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1
CHAPTER 30
RADIOACTIVITY
DISCOVERY – BECQUEREL
DEVELOPMENT – Pierre and Marie Curie
And others
THREE RADIATIONS
ALPHA – nucleus of Helium
BETA - electrons
GAMMA – electromagnetic
2
ALPHA is Nucleus of Helium
BETA PARTICLES are electrons
GAMMA – electromagnetic energy
A High Energy Photon
3
NUCLEAR TRANSMUTATIONS
ALPHA DECAY
�������� �� ℎ� + �ℎ��
�����
���
Masses and Charges must balance
�������� ���
���
��� + �ℎ�����
4
BETA DECAY
�ℎ������� ���� + ����
�����
���
Masses and Charges must balance
�ℎ������� � + ����
������
�����
5
ACTIVITY
NUCLEAR DECAY RATE
NUMBER OF NUCLEAR DECAYS PER
SECOND
ACTIVITY
t
N=
∆
∆
PROPORTIONAL TO NUMBER OF
NUCLEI PRESENT, N
N
t
N∝
∆
∆
6
THEREFORE
N
t
NRATE λ=
∆
∆−=
WHERE λ, THE CONSTANT OF
PROPORTIONALITY, IS THE DECAY
CONSTANT.
Can use calculus to find number of nuclei
(N) as function of time.
8
HALF LIFE
IF YOU START WITH N0 NUCLEI HOW
MUCH TIME WILL IT TAKE TO ONLY
HAVE HALF THAT NUMBER?
THAT WILL BE CALLED THE HALF-
LIFE.
START WITH N0
WHEN WILL HAVE 2
0N
11
Insert FIGURE 30.6
EXAMPLE
If a radioactive material initially contains
3.00 mg of U234
92 , how much will remain
unchanged after 62,000 years? (For U234
92
t1/2 = 2.48 x 105 y and λ = 8.88 x 10
-14 s
-1.)
teNN
λ−= 0
( ) atomsxg
atomsxxgxN
1823
3
0 1072.7234
1002.61000.3 == −
13
atomsXN1810494.6=
MASS = ?
( ) gxatomsx
gxatomsxm
3
23
18 1052.21002.6
23410494.6 −==
WHAT IS THE ACTIVITY OF THIS
SAMPLE?
N
t
NRATE λ=
∆
∆−=
17
MOST RADIOACTIVE NUCLEI ARE
IN ONE OF 4 SERIES
�������� ����
�����
���
�ℎ������� ����
�����
���
�������� ����
�� ��
��!
�"������� #$��
�����
���
18
NOTE THAT NO SERIES DECAYS TO
�������
IF AT TIME IN HISTORY MOLTEN
LEAD SOLIDIFIED THERE WOULD
BE A MIXTURE OF Pb ISOTOPES.
WHEN IT SOLIDIFIED FOR
EXAMPLE
%&'(
()*
%&'(()+ = -./�0��"�
WITH TIME ������� INCREASES
21
ANOTHER AGE DATING METHOD
CARBON 14 DATING
CARBON 12 IS THE MOST
ABUNDENT ISOTOPE OF CARBON
AND IS STABLE
CARBON 14 IS UNSTABLE AND
DECAYS TO NITROGEN (A GAS)
3������� 2 + ����
���
��
WITH HALF-LIFE OF 5730 YEARS
23
OVER TIME RATIO LIVING PLANTS
AND ANIMALS
8*
9+
8*9( = 3:27�62�;6<�5
FROM TIME OF DEATH ON
3������� 2 + ����
���
��
24
AND THEREFORE
8*
9+
8*9( = =�>?��-�-
MEASURE RATIO OF CARBON 14
TO CARBON 12 AND DETERMINE
YEARS SINCE DEATH OF PLANT OR
ANIMAL.
28
FUSION
� + �������� � + C + DE = 0.42J�;�
��� �
�
Then
� + �������� ���
� + KE = 5.49J�;��
��
Then
���� + ��
������� �� + � + ��
� ��
��
��
With E = 12.86J�;
30
FUNDAMENTAL PARTICLES AND
FORCES
FOUR FORCES FOUND IN NATURE
1. The Strong Interaction
2. The electromagnetic interaction
3. The weak interaction
4. The gravitational interaction