Term
A. Who first discovered radioactivity?
B. In what year did he discover it? 

Definition
A. Antonio Henri Becquerel (18521908) B. 1896. 


Term
Describe the process of radiation. 

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


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 = N_{0}e^{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 = A_{0}e^{}^{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 10^{10} Bq) 


Term
A. What is 'halflife'?
B. What is the symbol for halflife?
B. Derive the formula for halflife. 

Definition
A. Halflife is defined as the time required for a population of radioactive nuclides to decay to onehalf its original value.
B. T_{1/2}
C. N = N_{0}e^{λt}
N_{0} = 2N
1/2 = e^{}^{λt}
ln(1/2) = ln(e^{}^{λ}^{t})
0.693 = λT_{1/2}
T_{1/2} = 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 halflife? 

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 = A_{0}. 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 (N_{0}).
D. T_{a}
E. T_{a} = 1.44 T_{1/2}



Term
Derive the formula for mean life. 

Definition
ΔN/Δt = λN
Because A = A_{0},
ΔN/Δt = λN_{0}
ΔN = (λN_{0})Δt
Let ΔN = N_{0} (ΔN is now in units of disintegrations; We must replace λ with +λ):
N_{0} = (λN_{0)}t
There are N_{0} disintegrations in time t,
T_{a} is the time it takes for 1 disintegration to occur (because we are assuming constant activity):
N_{0}/N_{0} = λT_{a}
λT_{a} = 1
T_{a} = 1/λ = 1.44 T_{1/2} 


Term
All elements with Z > ______ are radioactive. 

Definition


Term
Name each radioactive series and indicate the origin and end point for each. 

Definition
1. Uranium series: ^{238}_{92}U > ^{206}_{82}Pb
2. Actinium series: ^{235}_{92}U > ^{207}_{82}Pb
3. Thorium series: ^{232}_{90}Th > ^{208}_{82}Pb 


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: T_{1/2,Parent} > T_{1/2,Daughter}
A_{2}/A_{1} = λ_{2} / λ_{2}λ_{1} = T_{1} / T_{1}T_{2}
Ex: ^{99}_{42}Mo (T_{1/2}=67hr) > ^{99m}_{43}Tc (T_{1/2}=6hr)
Secular Equilibrium: T_{1/2,Parent} >>> T_{1/2,Daughter}
A_{2} = A_{1}
Ex: ^{226}_{88}Ra (T_{1/2}=1622y) > ^{222}_{86}Rn (T_{1/2}=3.8d) 


Term
A. Describe the general reaction for αparticle decay.
B. When does αparticle decay most often occur and why?
C. What can be said about the kinetic energy of the emitted αparticle? 

Definition
A.
^{A}_{Z}X > ^{A4}_{Z2}Y + ^{4}_{2}He + Q
Ex: ^{226}_{88}Ra (T_{1/2}=1622y) > ^{222}_{86}Rn + ^{4}_{2}He + 4.87 MeV
B. αparticle 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. αparticles 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 m_{recoil nucleus} >> m_{emitted particles}) 


Term
What are the two types of Βparticle 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.
^{1}_{0}n > ^{1}_{1}p + ^{0}_{1}Β + v
^{A}_{Z}X > ^{A}_{Z+1}Y + ^{0}_{1}Β + v + Q
Ex: ^{32}_{15}P (T_{1/2}=14.3d) > ^{32}_{16}S + ^{0}_{1}B + 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.
^{1}_{1}p > ^{1}_{0}n + ^{0}_{+1}Β + v + Q
^{A}_{Z}X > ^{A}_{Z1}Y + ^{0}_{+1}Β + v + Q
Ex: ^{22}_{11}Na > ^{22}_{10}Ne + ^{0}_{+1}Β + 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 Βparticle energy discrete or continuous?
B. Why?
C. Who hypothesized the emission of a second particle in Βdecay and in what year? 

Definition
A. The Βparticle energy spectrum is continuous.
B. The spectrum of Βenergies 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 Βenergy in relation to E_{max}? 

Definition
Emitted Βparticles have E_{avg} ~ 1/3 E_{max} 


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.
^{1}_{1}p + ^{0}_{1}e > ^{1}_{0}n + v + Q
^{A}_{Z}X + ^{0}_{1}e > ^{A}_{Z1}Y + v + Q
B. Electron capture is an alternative to Β^{+} decay.
C. Kcapture is the most common type of electron capture. 


Term

Definition


Term
[image]
What type of radioactive equilibrium is this? 

Definition


Term
[image]
What type of radioactive equilibrium is this? 

Definition


Term
Characteristic xrays are also known as ______. 

Definition


Term
A. If characteristic xrays 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 xrays and the ejection of Auger electrons are competing processes. The fluorescent yield is defined as the ratio of characteristic (fluorescent) xrays to the number of electron shell vacancies.
B. ω
C. ω tends to increase with Z.
For lowZ materials, Auger electrons are favored. As Z increases (Z > 30), characteristic xrays are increasingly predominant.
Ex: Soft Tissue: ω ~ 0 Tungsten (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 γray 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 highenergy xray beams from linear accelerators?
B. Describe this nuclear reaction.
C. At what photon energies does this process generally occur? 

Definition
A. Photodisintegration
B. A highenergy photon interacts with an atomic nucleus, leading to the emission of one or more nucleons (n, p, d, t, α, etc.)
d = deuteron (^{2}_{1}H) t = triton (^{3}_{1}H)
C. >10 MeV 


Term

Definition

