Atomic Nuclei And Radioactivity Biology Essay


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There are three different types of radiation. Briefly describe each of these types of radiation and for each type name the scientist who first discovered the particular radiation. (3 x 4)


An alpha particle is a positively charged particle emitted in the radioactive decay of some unstable atoms. It consists of two protons and two neutrons (this is identical to the helium atom) the alpha particle is quite weak and can therefore be stopped quite easily. The particles are able to break chemical bonds due to the fact that they are heavy. These alpha emitters are harmful if they are inhaled or ingested.

The founder of the alpha particle was Ernest Rutherford in 1899 to 1900. [1]


A beta particle is also emitted during the radioactive decay of some atoms. Beta rays mostly carry a negative charge. They are smaller than alpha particles , yet, they are more penetrating. Beta particles can be stopped by a sheet of aluminium.

Henri Becquerel discovered these particles and Ernest Rutherford furthered his discovery and published a book on the Alpha and Beta particles in 1899 to 1900. [2]


Gamma rays are mostly neutral, they have a very short wavelength. Gamma rays are a highly energetic electromagnetic radiation. They cannot be stopped entirely, but they can be reduced by certain high density materials such as concrete or lead.

The founder of gamma rays was Paul Villard and Ernest Rutherford in 1899 to 1900. [3]

Question 2

Why do some isotopes of elements spontaneously undergo radioactive decay?


Certain isotopes of elements undergo radioactive decay. This happens when the element has an unstable nucleus that disintegrates. Whilst it disintegrates/decays it emits alpha, beta or gamma rays until stability is reaches. [4] 

Question 3

All substances which naturally undergo radioactive decay, continue to decay by a sequence of alpha and beta decays until they finally become stable isotopes of a particular element. What element is this? (2)

The element that naturally undergoes radioactive decay buy a sequence of alpha and beta decays is uranium. Uranium 238 decays to stable Lead 206. They are stable isotopes of Lead. [5]

Question 4

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

Half life: in nuclear physics is the term given to the amount of time required for half of a particular substance to react. It is the number of radioactive atoms in a radioactive material to fall to half of the initial value. Certain nuclei rates of decay are expressed in terms of their half-lives. The half life of an element can vary from a fraction of a second to millions of years.

The half life of:

Strontium is 28,8 years

Carbon is 5,730 years

Lead 206 is approximately 3 000 000 000 years. [6]

Question 5

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

Rdiocarbon dating method that uses the naturally occurring isotope carbon-14 (14C). carbon014 firstly collaborates with carbon dioxide, then, due to photosynthesisthis collaboration forms more carbon-containing-molecules within plants. Throughout its life, the plant or animal has a consistant carbon compound intake. This intake is represented in the ratio of Carbon14 to Carbon12. Therefore when the organism dies it will no longer take in the carbon compounds. The ratio of Carbon14 to Carbon12 will thus decrease. We can use its new ratio to estimate the age of the object by comparing its current Carbon Ratios to the Carbon Ratios in the atmosphere. [7] 

Question 6

What is Geiger Counter?


A Geiger counter, is also called a Geiger-muller counter. This counter is a particle detector that measures radioactivity. It operates by using the ionization of matter caused by radiation. " The counter consists of a metal tube filled with gas. The cylinder has a 'window' made of material that can be penetrated by alpha, beta, or gamma rays. In the centre of the tube is a wire. The wire is connected to one terminal of a source of direct current, and the metal cylinder is attached to the other terminal. Current flows between the wire and metal cylinder, whenever entering radiation produces irons." [8]




(Questions 7 - 10)


Question 7

It is possible to cause artificial radioactivity by bombarding a nucleus with high velocity neutrons. This process is called nuclear fission. This reaction is the basis of nuclear power stations as well as the nuclear bomb. With the aid of a diagram, briefly explain this fission reaction. (6)

Nuclear fission is the process used to generate energy in nuclear power plants. Uranium-235 was the first nuclear fission to be discovered. A heavy nucleus can be split in many different ways. Uranium 235 splits from one nucleus in two ways. These are represented in these two equations:

If one fission is able to produce two neutrons, these two neutrons cause two additional fissions. Therefore, four neutrons will produce four fissions. This results in the energy being released quickly and being multiplied even faster. The result? A violent explosion. This will then form a chain reaction.

Question 8

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

Critical mass is the term given to the minimum amount of fissile material which is required to maintain the chain reaction while, keeping a consistent rate of fission. [9] 

Question 9

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

Nuclear fusion refers to the joining of two light nuclei to form a large nucleus. These multiple light nuclei are able to release greater amounts of energy. An example of fusion is the combination of two hydrogen nuclei into one helium nucleus. This happens under extreme pressure and heat conditions. "The fusion process is the essential energy producing process in the sun". Fission refers to the splitting up of one large, heavy nucleus into two smaller ones, giving off energy whilst this occurs. Therefore when stars emit radiations it is because of the joining bonds between between nuclei.

Question 10

Nuclear fusion reactions produce no nuclear waste and would thus be an ideal source of energy. What are the main reasons why fusion reactions have not been used in nuclear reactors? (3)

The main reasons as to why nuclear fusion reactions have not been used are:

There are problems in attaining useful nuclear fusion conditions; They need extremely high temperatures. "The problem is that high energies, achieved by high temperatures, are needed to overcome the repulsion between nuclei". Therefore fusion reactions are known as thermonuclear reactions. They also need to combine a sufficient amount of reacting nuclei for long enough to allow the release of more energy that is needed. The major problem although seems to be the conversion from captured energy to electricity.



(Questions 20 - 23)


Question 20

In a nuclear reactor the fission chain reaction is 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)

A mass of fissile material in an atomic bomb must be assembled instantaneously and be able to be held together for about a millionth of a second to permit the chain reaction to occur before the bomb explodes. A heavy material was produced to surround the fissile mass. This material is called Tamper and it prevents the atomic bombs premature disruption. This special material also reduces the amount of neutrons that could escape.

Question 21

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


The United States dropped the first atomic bomb on the Japanese City of Hiroshima on the 6 of August 1945. The second was dropped on Nagasaki on the

9 August 1945.

Question 22

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

Approximately 66 000 people died after the atomic bomb was dropped on Hiroshima. Around 39 000 people died as a result of the second atomic bomb which was dropped on Nagasaki. The true tragedy was the deaths and deformations that followed years after the bombs were dropped due to the high levels of radiation caused by the atomic explosives.

TABLE A: Estimates of Casualties



Pre-raid population









Total Casualties



Question 23

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

The hydrogen bomb works on the physical principle known as nuclear fusion, whilst the atomic bomb works on fission. Nuclear fission refers to the joining of atoms to form one heavier nucleus. For this to happen the conditions need to be extremely hot. Therefore the atomic bomb is attached to the hydrogen bomb, the atomic bomb provides enough heat to start fusion.

Helium is formed as the hydrogen nuclei fuse together. The atoms compress the bomb to produce a very dense mass. Hydrogen bombs without uranium are called neutron bombs because without the uranium in the outer case of the bomb, the fission chain will be shorter.

These hydrogen nuclei release massive amounts of energy, resulting in a huge explosion. The hydrogen bomb is much more powerful than an atomic bomb. Tests have been done under water, in the sea, to discover just how powerful the hydrogen bomb is. The hydrogen bomb has the power of up to 10 megatons. This makes the atomic bomb seem tiny with its power of 13 kilotons. [10]



(Question 24)


Question 24

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)




Blood System


Gastrointestinal Tract

Reproductive Tract

Radiation is measured in rem. Rem stands for (Roentgen Equivalent Man). The total amount of rems determines how much damage a person can suffer.

Radiation affects most areas of the human body, yet there are seven main areas.

Starting with area 1, the hair. Amounts of radiation of 200 rems or higher causes hair to fall out in large clumps. The brain can also be affected by radiation. Radiation kills nerve cells and small blood vessels. This will most likely happen when exposed to 5 000 rems or more. Radioactive iodine specifically affects the thyroid. In significant amounts radioactive iodine can possibly destroy the thyroid completely. When a person is exposed to 100 rems, the blood cell count will be reduced, leaving the person extremely vulnerable to infection. This is known as mild radiation sickness. The symptoms of this radiation sickness appear similar to the flu, yet unlike the flu the symptoms may persist for as long as 10 years and also increases the body's chances of getting leukemia and lymphoma.

Heart failure and death is caused by exposure to 1 000 to 5 000 rems of radioactive material. A person who is exposed to 200 rems or more may experience nausea, diarrhea and bloody vomiting. This damage in the intestinal tract lining stops cells from dividing and can cause the victims to become sterile.

All of these effects of radiation are caused by 100 rems or more, therefore the victims may experience smaller side-effects if they are exposed to less than 100 rems of radiation. [11] 




(Question 25)


Question 25

Despite its harmful side effects, radiation is used in many ways in medicine. Write short paragraphs on each of the following medical applications: (10)

Cancer treatment


Radioactive tracers


Cancer produces tumors that are made up of cells that reproduce at abnormally high rates. The aim of radiation therapy is to prevent cancerous cells from reproducing/dividing when they come into contact with other cells. Normal cells are programmed to stop reproducing when they come into contact with other cells. The cancerous cells and tumors do not stop. The DNA makes it possible for the cell to reproduce. Radiation therefore damages the DNA within the cells by using high energy x-rays. This prevents the cancer cells from dividing and in some cases it can kill the cancerous cells. Radiation also however, affects normal cells, but because normal cells grow at a slower rate, they are mostly able to repair this radiation damage. Radiation treatments are usually given in small doses to reduce the patients side effects.


Radiation that can pass through our skin is known as an x-ray. X-rays are only possible because our bones are more dense that our skin, and therefore when x-rayed, bones and other dense materials cast enough extraordinary shadows that can be detected on photographic film. Doctors and dentists use x-rays daily to see the structures of our bones inside our bodies. They are thus able to locate broken bones and dental hazards. Cat scanners have also been invented. These are x-ray machines which have been connected to computers to provide doctors with colour and more accurate pictures to show the shape of internal organs.


Gamma rays are emitted from the body with radioactive tracers. These tracers are incorporated into a compound that is given to the patient. These tracers are generally short-lived isotopes linked to chemical compounds which permit specific physiological processes to be scrutinized. They can be admitted by injection, inhalation and orally. The first type of these tracers identify abnormal bodily processes, by a gamma camera which can view organs from many different angles. This gamma camera captures bone and kidney scans, and can also identify natural elements in certain parts of the body: iodine in the thyroid, potassium in the muscles, phosphorus in the bones and sodium 24 in the blood circulation. Radiotracers are further illustrated by positron emission tomography (PET) *. PET can be used for clinical diagnosis of countless diseases. This is done by compounds containing radionuclides that decay by positron emissions that are injected into the patient. This enables researchers to monitor oxygen, blood flow, glucose metabolic rates and other biological functions, including the study of the brain.


positron - a particle with the same mass as an electron but with a positive charge.

emission - the process of sending out heat, light or vapour

tomography - amethod of radiography displaying details in a selected plane within the body (Oxford Dictionary)


Alpha particles particles that are identical to Hellium-4 nuclei, consisting of two protons and two neutrons.


Electro magnetic a form of energy that has wave characteristics and radiation that propagates through a vacuum at the characteristic speed of 3.00x108 m/s.

Ionizing radiation radiation that has sufficient energy to remove an electron from a molecule, thereby ionizing it.

Fusion the joining of two light nuclei to form a more massive one.

Fission the splitting of a large nuleus into two smaller ones



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