Chapter 16~radioactivity Flashcards
Definitions, key ideas 💡 and formulae
What is an isotope?
Isotopes are nuclei of the same element with different numbers of neutrons but the same number of protons.
Explain the plum pudding 🍰 model
A model of an atom ⚛ in which negative charges are distributed throughout a sphere of positive charges. (positive pudding 🍰 with negative plums)
Describe the nuclear model of the atom :
A model of an atom in which negative charges (electrons) are distributed outside a tiny nucleus of positive charge.
5 details of the Rutherford experiment
- the alpha particle source was encased in metal with a small aperture, allowing a fine beam of alpha particles to emerge
- Done through a vacuum, so alpha particle is not absorbed by air
- Gold was chosen bec it could be made into a very thin sheet /foil
- The alpha particles were detected when they struck a solid ‘scintillating’ material. Each particle gave a tiny flash of light and these were counted
- The detector could be moved round to detect alpha particles scattered through different angles
From the alpha particle scattering experiment, Rutherford deduced 3 things (NB!!!)
- An alpha particle is deviated due to its repulsive force between the alpha particle and the positive charge in the atom ⚛
- Most alpha particles have little or no deviation - so most of the atom is empty space
- A very few alpha particles are deviated more than 90° - so most of the mass of an atom is concentrated in a small space (the nucleus) and most of the atom is empty space
Where are protons and neutrons situated?
The nucleus of the atom
Protons and neutrons are collectively called?
Nucleons
The total nucleon number in a nucleus is equal to?
The mass number, Ar
Definition of nucleon number or mass number:
The total number of protons and neutrons in the nucleus of an atom
What is the atomic number?
The total number of protons in the nucleus of an atom (also referred to as the proton number)
A (mass number) =
A = N (neutron number) + Z (proton number)
Definition of a nuclide :
A specific combination of protons and neutrons in a nucleus
Definition of a strong nuclear force :
A fundamental force which acts between hadrons
Sub-atomic particles are divided into 2 families, namely :
- HADRONS, such as protons and neutrons. These are particles affected by the strong nuclear force. ( h-heavy in mass)
- LEPTONS, such as electrons. These are particles that are unaffected by the strong nuclear force. (l - light in mass like e-‘s)
Definition of a quark :
The fundamental particles of which hadrons are made of.
can NOT be split further
Quark model of a proton :
uud
Two up quarks and one down quark.
(p are positive so you look more up than down)
The quark model for a neutron :
udd
-one up quark and two down quarks
The 4 types of radiation we learn in AS level :
- a-particle
- B^- particle
- B^+ particle
- Gamma ray
The symbol for an a-particle
a, He
Mass number =4
Proton number =2
Beta minus particle symbol
B^-, e
Mass number 1/1840 (relative to a proton, it is the mass of an electron)
Number of protons =0
Beta plus particle symbol
B^+, e^+
Mass number relative to a proton = 1/1840
Atomic number =0
Gamma ray symbol
Y
No mass or atomic number
Charge on all 4 radiations :
- a-particle = +2e
- B^-= - e
- B^+= +e
- Y= 0
Typical speeds of the 4 types of radiation :
- ‘slow’ 10^6 ms^-1
- ‘fast’ 10^8ms^-1
- ‘fast’ 10^8ms^-1
- ‘speed of light’ 3×10 ^8 ms^-1
What forms of radiation are particles of matter?
Alpha and beta radiation
What form of radiation is not a particle of matter and what is it?
Y-ray
It is a photon of electromagnetic radiation
Structure of an alpha particle
2 protons and 2 neutrons (helium-4)
What is a beta minus made of?
An electron
What is a beta plus particle made of (structure)
A positron
Definition of a neutrino : and its symbol
A lepton, released during beta plus decay.
Symbol : v
Definition of an antineutrino
And its symbol
A lepton released in beta minus decay.
Symbol: v with a line on top.
What is the equation for beta minus decay? Starting with 1,0n
Number written 1st represents the mass number
2nd represents the proton number
1, 0n ➡️1,1P + 0,-1e + antineutrino
Equation for beta plus decay starting with 1,1P
1,1P➡️1,0 n + 0,+1 e + v
Describe the process of ionisation :
When fast moving charged particles collide with or pass close to atoms, they may knock or drag electrons away from the atoms. In this process, the radiation loses some of its kinetic energy.
Order from most to least ionising radiation and the 3 main reasons why the most ionising radiation is the most.
Alpha (most), beta, Gamma (least)
Alpha is the most ionising because :
- It relatively large mass
- its charge is the greatest
- It travels the slowest
Mention the different penetrating abilities of the 3 radiations :
- Alpha-radiation is absorbed by a thin sheet of paper or a few centimetres of air
- Beta-radiation is absorbed by a few millimetres of metal
- Gamma is never completely absorbed but a few centimetres of lead, or several metres of concrete, greatly reduces its intensity.
Define the electronsvolt :
One electronvolt (1 eV) is the energy transferred when an electron travels through a potential difference of one volt
Nuclear decay occurs as a result of an….
Unstable nucleus
During nuclear decay 5 things are conserved :
on both sides of the equation
- Proton number
- Nucleon/mass number
- Momentum
- Mass - energy
- charge
Beta minus is called
An electron
Beta plus is called a
Positron
Gamma radiation will never occur alone, it will always only occur after
Alpha or beta radiation
Up quarks have the charge of?
+2/3
Down quarks have the charge of
-1/3
What are the 3 types of elementary particles :
- Quarks
- leptons
- bosons
*hadrons are Not bec they are made up of quarks
2 examples of hadrons :
- Proton
2. Neutron
Description of lepton and 2 examples
Lepton are fundamental particles. Therefore, they do NOT decay further.
Examples:
- neutrinos
- electrons
Quarks feel what force?
Strong nuclear force
Leptons feel what force?
Weak nuclear force
The 5 important facts of neutrinos and antineutrinos
- Are emitted by beta decay
- Beta decay from a particular nuclide produces a constant amount of energy (antineutrinos and neutrinos)
- However, the emitted beta particles emerge with a range of kinetic energies. Therefore, a neutrino, must be emitted with the remaining Ke
- Beta ➖ =antineutrino
Beta ➕ =neutrino
5.neutrinos are difficult to detect as the have nearly zero mass and no charge.
NB question of alpha scattering experiment:
The results of a-particle scattering experiment provide evidence for the structure of the atom
Result 1:
The vast majority of the a-particles pass straight through the metal foil / deviated by small angles.
Result 2:
A very small minority of a-particles are scattered through angles greater than 90°
State what may be inferred by the results :
- Most of the atom is empty space
2. The nucleus is positively charged and it is where the mass is concentrated.
