Chapter 6 Flashcards
Describe an atom
A posterity charged nucleus, consisting of protons and neutrons, surrounded by negatively charged electrons, with the nuclear radius much smaller than that of the atom and with almost all of the mass in the nucleus.
Describe the structure of a nucleus in isotopes
They contain the same number of protons but have different number of neutrons, this could be described as having the same atomic number but a different mass number
What characteristic do all nucleus have?
A positive charge, but isotopes of an element differ in mass by having different numbers of neutrons.
what is the charge of a proton and what is its mass?
+1 charge and 1 mass
what is the charge of a neutron and what is its mass?
0 (Neutral charge) and 1 mass
what is the charge of an electron and what is its mass?
-1 charge and 0.0005 mass
what is the charge of a positron and what is its mass?
+1 charge and 0.0005 mass
What is equal in an atom?
The number of protons equals the number of electrons and is therefore neutral
What orbits the nucleus of an atom
electrons, they orbit the nucleus at different set distances from the nucleus
When do electrons change orbit?
When there is absorption or emission of electromagnetic radiation
How do atoms form positive ions
They lose outer electrons to have complete shells
What is emitted from an unstable nuclei
alpha
beta
gamma rays can be emitted in a random process
What are alpha, beta and gamma rays?
Ionizing radiations
what is background radiation and give examples
Humans are exposed to radiation all the time. This radiation is called background radiation. Most of it the body is exposed to is from natural sources such as food eg- bananas and also radioactive rocks. However some of it is artificial eg medical sources such as X-rays or nuclear power stations.
Origins of background radiation from earth and space
Space- Cosmic radiation left over from the big bang
Earth- Radioactive rocks, human body and food,medical sources, nuclear power stations and nuclear weapons
How does Photographic film detect radioactivity
The photographic film gets darker when it absorbs radioactive substances, similar to when it absorbs visible light
How does a Gieger Müller tube detect radioactivity
Each time the counter absorbs radiation is transmits an electrical impulse to a counting machine. This makes a clicking sound or displays the count rate. The greater freuqncy of clicks or counts the more radiation is absorbed
What is an alpha particle equivalent to?
A helium nucleus
What is a beta partcle
An electron emitted from the nucleus
what is a gamma ray
electromagnetic radiation
Alphas ability to penetrate
least penetrating, can be absorbed by a sheet of paper
Betas ability to penetrate
Can penetrate air and paper however is stopped by thin sheet of aluminium
Gammas ability to penetrate
The MOST penetrating, can penetrate air, paper and metal. Higher levels can only be stopped by man cm of lead or m of concrete.
How has the atomic model changed over time
in 1803 John dalton= billiard ball which was just a circle, no understanding of what was in atom.
in 1904 JJ Thopsom made plum pudding model which was a positively charged sponge with negative electrons in it, he also discovered electrons were the smallest.
In 1911 Ernest Rutherford made the nuclear atom which has a central nucleus with electrons orbiting- he made this discovery through the alpha particle scattering experiment.
In 1913 The bohr model- electrons orbit nucleus on certain orbits/shells depending on energy levels of electrons.
What is the unit of activity of a radioactive isotope
The becquerel, Bq
What is a half life of a radioactive isotope
the time taken for half the undecayed nuclei to decay or the activity of a source to decay by half
What cannot be predicted?
When a particular nucleus will decay but half-life enables the activity of a very large number of nuclei to be predicted during the decay process
Describe uses of radioactivity
household fire smoke alarms irradiating food sterilization of equipment tracing and gauging thicknesses diagnosis and treatment of cancer
What are the dangers of ionizing radiation
it can cause tissue damage and possible mutations this is because it breaks down molecules into ions, these ions can take part in other chemicals reactions in living cells and can cause them to die or become cancerous
how to protect yourself from dangers of ionizing radiation
Wear protective clothing
Keeping far away as practical eg using tongs
Keeping exposure time as short as possible
Keeping radioactive materials in lead lined containers labeled appropriate hazard symbol.
Which radioactive source is the most harmful inside the body
alpha radiation is the most dangerous because its easily absorbed by cells, beta and gamma are less dangerous as they are less likely to be absorbed by a cell and will usually just pass right through it
Which radioactive source is the most harmful outside the body
alpha radiation is not as dangerous because its unlikely to reach living cells in the body whereas beta and gamma are the most dangerous sources because they can penetrate the skin and damage the cells inside
what is the difference between contamination and irradiation
Contamination=Radioactive materials can be swallowed or breathed in. While inside the body, the radiation it emit scan produce damage.
Irradiation- Radiation from the material can damage the cells of the person directly
Compare the treatment of tumors using radiation applied internally or externally
Internally- radiotherapy, the source of the radiation is inside the patient. A beta emitter, often iodine-131 is used.
High powered gamma rays are used to kill cancer cells inside the body, they also kill healthy cells around the tumor.
Both are usually restricted to the area where the radiation source is applied, treatments often require repeated doses and damages healthy tissue/
how are radioactive substances used in PET scanners
PET scan- uses radioisotope tracer drugs such as fluorine-18. The tracer is usually injected into the patients blood. Gamma rays emitted by the tracer are detected by the PET scanner- pics are taken and analysed by computers.
how are radioactive substances used in tracers
a radioactive tracer is used to investigate a patients body without using surgery. A small amount of radioactive material is put into the patients body (via drink, ingested or injected) and a radiographer puts a detector around the body to detect any gamma rays that pass out of the patients body to portray a picture on a screen.
Explain why isotopes used in PET scanners have to be
produced nearby or in the hospitals
The half life of radioisotopes used in PET scans are very short.
what are the main nuclear fuels
uranium and plutonium
Evaluate the advantages and disadvantages of nuclear power
for generating electricity
+=nuclear fuels don’t produce CO2 therefore reduces green house gas emissions, little amounts go a far way.
-= Non renewable, if there is an accident large amounts of radioactive material could be released into the environment. Nuclear waste remains radioactive and is hazardous to health for thousands of years.
What can be a source of energy?
nuclear reactions, including fission, fusion and radioactive decay.
What does the fission of U-235 produce?
2 daughter nuclei and the emission of two or more neutrons, accompanied by a release of energy.
What is a controlled nuclear chain reaction
The fission of uranium is an example- the uranium nucleus must be hit by a neutron. When this happens the nucleus split into smaller nuclei, energy is released and 2-3 neutrons are released.
Explain how the chain reaction is controlled in a nuclear
reactor, including the action of moderators and control rods
A reactor is designed to allow a controlled reaction to take place. A moderator eg- graphite slows down the neutrons. Movable control rods are placed between the rods of nuclear fuel. These control rods absorb some of the neutrons so fewer neutrons are available to split uranium nuclei therefore controls speed of reaction- how fast neutrons are released
What is a product from a chain reaction and what is it used for
thermal (heat) energy from the chain reaction is
used in the generation of electricity in a nuclear power station
What are the products of nuclear fission
RADIOACTIVE
What is nuclear fusion
nuclear fusion is the creation of larger nuclei
as a result of a loss of mass from smaller nuclei, accompanied
by a release of energy, eg fusion is the energy
source for stars
Explain the difference between nuclear fusion and nuclear
fission
Both fission and fusion are nuclear reactions that produce energy however…
Fission is the splitting of a heavy, unstable nucleus into two lighter nuclei, and fusion is the process where two light nuclei combine together releasing vast amounst of energy.
Why does nuclear fusion not happen at low temperatures and pressures?
electrostatic repulsion of protons
why are the conditions for fusion difficult for making a practical and economic form of power station.
It provides extremely high temperatures which are difficult to achieve, and its difficult to safely manage extremely hot gases produced, it is also expensive. Scientists believe its worth trying though as the ocean provide limitless amounts of hydrogen isotopes needed for nuclear fusion.
Explain the alpha particle scattering experiment
Beams of alpha particles were aimed at thin gold foil, particles scattered from the foil.
Some particles were deflected by the gold foil, a few alpha particles were bounced back from the gold foil and MOST alpha particles went straight through the foil without deflection
What was the alpha particle scattering experiment carried out in
A vacuum so that deflection of the alpha particles must have been due to the gold foil
What does a control rod do
Controls speed of reaction
What does a reactor do
Reduces number of neutrons entering at a given point
