Alpha Decay. Radioactive Decay Alpha Decay Radioactive Decay Alpha Decay Beta Decay.
Radioactive decay pt. 2 - BYU Physics and Astronomy 37 11... · Radioactive decay pt. 2 Class 37:...
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Radioactive decay pt. 2 Class 37: (ThT Q) What role does E = mc 2 play in nuclear physics?
Transcript of Radioactive decay pt. 2 - BYU Physics and Astronomy 37 11... · Radioactive decay pt. 2 Class 37:...
Radioactive decay pt. 2
Class 37: (ThT Q) What role does E = mc2 play
in nuclear physics?
Did you complete at least 70% of Chapter 44:5-7?
A.YesB.No
More on T½, Writing Nuclear reactions.
4-5 common onesQ of reaction.
Applications/ facts about Radioactivity.Natural Radioactivity. Facts
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Today: More on T½, Writing Nuclear reactions. 4-5 common onesQ of reaction. Applications/ facts about Radioactivity. Natural Radioactivity. FactsIf you used the physics tutorial lab this semester, we invite you to rate the tutors you received help from. The rating form, as well as the photos of the tutors, is at http://gardner.byu.edu/tas/tutorrating.html
Lab 8 & 9 began.
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Review eye & glasses think about �signs for p and q. �1. compound devices are all about �angular magnification.�2. What does the objective lens do? Next time: Physical optics: Diffraction.
Lab 8 Postponed.
-► Exam Redo was Due on Wed
Viewing assignment for Friday Apr. 10 Microwaves, Icebergs, and Global Warming; David Long; BYU Forum Address: January 27, 2009
http://www.byub.org/talks/Talk.aspx?id=2994
• Decay rate R = dN/dt = -λN; • N = # nuclei λ = decay constant• Solve for N: N = Noe–λt
• Half-life N = ½ N0
• T½ = ln 2/λ• Note: R = R0e-λt
Fig 44-9, p.1453
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Active Figure 44.9 Plot of the exponential decay law for radioactive nuclei. The vertical axis represents the number of undecayed radioactive nuclei present at any time t, and the horizontal axis is time. The time T1/2 is the half-life of the sample.
Suppose we are using a Geiger counter to measure the decay rate of several radioactive samples. One sample is more active than the others. Which of the following is a possible reason? (pp)
A. more radioactive nucleiB. shorter half-lifeC. either of the above
Video Encyclopedia of Physics Demos #16
What role does E = mc2 play in nuclear physics?
• Half-lives• Alpha decay
– Smoke detectors– Radon in environment
• Beta decay (also positron decay)– Evidences for the little neutral one– K 40 – Carbon dating
• Natural radioactivity – U and Th (Np)– Formation of solar system and extinct light elements
Fig 44-8, p.1453
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Figure 44.8 The radiation from radioactive sources can be separated into three components by using a magnetic field to deflect the charged particles. The detector array at the right records the events. The gamma ray is not deflected by the magnetic field.
When there is an alpha decay, the charge on the resulting nucleus
A. Stays the sameB. Increases by oneC. Increases by two D. Decreases by oneE. Decreases by two
Fig 44-11, p.1457
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Active Figure 44.11 The alpha decay of radium-226. The radium nucleus is initially at rest. After the decay, the radon nucleus has kinetic energy KRn and momentum pRn, and the alpha particle has kinetic energy Ka and momentum pa.
Consider the alpha decay of uranium 238 to thorium 234, which mass is greater?A.U 238B.Th 234 + helium-4Hint: think about
E=Mc2
Alpha decay
• U238 to Th234 + alpha + Q• mUc2 = mThc2 + mHec2 + Q• Thus, Q = 4.3 MeV• The greater the Q the shorter
the t½ . And not just a little bit.
Fig 44-12, p.1459
Tunneling
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Figure 44.12 Potential energy versus separation distance for a system consisting of an alpha particle and a daughter nucleus. Classically, the energy of the alpha particle is not sufficiently large to overcome the energy barrier, and so the particle should not be able to escape from the nucleus. In reality, the alpha particle does escape by tunneling through the barrier.
Fig 44-10, p.1457
Yellow is alpha decay
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Active Figure 44.10 A close-up view of the line of stability in Figure 44.4 from Z = 65 to Z = 80. The blue dots represent stable nuclei as in Figure 44.4. The other colored dots represent unstable isotopes above and below the line of stability, with the color of the dot indicating the primary means of decay.
• Americium 241- half-life 432 years
Fig 44-13a, p.1459
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Figure 44.13 (a) A smoke detector uses alpha decay to determine whether smoke is in the air. © 1998 by the AAAS
Fig 44-13b, p.1459
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Figure 44.13 (b) Smoke entering the chamber reduces the detected current, causing the alarm to sound..
Fig 44-17, p.1465
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Figure 44.17 Successive decays for the 232Th series.
Radon in environment222 218 4 86 Rn 84
Po + 2 He
T½ = 4 days 222 average home: 25 million 86 Rn/m3
222 entire earth composed of 86 Rn Mearth MRn
= 1.6 x 1049 atoms
164 half-lives less than 2 y
There are other alpha series.
Fig 44-10, p.1457
Red is beta decay
Green is beta plus or e-capture.
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Active Figure 44.10 A close-up view of the line of stability in Figure 44.4 from Z = 65 to Z = 80. The blue dots represent stable nuclei as in Figure 44.4. The other colored dots represent unstable isotopes above and below the line of stability, with the color of the dot indicating the primary means of decay.
Beta decay• Evidences for the little neutral one• K 40 • Carbon dating
Fig 44-14, p.1460
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Active Figure 44.14 (a) Distribution of beta particle energies in a typical beta decay. All energies are observed up to a maximum value. (b) In contrast, the energies of alpha particles from an alpha decay are discrete.
Fig 44-14a, p.1460
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Active Figure 44.14 (a) Distribution of beta particle energies in a typical beta decay. All energies are observed up to a maximum value.
Fig 44-15, p.1461
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Active Figure 44.15 (a) The beta decay of carbon-14. The final products of the decay are the nitrogen-14 nucleus, an electron, and an antineutrino. (b) The beta decay of nitrogen- 12. The final products of the decay are the carbon-12 nucleus, a positron, and a neutrino.
Fig 44-15a, p.1461
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Active Figure 44.15 (a) The beta decay of carbon-14. The final products of the decay are the nitrogen-14 nucleus, an electron, and an antineutrino.
Fig 44-16, p.1464
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Figure 44.16 An energy-level diagram showing the initial nuclear state of a 12B nucleus and two possible lower-energy states of the 12C nucleus. The beta decay of the 12B nucleus can result in either of two situations: the 12C nucleus is in the ground state or in the excited state, in which case the nucleus is denoted as 12C*. In the latter case, the beta decay to 12C* is followed by a gamma decay to 12C as the excited nucleus makes a transition to the ground state.
Table 44-3, p.1464
Carbon-14 dating
14 Generation of 6 C
Cosmic rays neutrons 14 14 1 n + 7 N 6 C + 1 H
Decay 14 14 6 C 7 N + β– + ˉν
T½ = 5700 y
Potassium 40• This is really weird
– It is a heavier atom with odd number of protons and neutrons.
– Decaying could even up the score – Either β+ or β- or e- capture. Why doesn’t it do
it rapidly?
40 40 19 K 20 Ca + β– + ˉν
It does; it also does this.
• But why does it take so long? • T ½ = 1.3 billion years. • Carrying away angular momentum.
40 K 40 Ar + β+ + ν19 18
Table 44-5, p.1467
Natural radioactivity
Table 44-4, p.1465
Fig 44-17, p.1465
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Figure 44.17 Successive decays for the 232Th series.
Which element has long-lived mass 5? pp
A. Hydrogen (quintium)B. HeliumC. LithiumD. More than one of the
aboveE. None of the above
Nuclear-isotope trivia• Are there any even numbered (even atomic
number, Z) elements which only have one stable isotope?
• What elements with an atomic number less than 22 have an isotope which is radioactive with a half life greater 10,000 year? Which isotopes are they? Extinct isotopes in meteors.
• What element has an isotope with an A =8?
• Are there any nuclear reactions with a Q>10 which do not involve absorption of a neutron? What is the consequence for nuclear research/devices?
• What element has a stable isotope with an A =5?
• Why are there only four alpha-decay series of the heaviest elements? Why are only 3 of the 4 series naturally producing daughters on earth?
