Radioactivity Flashcards
The nuclei of radioactive substances are ………..
Unstable
How do radioactive substances become stable
Radioactive decay
What do radioactive substances do during radioactive decay?
They emit radiation and turn into other elements
Can we predict when an unstable nuclei will decay?
No, it is a random process and is not affected by external conditions
What is background radiation?
Radiation from radioactive substances in the environment, from space, from devises such as x-Ray’s which is around us all the time
Why did the model of the atom become know as the plum pudding model?
At the time scientists thought that atoms consisted of spheres of positive charge which electrons stuck into them, like plums in a pudding
What did the alpha scattering experiment consist of?
Rutherford, Geiger and mars den fired alpha particles at thin gold foil
Most of the alpha particles passed straight through the foil what does this mean about the atom?
Most of the atom is just empty space
Some of the alpha particles were deflected through small angles what does this tell us about the nucleus?
It has a positive charge
A frpew alpha particles rebound through very large angles what does this suggest about the nucleus?
It has a large mass and a very large positive charge
What did the alpha particle scattering experiment suggest about the structure of the nucleus?
It is where most of the mass of the atom is concentrated, very small and positive,y charged
What change occurs in the nucleus in alpha decay?
The nucleus loses 2 protons and 2 neutrons
What particles are emitted in alpha decay
2 protons & 2 neutrons as an α particle
What change in the nucleus occurs in beta decay?
A neutron in the nucleus changes into a proton and an electron
What particles is emitted in beta decay?
The electron created in the nucleus is instantly emitted
Give the relative mass of a proton, neutron and electron
P - 1
N - 1
E - 0.0005
What are the relative charges of protons neutrons and electrons
P - +1
N- 0
E -1
Why does an atom have no overall charge?
They have the same no of protons and electrons
When does an atom become an ion?
When it loses or gains electrons and becomes charged
All atoms of a particular element have the same number of ………..
Protons
What is an isotope?
An atom of the same element with different numbers of neutrons
What is the atomic number?
The number of protons in an atom
What is the mass number?
The total number of protons plus neutrons
What does an alpha particle consist of?
2protons
2 neutrons
What is the relative mass of an alpha particle?
4
What is the relative charge of an alpha particle?
+2
When a nucleus emits an alpha particle the ………. number goes down by …… And the ……… Number goes down by …….
Atomic
2
Mass
4
What does the nucleus contain?
Protons, neutrons and electrons
What is a beta particle?
A high speed electron from the nucleus emitted when a neutron in the nucleus changes to a proton and an electron
What is the relative mass of a beta particle?
0
What is the relative charge of a beta particle?
-1
In beta decay the …….. Stays in the nucleus so the …….. Number goes up by …… And the …….. Number is …………… The …….. Is instantly emitted
Proton Atomic 1 Mass number unchanged Electron
What happens when a nucleus emits gamma radiation?
There is no change in the atomic or mass number
A ……… Ray is an …………… Wave released from the ………… It has no …….. And no ………. Mass
Gamma Electromagnetic Nucleus Charge Mass
What will happen when nuclear radiation passes through a material?
It will collide with the atoms, knocking of electrons and creating ions (ionisation)
What can ionisation do to a living cell?
Damage or kill the cell
What are alpha particles strongly ionising
They are relatively large so have lots of collisions with atoms
Why will an alpha particle not penetrate a material very far?
As it is strongly ionising
What can alpha particles be stopped by
Thin paper, human skin or few cm of air
are alpha particles deflected by electric and magnetic firlds?
They have a positive charge so are deflected
What are beta particles like compared to alpha?
Beta particles are much smaller and faster than alphas so they are less ionising but penetrate further
What are beta particles stopped by?
Few m of air, thin sheet of aluminium
Are beta particles affected by a magnetic or electric field?
They have a negative charge so are deflected in the opposite direction to alpha
Gamma rays are electromagnetic waves so will travel a ……. Way before ……. With ……..
Long
Colliding
Atoms
Gamma days are….
Weakly ionising and very penetrating
What will absorb gamma radiation?
Several metres of concrete
Or cm of lead
Are gamma rays deflected by electric or magnetic fields
No
What happens to the count rate of a radioactive sample over time?
Decreases
What is the half life?
The time is takes for the number of unstable nuclei in a sample to halve
Or
The time taken for the count rate from the original isotope to fall to half its initial value
Th half life is the ……. for any sample of a particular ………
Same
Isotope
What would happen to the original count rate of a radioactive sample after two half lives have passed?
It will have decreased to one quatre of the original value
What are alpha sources used for?
In smoke alarms
What half life will an alpha source need for a smoke alarm?
A few years
What are beta sources used for?
Thickness monitoring
Why is beta radiation used for thickness monitoring?
Alpha particles would be stopped by the thin paper and gamma rays would pass through and be unable to detect small changes in thickness
What sort of half life will a beta source for thickness monitoring need?
Many years so that decreases in count rate are due to changes in the thickness of the paper
What are gamma and beta sources used as?
Tracers in medicine
What half life will of a gamma or beta tracer need to be?
A half life of a few hours ago that the patient is not exposed to unnecessary radiation
What is radioactive dating used for
Used to find the age of ancient material
What is carbon dating used for.
To find the age of wood and other organic material
What is used to find the age of igneous rocks
Uranium
