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9.8 Option - From Quanta to Quarks: 4. Applications of a knowledge of the structure of the atom

Syllabus reference (October 2002 version)
4. An understanding of the nucleus has led to large science projects and many applications	Students learn to: explain the basic principles of a fission reactor describe some medical and industrial applications of radio-isotopes describe how neutron scattering is used as a probe by referring to the properties of neutrons identify the ways by which physicists continue to develop their understanding of matter using accelerators as a probe to investigate the structure of matter discuss the key features and components of the standard model of matter, including quarks and leptons	Students: gather, process and analyse information to assess the significance of the Manhattan Project to society identify data sources, and gather, process, and analyse information to describe the use of: a named isotope in medicine a named isotope in agriculture a named isotope in engineering

Extract from Physics Stage 6 Syllabus (Amended October 2002) © Board of Studies, NSW.
[Edit: 14 Aug 08]

Prior learning: Preliminary modules 8.5.
HSC Modules 9.2, 9.4.

Background: Nuclear fission and an understanding of how elements could be transmutated to form useful radioactive isotopes changed the face of the world in terms of defence, medicine with medical isotopes, research science and elemental tracing, cancer treatment and the production of electrical power.

explain the basic principles of a fission reactor

The fission of heavy nuclei results in the release of significant amounts of energy that can be as much as 0.1% of the total mass of the reactants. This is much greater than the relative energy extraction in any chemical reaction. Mechanisms designed to do this are called nuclear fission reactors.
Nuclear fission reactors are large shielded structures that utilise controlled fission of uranium or the manufactured element plutonium for the production of heat that is used to generate electricity in a conventional sense. The following features are common to most or all fission reactors:
The fuel is U²³⁵ and/or plutonium in the form of compounds of oxides or carbides packed into long fuel rods

Additional information

These fuel rods are hollow tubes of metals such as stainless steel or can be alloys of magnesium or zirconium. Each fuel rod contains a sub-critical mass of fissionable material. When several of these rods are arranged vertically in the reactor core at suitable close distances in a geometric array usually a rectangular grid or concentric circles the effect is that a critical mass of fissionable material is achieved.

A moderator, either graphite blocks or heavy water, is used to fill the space between the fuel rods in thermal reactors. The purpose of the moderator is to slow the neutrons down from 1 MeV to less than 0.5 eV through multiple collisions. Slow neutron will be captured by atoms of the fissionable material and cause those atoms to undergo fission. As a safety precaution the reactor is designed to enable additional rods to be dropped vertically into the reactor core in the event of the core overheating. These rods must be able to withstand the high temperatures in the core to be effective.

Additional information

To ensure that a controlled fission reaction occurs control rods of boron or cadmium are inserted horizontally into the mass of the fuel rods from all sides to depth to keep the chain reaction at the critical phase but prevent the mass of fissionable material from becoming supercritical and the reaction becoming uncontrolled. The control rods absorb neutrons. The depth of control rod insertion is varied as needed.

To assist with temperature control and enable the heat produced during fission to be used a coolant is used to transfer the heat from the reactor core. The coolant is fluid that is circulated through the core. It absorbs heat from the neutrons and fission products. This heat is transferred to a separate water or steam system that drives conventional turbine electricity generators.

identify data sources, and gather, process, and analyse information to describe the use of:

a named isotope in medicine

a named isotope in agriculture

a named isotope in engineering

Identify data sources by refering to Internet sites, modern texts and journals for the latest information. The list below identifies some of the radioactive isotopes used in each of the fields listed above but is by no means a complete list.
Gather appropriate information from the various sources. You should identify one isotope for each example and then do detailed research on that isotopes use.
Process the information by assessing the accuracy of the information.
Analyse the information to find any trends or patterns in the relationship of isotopes for the different purposes.

Medicine: Radioactive isotopes are used in diagnosis as radioactive tracers or in scanning. Isotopes used as such include chlorine¹⁵¹ used for scanning the spleen, iodine¹³¹ used for scanning the lungs and thyroid, technetium⁹⁹ used for scanning the bones and lungs, cobalt⁶⁰ used for radiation treatment of cancers.

Agriculture: Radioactive isotopes are used in the agricultural industry as tracers in plants. Radioisotopes are added to fertilisers in small but known quantities. The uptake of the fertiliser can be measured by the researcher measuring how radioactive a plant has become. This technique is largely a research tool without practical application on farms. Examples of isotopes used for this purpose include phosphorous³² and nitrogen¹⁵.

Engineering: Applications of radioactive isotopes in engineering are varied but mainly centre around smoke detection, using the shielding capacity of a structure or component to measure its thickness. This concept is based on the idea that shielding from radioactivity is increased with greater thicknesses of material in a predictable manner. Another way of using radioactive isotopes themselves in machinery components is to use the rate of radioactive decay from the machine to predict the wear of non-visible radioactive parts. Some uses involve measuring the radioactivity of lubricants that are in contact with machinery that is itself radioactive. As the machine wears the lubricant becomes contaminated with radioactive material. Measuring the radioactivity of the lubricant indicates the amount of wear. Radioisotopes used in measuring the thickness of materials include cobalt⁶⁰ and iridium¹⁹⁰. Americium²⁴¹ is used in smoke detectors.

describe some medical and industrial applications of radio-isotopes

Medical applications of radio-isotopes:
- Radioactive isotopes are used in diagnosis as radioactive tracers or in scanning. A short-half-life isotope is administered into a biological system such as an animal or plant and the progress of that isotope through the system can be described. Its passage and accumulation can lead to important information such as pathways for certain elements or abnormalities in a biological system can be detected.
- Radiation therapy for patients with cancer is a common treatment. The radio-isotope can either be administered to the site of the cancer or radiation from a radio-isotope can be administered externally.
Industrial applications of radio-isotopes.
- Applications of radioactive isotopes in engineering are varied but mainly centre on smoke detection, using the shielding capacity of a structure or component to measure its thickness. This concept is based on the idea that shielding from radioactivity is increased with greater thicknesses of material in a predictable manner.
- Another way of using radioactive isotopes themselves in machinery components is to use the rate of radioactive decay from the machine to predict the wear of non-visible radioactive parts. Some uses involve measuring the radioactivity of lubricants that are in contact with machinery that is itself radioactive. As the machine wears the lubricant becomes contaminated with radioactive material. Measuring the radioactivity of the lubricant indicates the amount of wear.
- Radioactive isotopes such as those of phosphorous and nitrogen are used in the agricultural industry as tracers in plants. Radioisotopes are added to fertilisers in small but known quantities. The uptake of the fertiliser can be measured by the researcher measuring how radioactive a plant has become as a proxy for measuring the fertiliser uptake directly. This technique is largely a research tool without practical application on farms although it does provide farmers with useful information.
- Radioisotopes such as Americium²⁴¹ are used in the fire protection and fire warning industry as smoke detectors. Interruption of the regular stream of ionised radiation being disrupted by the fine smoke particles in the air causes the triggering of the smoke alarms.

describe how neutron scattering is used as a probe by referring to the properties of neutrons

Neutrons are neutral and as such can enter the nucleus much more easily than protons. They are also of a large enough mass to enable them to eject other subatomic particles and smash atoms apart to reveal their inner structure.

identify ways by which physicists continue to develop their understanding of matter using accelerators as a probe to investigate the structure of matter

From the 1930s onward, particle accelerators have enabled physicists to further their knowledge of nuclear structure and reactions. Many different designs have been developed but they all have some common features. The common features of all of these accelerators are:
- they can use any type of charged particle as a projectile and provide those particles with large amounts of kinetic energy. These particles can then be aimed at target atoms.
- they can provide these particles at great rates in a beam
- they can focus these particle beams to increase the probability of collisions and interactions with specific targets.

discuss the key features and components of the standard model of matter, including quarks and leptons

There are thought to be four fundamental forces in nature. They are:
- The gravitational force that acts on all mass in the Universe. Of the fundamental forces this is thought to be the weakest.
- The electromagnetic or coulomb force that acts on all charges and holds atoms and molecules together.
- The nuclear strong force that enables protons and neutrons to form nuclei. This weak force acts only over very short distances such as those within the confines of a nucleus.
- The nuclear weak force that can allow electrons and other types of subatomic particles to change into other types of particles.
The fundamental forces are thought to be associated with the exchange of particles that belong to a family of particles called the bosons. The electromagnetic force is carried by a photon, the gravitational force by a gravitron, the strong force by a gluon and the weak force by a W particle.
These forces interact with the 12 basic subatomic particles (and 12 subatomic anti-particles because every particle has an antiparticle equivalent in mass but opposite in charge) to form matter. How they interact determines whether they are classified as leptons or hadrons. There are six leptons and six hadrons.
The leptons interact by the electromagnetic and weak nuclear forces. They include the electron, muon, tau, electron neutrino, muon neutrino and tau neutrino. Leptons interact with coulomb, gravitational and weak forces.
The hadrons interact by the strong nuclear force. They include particles from the groups known as baryons and mesons. These particles are all made from combination of smaller particles called the quarks. Baryons are made from a combination of three quarks; mesons are made from a quark-antiquark pairs. Quarks interact with coulomb, gravitational and weak forces. Quarks have charges of either +2/3 or -1/3.

gather, process and analyse information to assess the significance of the Manhattan Project to society

Some of the best sources of data on the Manhattan Project can be found on the Internet. Typing in the search terms "Manhattan Project" and "the bomb" will bring up many relevant websites from which you can gather excellent historical and social perspectives on this turning point in human history.
Process and analyse the information from a number of sources to reliably assess the significance of the Manhatten Project to society.

Sample assessment

The Manhattan Project was the second chain reaction after Fermi's 1942 nuclear pile. The difference was this reaction was uncontrolled. In this case, subcritical-mass pieces of plutonium were imploded together by conventional explosives to achieve a critical mass and resulting explosion. This reaction was the first atomic bomb. It was detonated at Algomordo, New Mexico on 16 July 1945. This blast was not large by modern standards with an energy yield equivalent to 20 000 tonnes of TNT. The bomb, as it became known, was dropped on the Japanese cities of Hiroshima and Nagasaki. This cut short the war in the Pacific during WW II. After the war, the race to develop more powerful atomic bombs contributed to the Cold War and effectively split the world into two allied camps. This push for nuclear research led to the establishment of significant science programs and the laboratories at nuclear research laboratories at Los Alamos, and Berkeley in USA and Chalk River, Canada. Research in these locations although primarily aimed at weapons development also contributed positively to many peaceful advances in nuclear technology such as electricity generation and fission reactor power stations.