Download II. Radioactive Decay

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Rutherford backscattering spectrometry wikipedia, lookup

Isotopic labeling wikipedia, lookup

Mössbauer spectroscopy wikipedia, lookup

Electron scattering wikipedia, lookup

Proton wikipedia, lookup

Transcript
CHAPTER 22
Nuclear Chemistry
Types of Radiation
 Isotopes - atoms of the same element with the
same number of protons but different numbers
of neutrons
 Radioisotopes – isotope with an unstable
nucleus that emits radiation to become a more
stable nucleus
 Radioactive Decay – spontaneous reaction in
which unstable nuclei lose energy in the form of
nuclear particles
Nuclear Stability
 Why do atoms decay anyway…
 need stable ratio of neutrons to protons
• Small atoms are stable with a 1 to 1 ratio
of protons to neutrons
• As the atomic number increases, atoms
tend to have more neutrons than protons
with stable ratio increasing to 1 to 1.5
 The type of unbalance that is present in the
nucleus determines the type of decay.
Nuclear Stability
Half-life
 Half-life (t½)
 Time required for half the atoms of a
radioactive nuclide to decay.
 Shorter half-life = less stable.
C. Johannesson
Half-life
mf  m ( )
1 n
i 2
mf: final mass
mi: initial mass
n: # of half-lives
Half-life
 Fluorine-21 has a half-life of 5.0 seconds. If you start
with 25 g of fluorine-21, how many grams would remain
after 60.0 s?
GIVEN:
WORK:
t½ = 5.0 s
mi = 25 g
mf = ?
total time = 60.0 s
n = 60.0s ÷ 5.0s
n = 12
mf = mi (½)n
mf = (25 g)(0.5)12
mf = 0.0061 g
Types of Nuclear Particles
Alpha particle (α)
 Composition: 2 protons, 2
neutrons
 Symbol: 4He or α
 Charge: +2
 Penetrating power: low, stopped
by paper or cloth
Beta particle (β)
 Composition: 1 electron
 Symbol: -1 e
 Charge: -1
 Penetrating power: 100 times
greater than alpha, stopped by
wood or concrete
Gamma ray (γ )
 Composition: electromagnetic
waves
 Symbol: γ
 Charge: 0
 Penetrating power: 1000 times
greater than beta, stopped by lead
or 6 feet of concrete
Types of Nuclear Decay
 Alpha Emission
238
92
parent
nuclide
U
Th  He
234
90
daughter
nuclide
4
2
alpha
particle
Numbers must balance!!
Types of Nuclear Decay
 Beta Emission
131
53
I
131
54
Xe  e
0
-1
electron
 Positron Emission
38
19
K
38
18
C. Johannesson
Ar 
0
1
e
positron
Types of Nuclear Decay
 Electron Capture
106
47
Ag  e 
0
-1
106
46
Pd
electron
 Transmutation
 One element becomes another.
Fission vs. fusion
Fission
 splitting a nucleus into two or more smaller
nuclei
 1 g of 235U =
3 tons of coal
235
92
U
Fission
 chain reaction - self-propagating reaction
 critical mass mass required
to sustain a
chain reaction
Fusion
 combining of two nuclei to form one
nucleus of larger mass
 thermonuclear reaction – requires temp of
40,000,000 K to sustain
 1 g of fusion fuel =
20 tons of coal
 occurs naturally in
stars
2
1
H H
3
1
C. Johannesson
Fission vs. Fusion
F
I
S
S
I
O
N
 235U is limited
 danger of meltdown
 toxic waste
 thermal pollution
F
U
S
I
O
N




fuel is abundant
no danger of meltdown
no toxic waste
not yet sustainable