Define the alpha-particle scattering experiment .

The alpha-particle scattering experiment was Rutherford's experiment in which alpha particles were fired at thin gold foil, with a detector recording the deflection of particles at various angles, used to determine the structure of the atom.

What did the observation that most alpha particles passed straight through the gold foil suggest?

It suggested that the atom is mainly empty space .

What did the observation that some alpha particles deflected through small angles (less than 10°) suggest?

It suggested there is a positive nucleus at the centre of the atom, since two positive charges repel.

What did the observation that a small number of alpha particles deflected straight back at angles greater than 90° suggest?

It suggested the nucleus is extremely small , and that the mass and charge of the atom are concentrated there.

In the alpha-particle scattering experiment, alpha particles were fired at a thin .......... foil.

In the alpha-particle scattering experiment, alpha particles were fired at a thin gold foil.

True or False? The alpha-particle scattering experiment showed that the positive charge of an atom is spread evenly throughout its volume.

False. The experiment showed that the positive charge is concentrated in a small, dense nucleus , not spread evenly (which the earlier 'plum pudding' model had assumed).

State the relative charge and relative mass of a proton .

Relative charge: +1 Relative mass: 1

State the relative charge and relative mass of a neutron .

Relative charge: 0 Relative mass: 1

State the relative charge and relative mass of an electron .

Relative charge: -1 Relative mass: 1/2000 (negligible)

Define an antimatter particle .

An antimatter particle is identical to its matter counterpart but with the opposite charge.

What is the antimatter counterpart of a proton , and what is its charge?

The anti-proton , with a charge of -1 .

The atomic mass unit ( u ) is approximately equal to the mass of what?

The mass of one proton or neutron .

One atomic mass unit ( u ) is defined as 1/12 of the mass of a .......... atom.

One atomic mass unit ( u ) is defined as 1/12 of the mass of a carbon-12 atom.

True or False? Most of the mass of an atom is due to its electrons.

False. Electrons have negligible mass (about 1/2000 of a proton or neutron); most of an atom's mass comes from the protons and neutrons in the nucleus.

Define the nucleon number (mass number).

The nucleon number is the total number of protons and neutrons in the nucleus of an atom.

Define the proton number (atomic number).

The proton number is the number of protons in the nucleus of an atom. In a neutral atom, it is also equal to the number of electrons.

How do you calculate the number of neutrons in an atom, given its nucleon number and proton number?

Number of neutrons = nucleon number ( A ) − proton number ( Z )

An isotope is an atom (of the same element) that has an equal number of protons but a different number of neutrons.

Why are isotopes generally unstable?

Because they have an imbalance of neutrons and protons, so they constantly decay and emit radiation to reach a more stable form.

True or False? Isotopes of an element have a different number of protons.

False. Isotopes have the same number of protons (they are the same element) but a different number of neutrons.

Define an alpha (α) particle .

An alpha particle is a high energy particle made up of 2 protons and 2 neutrons (the same as a helium nucleus), usually emitted from nuclei that are too large.

Why are alpha particles strongly ionising but weakly penetrating?

Alpha particles have a large charge (+2 e ), so they interact strongly with matter (highly ionising). This means they lose energy quickly and cannot travel far, so they are weakly penetrating and can be blocked by skin or a sheet of paper.

What is the difference between a β⁻ particle and a β⁺ particle?

A β⁻ particle is a high energy electron, emitted by nuclei with too many neutrons. A β⁺ particle is a high energy positron, emitted by nuclei with too many protons.

Define a gamma (γ) ray .

A gamma ray is a high energy electromagnetic wave, emitted by a nucleus that needs to lose energy.

Beta particles are moderately penetrating and can be stopped by a few millimetres of .......... .

Beta particles are moderately penetrating and can be stopped by a few millimetres of aluminium .

True or False? Gamma rays are the most ionising type of radiation.

False. Alpha particles are the most strongly ionising, due to their large +2 e charge; gamma rays are the least ionising of the three.

State the approximate range in air of alpha particles compared with beta particles.

Alpha : a few cm in air Beta : around 20 cm to 3 m in air, depending on energy

Define an electron neutrino .

An electron neutrino is a subatomic particle with no charge and negligible mass, emitted from the nucleus (produced during β+ decay).

What are the changes in proton number and nucleon number when a nucleus emits an alpha particle?

Proton number decreases by 2 Nucleon number decreases by 4

What are the changes in proton number and nucleon number when a nucleus emits a β⁻ particle?

Proton number increases by 1 Nucleon number stays the same

What are the changes in proton number and nucleon number when a nucleus emits a β⁺ particle?

Proton number decreases by 1 Nucleon number stays the same

In β⁻ decay, a .......... in the nucleus turns into a proton, emitting an electron and an anti-electron neutrino.

In β⁻ decay, a neutron in the nucleus turns into a proton, emitting an electron and an anti-electron neutrino.

True or False? A neutrino carries an electric charge.

False. Electron neutrinos (and antineutrinos) are uncharged , with negligible mass.

Why do beta particles have a continuous range of kinetic energies, unlike alpha particles which have discrete energies?

The energy released in beta decay is shared between the beta particle and the neutrino (or antineutrino) in varying proportions, giving a continuous range of energies.

A LevelPhysicsCambridge (CIE)Flashcards11. Particle PhysicsAtoms, Nuclei & Radiation

Atoms, Nuclei & Radiation (Cambridge (CIE) A Level Physics): Flashcards

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Define the alpha-particle scattering experiment.

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Define the alpha-particle scattering experiment.
The alpha-particle scattering experiment was Rutherford's experiment in which alpha particles were fired at thin gold foil, with a detector recording the deflection of particles at various angles, used to determine the structure of the atom.
What did the observation that most alpha particles passed straight through the gold foil suggest?
It suggested that the atom is mainly empty space.
What did the observation that some alpha particles deflected through small angles (less than 10°) suggest?
It suggested there is a positive nucleus at the centre of the atom, since two positive charges repel.
What did the observation that a small number of alpha particles deflected straight back at angles greater than 90° suggest?
It suggested the nucleus is extremely small, and that the mass and charge of the atom are concentrated there.
In the alpha-particle scattering experiment, alpha particles were fired at a thin .......... foil.
In the alpha-particle scattering experiment, alpha particles were fired at a thin gold foil.
True or False?
The alpha-particle scattering experiment showed that the positive charge of an atom is spread evenly throughout its volume.
False.
The experiment showed that the positive charge is concentrated in a small, dense nucleus, not spread evenly (which the earlier 'plum pudding' model had assumed).
According to the conclusions of the alpha-particle scattering experiment, roughly how much larger is an atom than its nucleus?
Roughly 100,000 times larger.
State the relative charge and relative mass of a proton.
Relative charge: +1
Relative mass: 1
State the relative charge and relative mass of a neutron.
Relative charge: 0
Relative mass: 1
State the relative charge and relative mass of an electron.
Relative charge: -1
Relative mass: 1/2000 (negligible)
Define an antimatter particle.
An antimatter particle is identical to its matter counterpart but with the opposite charge.
What is the antimatter counterpart of a proton, and what is its charge?
The anti-proton, with a charge of -1.
The atomic mass unit (u) is approximately equal to the mass of what?
The mass of one proton or neutron.
One atomic mass unit (u) is defined as 1/12 of the mass of a .......... atom.
One atomic mass unit (u) is defined as 1/12 of the mass of a carbon-12 atom.
True or False?
Most of the mass of an atom is due to its electrons.
False.
Electrons have negligible mass (about 1/2000 of a proton or neutron); most of an atom's mass comes from the protons and neutrons in the nucleus.
Define the nucleon number (mass number).
The nucleon number is the total number of protons and neutrons in the nucleus of an atom.
Define the proton number (atomic number).
The proton number is the number of protons in the nucleus of an atom. In a neutral atom, it is also equal to the number of electrons.
How do you calculate the number of neutrons in an atom, given its nucleon number and proton number?
Number of neutrons = nucleon number (A) − proton number (Z)
Define an isotope.
An isotope is an atom (of the same element) that has an equal number of protons but a different number of neutrons.
Why are isotopes generally unstable?
Because they have an imbalance of neutrons and protons, so they constantly decay and emit radiation to reach a more stable form.
In $_Z^{A} X$ notation, A represents the .......... number and Z represents the proton number.
In $_Z^{A} X$ notation, A represents the nucleon number and Z represents the proton number.
True or False?
Isotopes of an element have a different number of protons.
False.
Isotopes have the same number of protons (they are the same element) but a different number of neutrons.
Define an alpha (α) particle.
An alpha particle is a high energy particle made up of 2 protons and 2 neutrons (the same as a helium nucleus), usually emitted from nuclei that are too large.
Why are alpha particles strongly ionising but weakly penetrating?
Alpha particles have a large charge (+2e), so they interact strongly with matter (highly ionising). This means they lose energy quickly and cannot travel far, so they are weakly penetrating and can be blocked by skin or a sheet of paper.
What is the difference between a β⁻ particle and a β⁺ particle?
A β⁻ particle is a high energy electron, emitted by nuclei with too many neutrons.
A β⁺ particle is a high energy positron, emitted by nuclei with too many protons.
Define a gamma (γ) ray.
A gamma ray is a high energy electromagnetic wave, emitted by a nucleus that needs to lose energy.
Beta particles are moderately penetrating and can be stopped by a few millimetres of ...........
Beta particles are moderately penetrating and can be stopped by a few millimetres of aluminium.
True or False?
Gamma rays are the most ionising type of radiation.
False.
Alpha particles are the most strongly ionising, due to their large +2e charge; gamma rays are the least ionising of the three.
State the nuclide notation for an alpha particle, a β⁻ particle and a γ ray.
Alpha particle: $_2^{4} α$
β⁻ particle: $_{- 1}^{0} β$
γ ray: $_0^{0} γ$
State the approximate range in air of alpha particles compared with beta particles.
Alpha: a few cm in air
Beta: around 20 cm to 3 m in air, depending on energy
Define an electron neutrino.
An electron neutrino is a subatomic particle with no charge and negligible mass, emitted from the nucleus (produced during β+ decay).
Which particle is emitted during β⁻ decay: an electron neutrino or an electron antineutrino?
An electron antineutrino.
What are the changes in proton number and nucleon number when a nucleus emits an alpha particle?
Proton number decreases by 2
Nucleon number decreases by 4
What are the changes in proton number and nucleon number when a nucleus emits a β⁻ particle?
Proton number increases by 1
Nucleon number stays the same
What are the changes in proton number and nucleon number when a nucleus emits a β⁺ particle?
Proton number decreases by 1
Nucleon number stays the same
In β⁻ decay, a .......... in the nucleus turns into a proton, emitting an electron and an anti-electron neutrino.
In β⁻ decay, a neutron in the nucleus turns into a proton, emitting an electron and an anti-electron neutrino.
True or False?
A neutrino carries an electric charge.
False.
Electron neutrinos (and antineutrinos) are uncharged, with negligible mass.
Why do beta particles have a continuous range of kinetic energies, unlike alpha particles which have discrete energies?
The energy released in beta decay is shared between the beta particle and the neutrino (or antineutrino) in varying proportions, giving a continuous range of energies.

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