays are used to identify any obstructions in the colon or leaking fluids. X-rays can be used in other regions of the body as well to identify any abnormalities internally in the human body. X-rays are also used for processes such as "x-ray crystallography" in which the nature of a crystal lattice can be studied, "x-ray astronomy" which is the study of the x-ray emissions from "celestial" bodies, "industrial radioaraphy" in which x-rays are used to inspect industrial parts, "border security" where x-rays are used to scan the inside of trucks in order to detect any weapons or other objects that may pose a threat to the country as well as many other uses. [30] 

File:Anna Berthe Roentgen.gif

Source I

A picture of the very first x-ray taken by Wilhelm Conrad Röntgen of his wife's hand on the 22nd December 1985. The lump on her wedding figure is a ring. 30

Source J

An example of a mobile x-ray surgery unit J

Radioactive tracers

A radioactive tracer is a substance which contains a "radioactive atom". The tracers can be used to moniter chemical and biological processes as well as the movements which occur in natural systems (in this case cells and tissues). Radioactive tracers can be used to moniter and record plant growth by water plants with this substance. The plant would take up the water as normal and a Geiger Counter would be used in order to detect the rate at which the plant absorbed the water and where exactly the water had gone. [31] In medicine, doctors who suspect a patient of having thyroid problems can give the patient a glass of water containing sodium iodide to drink. Sodium iodide is known to travel mainly to the thyroid gland and can be traced using a Geiger counter and thus the doctor is able to determine whether or not the uptake as well as the place where the uptake occurs is normal or not and treat the patient accordingly. [32]