1
Q
nuclear chemistry
A
- studies radioactivity, nuclear processes, and nuclear properties
- Nuclear radiation results from reactions that take place in the unstable nuclei of some atoms
- applications:
- Dating items (14C, 238U, etc.)
- Treatment and diagnostics (60Co, 67Ga, etc.)
- Nuclear power
2
Q
mass defect(Δm)
A
- the difference between the mass of a stable nucleus and the masses of the individual nucleons that make it up
3
Q
binding energy(BE)
A
- the energy that would be released when free nucleons combine to form the nucleus of an atom
- It is also the energy needed to split the nucleus into free nucleons
- energy equivalent to the mass defect of a nucleus = BE
4
Q
strong nuclear force
A
- the fundamental force of nature that keeps nucleons together in atomic nuclei
- this is neede bc protons in nucleus will repel each other
- 56Fe is the most stable nuclide because it has the highest binding energy per nucleon
5
Q
nucleons
A
protons and neutrons
protons+neutrons = nucleus
6
Q
isotopes
A
- same number of protons, different number of neutrons
- Same atomic number, different mass number
7
Q
nuclide
A
- an atom with a particular number of neutrons and protons in its nucleus
- Radioactive nuclides spontaneously decay and emit radiation to become more stable
8
Q
unstable nuclei
A
- Unstable nuclides undergo radioactive decay: which is the spontaneous disintegration accompanied by the release of radiation
- Nuclear reaction: a process that changes the number of protons or neutrons in the nucleus of an atom
9
Q
Beta (β) decay
A
- spontaneous ejection of a β particle (high speed electron) by a neutron-rich nucleus
- neutron disintegrates, producing a proton that remains in the nucleus and a high-speed, high-energy electron, called a β particle, that is emitted from the atom
10
Q
positron emission
A
- spontaneous emission of a positron from a neutron-poor nucleus
- Positron = particle with the mass of an e- but a positive charge
11
Q
electron capture
A
- when a neutron-poor nucleus draws in one of its surrounding electrons
12
Q
Alpha (α) decay
A
- nuclear reaction in which an unstable nuclide spontaneously emits an alpha particle
- α particle = helium nucleus
- produce a nuclide with two fewer protons and two fewer neutrons
13
Q
predicting decay pathways
A
- Above the belt – neutron rich, so will usually undergo β decay. # of protons ↑, # of neutrons↓
- Below the belt – neutron poor, so positron emission or electron capture. # of protons ↓, # of neutrons ↑
- Z ≥ 84. These are heavy nuclei, so typically α decay or β decay. # of protons and # of neutrons ↓ with α decay.
14
Q
gamma rays
A
- high energy photons
- therefore, mass and atomic numbers remain the same when they are emitted
- Gamma rays accompany other decays because it represents the energy released when nucleons reorganize to something more stable
- highest energy in the EM spectrum
- are emitted when matter and antimatter collide
15
Q
detecting radioactivity
A
- Radiation was first discovered when Becquerel discovered film darkening in the presence of radiation
- This is still used today in film dosimetry badges
- Scintillation counters use phosphors to absorb energy released by radioactive decay. The phosphors will emit the absorbed energy as visible light.
- measures the intensity of light emitted by phosphors in contact with the samples
16
Q
geiger counter
A
- measures radiation by measuring how much the radiation ionizes the gas inside a sealed detector
17
Q
decay rates
A
- Decay can occur quickly (less than a second) or slowly (see 238U-millions of yrs-used to date rocks)
- Radioactive decay is a 1st order process
- We refer to radioactivity (A) instead of rate and number of atoms (N) instead of concentration
18
Q
biological effects
A
- Depends on exposure, time, whether radiation source is internal or external
- Ionizing radiation – high energy products of radioactive decay that can ionize molecules
- This will produce free electrons and cations
- Inside the body this can lead to burns, cancer, birth defects, etc.
- In medicine ionizing radiation is limited to photons and particles with enough energy to remove an electron from water (~1220 kJ/mol)
- OH is a free radical (i.e. has unpaired electrons) that can rapidly react in the body and disrupt body functions
19
Q
Medical applications
A
- Radiation Therapy – kill diseased tissue. Can be used externally or internally
- Medical imaging – inject a radioactive isotope that will concentrate in certain areas. Use external devices to detect any unusual patterns
20
Q
nuclear fission
A
- Nuclear fission – a nuclear reaction in which a heavy nucleus splits into two lighter nuclei after being hit by another particle. Typically one or more neutrons and energy is also released
- Different fission pathways produce different products – there are often hundreds of pathways
- Chain reactions can start during this process – once started, these can be difficult to control
- A critical mass of fuel is needed for a chain reaction to occur
- **In these reactions the sum of masses of products is less than the sum of masses of reactants. This difference is the energy released (ΔE)**
21
Q
chain rxn(nuclear fission)
A
- a self sustaining series of fission reactions in which the neutrons released when nuclei split apart initiate additional fission events and sustain the reaction
22
Q
critical mass(nuclear fission)
A
- minimum quantity of fissionable material needed to sustain a chain reaction
23
Q
breeder reactor
A
- a nuclear reactor in which fissionable material is produced during normal reactor operation
24
Q
nuclear fusion
A
- a nuclear reaction in which subatomic particles or atomic nuclei collide at high speeds and fuse, forming more massive nuclei and releasing energy
25
26
belt of stability
* the region on a graph of number of neutrons versus number of protons that includes all stable nuclei
27
antimatter
* particles that are the charge opposites of normal subatomic particles
28
electron capture
* a nuclear reaction in which a neutron-poor nucleus draws in one of its surrounding electrons, which transforms a proton in the nucleus into a neutron
29
relative biological effectiveness(RBE)
* a factor that accounts for the differences in physical damage caused by different types of radiation
* see chart to memorize order
