Download HChemTROCh17Sec3PositronsAND10Exposure

Chapter 17
Section 3 Continued – Positron
emission
Section 10 Effects of Radiation on Life
Background Radiation
• Radiation from natural sources including:
▫ Cosmic rays, radioisotopes in the air, water, soil,
and rocks
• And from artificial sources such as:
▫ X-rays, nuclear medicine
• We are exposed to about 100mrem each year
depending upon where we live. (lower altitudes
exposes people to less radiation because air
absorbs some of the rays)
Uranium-238
• It takes over 4.5 billion years for Uranium-238
to decay, through a series of 14 nuclear
reactions, into stable lead-206 (see figure 17.9
on page 625)
• Realize that Uranium and Thorium are only a
serious threat when swallowed or inhaled
because they breakdown into other radioactive
elements like radium which can destroy cells
when trapped inside the body.
Exposure
• 82% of our exposure is from natural sources
▫ (Of which 55% is from Radon)
• 18% from Artificial sources (ex. X-rays)
• Exposure to Radon polluted air can cause lung
cancer. (same as smoking cigarettes)
• For the most part, since we have been exposed to
natural radiation our entire lives, there is little
permanent damage to our bodies.
Artificial Transmutations
• Do not occur naturally
• First produced by Ernest Rutherford in 1919
when he bombarded nitrogen with alpha
particles and produced oxygen and a proton
(hydrogen).
14
7
N  He  O  H
4
2
17
8
1
1
• 11 H is used to represent the 1 proton.
• This proved the existence of protons
James Chadwick and the Neutron
• 1932, discovered the neutron when he
bombarded beryllium with alpha particles.
9
4
Be  He  C  n
4
2
12
6
1
0
Nuclear Bombardment
• Example problem: When aluminum-27 is
bombarded with alpha particles, phoshporous 30 is produced along with what other particle?
27
13
Al  He  P  ?
4
2
30
15
• Solution:
27
13
Al  He  P  n
4
2
30
15
1
0
Induced Radioactivity
• 1934, Discovered by Marie Curie’s daughter
Irene and her husband Frederic Joliot
• Up to this point only stable nuclei had been
produced from artificial transmutation.
• They were able to produce phosphorous-30 an
unstable isotope when they bombarded
Aluminum-27 with alpha particles.
• The phosphorus-30 emits positrons, 10 e
30
15
P  e Si
0
1
30
14
Where does the positron come
from?
• A hydrogen proton is changed into a neutron
and a positron is emitted from the nucleus.
• Once the positron is emitted the nucleus has one
less proton but an additional neutron. Same
mass number but different atomic number.
1
1
H  e n
0
1
1
0
Example Problem
• Write a balanced nuclear equation for the
emission of a positron by sulfur-31.
• Solution:
31
16
S  e P
0
1
31
15
More Example problems
• Neptunium-238 is unstable and emits a beta
particle when it decays. Write a balanced
equation showing this decay and the new
element formed.
• Solution:
238
93
Np  e Pu
0
1
238
94
Homework
• Read pages 619-621 and 631-632
• Answer questions on page 637- #16, 24, 56, &64