Nuclei and their labels
Nuclear “strong” force holds them together
Strong force is same between, n,n n,p, p,p
Fig. 29-2 , p.9 41
Z = the number of protons in the nucleus
N = the number of neutrons
A =the number of nucleons
Proton number (Z) determines the chemical (elemental)
name of nucleus: eg Z = 23 is 8 is always oxygen, no
matter what N (or A) is!
A=N+Z
Z
Atomic Number
Symbol
6
C
Name
Carbon
Atomic Mass
12.0107
Fig. 29-3, p.943
Mass Number
A
Atomic Number
Z
X
Symbol
15
17
How many neutrons are in 8 O 8 O ,?
In HW submission, you give e.g O15 as an
answer.
Binding energy is the energy holding the nuclei
Why do we need two kinds to have more stable nuclei?
Why is N>Z more common ?
Calculating binding energy
together
Ebinding
= Eseparated
protons, neutrons
- Enucleus
Ebinding
= Eseparated
protons, neutrons
- Enucleus
Which is the most stable?
Fission
Fusion
(Would work for chemical binding energies,
but mass differences are too small to measure)
Nuclear decay mechanisms
Unstable nuclei decay to more stable nuclei
Gamma Decay
C * → 126 C + γ
12
6
Alpha Decay:
A
Z
X → ZA−−42Y + 24He
P1. In this decay, what other particle must have been
emitted?
A. alpha
B. electron
C. positron
D. gamma
P2. In the following fission reaction
Beta Decay:
A
Z
X → Z +A1 X + e −
A
Z
X → Z −A1 X + e +
niucleus X has which Z?
A. 54 B. 144 C. 172 D. 198
Something was missing!
Proton can turn into:
Neutron can turn into:
Dynamics of nuclear
decay
The half-life of 131I is 8.04 days.
A) Calculate the decay constant for this isotope.
N = N 0 e − λt
Rate is magnitude of the
_________ of N(t)
R=
∆N
= λN
∆t
B) If there are one million 131I nuclei, what is the
decay activity in Curies?
R(t ) = λ N (t ) = λ N 0 e − λt
T1 =
2
ln 2
λ
=
0.693
λ
C) P3. How many of the 131I nuclei are left after a
time of four half-lifes?
A. none B. ½ C. ¼ D. 1/8 E. 1/16
Units of decay rate (activity)
Curie
1 Ci ≡ 3.7 × 1010 decay
Becquerel
1 Bq = 1 decay
s
s
D) P4. How much of the initial radioactivity (decay
rate) is left?
A. none B. ½ C. ¼ D. 1/8 E. 1/16