1. Aim # 25: What is Radioactivity?
H.W#. # 25
Study pp
Ans. ques. p. 919 # 11,15,16,18,21
Do Now: Solve problem on handout sheet.

2. I Review of basic nuclear terms A
I Review of basic nuclear terms A. nucleons- sub-atomic particles in the nucleus (protons and neutrons)
B. mass number- sum of the protons and neutrons in a nucleus
C. atomic number - number of protons in a nucleus
D. isotopes – atoms with the same at. no., but different mass nos.
e.g. C-12 and C-14
All elements have naturally occurring isotopes Their abundance varies from element to element.
e.g. 1H 2H U U U
99.985% % trace % %

3. E. nuclide – a nucleus with a specific number of protons and neutrons
F. radionuclides – nuclei that are radioactive
G. radioisotopes – atoms containing radionuclides
II Predicting Nuclear Stability
A. Nuclei with 2,8,20,28,50,82,or 126 protons and neutrons are more stable than those with other numbers.
B. Nuclei with even numbers of both protons and neutrons are generally more stable than those with odd numbers of nucleons.

4. III Radioactivity – the spontaneous breakdown of atomic nuclei accompanied by the release of particles and/or radiant energy.
All isotopes of elements with atomic numbers greater than 83 (Bi) are radioactive (unstable).

5. IV Radioactive Decay A. Types of Radiation
Name of Radiation composition charge (amu) symbol
alpha He nucleus He (α)
beta electron / e (β-)
gamma high energy γ photon

6. positron positive +1 1/1837 0e (β+) electron 1
electron neutron n capture
B. Decay Modes
1. alpha decay- at. no. decreases by 2, mass no. decreases by e.g. 226Ra → 222Rn + 4He
Problem: Identify the missing product in the following alpha decay scheme U → AX + 4He Z

7. Ans: 234Th
Problem: X → 208Pb + 4He What is X?
Ans: 212Po
2. beta decay- at. no. increases by mass no. remains the same e.g. 234Th → 234Pa + 0e
Note: the electron (beta particle) comes from the nucleus n → 0e + 1p

8. Problem: 234Pa → AX + 0e Identify X 91 Z -1
Ans: 234U
Emissions of alpha and beta particles are often accompanied by the emission of gamma rays.
e.g. 238U → 234Th + 4He + 20γ
3. positron emission-
A positron is a particle with the same mass as an electron, but with a positive charge.
This emission occurs in radioisotopes with a low
neutron to proton ratio.
e.g. 11C → 11B + 0e

9. The atomic no. decreases by one, and the mass no. remains the same
The atomic no. decreases by one, and the mass no remains the same WHAT BECOMES OF THE PROTON?
Note: the proton is converted to a neutron p → 1n + 0e
4. electron capture – an inner orbital electron is captured by the nucleus to form a neutron by combining with a proton.
e.g. 201Hg + 0e → 201Au + 0γ
Note: the process is accompanied by the emission of γ radiation.

10. Problem: Supply the missing particle
38K → 38Ar + ?
Ans: 0e
7Be + 0e (orbital electron) → ?
Ans: 7Li + 0γ

11. V Radioactive Decay Series – a series of reactions that begins with an unstable nucleus, and ends with a stable one.
238U
234Th → 234Pa → 234U
230Th
226Ra
222Rn
218Po
214Pb → 214Bi → 214Po
210Pb → 210Bi → 210Po
206Pb
atomic no

12. There are 3 such series that occur in nature
238U → → 206Pb
235U → → 207Pb
232Th → → 208Pb