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Physics 145 Introduction to Experimental Physics I Instructor: Karine Chesnel

Physics 145 Introduction to Experimental Physics I Instructor: Karine Chesnel Office: N319 ESC Tel: 801- 422-5687 kchesnel@byu.edu Office hours: on appointment Class website: http://www.physics.byu.edu/faculty/chesnel/physics145.aspx . Your lab assignments.

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Physics 145 Introduction to Experimental Physics I Instructor: Karine Chesnel

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  1. Physics 145 Introduction to Experimental Physics I Instructor: KarineChesnel Office: N319 ESC Tel: 801- 422-5687 kchesnel@byu.edu Office hours: on appointment Class website: http://www.physics.byu.edu/faculty/chesnel/physics145.aspx

  2. Your lab assignments Prepare by reading the introduction material Answer quiz questions (within the first half hour) and submit the sheet to your TA Proceed to the experiments: L2.1, L2.2, etc… Write a report of your findings for each experiment, in your lab notebook (individual reports)

  3. Lab 4/ Lab 5 Radioactivity Curve fitting Error propagation

  4. Curve fitting Experimental data Linear fit Attempts for fitting the experimental curve

  5. Curve fitting: Examples in crystallography 00-043-1002> Cerianite- - CeO ZrO2 46nm 2 CeO2 19 nm Intensity (a.u.) CexZr1-xO2 0<x<1 Intensity (a.u.) Intensity (a.u.) 28.5 29.0 29.5 30.0 2 q (deg.) 45 46 47 48 49 50 51 52 2 q (deg.) 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 2 q (deg.) Identify different peaks in a spectrum Fit a diffraction peak: Being able to separate peaks in a spectrum

  6. Lab experiment: Radioactivity a - rays (4He nuclei) b - rays (electrons) • - rays (photons)

  7. Lab experiment: Radioactivity Aluminum shield or Lead shield • - rays (photons)

  8. Lab experiment: Radioactivity N • - rays R Radioactive decay: R0 /2 t T1/2 Decay rate: Half-life:

  9. Lab experiment: Radioactivity x2 x1 Counts: N1 N Counts: N2 X R Radiation absorption Number of particles absorbed: R0 /2 x x1/2 Decay rate: Half-length:

  10. Lab 4: Radioactivity- curve fitting A. Experiment • L4.1: get familiar with the equipment: 137Cs source, counting chamber, and Geiger counter • L4.2: Background radiation counts RB • L4.3: Qualitative measure of absorption decay using aluminum sheets

  11. Lab 4: Radioactivity- curve fitting B. Quantitative measure of hal-length in lead • L4.4: Measure counts for varying thicknesses (get ~20 points) Make sure to measure the thicknesses and count for at least 60 sec • L4.5: Plot your results in Excel spreadsheet: Thickness (x), time (T), counts (N), rate (R=N/T) , ln (R-RB) • L4.6: plot R as function of x • L4.7: plot ln (R-RB) as function of x • L4.8: fit with linear regression- use the parameters of fit to estimate: - absorption coefficient m - half length in lead

  12. Lab 4: Radioactivity- curve fitting B. Perform non –linear least square fit • L4.9: Copy your data in Logger Pro: Plot Rate as function of thickness • L4.10: use logger Pro to do an exponential fit use the parameters of fit to estimate: - absorption coefficient m - half length in lead - the background radiation RB Compare results from linear fit and exponential fit

  13. Experimental uncertainties Uncertainty = Accuracy + Precision Difference between Measured/ Expected value Instrument Resolution Statistical Error • - Histogram • - Gaussian distribution • Poisson distribution • mean value • standard deviation / variance

  14. Uncertainty propagation Gaussian error propagation If then If then

  15. Lab 5: Radioactivity- experimental uncertainty • L5.1: Reapeat counts measurements 100 times (10 sec each) • L5.2: Make an histogram • L5.3- 5: analyze distribution • L5. 6- 8 : propagation of error, N , T and rate R • L5.8: perform an non-linear least square fit with error included use the parameters of fit to estimate: - absorption coefficient m - half length in lead - Background counts

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