8. Radioactivity Flashcards
Relative mass of a proton
1
Relative mass is the mass compared with that of a …
Proton
Relative charge of a proton
+1
Location of a proton
Within the nucleus
Relative mass of a neutron
1
Relative charge of a neutron
0
Location of a neutron
Within the nucleus
Relative mass of an electron
1/1840
Relative charge of an electron
-1
Location of an electron
In circular shells orbiting the nucleus
All nuclei, except the … nucleus, contain both protons and neutrons
hydrogen
Name the three types of radiation and their symbols
Alpha (a), beta (ß) and gamma (γ)
Radiation is emitted from the nuclei of heavy atoms. What is a heavy atom?
A heavy atom has a nucleus containing a large number of protons and neutrons and its nucleus is unstable.
What happens to an unstable nucleus?
It decays and emits radiation.
All types of radiation originate from an …
Unstable nucleus
Nature of alpha radiation
Particle
Nature of beta radiation
Particle
Nature of gamma radiation
Wave
Relative charge of alpha radiation
+2
Relative charge of beta radiation
-1
Relative charge of gamma radiation
Uncharged
Relative mass of alpha radiation
4
Relative mass of beta radiation
1/1840
Relative mass of gamma radiation
Zero
Identity of alpha radiation
Helium nucleus consisting of two protons and two neutrons
Identity of beta radiation
Fast moving electron
Identity of gamma radiation
Electromagnetic wave of high energy
Ionising power of alpha radiation
Enormous
Ionising power of beta radiation
Moderate
Ionising power of gamma radiation
Poor
Penetrating ability of alpha radiation
Stopped by 2-4 cm of air or thin tissue paper
Penetrating ability of beta radiation
Stopped by several metres of air or about 5 mm of aluminium
Penetrating ability of gamma radiation
Thick lead is an effective shield but cannot stop the radiation completely
Describe the plum pudding model of the atom
The atom consisted of negatively charged electrons embedded in a uniform, positively charged sphere like currants in a bun, in sufficient numbers to make the atom as a whole electrically neutral.
How did Rutherford detect the alpha particles during his alpha particle scattering experiment?
The alpha particles were detected by flashes of light that they produced when they hit a glass screen coated with zinc sulphide.
Why was the alpha particle scattering experiment carried out in a vacuum?
To prevent collisions between alpha particles and air atoms
What does the alpha particle scattering experiment serve as evidence for?
The existence of nuclei
What did Rutherford’s alpha particle scattering experiment involve?
Rutherford fired positively charged alpha particles from an alpha source at a positively charged thin gold foil inside a vacuum.
He set up a glass screen coated with zinc sulphide and a microscope to detect when alpha particles hit it, producing a flash of light.
Describe the observations of the alpha particle scattering experiment
- Most alpha particles were undeflected by the gold foil
- Some alpha particles were scattered through large angles
- About 1 in 8000 alpha particles were back-scattered through very large angles.
Because most of the alpha particles missed the nucleus, it had to be …
Very small
Since the nucleus appeared to repel the positively charged alpha particles, it had to be …
Positively charged, since like charges repel
Why did most of the alpha particles pass straight through the atom during the alpha particle scattering experiment?
Rutherford correctly argued that most of the atom is just empty space.
What did Rutherford realise because of the fact that the electron was so light?
Most of the atom’s mass was contained within the nucleus itself.
How did Rutherford explain why certain elements would give out light?
Rutherford suggested that the electrons orbited the nucleus in circular paths.
What did Rutherford find the negative charge to be?
A cloud of electrons surrounding the positive nucleus
Rutherford’s alpha particle scattering experiment lead to the abandonment of the …
Plum pudding model
The model of the atom accepted by physicists today is the …
Rutherford-Bohr model
Define a nucleon
A proton or neutron
The value of A is …
The relative mass of the nucleus compared to the proton
Z gives the number of …
Protons within the nucleus and hence the charge of the nucleus.
Notation:
A =
Z =
X =
A = mass number
Z = atomic number
X = chemical symbol of the element
For A
X
ZSymbol for a beta particle
0
e
-1
Symbol for a proton
1
p
1
Symbol for a neutron
1
n
0
Symbol for an alpha particle
4 a 2 Or 4 He 2
Define isotopes
Isotopes are atoms of an element with the same atomic number but different mass numbers indicating a different number of neutrons
Isotopes are caused by different numbers of … but same numbers of protons, the latter meaning it is the same element
neutrons
What is the number in Uranium-235?
The mass number
In a nuclear disintegration equation, the mass numbers and the atomic numbers on both sides must …
Balance
An * in a nuclear disintegration equation indicates that an element …
Is in an excited state
The new element formed in a nuclear disintegration equation is called the …
Daughter nucleus
When writing a gamma ray symbol in a nuclear disintegration equation, you write it without …
Numbers, as they have neither mass nor charge
Name a nuclear radiation detector and state briefly how it works
Geiger-Müller (GM) tube connected to a counter, which detects and measures radiation in counts per minute
Define background radiation
Background radiation is radiation from natural sources all around us, for example from the human body
Actual count rate =
Measured count rate - background activity
Define an ion
An electrically charged particle obtained from an atom by adding or removed electrons
Define ionisation
The process of changing a neutral atom into an ion
How does ionisation happen?
Ionising radiation passes through an atom and knocks an electron out of orbit around the positive nucleus, forming a positive ion.
Alpha particles, beta particles and gamma rays are called …
Ionising radiations - because they can remove orbiting oelectrons from atoms as they collide with them, leaving behind a positive ion
Explain how ionising ability is related to penetrating ability.
Highly ionising radiation loses energy rapidly and will therefore have less penetrating ability.
Weakly ionising radiation interacts little with matter and will therefore be very penetrating.
Explain why alpha, beta and gamma are dangerous ionising radiations.
They can disrupt the DNA contained within cells and cause cancer.
State safety precautions for using radioactive materials
- Radioactive sources should be stored in a lead-lined box in a locked cabinet
- Experiments with radioactive sources should be done as quickly as possible to minimise exposure to radiation
- Individual sources should be handled with forceps at arm’s length
- Students under 16 years old should never handle radioactive sources at all.
Define half life
The time taken for the activity of a radioactive material to fall to half of its original value
The activity of a radioactive material is measured in …
Becquerels (Bq), where 1 Bq means 1 disintegration per second
Give two uses of radiation in industry
Controlling the thickness of steel in rolling mills and detecting leaks in underground pipes
Why must a radioactive tracer used to detect leaks underground in pipes have a short half life?
To ensure that the source quickly disappears from the soil
Give a use of gamma radiation
Sterilisation of surgical instruments
