Section 4.4 Unstable Nuclei and Radioactive Decay

1
Section 4-4
Section 4.4 Unstable Nuclei and Radioactive
Decay

• Explain the relationship between unstable nuclei
  and radioactive decay.

• Characterize alpha, beta, and gamma radiation in
  terms of mass and charge.

element a pure substance that cannot be broken
down into simpler substances by physical or
chemical means
2
Section 4-4
Section 4.4 Unstable Nuclei and Radioactive
Decay (cont.)
radioactivity radiation nuclear
reaction radioactive decay alpha radiation
alpha particle nuclear equation beta
radiation beta particle gamma rays
Unstable atoms emit radiation to gain stability.
3
Section 4-4
Radioactivity

• Nuclear reactions can change one element into
  another element.

• In 1895, Wilhelm Roentgen found that invisible
  rays were emitted when electrons bombarded the
  surfaces of certain materials.
• These rays had high-energy and caused
  photographic plates to darken. Roentgen named
  these rays Xrays.

4

• A French scientist Henri Becquerel was studying
  minerals that were phosphorescent.that emitted
  light after being exposed to sunlight.
• Becquerel wanted to see if phosphorescent
  minerals also emitted Xrays, so he studied
  uranium salts.
• He found that uranium salts made emissions that
  would darken photographic plates even when they
  werent exposed to light.

5

• Marie Curie and husband Pierre found that the
  darkening of the photographic plates was due to
  rays emitted from the uranium atoms in the
  mineral sample that Becquerel used.
• Marie Curie named this process, by which some
  substances spontaneously emitted radiation,
  radioactivity.
• The rays and particles emitted by a radioactive
  source are called radiation.
• A reaction that involves a change in an atom's
  nucleus is called a nuclear reaction.

6
Section 24-1
The Discovery of Radiation
7
Section 4-4
Radioactive Decay

• Atoms that contain too many or two few neutrons
  are unstable and lose energy through radioactive
  decay to form a stable nucleus.

• Few exist in naturemost have already decayed to
  stable forms.

8
Section 4-4
Radioactive Decay

• Isotopes of atoms with unstable nuclei are called
  radioisotopes.

• Unstable nuclei lose energy by emitting radiation
  in a spontaneous process called radioactive decay.

• Unstable radioactive elements undergo radioactive
  decay thus forming stable nonradioactive elements.

• The three most common types of radiation are
  alpha, beta, and gamma.

9
Section 4-4
Radioactive Decay (cont.)

• Alpha radiation is made up of positively charged
  particles called alpha particles.

• Each alpha particle contains two protons and two
  neutrons and has a 2 charge.
• No electrons

2

• Alpha particle (?)
• helium nucleus

paper
10
Section 24-1
Types of Radiation (cont.)

• Alpha radiation is not very penetratinga single
  sheet of paper will stop an alpha particle.

11
Section 4-4
Radioactive Decay (cont.)

• Beta radiation is radiation that has a negative
  charge and emits beta particles.

• Each beta particle is an electron with a 1
  charge.

• Beta particle (?-)
• electron

1-
foil
12
Section 24-1
Types of Radiation (cont.)

• Beta radiation is a stream of fast moving
  particles with greater penetrating powera thin
  sheet of foil will stop them.

13
Types of Radiation (cont.)

• Gamma rays are high-energy radiation with no mass
  and are neutral.

• Gamma rays almost always accompany alpha and beta
  radiation.
• Gamma rays account for most of the energy lost
  during radioactive decay.

• The ability of radiation to pass through matter
  is called its penetrating power.

• Gamma rays are highly penetrating because they
  have no charge and no mass.

14
Section 4-4
Radioactive Decay (cont.)

• Gamma (?)
• high-energy photon

concrete
0
15
Section 4-4
Radioactive Decay (cont.)
16
Section 4-4
Section 4.4 Assessment
A reaction that changes one element into another
is called what? A. chemical reaction B. beta
radiation C. nuclear reaction D. physical
reaction

1. A
2. B
3. C
4. D

17
Section 4-4
Section 4.4 Assessment
Why are radioactive elements rare in nature?
A. They do no occur on Earth. B. Most have
already decayed to a stable form. C. They take
a long time to form. D. They are too hard to
detect.

1. A
2. B
3. C
4. D