Transcript 18 NuclearDecay

Nuclear Decay
Graphic: www.lab-initio.com
Nuclear Symbols
Mass number, A
(p+ + no)
235
92
U
Atomic number, Z
(number of p+)
Element symbol
Balancing Nuclear Equations
Areactants
235
+ 1
= 142
U  n
235
92
92
1
0
+
0
=
=
Aproducts
+
91
+ 3(1)
Ba  Kr  3 n
142
56
56
Zreactants
=
91
36
+
36
Zproducts
1
0
+ 3(0)
Balancing Nuclear Equations #2
222
226 = 4 + ____
226
88
Ra   
4
2
222
86
Rn
88 = 2 + ___
86
Atomic number 86 is radon, Rn
Balancing Nuclear Equations #3
95
235 + 1 = 139 + 2(1) + ____
U n
235
92
1
0
I 2 n
139
53
1
0
95
39
39
92 + 0 = 53 + 2(0) + ____
Atomic number 39 is yttrium, Y
Y
Alpha Decay
Alpha production ():
an alpha particle is a
helium nucleus
4
2
He or 
2
U  He 
238
92
4
2
U 
238
92
4
2
4
2
2
234
90
Th
234
90
Th
Alpha decay is limited to heavy, radioactive
nuclei
Alpha
Radiation
Limited to
VERY large
nucleii.
Beta Decay
Beta production (b):
A beta particle is an
electron ejected from
the nucleus
0
1
Th 
234
91
Th 
234
91
234
90
234
90
e or
b
0
1
Pa  e
0
1
Pa  b
0
1
Beta emission converts a neutron to a proton
Beta
Radiation
Converts a
neutron into
a proton.
Gamma Ray Production
Gamma ray production (g):
g
U

He
Th

2
23
4
8
2 30
4
92
2 90
0
Gamma rays are high energy photons
produced in association with other forms of
decay.
Gamma rays are massless and do not, by
themselves, change the nucleus
Gamma Ray Production
Gamma ray production (g):
g
U

He

Th

2
238
4 234
0
92
2
90
0
Gamma rays are high
energy photons produced in
association with other
forms of decay.
Gamma rays are
massless and do not,
by themselves,
change the nucleus
Positron Production
Positron emission:
Positrons are the antiparticle of the electron
0
1
e
Na

e

Ne
22
11
0 22
1 10
Positron emission converts a proton to a neutron
Electron Capture
Electron capture: (inner-orbital electron
is captured by the nucleus)
g
Hg

e

Au

201
0 201
0
80

1 79
0
Electron capture converts a proton to a
neutron
Types of Radiation
Nuclear
Stability
Decay will occur in
such a way as to
return a nucleus to
the band (line) of
stability.
The most stable
nuclide is Iron-56
If Z > 83, the
nuclide is radioactive
Graphic – Wikimedia user : Napy1kenobi
A Decay
Series
A radioactive nucleus
reaches a stable state
by a series of steps
Graphic – Wikimedia Commons User Tosaka
Half-life
Graphic - http://cafreetextbooks.ck12.org/science/CK12_Earth_Science_rev.pdf
Decay Kinetics
Decay occurs by first order kinetics (the
rate of decay is proportional to the number
of nuclides present)
N0 = number of nuclides
present initially
 N 
   kt
ln 
 N0 
N = number of nuclides
remaining at time t
k = rate constant
t = elapsed time
Calculating Half-life
ln( 2) 0.693
t1/ 2 

k
k
t1/2 = Half-life (units dependent
on rate constant, k)
Sample Half-Lives