Chapter 19

Question 1

nuclear chemistry

Answer 1

• 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

Question 2

mass defect(Δm)

Answer 2

• the difference between the mass of a stable nucleus and the masses of the individual nucleons that make it up

Question 3

binding energy(BE)

Answer 3

• 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

Question 4

strong nuclear force

Answer 4

• 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

Question 5

nucleons

Answer 5

protons and neutrons

protons+neutrons = nucleus

Question 6

isotopes

Answer 6

• same number of protons, different number of neutrons
  
  • Same atomic number, different mass number

Question 7

nuclide

Answer 7

• an atom with a particular number of neutrons and protons in its nucleus
• Radioactive nuclides spontaneously decay and emit radiation to become more stable

Question 8

unstable nuclei

Answer 8

• 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

Question 9

Beta (β) decay

Answer 9

• 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

Question 10

positron emission

Answer 10

• spontaneous emission of a positron from a neutron-poor nucleus
  
  • Positron = particle with the mass of an e- but a positive charge

Question 11

electron capture

Answer 11

• when a neutron-poor nucleus draws in one of its surrounding electrons

Question 12

Alpha (α) decay

Answer 12

• 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

Question 13

predicting decay pathways

Answer 13

• 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.

Question 14

gamma rays

Answer 14

• 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

Question 15

detecting radioactivity

Answer 15

• 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

Question 16

geiger counter

Answer 16

• measures radiation by measuring how much the radiation ionizes the gas inside a sealed detector

Question 17

decay rates

Answer 17

• 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

Question 18

biological effects

Answer 18

• 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

Question 19

Medical applications

Answer 19

• 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

Question 20

nuclear fission

Answer 20

• 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)**

Question 21

chain rxn(nuclear fission)

Answer 21

• a self sustaining series of fission reactions in which the neutrons released when nuclei split apart initiate additional fission events and sustain the reaction

Question 22

critical mass(nuclear fission)

Answer 22

• minimum quantity of fissionable material needed to sustain a chain reaction

Question 23

breeder reactor

Answer 23

• a nuclear reactor in which fissionable material is produced during normal reactor operation

Question 24

nuclear fusion

Answer 24

• a nuclear reaction in which subatomic particles or atomic nuclei collide at high speeds and fuse, forming more massive nuclei and releasing energy

Question 26

belt of stability

Answer 26

* the region on a graph of number of neutrons versus number of protons that includes all stable nuclei

Question 27

antimatter

Answer 27

* particles that are the charge opposites of normal subatomic particles

Question 28

electron capture

Answer 28

* 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

Question 29

relative biological effectiveness(RBE)

Answer 29

* a factor that accounts for the differences in physical damage caused by different types of radiation * see chart to memorize order