Physics - Half life Flashcards
What are daughter nuclei?
The nucleus of a new element formed from the decay of the starting parent nucleus.
What determines the time of half life of a radioactive atom?
the activity to halve
the number of parent nuclei to halve
the mass of the parent nuclei to halve
How can you model radioactive decay using coins?
Step one. Collect the coins and count them. This is the starting number of parent radioactive atoms. Record this number. Between 60 and 100 coins is a good starting number.
Step two. Put the coins into a container, shake them, and then throw them into a tray.
Step three. Remove coins showing heads. These represent atoms that have decayed.
Step four. Count the remaining coins and record the number in a table against the throw number.
Step five. Repeat steps two to four until only two or three coins remain.
Step six. Plot a graph of number of coins remaining (-axis) against throw number (-axis).
How can radioactivity be used in measuring the thickness of paper?
In a paper rolling mill, the thickness of the paper is monitored by how much beta radiation is received at the detector.
How can radioactivity be used in sterilizing medical instruments and prolonging the life of fruit?
Gamma radiation kills microbes and can be used to sterilize medical instruments and kill the bacteria on fruit and vegetables so they stay fresh longer.
How can radioactivity be used in smoke alarms?
An isotope of americium which emits alpha particles is used in smoke alarms. Alpha radiation ionises the air and this allows a small current to flow between two electrodes. Alpha is weakly penetrating so smoke stops it, the current drops and the alarm goes off.
How can radioactivity be used in blood and fluid tracers?
A tracer is something that shows how an object moves. Radioactive tracers are added to liquids to show if they are flowing correctly. They can show the movement of pollution, eg sewage or waste oil from factories. However, they are used mainly in medicine to monitor blood flow.
Technetium-99m, which is a gamma source with a short half-life of about six hours, is injected into blood. Arterial blockages or internal bleeds cause a build-up of radioactivity that can be easily detected outside the body. The same principle is used in leak detection of underground pipes. A leak will cause a buildup of radioactivity that can be detected above the ground.
How can radioactivity be used in cancer treatment?
Externally gamma radiation can be beamed at cancer cells to kill them. The gamma source used should have a long half-life to maintain the dose of radioactivity delivered to the tumour. A long half-life also means that the source in the radiotherapy equipment will not need changing regularly.
Internally an alpha source with a short half-life can be injected directly into the tumour. This is called targeted alpha therapy (TAT). Alpha is strongly ionising – so will kill the cancer cells. It is also weakly penetrating so stays within the tumour and doesn’t harm the healthy cells outside the tumour.
How can radioactivity be used in carbon 14 dating?
Living things, such as plants and animals, absorb carbon-14 daily. When we die, we no longer absorb carbon-14. Carbon-14 can be used to date organic objects up to about 100,000 years old. The isotope decay follows the usual decay curve.
Carbon-14 has a half-life of 5,730 years. If we find a dead plant or bone that has 25 % of the carbon-14 its living version would have had, we’d know that the fossil is 11,460 years old because two half-lives would have passed.
