Chapter 7: Atomic and nuclear physics

Question 1

Describe a model of the atom that features a small nuclear surrounded by electrons

Answer 1

• electrons kept in orbit around the nucleus as a result of the electrostatic attraction between the electrons and the nucleus

Question 2

Evidence for that supported the nuclear model of the atom

Answer 2

Geiger Marsden/ Rutherford/ Gold-Foil experiment

Question 3

Outline one limitation of the simple model of the nuclear atom

Answer 3

• The problem in this theory was that acceleration changes are known to lose energy. If the orbiting electrons were to lose energy they would spiral into the nucleus. The Rutherford experiment cannot explain to us how atoms are stable.

Question 4

Outline evidence for the existance of atomic energy levels

Answer 4

Evidence is found in the emission and absorption spectra.

• Elements with enough energy can emit light by using either diffraction grating or a prism, it is possible to analyse the different colours within the given light.
• A continuous spectrum would mean that all frequencies of the electromagnetic spectrum are present - light from the sun contains all visible wavelengths of light.
• An emission spectrum is not continuous, but contains certain frequencies of light relative to the discrete energy levels present in the atom. Each possible combinations of drops in energy level emit differenr wavelengths of light enabiling us to deduce what element created that light

Question 5

Nuclide

Answer 5

a particular species of atoms whose nucleus contains a specified number of protons and neutrons

Question 6

Isotopes

Answer 6

atoms of the same element but have different atomic number (differ with the number of neutrons)

Question 7

Nucleons

Answer 7

Protons and neutrons

Question 8

Nucleon number (A)

Answer 8

mass number, number of protons and neutrons

Question 9

Proton number (Z)

Answer 9

atomic number, number of protons in the nucleus

Question 10

Neutron number (N)

Answer 10

Mass number, proton number, equal to the number of neutrons in the nucleus

Question 11

Describe the interactions in a nucleus

Answer 11

• Coulomb interactions between protons and the strong, short-rangesd nuclear interaction between the nucleons

Question 12

Natural radioactive decay

Answer 12

a random and spontaneous process in which an unstable nucleus emits a particle. (the element of the nucleus changes)

Question 13

Alpha particle

Answer 13

• consists of 2 protons and 2 neutrons (=helium nucleus)
• has approximately 5MeV kinetic energy
• travels at approximately 5% of the speed of light

Question 14

Beta minus particle

Answer 14

• consists of 1 electron
• often travels at close to the speed of light
• They have a range of speeds and KEs depending on the element and the anti-neutrino

Question 15

Beta particle decay

Answer 15

In the nucleus, a neutron changes into a proton and electrin (which is emitted as a beta particle)

Question 16

Anti-neutrino

Answer 16

• particle emitted with beta minus particle

- carries away some of the KE

Question 17

Gamma ray

Answer 17

High energy (also frequency) electromagnetic radiation emitted by nucleus following alpha and beta decay (which left the nucleus in a excited state)

Question 18

Describe the ionizing properties of alpha, beta particles and gamma radiation

Answer 18

Ionisation can be throught of as “damage” to teh medium that radiation is passing through. The greater the ionisation energy, the less the penetration into the medium, since the radiation more rapidly loses energy. Thus the most ionisation us by alpha and the least (almost none) by gamma

Question 19

Strong nuclear force

Answer 19

the force that holds the particles of a ucleus together. It is strong enough to overcome electrostatic repulsion of protons and very short range so that the nuclei do not attract each other

Question 20

Stability

Answer 20

the nucleus is under the effect of strong nuclear attraction and proton -proton repulsion. This is therefore more stable with an excess of neutrons

Question 21

Radioactive half-life

Answer 21

the time taken for half of the nuclei in a sampleto decay

Question 22

7.3.1 Describe and give an example of an artifical (induced) transmutation

Answer 22

We can alo induce large nuclei to decay and release large energy by bombarding them with smaller particles. This is called fission and is how our nuclear power stations work. If we induce a nuclear decay then the process is called an artifical (or induced) transmutation. A good example is the induced transmutation of Uranium-235

Question 23

Unified atomic mass

Answer 23

the mass of 1/12 of the nucleus of a carbon-12 isotope

Question 24

Apply the Einstein mass-energy equivalent relationship

Answer 24

E=mc^2

Question 25

Binding energy

Answer 25

the amount of work required to pull apart the constituents of a nucleus. A large binding energy implies a stable nucles

Question 26

Mass deflect

Answer 26

the mass of the particles of the seperated nucleus is greater than when they are combined. Mass deflect=mass of parts-mass of nucleus

Question 27

Binding energy per nucleon

Answer 27

A graph is plotted for each isotope which shows which nuclides are the most stable. The graph can predict fission and fusion reactions

Question 28

The process of nuclear fission

Answer 28

A process where large nucleus splits to make samller ones. This is permitted when the BE/nucleon of the products is higher than the initional nucleus. The difference in mass/energy is treleased

Question 29

The process of nuclear chain reaction

Answer 29

A uranium nucleus can be split by an incident wneutron the fission reaction produces more neutrons. Of one of the products produced also causes fission, then a chain reaction will follow. If the number of fissions is greater than the one, the reaction wil go out of control

Question 30

What is the main source of the sun

Answer 30

Nuclear fusion

Question 31

Explain how atomic spectra provide evidence for the quantization of energy in atoms

Answer 31

When an electron moves between energy levels it must emit or absorbe energy. The energy emitted or absorbed corresponds to the difference between the two allowed energy levels. The enrgy is emitted or absorbed as photons. The lines in the atomic spectra correspond with the enrergy levels

Question 32

calculate wavelength of spectral lines from energy level differences and vice verse

Answer 32

E=hf=hc

Question 33

Heisenberg incertainty principle

Answer 33

the principle identifies a fundamental limit to the possibly accuracy of any physical measurement. Conjugate properties, position-momentum and energy-time, cannot be known precisely at the same time

Question 34

Decay constant

Answer 34

the probability of decay of a nucleus per unit time

Question 35

Methods of measuring the half-life of an isotope

Answer 35

activity against time