Niels BohrAn expert is a person who has made all the mistakes that can be made in a very narrow field.
If anybody says he can think about quantum theory without getting giddy it merely shows that he hasn’t understood the first thing about it!

Richard Feynman
It is safe to say that nobody understands quantum mechanics.
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How Small Is An Atom? Spoiler: Very Small Kurzgesagt – In a Nutshell Published on 20 Jan 2015

Essential idea: In the microscopic world energy is discrete.

7.1 – Discrete energy and radioactivity

Nature of science:
Accidental discovery: Radioactivity was discovered by accident when Becquerel developed photographic film that had accidentally been exposed to radiation from radioactive rocks. The marks on the photographic film seen by Becquerel probably would not lead to anything further for most people. What Becquerel did was to correlate the presence of the marks with the presence of the radioactive rocks and investigate the situation further. (1.4)

Understandings
• Discrete energy and discrete energy levels
• Transitions between energy levels
• Radioactive decay
• Fundamental forces and their properties
• Alpha particles, beta particles and gamma rays
• Half-life
• Absorption characteristics of decay particles
• Isotopes
• Background radiation

International-mindedness:
• The geopolitics of the past 60+ years have been greatly influenced by the existence of nuclear weapons

Theory of knowledge:
• The role of luck/serendipity in successful scientific discovery is almost inevitably accompanied by a scientifically curious mind that will pursue the outcome of the “lucky” event. To what extent might scientific discoveries that have been described as being the result of luck actually be better described as being the result of reason or intuition?

Applications and skills:
• Describing the emission and absorption spectrum of common gases
• Solving problems involving atomic spectra, including calculating the wavelength of photons emitted during atomic transitions
• Completing decay equations for alpha and beta decay
• Determining the half-life of a nuclide from a decay curve
• Investigating half-life experimentally (or by simulation)

Guidance:
• Students will be required to solve problems on radioactive decay involving only integral numbers of half-lives
• Students will be expected to include the neutrino and antineutrino in beta decay equations

Data booklet reference:
• E = hf
l = hc/E

Utilization:
• Knowledge of radioactivity, radioactive substances and the radioactive decay law are crucial in modern nuclear medicine
• How to deal with the radioactive output of nuclear decay is important in the debate over nuclear power stations (see Physics sub-topic 8.1)
• Carbon dating is used in providing evidence for evolution (see Biology subtopic 5.1)
• Exponential functions (see Mathematical studies SL sub-topic 6.4; Mathematics HL sub-topic 2.4)

Aims:
• Aim 8: the use of radioactive materials poses environmental dangers that must be addressed at all stages of research
• Aim 9: the use of radioactive materials requires the development of safe experimental practices and methods for handling radioactive materials

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What Does An Atom REALLY Look Like? external image photo.jpg The Science Asylum Published on 12 Jul 2017

Nucleus are 100,000 times smaller than the size of the atoms. The negatively charged electrons in atoms can exist at only well defined discrete energy levels (quantized steps) and they cannot exist in between the levels(Bohr). When I heat Hydrogen gas, the electron in an hydrogen atom can jump from low energy states to high energy states. When electrons do so, they can leave empty energy states but later on they fall back to occupy the energy states again. When electrons fall from higher energy states to low energy states, light energy releases and we can see the discrete emission spectrum (discrete frequencies/wavelenths).

Atomic spectra
  • atomic electrons can only exist in certain discrete energy levels.
  • light is made up of photons.
  • when electrons lose energy they give out light.
  • when light is absorbed by an atom it gives energy to the electrons.
>>when an electron changes from a high energy level to a low one, a photon of light is emitted. The electron can only exist in discrete energy levels.

DE = hf
DE : Change in energy
h : Plank constant
f : Photon frequency

EXAMPLE 1: In an atom with electrons in two energy levels, calculate the wavelength that gives the rise to a photon when the change in energy is from the -4 eV to the - 10 eV.
SOLUTION:
DE = 6 eV = 6 x 1.6 x 10-19 = 9.6 x 10-19
f = DE/h
= ( 9.6 x 10-19 ) / ( 6.63 x 10-34 ) = 1.45 x 10-15 Hz

c = f l
l = ( 3 x 10 8 ) / ( 1.45 x 10-15 ) = 207 nm [UV light]

Four fundamental forces
Gravitational force
Electromagnetic force
Strong Nuclear Force
Weak Nuclear Force


Radioactivity: The emission of radiation by unstable atomic nuclei undergoing radioactive decay.
It is a process in which atoms with unstable nuclei spontaneously decay emitting subatomic particles and energy as they reconfigure into more stable forms.

Decay: 1. a spontaneous transformation of an elementary particle into two or more different particles 2. of an excited atom or molecule, losing energy by the spontaneous emission of photons

Radioactive decay: The spontaneous transformation of an unstable atomic nucleus into a lighter one, in which radiation is released in the form of alpha particles, beta particles, gamma rays, and other particles. The rate of decay of radioactive substances such as carbon 14 or uranium is measured in terms of their half-life.
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Alpha decay from phet.colorado.edu
Beta decay from phet colorade.edu
nuclear decay.PNG
Nuclear equations from BBC GCSE Bitesize
Uranium 238 decay chain from www.unitednuclear.com

Half-life
The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decay. The decay of radioisotopes can be used to measure the material’s age.

The half-life of radioisotopes varies from seconds to billions of years. from ndt-ed.org
Half life.jpg
Half life.jpg


Science in Focus Radioactivity S100LS05 Lammas Science Published on 15 Nov 2012
Half lives of various elements from no-nukes.org


Task: Simulate decay by rolling dice and to estimate the decay constant and half-life from the decay curve.

Aim: To simulate decay by rolling die and to estimate the decay constant and half-life from the decay curve. Apparatus: 100 six sided die.



Instructions:

  1. Count and record the total number of die. Each dice must have the same number of sides (for our experiment we will use six-sided dice.)
  2. Roll all the die at the same time onto a level table. A plastic container can be used to hold all the dice so they can be easily rolled simultaneously. The table should have some friction so that the dice don't slide off the edge. If some of the dice stack up, gently nudge the table so they all lay down flat on the surface.
  3. Remove all the dice which turn up "1".
  4. Count and record the number removed.
  5. Repeat the experiment with the remaining die.
  6. Record the time interval between each roll as one second and continue the experiment until no dice
    remain from the original batch.
  7. Plot the decay curves using total number of dice (as a function of time) as well as the activity of the
    sample (as a function of time).
  8. Estimate the decay constant and half-life from the sample.
  9. Repeat steps 2-8 except remove all the dice which turn up "1" or "2".
  10. Interpret the value of the decay constant you find from the graphs, is it what you could have expected?
  11. Include your graphs and data tables along with your report.



Reference:

  • Giancoli, 6th Edition Physics



Assessment Criteria:

  • Time: 1.0 hrs.



Due Dates: 13th December 2013


dN/dt = - λN
where λ = decay constant (ln 2 / t1/2)
the number of nuclei present, N,



Essential idea: Energy can be released in nuclear decays and reactions as a result of the relationship between mass and energy.

7.2 – Nuclear reactions
Nature of science:
Patterns, trends and discrepancies: Graphs of binding energy per nucleon and of neutron number versus proton number reveal unmistakable patterns. This allows scientists to make predictions of isotope characteristics based on these graphs. (3.1)

Understandings:
• The unified atomic mass unit
• Mass defect and nuclear binding energy
• Nuclear fission and nuclear fusion

Applications and skills:
• Solving problems involving mass defect and binding energy
• Solving problems involving the energy released in radioactive decay, nuclear fission and nuclear fusion
• Sketching and interpreting the general shape of the curve of average binding energy per nucleon against nucleon number

Theory of knowledge:
• The acceptance that mass and energy are equivalent was a major paradigm shift in physics. How have other paradigm shifts changed the direction of science? Have there been similar paradigm shifts in other areas of knowledge?

Utilization:
• Our understanding of the energetics of the nucleus has led to ways to produce electricity from nuclei but also to the development of very destructive weapons
• The chemistry of nuclear reactions (see Chemistry option sub-topics C.3 and C.7)

Guidance:
• Students must be able to calculate changes in terms of mass or binding energy
• Binding energy may be defined in terms of energy required to completely separate the nucleons or the energy released when a nucleus is formed from its nucleons

Data booklet reference:
D E = D mc2

Aims:
• Aim 5: some of the issues raised by the use of nuclear power transcend national boundaries and require the collaboration of scientists from many different nations
• Aim 8: the development of nuclear power and nuclear weapons raises very serious moral and ethical questions: who should be allowed to possess nuclear power and nuclear weapons and who should make these decisions? There also serious environmental issues associated with the nuclear waste of nuclear power plants.



Nuclear fission
Nuclear Fission
Click to Run


7.3 – The structure of matter

Nature of science:
Predictions: Our present understanding of matter is called the Standard Model, consisting of six quarks and six leptons. Quarks were postulated on a completely mathematical basis in order to explain patterns in properties of particles. (1.9)
Collaboration: It was much later that large-scale collaborative experimentation led to the discovery of the predicted fundamental particles. (4.3)

Understandings:
• Quarks, leptons and their antiparticles
• Hadrons, baryons and mesons
• The conservation laws of charge, baryon number, lepton number and strangeness
• The nature and range of the strong nuclear force, weak nuclear force and electromagnetic force
• Exchange particles
• Feynman diagrams
• Confinement
• The Higgs boson

Applications and skills:
• Describing the Rutherford-Geiger-Marsden experiment that led to the discovery of the nucleus
• Applying conservation laws in particle reactions
• Describing protons and neutrons in terms of quarks
• Comparing the interaction strengths of the fundamental forces, including gravity
• Describing the mediation of the fundamental forces through exchange particles
• Sketching and interpreting simple Feynman diagrams
• Describing why free quarks are not observed

Guidance:
• A qualitative description of the standard model is required International-mindedness:
• Research into particle physics requires ever-increasing funding, leading to debates in governments and international research organizations on the fair allocation of precious financial resources

Theory of knowledge:
• Does the belief in the existence of fundamental particles mean that it is justifiable to see physics as being more important than other areas of knowledge?

Utilization:
• An understanding of particle physics is needed to determine the final fate of the universe (see Physics option sub-topics D.3 and D.4)

Aims:
• Aim 1: the research that deals with the fundamental structure of matter is international in nature and is a challenging and stimulating adventure for those who take part
• Aim 4: particle physics involves the analysis and evaluation of very large amounts of data
• Aim 6: students could investigate the scattering angle of alpha particles as a function of the aiming error, or the minimum distance of approach as a function of the initial kinetic energy of the alpha particle
• Aim 8: scientific and government organizations are asked if the funding for particle physics research could be spent on other research or social needs

Data booklet reference:


Aim: To define the relationship between the impact parameter b and the scattering angle theta.
Task: Plot a graph using your data collected from simulation and draw conclusion showing the relationship below.
The relation between the impact parameter and the scattering angle simplifies with the use of the distance of the closest approach parameter.
Rutherford scattering eq.jpg
Rutherford scattering trajectories of alpha particles.jpg
Rutherford scattering trajectories depend on the impack parameter.jpg
Quarks Proton and neutron structure Fundamental forces Fermi theory of beta decay Some nuclcear units from hyperphysics
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Fusion: How to Put the Sun in a Magnetic Bottle - with Ian Chapman
The Royal Institution Published on 8 Jun 2016


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Breakthrough in Nuclear Fusion? - Prof. Dennis Whyte MIT Club of Northern California Published on 25 Feb 2016


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A Capella Science - Rolling in the Higgs (Adele Parody) acapellascience Published on 20 Aug 2012