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P7- Radioactivity - Coggle Diagram
P7- Radioactivity
Changes in the nucleus:
Radioactive decay, is where an unstable nucleus becomes more stable by emitting an alpha or beta particle of gamma ray.
Beta:
an electron created and emitted by a nucleus that has too many neutrons compared to protons. The relative mass is basically 0 and relative charge is -1. When an unstable nucleus emits a Beta particle the atomic number goes up by 1, the mass number stays the same.
Alpha: made up of two protons and two neutrons, relative mass of 4, relative charge of +2. 4/2 a. When an unstable nucleus emits an alpha particle, it's atomic number goes down by 2 and its mass number by fours.
Gamma:
A ray from the nucleus of an atom, it is uncharged and has no mass. It does not change the number of protons or neutrons in the nucleus.
Neutrons are emitted by some radioactive substances as a result of Alpha particles colliding with unstable nuclei in the substance. Such a collision causes the unstable nuclei to become even more unstable and emit a neutron.
Alpha, Beta and Gamma radiation
Penetrating power:
You can measure this with a Geiger counter, you:
- measure the count rate (the number of counts per second) without the radioactive source present. This is background count rate.
- measure the count rate with the source in place. Subtracting the background count rate from this gives you the count rate from the source alone.
You can test absorber materials.
Radioactivity dangers:
The radiation can knock electrons out of atoms. The atoms become charged because they lose electrons. The process is ionisation. When an object is exposed it is said to be irradiated.
Radioactive substances can contaminate other materials that they come into contact with. Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials.
Radiation in use:
Smoke alarms contain a radioactive isotope that send out alpha particles into a gap in a circuit in the alarm. The alpha particles ionise the air in the gap so there is a current across the gap. In a fire, smoke absorbs the alpha particles, preventing them from ionising the air, so the current across the gas drops and the alarm sounds.
Atoms and radiation:
Geiger counter:
Made up of a detector called a Geiger- muller tube this is connected to an electronic counter. This counter clicks each time a particle of radiation enters.
Activity and half-life:
The activity of a radioactive source is the number of unstable atoms in the source that decay per second. (Bq), which is 1 decay per second.
The average time taken for the count rate (and so the number of parent atoms) to fall by half is always the same. This time is called the half-life.
The half life of a radioactive isotope is the average time it takes:
For the number of nuclei of the isotope in a sample to halve.
For the count rate from the isotope in a sample to fall to half its initial value.
Random nature:
It is a random process, no one can predict exactly. However, you can predict how many atoms will decay in a given time. starting with 1000 atoms if 10% decay every hour then: 900,810 ....
Uses in medicine
Nuclear radiation is used in medicine to help doctors diagnose internal disorders in patients and to make patients well again. For each use, a radioactive isotope is needed that emits a specific type of radiation and has a suitable half-life.
- Radioactive tracers are used to trace the flow of a substance through an organ. The tracer contains a radioactive isotope that emits gamma radiation as it can be detected outside the system. For example, doctors use radioactive iodine to find out if a patients kidney is blocked.
Before the test, the patient drinks water containing a tiny amount of the radioactive substance. A detector is then placed against each kidney. Each detector is connected to a chart recorder.
• The radioactive substance flows in and out of a normal kidney. So the detector reading goes up and then down.
• For a blocked kidney the reading goes up and stays up. This is because the radioactive substance goes into the kidney but doesn't flow out again
Radioactive iodine is used because:
• It's half-life is eight days, so it lasts long enough for the test to be done, but decays almost completely after a few weeks.
• It emits gamma radiation, so it can be detected outside the body.
• It decays into a stable product.
Gamma cameras are used to take images of internal body organs. Before an image is taken, the patient is injected with a solution that contains gamma-emitting radioactive isotope. The solution is then absorbed by the organ, and a gamma camera detects the gamma radiation emitted solution. The gamma rays pass through the holes in the thick lead grid in front Of the detector. The detector only detects gamma rays from nuclei directly in front of it. The detector signals build an image as to where the radioactive isotope is located in the organ.
The radioactive isotope must be gamma emitter with a half-life long enough to give a useful image, but start enough so that its nuclei have mostly decayed after the image has been taken.
Gamma radiation in a narrow beam is used to destroy tumors, The radiation is emitted from a radioactive isotope of cobalt. It has a half-life of five years. Gamma radiation is used because it can penetrate deeper into the body than beta radiation and alpha radiation.
Radioactive implants are used to destroy cancer cells in some tumors or gamma-emitting isotopes are used in the form of small seeds or tiny rods. Permanent implants use isotopes with has-lives Iong enough to irradiate the tumor over a given time, but short enough so that most of the unstable nuclei will have decayed soon afterwards.
Everybody is exposed to background radiation, which is Ionising radiation from radioactive substances in the environment such as radon gas or other sources. F The risk to the general public is very small but workers who use ionising radiation need to reduce their exposure to the radiation by following certain rules. Each worker must also wear a personal radiation monitor, such as a film badge, while he or she is in at-risk areas.
Nuclear issues:
Background radiation can cause health issues, it also causes problems when using a Geiger counter as it can cause a false result.
Nuclear waste is left when fuel rods have been removed from decommissioned reactors. These rods have to be stored carefully to prevent the release of dangerous waste.
Chernobyl and Fukushima both represent nuclear accidents that have happened in recent history. Both accidents affected thousands of people across wide areas and reiterate for us the dangers of nuclear energy.
New nuclear reactors may be required within the next 20 years, these will come at a vast cost no doubt.
Half-lives correspond with instability, this is because a isotope with a half life of one second will have an unstable nuclei and will release a lot of radiation in a short time. Nuclei with longer half lives will release less radiation as it is spread out over a longer period of time.
Radioactive risks to living cells range from serious to minor. Obviously, the bigger the radiation dose the more dangerous it is but the threat can range dependent on the type of radiation, length of exposure and whether the source is inside or out of the body
Nuclear Fission and fusion:
Fission:
Energy is released in a nuclear reactor because of nuclear fission. In induced fission the nucleus of an atom causes the nucleus to split into two smaller fragment nuclei of a roughly equal size and to thus release several neutrons. Very rare it can happen without neutron being absorbed (spontaneous fission).
When a neutron under goes fission it releases:
two or three neutrons at high speeds
Energy, the form of gamma radiation.
Nuclear fusion:
Two small nuclei release energy when they are fused together to form a single large nucleus.
Some of the mass is converted to energy.
When two protons fuse together, they from a "heavy hydrogen" nucleus.
Two more protons collide seperately, with two nuclei and turn them into heavier nuclei.
The two heavier nuclei collide to form the helium nucleus.
The energy released at each stage can be stored.