9.6 Qanta to Quarks

Physics 9.6 Quanta to Quarks

1. Recognise that problems with the Rutherford model of the atom led to the search for a model that would better explain the observed phenomena

What are models and why are they used? • Models are simplified explanations to describe complex phenomenon used to improve our

understanding. The main benefits of models are that they are based on experimental data and cam therefore can be tested and improved upon. In physics, models are used to explain how the universe works and allow us to create technologies to harness there phenomenon.

The models of the atom that existed before the up until the current model were:

• Dalton’s Billiard Ball model • Thompson’s Plum Pudding model • Rutherford’s Free Space Model • Bohr’s Shell’s Model • Quantum Model

1. Discuss the structure of the Rutherford model of the atom, the existence of the nucleus and

electron orbits The Rutherford model of the atom aimed to explain the results of an experiment that was carried out by Hans Geiger and Ernest Marsden and was directed by Rutherford. In the experiment, alpha particles from a radioactive source were fired at a thin gold foil in a vacuum tube and the deflections were then measured. According to Thompson’s model of the atom, there should only have been minor if any. What they found was that almost all of the particles passed straight through un-deflected. Occasionally (1/8000), the alpha particles would deflect as at angle greater than 90°, including some that would return to the source. This was due to the presence of a dense positive nucleus, which caused the deflections. The LIMITATIONS of the Rutherford model were:

• The electrons orbiting the nucleus are accelerating thus electrons are expected to lose energy by emitting radiation, and thus collapse into the nucleus (positively charged)

• The model did not show how the electrons were arranged within the atom • The model did not show the composition of the nucleus.

In the Rutherford model, the electrons were in circular motion thus were accelerating. As a result, energy was lost. When energy was lost, it would eventually spiral into the nucleus, while passing through many differing energy levels. As a result, a continuous spectrum was emitted. In Bohr’s model, the electrons were in energy shells, where the increase/decrease in energy would only result in a discrete emission,

2. Perform a first-hand investigation to observe the visible components of the hydrogen spectrum THE HYDORGEN SPECTRUM

This is the set of characteristic wavelengths of light that is emitted or absorbed by the hydrogen atom. All elements have a unique absorption and emission spectrum which can be used to identify them. These are created by the electrons which orbit around the atom in discrete stationary states. When the electrons move from one state to another, they must absorb or release energy which is equal to the difference between these two states. The absorption spectrum is a spectrum of visible light where particular frequencies are missing. This is because these have been absorbed by the atom. The hydrogen spectrum displayed discrete wavelengths suggesting that the energy of the electron must also be discrete. This led Bohr to hypothesise that electrons existed in discrete energy levels or shells.


3. Analyse the significance of the hydrogen spectrum in the development of Bohr’s model of the

atom • Bohr’s model of the atom was similar to Rutherford’s model, but differed in the fact that he specific

positions to electrons and stated that the electron energy level were quantised. This meant that electrons could absorb and release discrete amounts of energy to change from one level to another.

• Bohr also recognised that if his model was correct, then each type of atom would have a spectral fingerprint that related to the difference between electron energy levels in that particular atom

• The hydrogen spectrum was vital to the development of Bohr’s model of the atom because it provided the only evidence at the time for an otherwise purely theoretical model.

4. Discuss Planck’s contribution to the concept of quantised energy

• Quantised energy refers to the idea that energy can only occur in small discrete packets of energy. • Planks hypothesis involved the notion that energy could only be emitted or absorbed in small

discrete amount, called quanta of energy that could be described as 𝐸 = ℎ𝑓. Plank’s experiment could explain why there were different peaks within the curves.

• (+) This significant contribution allowed further developments in quantum physics to occur. • (-) Einstein improved upon Planck’s idea by recognising that the radiation itself was quantised. • (-) Planck believed that it was a mathematical trick rather than a functioning model.

5. Define Bohr’s postulates

1. Electrons orbit the nucleus in stationery states with discrete energy levels 2. When an electron moves from one energy level to another, energy is radiated or absorbed,

proportional to the difference in energy between the two levels 3. Electrons in orbit have a quantised angular momentum that is an integral multiple of !

!!

𝐿 = 𝑚𝜔 = 𝑚𝑣𝑟 =𝑛ℎ2𝜋

6. Describe how Bohr’s postulates led to the development of a mathematical model to account for

the existence of the hydrogen spectrum: Bohr assumed that the only force acting to hold an electron in orbit was that of electrostatic attraction. He reasoned that this electrostatic force provided centripetal force needed for circular motion of the electron/ From this, he determined the kinetic energy of the electron and added this to the electron’s electric potential energy to obtain an expression for the total energy. He then applied his 3rd postulate, his quantised condition, to his classical hydrogen model allowing him to determine the radius if a particular stationary state. Bohr was able to derive a theoretical expression that matched Rydberg’s version of the Balmer empirical equation and this strongly supported the Bohr model of the atom, allowing him to determine the radius of a particular stationary state. The Rydberg equation allows the wavelength of a photon that is absorbed or released as an electron

transitions between energy levels to be determined. !!= 𝑅 !

!!! −

!!!!

Bohr’s model explained why there are more lines in emission spectra than absorption spectra. Electrons in unexcited gases can only move up to higher levels from the ground state (n =1) when they absorb energy whereas emission spectra show electron transitions from higher energy levels to all lower energy levels (eg. n = 4 to n = 2) and not only the Lyman series which is to the ground state.


7. Solve problems and analyse information using: !!= 𝑅 !

!!! −

!!!!

Calculate the wavelength and energy of the photon emitted when the electron moves from the 3rd state to the 1st state.

𝜆 =1

1.097 ×10! 1 − 19

= 1.0255 ×10!!

𝑐 = 𝑓𝜆 = 2.926829 ×10!"

∴ 𝐸 = ℎ𝑓 = 6.626×10!!" ×𝑓 = 1.939317 ×10!!" = 1.9 ×10!!" 𝐽(2𝑠𝑓)

8. Process and present diagrammatic information to illustrate

Bohr’s explanation of the Balmer series According to Bohr, the spectral lines in Balmer series are caused by photons of light released by electrons when moving from a higher energy level (n ≥ 3) down to the electron energy level of n = 2. Larger energy changes produce more energetic photons (ie. photons with shorter wavelengths, higher frequencies) with the greatest change happening between levels furthest apart.

9. Analyse secondary information to identify the difficulties with the Rutherford-Bohr model, including its inability to completely explain:

THE SPECTRA OF LARGER ATOMS The Bohr model works reasonably for atoms that have one electron in their outer shell, but does not work for any others. It is not possible to calculate the wavelength of the spectral lines of any other atom. It was also unable to explain the arrangement of multiple electrons around the atoms.

THE RELATIVE INTENSITY OF SPECTRAL LINES The examination of the spectrum shows that the spectral lines are not of equal intensity and this means that some of the energy transitions were more favoured than others. However, Bohr’s model does not show why some electron transitions were favoured over others.

THE EXISTENCE OF HYPERFINE SPECTRAL LINES Careful observations of characteristic spectra showed that the discrete spectral lines were in fact not singular, but split into multiple hyperfine lines. This implied that there must be some splitting of the energy levels of the Bohr atom but the Bohr model could not account for this.

THE ZEEMAN EFFECT When a hydrogen gas lamp is excited while in the presence of a magnetic field, the emission spectrum produced shows a splitting of spectral lines and the Bohr model cannot account for this.

10. Discuss the limitations of the Bohr model of the hydrogen atom The main limitations of the Bohr’s model was that he was unable to explain why the postulates held, rather he stated that they did.


2. Identify that the limitations of classical physics gave birth to quantum physics 11. Describe the impact of de Broglie’s proposal that any kind of particle has both wave and particle

properties Wave particle duality – The hypothesis that every wave has an associated momentum and every particle has an associated wavelength. In other words, waves and particles are not discrete concepts, but are in fact different methods of observing properties of the phenomenon. De Broglie’s work was based on that of Einstein, Plank and Bohr, where he was able to show that every particle had an associated wavelength and thus must behave like a wave. The mathematical description is known as the de Broglie hypothesis. It states that the wavelength of any particle is associated with its momentum. This can be mathematically written as 𝜆 = !

!= !

!!

12. Solve problems and analyse information using: 𝜆 = !

!"

Calculate the de Broglie wavelength of a 1.0 kg mass fired through the air at 100.0 kmh-1.

𝜆 =ℎ𝑚𝑣

=6.626 ×10!!"

1 × 1003.6

= 2.38536 ×10!!" = 2.4 ×10!!" 2𝑠𝑓

13. Define diffraction and identify that interference occurs between waves that have been diffracted

Diffraction of light occurs when light passes through a very finely ruled gratin, or when it is reflected from a surface with fine lines ruled across it. It also occurs when light passes a barrier or passes through a small opening. It is not easy to observe, because the dimensions of the barrier or opening must be comparable to the wavelength of light. Christian Huygens proposed that light was a wave. He proposed what is now known as the Huygens’ Principle which states “Every point on a wavefront may be considered to act as a source of circular secondary wavelets that travel in the direction of the wave. The new wavefront will be tangential to the secondary waves” A transmission diffraction grating is a transparent material that has many fine lines ruled across it. These lines can be considered to be breaking that wavefront into point sources. A reflection grating is a reflecting surface with many lines ruled across it.

14. Describe the confirmation of de Broglie’s proposal by Davisson and Germer The Davison and Germer experiment was initially used to prove that particles also had wave nature. This experiment confirmed that de Broglie hypothesis, 𝜆 = !

!= !

!". The results that were recorded are as

shown in the graph shown. The diffraction pattern on the right, proves that it has a wave nature. Fast moving electrons were bombarded at a nickel crystal that was able to be rotated in order view the reflection at various angles. The electrons were deflected by a Faraday box. It was seen that at some angles, there was a peak in the intensity of electrons and could be explained by Braggs Law𝑛𝜆 = 2𝑑𝑠𝑖𝑛𝜃. It was proposed that what they saw was the diffraction of electrons, and showed that the particles had wave characteristic. This could be related to Bohr’s model of the atom as they were to be similar to standing waves, which propagated without the loss of


energy. This explained how electrons didn’t radiate energy. The electrons were seen to have a wavelength 𝜆 = !!"

!.

Because the De Broglie hypothesis and the Braggs Law were able to t prove that particles had a wave nature, they were seen as equivalent. In the Davisson-Germer experiment, an experimental wavelength was obtained from the diffraction pattern. In Braggs experiment, because NaCl, which has a set lattice structure was used, there wavelength could also be determined from the Braggs Law 𝑛𝜆 = 2𝑑𝑠𝑖𝑛𝜃. Both were seen to match, thus were seen as true.

15. Explain the stability of the electron orbits in the Bohr atom using de Broglie’s hypothesis De Broglie was able to show that the Bohr stationary states correspond to standing waves that form within the orbit. A stationary wave is one that does not lose energy when propagating, but rather, maintains it within the system. As waves have an associated momentum, it was then seen that electrons must also possess this characteristic, and as a result, did not radiate energy when in their stationary states.

16. Gather, process, analyse and present information and use available evidence to assess the contributions made by Heisenberg and Pauli to the development of atomic theory

WOLFGANG PAULI Pauli made significant contributions to the quantum theory. He was able to derive Balmer’s equation and Rydberg’s quantum mechanics to the hydrogen atom. He realised that if another quantum number was added, he would be able to explain the maximum number of electrons in each shell that Bohr had proposed, but could not explain. The maximum number of electrons in each shell was the maximum number of different quantum number sets for each shell. He developed the exclusion principle which states which states that no two electrons in an atom can have the same quantum numbers and thus must have different integer spin. There were four quantum numbers that could be chosen from: principle quantum (energy level), azimuthal quantum (shape of energy level), orbital magnetic quantum (orientation of orbit; x,y,z axes), spin quantum. He also provided an explanation for the positioning of the elements on the periodic table.

HEISENBERG Heisenberg also made significant contributions to the quantum theory. He proposed the Heisenberg uncertainty principle. In this principle, it states that given two quantities, one cannot measure both to an exact level of accuracy. He stated that the product of the uncertainty in both position and momentum must be greater than Plank’s constant on two pi and this could be shown through:

∆𝑥∆𝑝 ≥ℎ2𝜋

This means that if you know exactly where something is, you cannot exactly know its momentum. Similarly, if you know its momentum, you cannot determine its exact location.

3. State that the work of Chadwick and Fermi in producing artificial transmutations led to practical applications of nuclear physics

17. Define the components of the nucleus (protons and neutrons) as nucleons and contrast their properties

The nucleus contains two major components: protons and neutrons and together, these are known as nucleons. The differing characteristics between a proton and a neutron are listed below: Proton Neutron Charge (c) 1.602 x 10-19 0 Mass (kg) 1.673 x10-27 1.675 x 10-27


18. Discuss the importance of conservation laws to Chadwick’s discovery of the neutron

EXPERIMENT TO DETERMINE NATURE OF NEUTRONS Chadwick has a source of alpha particles, which he placed in front of a Beryllium target. The alpha particles would hit the Beryllium target and produce a neutral form of radiation

. 94𝐵𝑒 + 42𝐻𝑒 →

126 𝐶 +

10𝑛. This

unknown radiation was then placed in front of paraffin wax (hydrocarbons). When it came into contact with the wax, it produced protons which could then be detected. The cloud chamber was used in order to detect protons, since they were able to ionise the supersaturated alcohol vapour. The unknown radiation was thought to be gamma rays as they shared similar properties. They both:

− Had a neutral charge − Possessed high energy that broke hydrogen from hydrocarbons − Hard to detect.

However, Chadwick did not accept the fact that the unknown radiation was gamma rays, so he analysed the conservation laws to prove this. By using the conservation law of energy in elastic collisions between gamma ray photons and protons, Chadwick showed that the energy required for the gamma ray would be 50MeV in order to allow them to have enough energy to eject the photons which were being detected. This was much greater than the amount of energy that the incident alpha particles. Hence, he conclude that the neutral radiation could not be gamma rays.

IMPORTANCE OF CONSERVATION LAWS Conservation of Momentum – Used to calculate the mass of the radiation, found to be similar to a proton Conservation of Energy – Used to disprove that the unknown radiation was gamma rays. This was because the energy of the alpha particles which equals the energy of the unknown radiation was not enough energy for the gamma rays to eject the protons from the wav. They are important as they led to the discovery of new sub-atomic particles, as opposed to assuming it was something that had been discovered, namely gamma rays. The radiation discovered with no charge and a mass similar to that of a proton was unlike any particle that had been seen.

19. Define the term ‘transmutation’ TRANSMUTATION is the process by which the constituents of a nucleus in an atom are altered as a result of either radioactive decay or bombardment with external particles. During nuclear transmutation one element or isotope is converted into another. There are three different types of transmutation:

Radiation Constituents Charge Ionisation Ability

Penetration Power Mass (amu) Example for

Penetration

Alpha (α) 42𝐻𝑒 +2 High Low 4 Sheet of

Paper

Beta (β) 0−1𝑒 -1 Med Med 1/2000 2-3mm

Aluminium

Gamma (γ) EM Wave 0 Low High 0 Several m concrete


20. Describe nuclear transmutations due to natural radioactivityia Transmutation is a natural process that we can observe in nature. All elements with an atomic number greater than 83 undergo natural transmutation and are therefore known as radioactive elements. Natural transmutation occurs when the nucleus is too large and therefore unstable. As a result, it has to undergo radioactive decay to become stable. This is in the form of α, β, γ. Some atoms are unstable because their nuclei exist outside the zone of stability due to the proton-neutron ratio or because there are too many protons Z à the number of protons Nà the number of neutrons

1. For elements Z1 – Z20, the ideal !! ratio is 1, so elements with !

! ratio ≠ 1 are radioactive.

2. Elements Z21 – Z50, the ideal !! ratio is 1.23.

3. Elements Z51 – Z83, the ideal !! ratio is 1.5.

4. >Z83, all elements are unstable.

21. Describe Fermi’s initial experimental observation of nuclear fission Nuclear fission is the process whereby a large unstable nucleus undergoes radioactive decay and form two smaller nuclei. There are two ways that a nuclear fission can occur. The first is the spontaneous fission. This is known as bombardment or induced nuclear fission. This process was induced within a nuclear reactor. Fermi tried to produce radioactive elements heavier than uranium (transuranic elements) by bombarding uranium with neutrons as this type of bombardment of heavy elements sometimes results in a delayed beta particle emission (which increase atomic number by 1). The products of neutron bombardment can be identified by measuring the half-life of any radiation emitted. Although he didn’t realise it at the time, Fermi was the first to observe nuclear fission. In 1934, he reported the discovery of a transuranic element that with a different half-life to any known isotopes. It is now understood that the radioactivity that Fermi measured was associated with lighter nuclear fission products and not transuranic elements. Fermi also discovered that neutrons slowed by paraffin wax were more effective than fast neutrons. This is because their lower speed means that they spend more time close to the nucleus and so have more chance of being captured.

22. Perform a first-hand investigation or gather secondary information to observe radiation emitted from a nucleus using Wilson Cloud Chamber or similar detection device

The Wilson Cloud Chamber is used for detecting particles of ionising (α,β) radiation. A simple cloud chamber is a sealed environment containing supercooled, supersaturated alcohol vapour. When an alpha particle or beta particle interacts with the mixture, it ionises it. There high energies of alpha and beta particles therefore leave trails,

due to many charged ions being produced, along the motion of the charged particle. These tracks has distinct shapes (alpha – broad straight, beta – thin and shows signs of deflection). The cloud chamber can be combined with electric or magnetic fields to show more evidence of deflection, allowing for a clearer detection and identification of the radiation.


23. Discuss Pauli’s suggestion of the existence of neutrino and relate it to the need to account for the energy distribution of electrons emitted in β-decay

The neutrino is an elementary particle whose existence was theorised by the physicist Wolfgang Pauli. There are two types of beta decay. Beta minus decay is where an electron is emitted 𝑛 → 𝑝!! + 𝑒!!!

!!!

and beta positive decay is where a positron (an electron anti-particle) is ejected 𝑝!! → 𝑛!! + 𝑒!!!!

What Pauli notice was that the beta particles that were emitted did not have specific energy. In fact, when Pauli observed the beta particles being ejected from radioactive sources, he noted that the individual particles could have quite varied energy levels. On plotting the energies of the ejected beta particles formed the graph on the right What this showed was that the energy of the beta particles varied as they were being ejected; they were not a constant value that was consistent. This resulted in a discussion due to the breaking of the conservation laws. It was clear that the original neutrons and protons before the beta decay had a constant amount of energy, so it did not make sense that the beta particles being ejected could vary drastically, as each individual beta decay process should have been identified. There was a clear difference in the energies of the neutron, and that of the proton and electron that was released during beta minus decay. To account for this difference between the parent and daughter, Pauli said that there was another particle present. He called the particle the neutrino, meaning little neutron. The variance in this energy distribution indicates that not all beta decay reactions are identical to one another. The difference in energy indicates that the energy is being released in other forms as well throughout these differing reactions. Paul theorised and later confirmed that there existed another product particle that accounted for the difference in energy. β- decay: 𝑛 → 𝑝!! + 𝑒!!!

!!! + 𝑉

β+ decay: 𝑝!! → 𝑛!! + 𝑒!!!! + 𝑉

24. Evaluate the relative contributions of electrostatic and gravitational forces between nucleons • Both the gravitational and electrostatic forces are inverse square forces, and therefore should

become large at the small separation of nucleons in a nucleus • Electrostatic repulsion between like-charged positive protons and gravitation attraction between

masses in the nucleus are two of the forces that act between nucleons. • Electrostatic repulsion is stronger than gravitational attraction. • Electrostatic and gravitational forces are 36 orders apart making the gravitational force

significantly weaker than the electrostatic repulsion.


25. Account for the need for the strong nuclear force and describe its properties It was seen that the dominant force present in the nucleus is a repulsive force, yet the nucleus is still able to be held together.

PROPERTIES OF STRONG FORCE

• It acts between all nucleons, and holds them together. The more nucleons there are present, the stronger the strong force

• The strong force only acts over very short distances max of 1.0 x 10-15m • At distances closer than 1.0 x 10-15m, it becomes repulsive • It is mediated through the exchange of gluons • At distances over 3.0 x 10-15m the force is considered to be 0, negligible • The strong force is much stronger than the repulsive force, by a factor of at least 60.

This shows that the nucleus is mainly held together by the strong nuclear force, which exists between all nucleons. This also highlights the importance for neutrons to the existence of the nucleus, as they contribute to the strong nuclear attractive force without contributing to the repulsive force of protons, This is why larger nucleus tend to have more neutrons than protons, as there is a need for more strong nuclear attractive force to overcome the repulsive force due to the large number of protons.

26. Explain the concept of a mass defect using Einstein’s equivalence between mass and energy MASS DEFECT is the difference in the mass of the stable nucleus and the mass of the isolated neutrons and protons. The TOTAL BINDING ENERGY is the energy that must be supplied to the nucleus in order to break it up into its constituent parts. The AVERAGE BINDING ENERGY PER NUCLEON is the total binding energy of a nucleus divided by the total number of nucleons (number of protons and neutrons in nucleus) and is a measure of the stability of the nucleus. The mass defect is a representation of the binding energy. The link between mass and energy is Einstein’s energy mass equivalence. The most important quantity when looking at stability of a nucleus is the binding energy per nucleon ,which is the mass of the atom.

27. Solve problems and analyse information to calculate the mass defect and energy released in natural transmutation and fission reactions


28. Describe Fermi’s demonstration of a controlled nuclear chain reaction in 1942

29. Compare requirements for controlled and uncontrolled nuclear chain reactions CONTROLLED CHAIN REACTIONS

• Fission reactions that allow the extra neutrons produced during the reaction to be absorbed, so that approximately the same number of neutrons will be present for each of the subsequent fission reactions

• These are adopted in nuclear power plants to produce heat energy at a steady rate

UNCONTROLLED CHAIN REACTIONS

• Fission reaction was all the neutrons produced during the reaction are allowed to strike more fissionable material to cause further nuclear fission so that the process continues exponentially.

• These are adopted in nuclear weapons Uncontrolled Chain Reactions Controlled Chain Reactions

Similarities • Require fuel (U-235) • Moderator (required for slow neutrons for capture e.g. heavy water) • Critical mass of fissile material

Differences • Control Rod • Coolant • Radiation Shield


4. Describe how an understanding of the nucleus has led to large science projects and many applications

30. Explain the basic principles of a fission reactor

STRUCTURE OF BASIC NUCLEAR FISSION REACTOR

A basic nuclear fission reactor is quite complicated, however all nuclear reactors contain the same basic constituents: SOURCE OF NEUTRONS (FUEL) – required for the chain reactions. This is placed into the core of a nuclear reaction (fuel steel rods) and closely monitored to ensure that the amount ejected does not fall below or exceed the critical level. In most cases enriched Uranium-235 is used as the source. CONTROL RODS – required to control the number of neutrons present. These allow the core to cool down by the insertion of materials that absorb neutrons since fission chain reaction will stop if starved of neutrons. They are generally made of steel or cadmium. COOLANTS – Used as a removal system for the energy. The energy produced is often used to superheat water, which in turn, spins the turbine. An example is heavy water MODERATORS – When fast moving neutrons collide with certain materials, they lose kinetic energy and slow down to form thermal neutrons. They are used to slow down the neutron and allow it to be captured by neighbouring atoms. An example is deuterium LEAD PROTECTIVE SHIELDING – used to reflect all radiation and absorb excess neutrons. 31. Gather, process and analyse information to assess the significance of the Manhattan Project to

society POSITIVE ASPECTS

• It resulted in the conclusion of World War II • The invention of Nuclear Power Plants, based on the work of Fermi on producing a self-

sustaining chain reaction • The application of nuclear physics to medicine resulting in treatment which has saved millions of

people worldwide.

NEGATIVE ASPECTS

• The subsequent beginning of the arms race, or the Cold War, and loss of funds which otherwise could have been spent on social needs and aid.

• An excess of unstable nuclear weaponry. • The mass annihilation of the people inhabiting Hiroshima and Nagasaki • The environmental degradation at both the drop zones and nuclear testing sites leading to birth

defects, low crop yields and the mass radiation poisoning of the blast survivors. • The Manhattan Project has led to many ethical dilemmas in the scientific community. This also

led to some debate and conflicting views on whether scientists should boycott any further nuclear development.

ASSESSMENT

Despite the negative impacts of the Manhattan Project, overall it has had a positive societal outcome of incomprehensible significance. Cleaner and cheaper energy is not available from nuclear plants and we are in a time of nuclear disarmament. Relative to today’s society the Manhattan Project had a net positive impact, especially from a medical perspective.


32. Describe some medical and industrial applications of radio-isotopes AND

33. Identify data sources, and gather, process, and analyse information to describe the use of a named isotope in:

TECHNETIUM-99M (MEDICINE) is a radioisotope that emits gamma radiation and is often used in medicine as a diagnostic tool. It is formed through within a cyclotron through the bombardment of molybdenum.

9842𝑀𝑜 +

10𝑛 → 9942𝑀𝑜

9942𝑀𝑜 → 0−1𝑒 +

9943𝑇𝑐 −𝑚

9943𝑇𝑐 −𝑚 → 9943𝑇𝑐 + 𝛾

The main entry route into the body for Tc-99m is through ingestion, by drinking water or eating food. Once it has entered the body, due to its chemically reactive nature, it is able to combine with various other substances to form complexes that are absorbed by specific body parts allowing for precise imaging and diagnostic procedures. For example, when it is combined with tin compounds, it is able to bind to red blood cells which allow for the detection of blood clots and bleedings sites and also allow for the mapping of any circulatory system disorders. Also, if it combines with pyrophosphate, it can join to calcium deposits in damaged heart muscles, making it useful in analysing damage after a heart attack. Furthermore, Tc-99m emits low energy gamma radiation, where the low ionising ability of gamma reduces the possibility of damage to healthy tissues. Furthermore, as gamma radiation has high penetration power, even at low intensity, is able to be detected from outside the body by a gamma detector computer that is able to form precise images. This means that it is a non-invasive diagnostic tool. It has a short half-life of 6 hours, thus there is minimal exposure of the radiation to the patient. Yet this means that the source of the radioisotope must be close to the hospital and this is a costly process. As Tc-99m decays through gamma radiation, the presence of the radiation can be determined through a Geiger Muller Counter, however, in order to establish an image of the examined situation, it is best to use an imaging machine. COBALT-60 (INDUSTRY) is a radioisotope that emits both beta (-) and gamma radiation and is often used in industry to sterilise food and detection of welds in metal gauges. It is formed within a particle accelerator through the bombardment of Co-59 by the following equation:

𝐶𝑜!"!" + 𝑛!! → 𝐶𝑜!"

!" Co-60 is used to detect any defects in welds water pipes and gauges. This is done through firing Co-60 at the metal surface. Because gamma radiation is high penetrating, it passes through the metal to the Geiger counter which is behind. The concentration of the gamma radiation passing through the metal is a constant if the thickness is constant. If there is a weld or a crack in the metal, then the concentration will increase dramatically, which will show on the Geiger counter. Furthermore, as it has a long half-life of 5.27 years, it does not need to be replaced regularly and as a result, there are lowered costs. As gamma radiations are not water soluble, it does not contaminate the water thus does not harm humans that drink it through ingestion.


PHOSPORUS-32 (AGRICULTURE) is a radioisotope that emits beta radiation and is often used for tracking a plant’s uptake of fertiliser from the roots to the leaves.

It is formed by the irradiation of sulfur-32 with moderately fast neutrons as shown in the equation:

𝑆!"!" + 𝑛!! → 𝑃!"

!"

It is inserted through use of phosphorus-32 fertiliser via water in the soil and the usage of the phosphorus can be mapped. As it is a beta emitter, it has moderate penetration power it is able to be detected through a Geiger counter thus enabling the monitoring the absorption of the fertiliser. However, as the beta radiation has moderate ionising abilities, the healthy tissues of the plant may be altered through extensive use. Because phosphorus-32 acts identically to phosphorus-31, the plant uses it in the same way, thus an accurate depiction of how fertiliser is used in the plant can be determined. As it has a half-life of 14.28 days, it is suitable for the monitoring without being too expensive.

34. Describe how neutron scattering is used as a probe by referring to the properties of neutrons Neutron scattering is used to probe the nucleus. There are two forms of probing:

• Elastic (to determine the constituents of matter) • Inelastic (dynamics of matter – e.g. strength of bonds)

The properties of the neutron that allow it to be used for probing are: • Neural charge – this allows it to penetrate further through the electron shells, allowing for an

increased understanding of the atom • Mass similar to proton – allow for elastic collisions • De Broglie wavelength – able to interact with all matter with known lattice spacing. Also they are

able to be absorbed by the nucleus. • Magnetic moment – allows them to interact with substances of magnetic structure. • Diffraction – creates an interference pattern that is similar to that of electrons, allowing the lattice

‘d’ to be determined

35. Identify ways by which physicists continue to develop their understanding of matter, using accelerators as a probe to investigate the structure of matter

LINEAR PARTICLE ACCLERATOR A linear particle is neutron rich. An element is fired at the nucleus, where it is absorbed and becomes a new radioactive element. Within the particle accelerator, the accelerator increases the velocity of a charged atom to a series of oscillating electric potentials along a linear beam line, through the cylindrical electrodes which are electronically isolated. The electrodes are energised by one or more sources of radio frequency energy. Additionally there may be magnetic or electrostatic lenses which ensure the particle stays in the centre of the pipe. This new radioactive element may then undergo nuclear fission, which is when a large nuclei breaks down into two smaller nuclei, whilst releasing large amounts of energy.

CYCLOTRON Charged [articles travel in an evacuated space between two D-shaped magnets (that force them travel in a circular motion) and are accelerated by an electric field applied across the space between the D’s. Increasing speed causes the particles to spiral outwards until they reach the edge of the magnetic field. They are then deflected to their target. In a cyclotron, charged particles are emitted continuously from the source and accelerated to hit various targets using various deflecting fields.


SYNCHROTRONS Particles are introduced into the synchrotron and accelerated to much higher speeds than in cyclotrons. An increasing magnetic field keeps the radios of the path of the particles between the D’s constant until they reach the required speed, when they are deflected into the target. Synchrotrons may be like circular accelerators. The disadvantage of a synchrotron is that it can accelerate only one packet of charged particles at a time. These must be removed before another package can be started. 36. Discuss the key features and components of the standard model of matter, including quarks and

leptons

The development of these components has allowed for scientists to predict the properties of newly discovered particles. This is because all the combinations of the quarks can be determined beforehand.

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9.6 Qanta to Quarks