Chapter 28 Notes, part I

Nuclear Reactions: a, b, g Decay

Radiation and Radioactivity

•

Radioactivity

was discovered by Henri Becquerel in 1896.

•It is the spontaneous emission of particles or energy by unstable atomic nuclei.

•The emitted particles are called

radiation

, and the change in nucleus that results is called

radioactive decay

.

Radiation

•There are three types of radiation we will discuss, alpha ( a ), beta ( b ) and gamma ( g ) particles.

•Alpha particles have the least amount of energy, while gamma particles have the most.

1) Alpha Decay

•Alpha decay occurs when unstable isotopes try to stabilize by emitting an

alpha particle

.

•An alpha particle is made of two protons and two neutrons, and its symbol is a or He.

• 236 88 Ra a 4 2

2) Beta Decay

•There are three types of beta decay;

beta emission, positron emission and electron capture

.

•A an electron with a symbol of e .

beta particle

is the same thing as b or •Beta emission looks like 6 • C a -1 e 14 7 + N

Electron Capture and Positron

•

Electron capture

of emitting an electron, one is pulled into the nucleus.

occurs when instead • 195 79 Au + e a 195 78 Pt •A

positron

is an odd particle; it is an electron with a positive charge!

• 116 51 Sb a 0 +1 e -

3) Gamma Radiation

•Frequently rays ( g ).

a or b decay produces energy, which is released as gamma •In most cases, it is only given off when other types of radiation occur, and since it has no particles, its symbol is just g .

Why does radioactive decay occur?

•All stable isotopes of an atom lay inside what is called the band of stability.

•This is a ratio of protons to neutrons that is inherently stable.

•Atoms not in this band will undergo radioactive decay to do so.

Predicting how an isotope will decay:

•An isotope is just too big: – a decay •An isotope has too many neutrons: – b decay •An isotope has too few neutrons: – e capture, positron emission

Write the Nuclear Reaction for:

•The a decay of Americum-245 •The b decay of Thorium-236 •The electron capture of Iodine-125 •The positron emission of Potassium 40