Nuclear Spectroscopy

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186 keV (3.3%) 218 Po 84 γ 222 Rn 86 226 Ra 88 As with the thorium decay chain, the 238 U decay chain has isotopes of very different half-lives, only a few of which emit gammas. In equilibrium the activity of each isotope of a decay series is the same, resulting in a significant number of radium atoms. Chemically, radium is calcium-like and can be found naturally in many biological systems that concentrate calcium. 214 Pb 82 214 83 Bi γ 53.2 keV (2%) 241.9 keV (8%) 295.2 keV (19%) 352 keV (37%) The following exercises are observations of the presence or absence of elements in the the uranium decay series, and a few measurements of their physical properties. Exercise 13.1 Gamma Spectra from Materials Containing Uranium γ 609 keV (46%) 768 keV (5%) 934 keV (3%) 1,120 keV (15%) 1,238 keV (6%) 1,378 keV (4%) 1,764.5 keV (16%) 2,204 keV (5%) 2,448 keV (2%) OBJECTIVE Observe gammas from sources containing uranium and members of the uranium decay series. Gammas from isotopes of radium and lighter members of the decay series should be seen only in old sources. You may determine the meaning of old from your own observations. Relative activities of each isotope relative to 214 Bi will be measured. Stable 210 82 Pb 210 83 Bi 214 84 Po 210 206 82 Pb 84 Po Figure 13.2 The Uranium-238 decay series from radium to the stable lead isotope, mass 206. γ 46.5 keV (4% + IC) SUPPLIES • Uranyl nitrate (new) • Any OLD bottle of a uranium compound that is sealed •Uranium ore, orange Fiesta Ware, Depression-era glass •A uranium source with enriched 235 U SUGGESTED EXPERIMENTAL PROCEDURE 1. Prepare your detector system for PHA of energies up to 1,300 keV. 2. Acquire and save a good spectrum from each uranium sample. 3. Correct the spectra for background radiation. DATA ANALYSIS Record the photopeak energies and net counts for all significant peaks that you observe in your spectra. Can you explain the absence or presence of gamma 41
1 0.8 which is coincident with the gamma from the 226 Ra decay. An enriched source will have a much larger peak at 185 keV than you have observed for the natural uranium ores. Activity 0.6 0.4 Pb-214 Bi-214 Exercise 13.2 Gamma Spectra from Materials Containing Radium and Radon 0.2 ratio (Bi/Pb) 0 0 50 100 150 200 250 300 Time (min) Figure 13.3 Uranium daughter activities as a function of time. photopeaks with energies above 400 keV in your spectra? Refer to Figures 13.1 and 13.2 to guide your analysis. If the isotopes of a decay series, such as uranium, are left undisturbed, then the series approaches an equilibrium (see Figure 13.3) with the property that the activities of each isotope are the same (See the discussion in Appendix C). Using your measured net counts, the gamma decay factors from Appendix E, and the detector efficiency of Figure 10.1, calculate the ratio of measured activities relative to the activity of the 352 keV photopeak from 214 Pb. The detector’s solid angle cancels in all ratios, so the use of the efficiencies from Figure 10.1 is valid for these calculations. Are the activity ratios of the gamma intensities from 214 Bi consistent with each other? Are the activity ratios from gammas emitted by 214 Pb and 214 Bi (and any other observed isotopes) consistent with each other, and should they be so? What are the statistical limitations to your net photopeak counts? If any photopeaks lie on Compton edges or overlap possible backscattering peaks, then your measurements of the net counts in those peaks is very suspect. If you located and observed an enriched uranium source, the signature gamma for 235 U decay series is the 185 keV gamma (from 54% of all 235 U decays), OBJECTIVE Observe gammas from sources containing radium and radon. Radon, an inert gas, can diffuse easily through many materials, disrupting the equilibrium activities of the rest of the decay series. Not all radium sources will show good series equilibrium, even if the sources are old enough for equilibrium to exist. SUPPLIES •Radon charcoal canister •An old clock or watch with a luminous (radium) dial •Brazil nuts (two pounds, shelled) SUGGESTED EXPERIMENTAL PROCEDURE 1. Start the MCA and check your calibration, as in #13.1. 2. Acquire and save a good spectrum from each radium/radon sample. 3. Correct the spectra for background radiation. 4. Place the charcoal canister in a basement with poor or no ventilation for a few days. Retrieve the canister and acquire a spectrum. 5. Finely chop the Brazil nuts in a blender and store them in a plastic bag. Remove the detector from its shielding and cover it with a plastic bag. Surround the detector with the nuts, and surround the entire assemblage with lead or iron shielding. Acquire a spectrum from the nuts. DATA ANALYSIS Record the photopeak energies and net counts for all significant peaks that you observe in your spectra. The Brazil nuts and the clock contain the radium isotope, 226 Ra. Are the spectra of the two radium sources 42
Page 1 and 2: Experimental γ Ray Spectroscopy an
Page 3 and 4: Published by Spectrum Techniques Al
Page 5 and 6: I N T R O D U C T I O N INTRODUCTIO
Page 7 and 8: Cardwell, and especially Robert Bra
Page 9 and 10: OBJECTIVE Calibrate the gamma-ray s
Page 11 and 12: E X P E R I M E N T 2 Gamma Spectra
Page 13 and 14: E X P E R I M E N T 3 Detector Ener
Page 15 and 16: E X P E R I M E N T 4 Compton Scatt
Page 17 and 18: DATA ANALYSIS, A CLASSICAL APPROACH
Page 19 and 20: Figure 5.3. Spectrum for the β −
Page 21 and 22: SUPPLIES •NaI(Tl) detector with M
Page 23 and 24: 14 12 X-Ray Energy (keV) 10 8 6 4 2
Page 25 and 26: E X P E R I M E N T 8 Multichannel
Page 27 and 28: E X P E R I M E N T 9 Counting Stat
Page 29 and 30: E X P E R I M E N T 10 Absolute Act
Page 31 and 32: gammas. This is true for 22 Na and
Page 33 and 34: E X P E R I M E N T 11 Potassium 40
Page 35 and 36: Exercise 11.2 Potassium in Fertiliz
Page 37 and 38: tern mantles, will have observably
Page 39 and 40: is needed. The activities of all is
Page 41: E X P E R I M E N T 13 Uranium 238
Page 45 and 46: of this type data, more is learned
Page 47 and 48: SUPPLIES •Some form of air pump t
Page 49 and 50: Exercise 14.4 Nuclear Fission Sever
Page 51 and 52: Table 14.1 Gamma-emitting Radioisot
Page 53 and 54: INSTALLATION ON A MACINTOSH MICROCO
Page 55 and 56: Regions of Interest. Region of inte
Page 57 and 58: Position the marker at the channel
Page 59 and 60: View Settings The VIEW SETTINGS men
Page 61 and 62: First acquire a spectrum of the sam
Page 63 and 64: Na I (Tl) D2 Electrons Anode θ θ
Page 65 and 66: the multichannel analyzer’s typic
Page 67 and 68: The solutions to these coupled diff
Page 69 and 70: A P P E N D I X D Radioactive Decay
Page 71 and 72: 7/2+ 137 55 Cs 93.5% β 30.0 y - 90
Page 73 and 74: A P P E N D I X E List of Commonly
Page 75 and 76: Energy Element Half Life Associated
Page 77 and 78: Atomic K α1 Energy K α2 Energy K-
Page 79 and 80: C. Hohenemser and I. M. Asher,“A
Page 81: General References. Nuclides and Is

Nuclear Spectroscopy

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