Ch. 25 Nuclear Changes Begins on p. 35 of your PACKET

Ch. 25 Nuclear Changes

Begins on p. 35 of your PACKET

Section 1 - RadioactivityA. The nucleus of an atom is composed of protons and neutrons which comprise most of the atom’s mass.

Section 1 - RadioactivityB. The strong force causes protons and neutrons to be attracted to each other in the nucleus.

Section 1 - Radioactivity1. The strong force is powerful only when neutrons and protons are close to each other.

Section 1 - Radioactivity2. The protons and neutrons in a large nucleus are held less tightly by the strong force than protons and neutrons in a small nucleus.

Section 1 - RadioactivityC. Radioactivity is the nuclear decay that occurs when the strong force is not large enough to hold the nucleus together and the nucleus gives off matter and energy.

Section 1 - Radioactivity1. Isotopes are atoms of the same element with varying numbers of neutrons.

Section 1 - Radioactivity2. A nucleus with too many or too few neutrons compared to protons is radioactive.

Section 1 - Radioactivity3. Atomic number – number of protons in an atom (it’s how we arrange the Periodic Table).

Section 1 - Radioactivity4. Mass number – number of protons and neutrons (added together) in a nucleus.

Section 1 - Radioactivity5. Mass number minus atomic number equals the number of neutrons in an atom.

Section 1 - RadioactivityD. Uranium radioactivity was discovered in 1896 by Henri Becquerel; Marie and Pierre Curie discovered the radioactive elements polonium and radium in 1898.

Health Affects of Radiation

Radiation can be used to kill cancer cells.

However, it can also kill good cells. It can lead to cancer, leukemia and death.

The Curies Die• Pierre was run over by a

horse and carriage in Paris at the age of 46. Marie survived to the age of about 65. Both were exposed to large amounts of dangerous radiation and suffered many health effects.

Section 1 - RadioactivityDiscussion question: Why are large nuclei more likely to be radioactive than small nuclei?

Section 1 - RadioactivityDiscussion question: Why are large

nuclei more likely to be radioactive

than small nuclei? Strong force only works up close, and in a big nucleus, they aren’t as close together to each other.

End of Section 1 Notes.

Section 2 Nuclear Decay (p. 35)

A. Nuclear radiation – particles and energy are released from a decaying nucleus.

Section 2 Nuclear Decay

B. An alpha particle is two protons and two neutrons with an electric charge of +2.

Alpha Particle


1. Alpha particles leave charged ions in their path when they travel through matter.


2. Alpha particles are the least penetrating form of nuclear radiation.


3. Alpha particles can cause serious biological damage.


C. Transmutation is the process of one element changing to another through nuclear decay.


D. A beta particle is an electron released at high speed when a neutron decays into a proton; it is more penetrating than an alpha particle.

Beta Particle


E. Gamma rays are penetrating EM waves that carry energy but have no mass or charge.


F. The half-life of a radioactive isotope is the length of time it takes half of the atoms of a sample of the radioactive isotope to decay; ½ s - Gigayears


G.Carbon dating can be used to find a suitable mate. Works better than e-Harmony.com.


G.Carbon dating can be used to date once-living materials while uranium dating can be used to date rocks. (Finding the age…)


H. We use radioactive Carbon-14 to get ages up to 50,000 years. We need Uranium for really old rocks.


Discussion Question: What are the three types of nuclear decay?


Discussion Question: What are the three types of nuclear decay? Alpha, Beta and Gamma.

End of Section 2 Notes

Section 3 Detecting Radioactivity

A. Radiation detectors are instruments used to identify ions formed when radiation passes through matter.


1. A cloud chamber detects alpha or beta particles by means of a trail of condensed vapor.

Extra Credit

• Build your own cloud chamber to donate to DHS. 30 EC.


2. A bubble chamber detects radioactive particles by means of a bubble trail in a superheated liquid.


3. Electroscopes can measure charged particles in the air.


B. A Geiger counter measures radioactivity by producing an electric current when radiation is present.

Section 3 Detecting RadioactivityC. Background radiation

comes from radon gas produced in Earth’s crust, from cosmic rays, and from radioactive isotopes in the body.

Discussion Question

What three devices are used to detect ionizing radiation?

Discussion Question

What three devices are used to detect ionizing radiation? Ans: Bubble chamber, cloud chamber and Geiger counter.

End of Section 3 Notes

Section 4 – Nuclear Reactions

Section 4: Nuclear ChangesA. Nuclear fission is the process

of splitting a nucleus into two nuclei with smaller masses; it releases a large amount of energy.

Section 4: Nuclear Changes1. A chain reaction is an ongoing

series of fission reactions.

2. Critical mass is the amount of fissionable material required to continue a reaction at a constant rate.

Section 4: Nuclear ChangesB.In nuclear fusion, two nuclei

with low masses are combined to form one nucleus of larger mass.

1. Nuclear fusion can happen only when nuclei are moving fast enough to get close to each other.

Section 4: Nuclear Changes2. Temperatures in stars (millions

of degrees Celsius) are high enough for fusion to occur.

C. Nuclear reactions have medical uses.

Section 4: Nuclear Changes1. Radioisotopes are used as

tracers to find or keep track of molecules in an organism.

2. Cancer cells can be killed with carefully measured doses of radiation.

Section 4: Nuclear ChangesDiscussion Question: What is

the difference between fission and fusion?

Section 4: Nuclear ChangesDiscussion Question: What is

the difference between fission and fusion?

Answer: Fission splits a larger nucleus into two smaller ones; fusion combines two smaller nuclei to form a larger one.

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Ch. 25 Nuclear Changes Begins on p. 35 of your PACKET