P2.6 Radioactivity Flashcards
When was the plum pudding model invented?
1987
What charge does the pudding represent in the plum pudding model?
Positive
What charge do the plums represent in the plum pudding model?
Negative
What do most particles do when faced with a sheet of foil? What does this mean?
Most go whizzing straight through the foil undeflected
This means most of an atom is empty space
What do some alpha particles do when faced with foil? What do this mean?
Some are slightly defected
This means that there’s concentrated positive mass somewhere in the atom
What do a very small amount of particles do when faced with foil? What does this mean?
Deflected backwards
This means that the concentrated mass is minuscule compared to the size of the rest of the atom, but contains most of the mass
What’s the composition of alpha radiation?
2 protons and 2 neutrons
Biggest mass of all radiation
What’s the charge of alpha radiation?
+2
What’s the penetration of alpha radiation?
Stopped by a few cm of air or by a piece of paper
What is an alpha particle also referred to as?
A helium nucleus
What’s the composition of a beta particle?
It’s an electron
In a nucleus a neutron turns into a proton inside and gives off an electron (beta)
What’s the charge of a beta particle?
-1
What’s the penetration of beta radiation?
Can be stopped by a thin sheet of aluminium
Can get through your skin
What’s the composition of gamma?
High energy electromagnetic wave
What’s the charge of gamma?
0
What’s the penetration of gamma?
Can only be stopped by a very thick piece of lead or concrete
How fast is gamma?
Travels at the speed of light like all EM waves
3x10 to the 8 m/s
Radioactivity is a ________ process.
Random
How are alpha, beta and gamma deflected at electric fields?
Alpha and beta particles are deflected I’m opposite direction due to their opposite charges.
Due to their much larger mass alpha particles are deflected much less than beta.
Gamma rays are not deflected because they are not charged.
How are alpha, beta and gamma deflected at magnetic fields?
Alpha and beta particles are deflected in opposite directions due to their opposite charges.
Due to their much larger mass alpha particles are deflected far less than beta.
Gamma rays are not deflected because they’re not charged.
What’s ionisation?
It occurs when an atom loses or gains one or more electrons.
When an atom loses an electron, it becomes a positive ion. When an atom gains an electron, it becomes a negative ion.
How ionising is alpha? Why?
Strongly ionising
Because it has a very large mass
How ionising is beta?
Moderately ionising
How ionising is gamma?
Weakly ionising
What’s an isotope of an element?
It has the same number of protons but a different number of neutrons.
Where does radiation come from?
The nucleus
What happens to the atomic number and mass number during alpha decay?
Atomic number: down by 2
Mass number: down by 4
What happens to the atomic number and mass number during beta decay?
Atomic no. Up by 1
Mass no. No change
What happens to the atomic number and mass number during gamma decay?
Atomic number: no change
Mass number: no change
Practise alpha, beta and gamma decay!!!
03/03/17
👏🏽👏🏽👏🏽👏🏽☺️
What is a substance of it is radioactive?
Unstable
The nucleus is more _______ after emitting some radiation and this is ___________.
Stable
Radioactive decay
Radioactive decay is not affected by what?
Temperature or any other physical conditions
Eg. If you put radiation in a cool area it WON’T slow down
ITS THE SAME IN ALL PHYSICAL CONDITIONS
What radiations are dangerous outside the body?
Beta and gamma because they can get through skin
Alpha can’t get through skin
What radiation is dangerous inside the body?
Alpha because it can’t get through your skin so once you’ve consumed it, it can’t get out and it’s the most ionising.
What radiations are the most, least and medium penetrating?
Alpha - least
Beta - medium
Gamma - most
What radiations have the longest, shortest, medium range of radiation?
Alpha - shortest
Beta - medium
Gamma - longest
Which radiations are affected by a magnetic field?
Alpha - YES
Beta - YES
Gamma - NO
What safety precautions do you have to take when dealing with radiation?
Keep exposure times as short as possible
Monitor exposure with a film dose badge
Label radioactivity sources clearly
Store radioactive sources in shielded containers (made of lead)
Wear protective clothing
Use tongs or a robotic arm to handle radioactive materials
What’s half-life?
The time it takes the number of radioactive nuclei in a sample to decrease by 50%
How would you calculate half life on a graph?
Half the counts of the y axis and then go along to the curve and down to the time.
At 10am a radioactive sample contains 80g of a radioactive isotope. If the isotope has a half life of 20 mins, calculate the mass of the isotope remaining at 11am.
1hour = 3 half lives Half 80 three times 80/2 = 40 40/2 = 20 20/2 = 10
= 10g
Calculate the half life of the radioactive isotope in a source of its mass decreases fro, 24g to 6g over a period of 60 days.
24 X 0.5 = 12
12 X 0.5 = 6
2 half lives in 60 days
Therefore 1 half life is 30 days
How does smoke alarms used radiation?
They contains a weak source of alpha radiation. The alpha particles ionise the air and create a current. If there is smoke present, it blocks the ions and so there is less current and then the alarm sounds. Beta and gamma aren’t affected by smoke so alpha needs to be used. A long half life source must be used or else a drop in current would set off the alarm.
How do paper mills use radiation?
Beta radiation monitors and controls the thickness in paper. The thicker the material, the more radiation absorbed and less radiation reaches the detector. It then sends signals to the equipment that adjusts the thickness of the material. Beta is used because alpha doesn’t go through paper and all of gamma would go through. A long half life source must be used or else a false thickness increase will be detected as the activity of the source decreases.
How do people use radiation to detect leaks in pipes?
A radioactive tracer is added to a fluid. Where a leak occurs will be shown by an increase in the count rate detected. Beta radiation is used. Alpha wouldn’t be able to pass through the ground. Gamma wouldn’t be able to detect a leak. The source needs a long enough half life to remain reasonably active over a period of investigation but not too long that it remains in the environment.
How is radiation used in radiotherapy?
Cancer cells are targeted with gamma radiation which kills them. But it can be dangerous because radiation can’t tell healthy and unhealthy cells apart.
How is radiation used in sterilisation?
Gamma radiation kills microorganisms on objects which means plastic can be cleaned with radiation rather than heating it.
How is radiation used in food?
Gamma radiation kills the microorganisms in your food. All rays go straight through so is harmless. This also increase shelf life.
How is radiation used in medical tracers in diagnosis?
A gamma camera can show where a patient has absorbed a tiny amount of radioactive substance.
Overall, how is alpha, beta and gamma radiation used?
Alpha - smoke alarms
Beta - paper mills and leak detection in pipes
Gamma - sterilising medical equipment, radiotherapy, killing bacteria in food
What’s radioactive dating?
Carbon-14 is a radioactive isotope of carbon. We all have a certain amount in us. You can find out how old someone is by knowing the amount of Carbon-14 in them. The older you are, the less you have.
What’s used to date fossils?
Uranium
A fresh bone gives a radioactive count of 170 counts per minute. Another ancient bone of the same mass gives a count rate of 50 counts per minute. The background count is 10 counts per minute. How old is the bone? Carbon-14 has a half life of 5600 years
170-10 = 160 50-10 = 40 The count rate of carbon-14 has fallen to 1/4 of its original value 160/2=80 80/2=40 2 half lives 5600 X 2 = 11200 years old
What’s the half life of carbon-14?
5600 years
What are the natural background radiations? What percentage is that?
Radon gas Food Cosmic rays Gamma rays 87%
What background radiations are man made? What percentage are they?
Medical
Nuclear power
13%
How many counts per minute would you have in earths atmosphere?
30-40 counts per minute
