SCHOOL OF PHYSICS QUANTA TO QUARKS HSC KICKSTART PHYSICS WORKSHOP List of experiments 1. Emission spectrum 2. The Wilson Cloud Chamber 3. Detecting sub-atomic particles 4. Mass defect in radioactive decay 5. Penetration of radioactive emission Name: Find us on vbcvcxz
The spectrum of Hydrogen - solve problems and analyse information using: 1/λ = R(1/n 2 f - 1/n 2 i) - perform a first-hand investigation to observe the visible components of the hydrogen spectrum Hydrogen computer simulation Use the computer program to simulate various transitions. Write down the wavelength for the Balmer series the transition from higher levels ending at energy level 2. Initial level Final Level Frequency Colour 2 2 3 2 4 2 5 2 Hydrogen spectrum Look at the spectrum of the Hydrogen lamp using a hand held spectrometer. Tick off the lines predicted by the computer program. Calculating the energy levels The light that is emitted from excited Hydrogen gas was first observed in the 19 th Century by Anders Angstrom. Johann Balmer later realised could be described by the equation As a cross-check of your observation, now calculate the wavelength of the spectral line that you observed using the Balmer equation: The Balmer Equation Lambda (λ) is the wavelengths in metres, The series of frequencies of light were created by electrons shifting from higher energy levels to lower levels; n f and n i are the energy levels of the electron s final and initial energy levels Show your working on the next page: Page 2
Other spectra Using the spectrometer look at the other lamps. Compare them with the chart on the wall and see if you can identify the element in the lamp. Lamp Number Colour Element various various Bar Heater red All Black body Fluorescent lights white Mercury Page 3
The University of Sydney The Wilson Cloud Chamber - perform a first-hand investigation or gather secondary information to observe radiation emitted from a nucleus using a Wilson cloud chamber or similar detection device - 13.1e (present information): using a variety of pictorial representations to show relationships and present information clearly and succinctly High-energy emissions created in supercolliders are often difficult to detect: they are invisible to our eyes and penetrate many materials. However, as these high-energy particles travel, they have the ability to ionise the surrounding material. The radiation we are observing comes from Radium, which emits α and β radiation. What is the difference between the two emissions? In the space provided, make a sketch of what you see in the cloud chamber. In your sketch, label the following elements: Cloud Chamber, Super saturated methanol layer, Liquid Nitrogen, Radium, α particles, β particles. Liquid Nitrogen Once it was discovered that these fundamental particles were no longer fundamental, the next challenge was to figure out what the particles were. Page 4
Propose a way that you could tell the difference between the α and β particles. Write your contribution in the following appropriate spaces. We will consider your proposals. Point of View: - Students POV - Idea: - Use helmoltz coil around WCC - - Students idea Argument: - Alpha particles absorbes earlier - Students argument Suggestion: - Use different source - Students suggestion The Spark chamber Getting accurate measurements from a Wilson Cloud Chamber was tricky. The spark chamber was the next generation of detector after the cloud and bubble chambers. It was an improvement because it provided and electronic way of collecting the track data. Page 5
Detecting sub-atomic particles with a supercollider - identify ways by which physicists continue to develop their understanding of matter, using accelerators as a probe to investigate the structure of matter Analysing event data from a supercollider is fascinating detective work analysing the energy, mass and momentum of the resulting particles. By analysing the tracks of the secondary particles you can work out the identity of the short-lived particles. This is the problem we are tackling today Page 6
The Mystery particle The screen shows two tracks that do not originate from the centre of the collision. These tracks are the decay products of a mystery particle. Our job is to solve the mystery! p x (GeV/c) p y (GeV/c) p z (GeV/c) E (GeV) Particle 3 Particle 4 Total From sim Rearranging the four-vector from above, the rest mass energy E = mc 2 is: Total mass of Mystery Particle : 0.505 GeV Examine the table of rest-mass energies of particles on the following page and work out which particles are possible candidates for the mystery particle. Which particle(s) could it be? The Mystery particle is : K S Page 7
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Measuring the Mass defect in radioactive decay - explain the concept of a mass defect using Einstein s equivalence between mass and energy - solve problems and analyse information to calculate the mass defect and energy released in natural transmutation and fission reactions - 11.3b (choose equipment or resources): carrying out a risk assessment of intended experimental procedures and identifying and addressing potential hazards Risk Analysis A very important part of any experimentation in physics is the identification of any risks, and the subsequent mitigation of those risks. As you can imagine, scientists use some very cool, and technical pieces of apparatus and equipment. radioactivity falls into this category. Before we begin, identify three risks associated with radioactive materials. Once these risks have been identified, you must identify what might happen if the risks were to eventuate, and of course, what we can do to mitigate against the risks. These would be our safety rules. Assign a number to each of your risks using the table to the left. Risk Consequence Precaution - Become ill - - Radiation poisoning - Lead poisoning - - Use caution - Wash hands - Store radiation carefully - Page 9
In this experiment we measure this mass defect for two radioactive elements. Cs 137 and Co 60 Photomultiplier tube The energy of a Gamma ray can measured using a photomultiplier tube. The first job is to calibrate the system. We do this by measuring the peak from a known source Cs 137 (662 kev). Once we know which bin this peak corresponds to we can calculate the energy for each bin and hence deduce the energy of unknown spectra. Page 10
Peak Cs137 = Bin From experiment Energy per bin = 662 kev / Bin = Next measure the unknown spectrum of Co 60. This will give us an experimental value for the energy defect Experimental Peak number Bin Number Calculated energy (kev) 1 From exp From exp 2 From exp From exp Total - From exp Now we can do the same thing, but this time Mathematically Theoretical The mass of a Co 60 Nucleus is 59.9338, and a Ni 60 nucleus weighs 59.9308 AMU. Calculate is the mass defect in the decay: Mass defect: 0.003 AMU From E = Mc 2 mass can be converted to its equivalent energy. The conversion factor from AMU to kev is 931,500. Calculate the energy defect. Energy defect: 2794.5 kev Does it match up with the energy of the gamma ray emission? Where is the rest of the energy? Difference in Energy defect kev Page 11
Penetration of Radioactive emission - 11.2a (plan first-hand investigations): demonstrate the use of the terms 'dependent' and 'independent' to describe variables involved in the investigation - 12.1a (perform first-hand investigations): carrying out the planned procedure, recognising where and when modifications are needed and analysing the effect of these adjustments - 12.2a (gather first-hand information): using appropriate data collection techniques, employing appropriate technologies including data loggers and sensors Penetration of radiation through air Choose a radioactive source and measure the number of counts on the Geiger tube for 30 seconds with it right next to the detector. Now try it at 4 more positions, each a bit further away Name of Source Am, Cs, Co or Sr Type of emission α, β or γ Counts in 30 seconds Position (cm) 0 Counts Compare with your colleagues measurements for other sources There are two types of variables in a physics experiment, dependant and Independent. Dependant variables are those that you measure, and independent variables, are those that you change. First, identify the control in this experiment. - No sources Identify the experimental variables in this experiment. 1. Dependant - Counts 2. Independent - Distance Page 12
Penetration of radioactivity through solids Put your source in the second slot in the lead castle and measure the counts in 30 seconds. counts Next, place various solids between your source and the detector and fill in the following table. Name of Source Am, Cs, Co or Sr Type of emission α, β or γ Material Counts in 30 s From exp For a spot of collaboration, compare with your colleagues results. Which particle penetrates the furthest? First, identify the control in this experiment. - No sources Identify the experimental variables in this experiment. 1. Dependant - Counts 2. Independent - Shields Page 13