1. Bettelheim, Brown, Campbell and Farrell Chapter 9
Nuclear Chemistry
Bettelheim, Brown, Campbell and Farrell
Chapter 9

2. Nuclear Chemistry Background Types of radiation Nuclear Equations
Half-Lives
Units
Uses
Medical
Other

3. Nuclear Reactions Involve changes in nuclei
Protons and Neutrons----NOT Electrons

4. Nuclear Chemistry- the study of the properties and reactions of atomic nuclei

5. Introduction
Nuclear radiation: radiation emitted from a nucleus during nuclear decay
Results from an unstable nuclei
alpha particle (a): a helium nucleus, He2+; contains two protons and two neutrons, has mass of 4 amu, and atomic number 2
beta particle (b): an electron; has a charge of -1, and a mass of amu
gamma ray (g): high-energy electromagnetic radiation;
positron (b+): has the mass of an electron but a charge of +1

6. Representing Isotopes
12C 6
14C
14N + 0e 6 7 -1
Example of a nuclear equation

7. Nuclear Radiation There are more than 300 naturally occurring isotopes
264 are stable
More than 1000 artificial isotopes have been made in the laboratory; all are radioactive

8. Alpha Emission
in alpha emission, the new element formed has an atomic number two units lower and a mass number four units lower

9. Beta Emission
beta emission: decomposition of a neutron to a proton and an electron
emission of a beta particle transforms the element into a new element with the same mass number but an atomic number one unit greater
Problem: carbon-14 is a beta emitter. When it undergoes beta emission, into what element is it converted?

10. Positron Emission
positron emission: decomposition of a proton in the nucleus to a give a “positive electron” (and a neutron)
in positron emission, the new element formed has an atomic number one unit lower but the same mass number

11. Electron Capture
electron capture: electron near the nucleus is “captured” and combines with a proton to form a neutron)
in electron capture, the new element formed has an atomic number one unit lower but the same mass number
12553I e → Te

12. Gamma Emission
In pure gamma emission, there is no change in either the atomic number or the mass number of the element
a nucleus in a higher-energy state emits gamma radiation as it returns to its ground state (its most stable energy state)
Usually accompanies  or  emission
60Co 27

13. Half-Life
half-life of a radioisotope, t1/2: the time it takes one half of a sample of a radioisotope to decay
Amount of radioactive material left is given by
Rt = (1/2n)Ri
where Ri is initial amount of radioactivity, Rt is the amount of radioactivity at time t, and n is the number of half-lives
Half-Life = 8 days

14. Amount left

16. If you start with 50 Curies of P-32, how much is left after 28. 6 days
If you start with 50 Curies of P-32, how much is left after 28.6 days? (t½ = 14.3 days)

18. Two factors determine how dangerous different kinds of radiation are
Ionizing power: Ability to cause damage
Penetrating power: How far radiation will travel into the body

19. Ionizing Power
Ionizing power is the ability to knock off electrons and thus cause damage
Alpha particles have highest ionizing power
Beta particles have moderate ionizing power
Gamma rays have least ionizing power

20. Ability to penetrate sample

21. Comparison of Radiation Types
Ionizing Power
(do damage)
How far will it penetrate?
Alpha
High
Stopped by piece of paper
Beta
Medium
Stopped by thin sheet of metal or plexiglass
Gamma
Low
Pass through tissue easily

22. Radiation Dosimetry
Curie (Ci) or millicurie (mCi): measure of the number of radioactive disintegrations occurring each second in a sample. (1Ci = 3.7 x 1010 dps)
Roentgen (R): amount of radiation delivered by a radiation source
Radiation absorbed dose (Rad): a unit for measuring the energy absorbed per g of material exposed to a radiation source
Roentgen-equivalent-man (Rem): measures the tissue damage caused by radiation
Preferred for medical purposes

24. Radiation Dosimetry
Average exposure to radiation from common sources

25. Measuring Devices Film Badge Geiger-Mueller Counter
Scintillation counters

26. Geiger-Müller Counter

27. Geiger-Müller Counter

28. Measurement of Radioactivity and Radioactive Exposure
Curie: amount of radioactivity which gives x 1010 dps
dps = disintegrations per second
Disintegration = decay of a single atom

29. Measurement of Radioactive Exposure
Roentgen = amount of radiation that produces ions which have 2.56 x 10-4 coulombs/kg
Radiation absorbed dose (Rad) = energy absorbed per gram of material exposed to a radiation source
REM = Roentgen Equivalent Man
Rem is measure of the effect of radiation when one Roentgen is absorbed

30. Medical/Research Uses
Experimental Tracers
Basic biochemical and medical research
Diagnostic Uses
Organ scans involving preferential uptake of isotopes
I-131 concentrates in thyroxine in thyroid gland
Medical Imaging
PET Scan – positron and electron →2 gamma rays
MRI—imaging of soft tissue, such as brain, spinal cord

31. Medical/Research Uses
Radiation Therapy
Aim high energy radiation at cancer cells
Radiation affects rapidly growing cells more
Cobalt-60 often used for brain tumors
Actinium- 225 attached to monoclonal antibody targets prostate cancer (binds to PSA on cell surface)

32. Fission and Fusion Fusion
Combining smaller nuclei to form a larger nucleus
Fission
“Splitting” of a larger nucleus to form smaller nuclei
Energy is released in both fusion and fission

33. Nuclear Fission “Split” a larger nucleus into smaller nuclei.
Used in nuclear power plants
Used in the Atomic bomb
Energy is released.

34. Chain Reaction Chain reaction:
Self-sustaining reaction in which the products of one reaction event initiate another reaction event
Critical Mass:
Minimum amount of an isotope needed to sustain a chain reaction

35. Chain Reaction 04-13 Title: Nuclear Chain Reaction Caption:
The process by which a chain reaction develops when uranium-235 undergoes fission. Note the different fission products.
Notes:
Uncontrolled chain reactions lead to powerful explosions.

36. Nuclear Power Plants Utilize “controlled” Fission Reaction
Fuel rods contain radioactive material
Moderator slows speed of neutrons (water or graphite)
Control rods contain neutron-absorbing material such as Cd or B
Control rods can be raised or lowered to control the number of neutrons available for the reaction

37. Nuclear Power Plant
Figure: 21-20C

38. Nuclear Reactor Control rods can absorb neutrons
Control rods can be lowered to absorb more neutrons (slow reaction)
Control rods can be raised to absorb fewer neutrons (increase reaction)
Figure: 21-19

39. Use of Nuclear Power % of total electricity France 75 Sweden 47
Europe
US 20
Canada 13

40. Comparison of Nuclear and Fossil Fuel Power Plants
Radioactive material NOT connected to outside world
Does NOT pollute air
Fossil Fuel:
Smoke stack open to air
DOES emit air pollutants

41. Major Problem Fuel rods need to be replaced periodically
Disposal of “spent” rods--nuclear waste
Currently dry cask storage on site
Yucca Mountain proposed as nuclear repository site

42. Recycling of spent fuel
Possible to reprocess spent fuel to concentrate Pu-239 and U-235
Pu-239 potentially used for nuclear weapons
US does not currently reprocess spent fuel

43. Problems with Plant Operation
Three Mile Island 1979
failure of water pump
partial core meltdown
Chernobyl 1986
poor design
only graphite moderator (burns)
inadequate reactor containment

44. Fusion Occurs in sun Theoretically wonderful source of energy
Lots of water and H sources available
Have not yet achieved fusion
Requires very high temperatures