Unit 3.5 - Nuclear Decay Flashcards
What may radioactive substances do?
Emit one or more of 3 kinds of radiations
3 kinds of radiations
Alpha particles
Beta particles
Gamma rays
Alpha particles:
Symbol
Nature
Consists of
Charge
Mass
Penetrating power
Ionising power
a or He
Particle
2p+ and 2n
+2
4u
Least penetrating : stopped by a thin sheet of paper or 5cm of air at atmospheric pressure
Most ionising
Beta particles:
Symbol
Nature
Consists of
Charge
Mass
Penetrating power
Ionising power
B or e-
Particle
1e-
-1
0.0005u
More penetrating than alpha particles: can travel through a 3mm aluminium sheet or 1m of atmospheric air
Less ionising than alpha particles
Gamma rays:
Symbol
Nature
Consists of
Charge
Mass
Penetrating power
Ionising power
(Photon symbol)
Em radiation
Magnetic field + electric field
No charge
No mass
Most penetrating: passes through several cm of lead or more than 1m of concrete
Least ionising
Describe the wavelengths of gamma rays
Much shorter than that of light
Describe the speeds or alpha and beta radiation and explain
Similar speeds
About the same as the speed of light
Which type of radiation is safest outside of the body?
Alpha
Which type of radiation is safest inside the body?
Gamma
Which type of radiation is the most dangerous inside and outside of the body?
Beta
What type of process is radioactive decay?
Nuclear (not chemical!)
What does the fact that radioactive decay is a nuclear process, not a chemical process, mean?
It’s independent of temperature, pressure, whether it’s ionised e.t.c.
Force that regulates radioactive decay
Weak force
How can we differentiate between the different types of radiations and why does this work?
Using a magnetic field
Since all radiations have a different charge (positive, negative and no charge)
What does moving charge in a magnetic field experience?
A force
Example of moving charge in a magnetic field experiencing a force
Electrons in the coil of a motor
Why will all of the types of radiation bet effected differently by a magnetic field?
Due to charge differences
What happens to gamma radiation In a magnetic field and why?
Undeflected
Has no charge
Which type of radiation has a less severe deflection in a magnetic field and why?
Alpha
Heavier
Which type of radiation has the most severe deflection in a magnetic field and why?
Beta
Negative charge and lightest
What are the relative penetrating powers of radiations due to?
The way they interact with matter
What happens when alpha, beta or gamma radiation passes through matter?
It tends to knock electrons out of the atoms, ionising them
What’s another type of radiation?
Positron emission
What’s another type of radiation that causes ionisation?
X-rays
Ionising radiation
When radiation passes through matter, it knocks electrons out of the atoms, ionising them
Why are alpha particles strongly ionising?
Large
Relatively slow moving
Carry 2 positive charges
Why are gamma rays weakly ionising?
Electromagnetic waves
Carry no charge
Ionising power of beta particles
Falls between alpha particles and gamma radiation in ionising power
Which energy transfer occurs during ionisation?
Form the radiation passing through the matter to the matter itself
Why are alpha particles the least penetrating of the 3 radiations?
The transfer of energy from the radiation to the matter itself happens most avidly in the case of alpha particles since they are the most strongly ionising, and this is why alpha particles are the least penetrating of the three radiations.
Why are gamma rays the most penetrating type of radiation?
They transfer energy from the radiation to the matter less rapidly as they’re weakly ionising
Methods used to detect ionising particles
Spark counter
Cloud chamber
What does a spark counter do?
Counts ionisation of the air caused by alpha radiation (or a match)
Describe how a spark counter works
Alpha particle ionises air particles between the gap, which is accelerated upwards and causes a cascade of ions hitting each other = a spark
Each ionisation particle coming in causes its own spark
What happens within a cloud chamber?
Radioactive sources leave trails as they streak through the saturated vapour
Describe what happens in a cloud chamber
Ionising particles ionise the air as they travel though, ripping electrons from the particles’ outer shells = ionise them
When the particle is ionised, the alcohol is drawn towards it and forms the track in the cloud chamber
Why are alpha particles stopped much more easily than beta particles with the same energy, yet alpha particles are much more massive than beta particles?
Alpha particles…
-move much slower
-have double the charge
= cause much more ionisation than beta particles
Most ionising, leat penetrating
Under which conditions does ionising ration travel further? Why?
If the pressure is reduced
Fewer molecules to interact with
What happens to ionising radiation if the pressure is reduced and why?
Travels further
Fewer molecules to interact with
Working out the range of a particle
Initial energy
———————
KE lost per collision x collisions per cm
=answer in cm
What has the highest range, alpha or beta particles? Why?
Beta particles
Alpha particles can’t travel through more than 5cm of air
When does radioactive decay occur?
When an unstable nucleus emits alpha, beta or gamma radiation in order to become more stable
Why does radioactive decay result in a reduction of the energy of a nucleus?
During the process, the radiation carries away energy as it is emitted from the nucleus, resulting in a reduction of the energy of the nucleus
What do alpha particles consist of?
2 protons, 2 neutrons
= helium Nuclei
When does the emission of an alpha particle occur?
When a nucleus ejects 2 protons and 2 neutrons
What happens to the original nucleus when it emits an alpha particle?
Reduces its nucleon number by 4
Reduces its proton (or atomic) number by 2
Another word for proton number
Atomic number
Name for when a new chemical element is formed
The original element has transmuted
What is a beta particle?
A high energy electron