Radioactivity

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Radioactivity

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??? ??????????????? (Radioactivity)
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Type of Radiation Alpha particle Beta particle Gamma ray
Symbol a b g(can look different,depends on the font)
Mass (atomic mass units) 4 1/2000 0
Charge 2 -1 0
Speed slow fast very fast (speed of light)
Ionising ability high medium 0
Penetrating power low medium high
Stopped by paper aluminium lead

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Nuclear Symbols for Subatomic Particles
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• ???????????????? (???????????????????????? 82
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Half-life
?????????? (half life) ?????????????????? ???????
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???????????????????? ???????????????? t1/2
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Half life
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????????? ? ??????
???????? ????????????? Tc-99 ????????????????
Tc-99 ????? 18 ?????????? 24 ??????? ??? Tc-99
???????????? 6 ???????
6 hrs.
12 hrs.
Tc-99 18 g
Tc-99 9 g
Tc-99 4.5 g
1 ??????????
2 ??????????
3 ??????????
18hrs.
24 hrs.
Tc-99 1.125 g
Tc-99 2.25 g
4 ??????????
?????????????????????? 24 ??????? ???? Tc-99
????????? 1.125 ????
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??????????? 2 ??????????????????????????????????
? 20 ???? ?????? 28 ??? ??????????????????????????
???? 1.25 ???? ??????????????????????????????????
??????????? 3 ?????????? I-131 ???????? ???????
I-131 ?????????????????????????? 40.5 ???
???????? ?????????? 0.125 ???? ?????????????
I-131 ??????? 8.1 ???
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??????????????? (Fission reaction) ???
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Fission reaction
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??????????????? (Fusion reaction) ???
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Fusion reaction
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Balancing Nuclear Equations

1. Conserve mass number (A).

The sum of protons plus neutrons in the products
must equal the sum of protons plus neutrons in
the reactants.
235 1 138 96 2 x 1

1. Conserve atomic number (Z) or nuclear charge.

The sum of nuclear charges in the products must
equal the sum of nuclear charges in the reactants.
92 0 55 37 2 x 0
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Nuclear equation
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Nuclear equation
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Nuclear equation
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?. 2714Si __________ 0-1e
?. 6629Cu __________ 0-1e
?. 2713Al 42He 3014Si __________
?. 166C 156C __________
?. 22689Ac 22688Ra __________
?. 22689Ac 22287Fr __________
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Geiger-Müller tube (GM tube)
???????????? ???????????????????????????????????
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?????????????????????????????????????? Ar
??????????????????????????????????? (Ar)
?????????? (e-) ?????????????????????????
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??????? Ar ???????? Ar
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Sources of ionizing radiation
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Pathways of strontium-90 from fallout
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Smoke Detectors
By Charlie, Laura, Katie, Nicky
Smoke alarms contain a weak source made of
Americium-241.Alpha particles are emitted from
here, which ionise the air, so that the air
conducts electricity and a small current flows.
If smoke enters the alarm, this absorbs the a
particles, the current reduces, and the alarm
sounds. Am-241 has a half-life of 460 years.
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Thickness Control
By George, Charlene, Naomi, Linnie
In paper mills, the thickness of the paper can be
controlled by measuring how much beta radiation
passes through the paper to a Geiger counter.
The counter controls the pressure of the rollers
to give the correct thickness. With paper, or
plastic, or aluminium foil, b rays are used,
because a will not go through the paper.We
choose a source with a long half-life so that it
does not need to be replaced often.
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Sterilising
By Joanna, Rhiann, Ella, Michela
Even after it has been packaged, gamma rays can be used to kill bacteria, mould and insects in food. This process prolongs the shelf-life of the food, but sometimes changes the taste. Gamma rays are also used to sterilise hospital equipment, especially plastic syringes that would be damaged if heated.
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Radioactive Dating
By Jon, Adam, Aaron, Ashley, Christie, Yvonne
Animals and plants have a known proportion of Carbon-14 (a radioisotope of Carbon) in their tissues. When they die they stop taking Carbon in, then the amount of Carbon-14 goes down at a known rate (Carbon-14 has a half-life of 5730 years). The age of the ancient organic materials can be found by measuring the amount of Carbon-14 that is left.
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Radioactive Tracers
By Ben, Dan, Adrian, Nick
The most common tracer is called Technetium-99 and is very safe because it only emits gamma rays and doesn't cause much ionisation. Radioisotopes can be used for medical purposes, such as checking for a blocked kidney. To do this a small amount of Iodine-123 is injected into the patient, after 5 minutes 2 Geiger counters are placed over the kidneys. Also radioisotopes are used in industry, to detect leaking pipes. To do this, a small amount is injected into the pipe. It is then detected with a GM counter above ground.
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Cancer Treatment
Because Gamma rays can kill living cells, they are used to kill cancer cells without having to resort to difficult surgery. This is called "Radiotherapy", and works because cancer cells can't repair themselves when damaged by gamma rays, as healthy cells can. It's vital to get the dose correct - too much and you'll damage too many healthy cells, too little and you won't stop the cancer from spreading in time.
Some cancers are easier to treat with
radiotherapy than others - it's not too difficult
to aim gamma rays at a breast tumour, but for
lung cancer it's much harder to avoid damaging
healthy cells. Also, lungs are more easily
damaged by gamma rays, therefore other treatments
may be used.
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PET (Positron Emission Tomography) And CT
(Computerized Tomography from X-rays)
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