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Nuclear Radiation• nuclear reactions different from other reactions –
________________________________________
________________________________________
1
Nuclear Radiation• in 1895 German physicist Wilhelm Roentgen
discovered that invisible rays were emitted when electrons bombarded the surface of certain materials– named these emissions _________________________
• Marie & Pierre Curie isolated the 1st radioactive material – Marie Curie came up with word ‘radioactive’
– Curies won Nobel Prize in 1903 & Marie won another in 1911
2
Nuclear Radiation• recall from Chapter 4
– nucleus made up of protons and neutrons
– atomic # (_____) is the number of protons
– mass # (______) is the protons + neutrons
– ______________________ are atoms with the same atomic
number but different atomic masses (different # of neutrons)
– nuclides represented by
A = Mass #
Z = Atomic #
X = Element Symbol
3
Nuclear Radiation• example – carbon series of isotopes
carbon–12
carbon–13
carbon–14
4
Nuclear Radiation
• isotopes of atoms with unstable nuclei are called
_______________________
• these radioisotopes emit radiation to try & get a more stable atomic configuration
• while undergoing radioactive decay, atoms lose energy by emitting radiation
• three most common types of radiation are alpha (α), beta (β), & gamma (γ)
5
Nuclear Radiation
Table 24.2 – Pg. 861
6
Nuclear Radiation
Figure 24.2 – Pg. 862
7
Nuclear Radiation• alpha particles (α) have same composition as
helium atoms (2 protons & 2 neutrons) with a +2 charge ( )
Figure 24.3 – Pg. 862
24 He
8
Nuclear Radiation• beta particles (β or e–) are very fast moving
electrons with a –1 charge ( )– emitted when a neutron converts to a proton
10e
Figure 24.4 – Pg. 863
10e
9
Nuclear Radiation• gamma rays (γ) are high energy photons with no
mass or charge ( )– always accompanies other nuclear decays
00
92238U 2
4He + 90234Th + 20
0
10
Nuclear Radiation• x–rays are a form of high-energy electromagnetic
radiation
– not produced by radioactive sources
– emitted from certain materials in an excited state
11
Penetrating Power• the more energy content of the
radiation, the more damage it can cause
• different rays can penetrate different levels of the human body (α stopped by skin, β can penetrate 1cm, are highly penetrating)
12
Radioactive Decay• all decay (except gamma radiation) involves the
conversion of an element into another element
• ______________________________ – when an
atom’s atomic number is altered
• protons & neutrons also called ___________________
• nucleons held in the nucleus by the strong nuclear force
13
Radioactive Decay• ________________________________________
– acts on subatomic particles that are extremely close together & it overcomes the electrostatic repulsion among protons
Figure 24.6 – Pg. 865 14
Radioactive Decay• atoms undergo radioactive decay to gain stability
• types of decay – ___________________________
________________________________________
________________________________________
15
Radioactive Decay• beta decay decreases the # of neutrons in an atom by
converting it to a proton
• results in a new atom with no loss in the
_______________________ & gain of 1 in
_______________________
Figure 24.8a – Pg. 86716
Radioactive Decay• alpha decay decreases the # of neutrons & protons
• results in a new atom with a loss of 4 in the
_______________________ & loss of 2 in
_______________________
Figure 24.8b – Pg. 867
17
Radioactive Decay• _______________________ –
a decay process that involves the emission of a positron from the nucleus to reduce protons
• _______________________ – a particle with the same mass as an electron, but opposite charge
• results in a new atom with no loss in the _______________________ & loss of 1 in _______________________
10e or e+ or +
Figure 24.9a – Pg. 868
18
Radioactive Decay• _____________________ –
occurs when the nucleus of an atom draws in a surrounding electron & combines it with a proton to form a neutron
• results in a decrease in protons
• results in a new atom with no loss in the _____________________ & loss of 1 in _____________________
Figure 24.9b – Pg. 868 19
Radioactive Decay
Table 24.3 – Pg. 868
20
Radioactive Decay• nuclear reactions are expressed by a balanced
nuclear equation
• in nuclear equations mass numbers & charges are conserved – treat the arrow like an equal sign & make sure the mass
numbers & atomic numbers equal on both sides of the equation
21
Radioactive Decay• Examples: Write balanced nuclear equations for the
following processes1. carbon–11 produces a positron
2. bismuth–214 produces a β particle
3. neptunium–237 produces an α particle
4. Uranium-235 undergoes electron capture
5. silver–116 produces a β particle
6. bismuth–211 produces an α particle and 3 gamma rays
22
Radioactive Decay• Examples: carbon–11 produces a positron
611C
611C ? + ?
611C 1
0e + ?
611C 1
0e + ZAX
_____________________________
_____________________________
_____________________________
23
Radioactive Decay• Examples: bismuth–214 produces a β particle
83214 Bi
83214 Bi ? + ?
83214 Bi -1
0e + ?
83214 Bi -1
0e + ZAX
_____________________________
_____________________________
_____________________________
24
Radioactive Decay• Examples: neptunium–237 produces an α
particle
93237Np
93237Np ? + ?
93237Np 2
4He + ?
93237Np 2
4He + ZAX
_____________________________
_____________________________
_____________________________
25
Radioactive Decay• Examples: uranium–235 undergoes electron
capture U23592
? ? + U23592
? e+ U 01-
23592
26
X e+ U AZ
01-
23592
_____________________________
_____________________________
_____________________________
Radioactive Decay• Examples: silver–116 produces a β particle
47116 Ag
27
Radioactive Decay
83211Bi
28
• Examples: bismuth–211 produces an α particle and 3 gamma rays
Radioactive Decay Series• many times a radioactive nucleus can not create a
stable (nonradioactive) atom through a single decay
• ___________________________________________
– a series of nuclear reactions that begins with an
unstable nucleus & results in the formation of a stable
nucleus– most well known series is of uranium–238 to lead–206 (it
takes 14 different radioactive decay steps)
92238U 82
206Pb29
Radioactive Decay Series
Figure 24.10 – Pg. 87030
Radioactive Decay• Example: The first 4 steps of uranium–238 decaying into lead–206 are alpha, beta, beta, alpha. Write the nuclear equation for each
step.
1..
2..
3..
4..
31
Radioactive Decay Rates• to measure the speed (rate) of decays, scientists
use half–lives
• ____________________________ – the amount
of time required for ½ of a radioisotope to decay
into its products
32
Radioactive Decay Rates• every radioactive nuclide has a specific half-life
• from seconds to billions of years
• example: gold–198 (used for cancer treatment) has a half–life of 2.7 days– how much would remain of a 50g implant after 1
week?
33
50g 2.7 days 25g 2.7days 12.5g 2.7 days 6.25g
Radioactive Decay Rates• Example: the half–life of strontium–90 is 29 years; if you
had 10.0 g of strontium–90 today, 29 years from now you would have 5.0 g left
Table 24.4 – Pg. 871
34
Figure 24.11 – Pg. 871
35
Radioactive Decay Rates• each radioisotope has a specific half–life– range from seconds to billions of years
Table 24.5 – Pg. 871
36
Radioactive Decay RatesExample: Krypton-85 is used in indicator lights of
appliances. The half-life of krypton-85 is 11 years. How much of a 2.000 mg sample remains after 33 years?
• 1st look at what is known/unknown:– initial amount = 2.000 mg amount remaining = ? mg
– elapsed time (t) = 33 years
– half-life (T) = 11 years
• 2nd solve for unknown
37
Radioactive Decay Rates• 2nd solve for unknown (cont.)
– since there have been 3 half–lives, then divide initial amount by 2 three times
38
2.0 mg 2
1.0 mg
1.0 mg 2
0.5 mg
0.5 mg 2
Radioactive Decay RatesExample: The half-life of cobalt-57 is 270 days. How
much of a 5.000 mg sample will remain after 810 days?
39
Radioactive Decay Rates• since half-lives are constant, radioisotopes can be
used to determine the age of an object
• ________________________________________
– the process of determining the age of an object
by measuring the amount of certain isotopes– carbon-14 (half-life = 5730 years) dating used to
measure the age of artifacts that were once part of a living organism
– other radioisotopes like uranium-238 (half-life = 4.5x109 years) to date older objects
40
Nuclear Reactions• we’ve seen where one element can be converted
into another through spontaneous emission of radiation (transmutation)
• elements can also be forced to transmutate by bombarding them with high-energy alpha, beta, or gamma radiation
41
Nuclear Reactions• ________________________________________
– the process of striking nuclei with high-velocity charged particles– Rutherford did this in his experiment
– particle accelerators use electrostatic & magnetic fields to accelerate charged particles at high speeds
Figure 24.13– Pg. 875 42
Nuclear Reactions• ________________________________________
– the elements with atomic numbers 93 & higher (right after uranium)
• all these elements were produced by induced transmutation
• they are also radioactive
43
Nuclear Energy• to gain stability heavy nuclei can split into smaller
nuclei
• ________________________________________
– the splitting of nuclei into fragments– fission comes with a very large release of energy
– produces 26 million times as much energy as the an equal amount of natural gas
44
Nuclear Fission• nuclear power plants use fission to produce
electricity– by bombarding uranium-235 with neutrons
45
Nuclear Fission• each fission of uranium-235 releases 2 neutrons
• these 2 neutrons can then cause another fission reaction– which then produces 2 more neutrons
• this self–sustaining process is called a
________________________________________
• amount of energy released can increase rapidly– how atomic bombs work
46
Nuclear Fission
Figure 24.16– Pg. 879 47
Nuclear Fission
48
Nuclear Fission• if exactly one neutron causes another fission event
then the process is said to be critical
• to get to critical state, a specific mass of fissionable
material is used called the ____________________
Figure 24.17– Pg. 880 49
Nuclear Fission• fission can be used to produce energy
• controlled reactions can occur in reactors
• energy produced is used to heat water to make steam to run generators
50
Nuclear Fission
Figure 24.20– Pg. 881 51
Nuclear Fission• inside the reactor core,
neutrons are slowed down by a moderator and by _______________________ (made of substances that absorb neutrons – ex. Cd, B)
• nuclear reactors produce highly radioactive waste
52
Nuclear Energy• can combine lighter elements (mass #s < 60)
• ________________________________________
– the combining of atomic nuclei
• the sun is powered by fusion reactions
53
Nuclear Fusion• fusion seen as better than fission– products are not generally radioactive
– produces much more energy
– lighter elements are more abundant
• however fusion requires extremely high energy for reaction to go– also known as
_________________________________
– ex. fusion of hydrogen atoms needs 5,000,000 K (8,999,540 °F)
54
• 2 types of nuclear energy
1. ________________ – combining 2 light nuclei to form a heavier nucleus
1. ________________ – splitting a heavy nucleus into 2 nuclei with smaller mass #s
Country (in order of total nuclear
output)
% of Total Power Production
1. United States 20.22. France 75.23. Japan 28.94. Russia 17.85. Germany 26.16. South Korea 31.17. Ukraine 48.68. Canada 14.89. United Kingdom 17.910. China 1.9
55
Nuclear Detection• radiation with enough energy to ionize matter that
it collides with is called ionizing radiation
• ______________________________________
uses this to detect radiation
Figure 24.24– Pg. 885 56
Nuclear Detection• also detected by _______________________________– they detect bright flashes when ionizing radiation excites
electrons of atoms
Figure 24.25– Pg. 886 57
Medicinal Uses• radioactive nuclides used to study how healthy areas
of the human body are
• _____________________________ – radioactive
nuclides that can be introduced into organisms and
traced by monitoring their radioactivity
• used to detect diseases & monitor the effectiveness of a drug
58
Medicinal Uses• radiation can damage or destroy healthy cells• can also destroy unhealthy cells (cancer)
• radiation therapy also destroys healthy cells in the process of destroying cancerous cells (side effects)
59
Medicinal Uses
60
Nuclide Half-Life Area of the Body Studied
131I 8.1 days thyroid59Fe 45.1 days red blood cells
99Mo 67 hours metabolism32P 14.3 days eyes, liver, tumors
51Cr 27.8 days red blood cells87Sr 2.8 hours bones99Tc 6.0 hours heart, bones,
liver, lungs133Xe 5.3 days lungs24Na 14.8 hours circulatory system
RadiationTable 24.6 – Pg. 889
61
RadiationTable 24.7 – Pg. 889
62