# Shared Flashcard Set

## Details

Ch. 2: Nuclear Transformations
N/A
31
Physics
07/17/2011

Term
 A. Who first discovered radioactivity? B. In what year did he discover it?
Definition
 A. Antonio Henri Becquerel (1852-1908)B. 1896.
Term
Definition
 A radioactive nucleus has excess energy, which is constantly being redistributed among the nucleons by mutual collisions.  By probability, one of the nucleons (or a byproduct of the decay of a nucleon) will gain enough energy to escape the nucleus.   This escaping particle is called radiation.   Radiation will continue until the nucleus reaches its ground state (becomes stable).
Term
 The process of radioactive decay is also known as ______.
Definition
 Disintegration
Term
 What formula governs the radioactive decay of a given population of radioactive nuclei?
Definition
 ΔN/Δt = -λN ΔN = the change in number of radioactive nuclei per unit time, Δt. λ = decay constant N = number of radioactive nuclei present   Solving for the differential equation dN/dt = -λN:   N = N0e-λt
Term
 A. What is activity? B. What is the SI unit for activity? C. What formula describes activity?
Definition
 A. Activity is the rate of decay of a radioactive nuclide.   B. The SI unit for activity is the becquerel, Bq. 1 Bq = 1 dps C. A = ΔN/Δt = -λN   A = A0e-λt
Term
 A. Besides the SI unit, what is another unit of activity? B. How was this unit traditionally defined?
Definition
 A. Another unit of activity is the curie, Ci.   B. The curie was traditionally defined as the activity of 1g of radium.  However, the activity of 1g of radium has been more accurately measured to be 0.976 Ci (3.61 x 1010 Bq)
Term
 A. What is 'half-life'? B. What is the symbol for half-life? B. Derive the formula for half-life.
Definition
 A. Half-life is defined as the time required for a population of radioactive nuclides to decay to one-half its original value.   B. T1/2   C. N = N0e-λt N0 = 2N 1/2 = e-λt ln(1/2) = ln(e-λt) -0.693 = -λT1/2   T1/2 = 0.693/λ
Term
 A. What is mean life? B. What is mean life also known as? C. How can mean life also be understood? D. What is the symbol for mean life? E. What is the relationship between mean life and half-life?
Definition
 A. Mean life is the average lifetime of a radioactive nucleus.     B. Mean life is also known as Average life.   C. Mean life can be understood by considering an imaginary source that decays at a constant rate, regardless of N:  A = A0.  The imaginary source produces the same number of total disintegrations as the real source decaying exponentially from t=0 to t=∞.  Thus, the mean life will be the total time it takes for all disintegrations to occur divided by the total number of disintegrations (N0).   D. Ta   E. Ta = 1.44 T1/2
Term
 Derive the formula for mean life.
Definition
 ΔN/Δt = -λN   Because A = A0,  ΔN/Δt = -λN0 ΔN = (-λN0)Δt   Let ΔN = N0 (ΔN is now in units of disintegrations; We must replace -λ with +λ):   N0 = (λN0)t   There are N0 disintegrations in time t, Ta is the time it takes for 1 disintegration to occur (because we are assuming constant activity):   N0/N0 = λTa λTa = 1   Ta = 1/λ = 1.44 T1/2
Term
 All elements with Z > ______ are radioactive.
Definition
 82Pb
Term
 Name each radioactive series and indicate the origin and end point for each.
Definition
 1. Uranium series: 23892U ----> 20682Pb     2. Actinium series: 23592U ----> 20782Pb      3. Thorium series: 23290Th ----> 20882Pb
Term
 A. Define radioactive equilibrium. B. Describe the two types of radioactive equilibrium.
Definition
 A. Radioactive equilibrium is a state in which the ratio of activity between a radioactive parent and its radioactive daughter is achieved.   B. Transient Equilibrium: T1/2,Parent > T1/2,Daughter A2/A1 = λ2 / λ2-λ1 = T1 / T1-T2   Ex: 9942Mo (T1/2=67hr) --> 99m43Tc (T1/2=6hr)   Secular Equilibrium: T1/2,Parent >>> T1/2,Daughter A2 = A1   Ex: 22688Ra (T1/2=1622y) --> 22286Rn (T1/2=3.8d)
Term
 A. Describe the general reaction for α-particle decay. B. When does α-particle decay most often occur and why? C. What can be said about the kinetic energy of the emitted α-particle?
Definition
 A. AZX --> A-4Z-2Y + 42He + Q   Ex: 22688Ra (T1/2=1622y) --> 22286Rn + 42He + 4.87 MeV B. α-particle decay most often occurs in radionuclides with Z > 82.  It occurs when the coulombic force of repulsion between protons is great enough to overcome the strong force. C. α-particles are emitted with discrete energies specific to the parent nuclide.
Term
 A. What is disintegration energy? B. Most of the disintegration energy is carried by ______?
Definition
 A. Disintegration energy, Q, is the total energy released in radioactive decay.  It is equivalent to the difference between the mass of the parent nucleus and the sum of the masses of the products.  It appears as the kinetic energy of the products (recoil nucleus, emitted radiation).   B. Most of the disintegration energy is carried by the emitted particles (Because mrecoil nucleus >> memitted particles)
Term
 What are the two types of Β-particle decay?
Definition
 1. Negatron emission (Β- decay) 2. Positron emission (Β+ decay)
Term
 A. Describe the general reaction for Β- decay. B. When does Β- decay occur?
Definition
 A.  10n ---> 11p + 0-1Β + v AZX ---> AZ+1Y + 0-1Β + v + Q     Ex: 3215P (T1/2=14.3d) ---> 3216S + 0-1B + v + 1.7 MeV   * v = antineutrino   B. B- occurs when N/P is too high (the nuclide lies above the region of stability)
Term
 The products of a radioactive decay can be divided into two categories.  They are?
Definition
 1. The recoil nucleus- the daughter nucleus 2. Emitted particles (α, Β, γ, ν, etc)
Term
 A. Describe the general reaction for Β+ decay. B. When does Β+ decay usually occur?
Definition
 A. 11p --> 10n + 0+1Β + v + Q AZX --> AZ-1Y + 0+1Β + v + Q   Ex: 2211Na --> 2210Ne + 0+1Β + v +Q   B. Β+ decay occurs when N/P is too low (the nuclide lies below the region of stability)
Term
 A. Is the spectrum of Β-particle energy discrete or continuous? B. Why? C. Who hypothesized the emission of a second particle in Β-decay and in what year?
Definition
 A. The Β-particle energy spectrum is continuous. B. The spectrum of Β-energies is continuous because more than one particle is emitted.  If only one were emitted, each would have E = Q and a sharp line spectrum would be seen. C. Wolfgang Pauli hypothesized the emission of a second particle, the neutrino, in 1931.
Term
 What is the average Β-energy in relation to Emax?
Definition
 Emitted Β-particles have Eavg ~ 1/3 Emax
Term
 A. Describe the general reaction for electron capture. B. Electron capture is an alternative to ______. C. What is the most common type of electron capture?
Definition
 A. 11p + 0-1e --> 10n + v + Q AZX + 0-1e --> AZ-1Y + v + Q   B. Electron capture is an alternative to Β+ decay.   C. K-capture is the most common type of electron capture.
Term
 1 Ci = ______ Bq
Definition
 3.7 x 1010
Term
 [image]   What type of radioactive equilibrium is this?
Definition
 Transient Equilibrium
Term
 [image]   What type of radioactive equilibrium is this?
Definition
 Secular Equilibrium
Term
 Characteristic x-rays are also known as ______.
Definition
 Fluorescent x-rays
Term
 A. If characteristic x-rays interact with orbital electrons, _____ can be produced. B. This process is known as ______.
Definition
 A. Auger electrons   B. Internal photoelectric effect
Term
 A. What is fluorescent yield? B. What is its symbol? C. What is its relationship with atomic number?
Definition
 A. The emission of characteristic x-rays and the ejection of Auger electrons are competing processes.  The fluorescent yield is defined as the ratio of characteristic (fluorescent) x-rays to the number of electron shell vacancies.   B. ω   C. ω tends to increase with Z. For low-Z materials, Auger electrons are favored.  As Z increases (Z > 30), characteristic x-rays are increasingly predominant.   Ex: Soft Tissue: ω ~ 0Tungsten (Z = 74): ω ~0.93
Term
 A. Describe the process of internal conversion.   B. What other process does internal conversion compete with?
Definition
 A. Internal conversion is a process by which excess nuclear energy is passed on to an orbital electron, which is ejected.   B. Internal conversion competes with the direct emission of a γ-ray from the nucleus.
Term
 A. A daughter nuclide can be unstable, yet remain in this excited state for an appreciable amount of time before returning to its stable ground state.  When this happens, the excited state is known as ______. B. When a nuclide of this type of excited state eventually returns to its ground state, the transformation is called ______.
Definition
 A. the metastable state   B. an isomeric transition
Term
 A. What type of nuclear reaction is responsible for the contamination of high-energy x-ray beams from linear accelerators?   B. Describe this nuclear reaction.   C. At what photon energies does this process generally occur?
Definition
 A. Photodisintegration   B. A high-energy photon interacts with an atomic nucleus, leading to the emission of one or more nucleons (n, p, d, t, α, etc.)   d = deuteron (21H)t = triton (31H)    C. >10 MeV
Term
 What is the value of e?
Definition
 e ~ 2.718
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