Assignment 15: Atomic Nucleus and Radioactivity. Nuclear Fission and Fusion

Why aren't gamma rays deflected in a magnetic field?

Gamma rays are electromagnetic radiation and so have no charge. Electric and magnetic fields deflect charges.

What becomes of the "lost" mass per nucleon in fission and fusion reactions?

It becomes kinetic energy.

How does the number of silver atoms change when time advances each second?

A fixed fraction of silver atoms changes each second.

What is a radioactive tracer?

A radioactive isotope of an element that by itself or in a molecule is used to trace biochemical pathways in plants and organisms

What kind of trail is left when an energetic particle shoots through matter?

A trail of free electrons and positive ions

What components are the safeguards to prevent a reactor from generating energy out of control?

Control rods

What isotopes of hydrogen fuse best at "moderate" temperatures?

Deuterium and tritium

What kind of force pushes particles in the atomic nucleus apart?

Electric force

What kind of rays are X-rays?

Electromagnetic

How can you predict the number of silver atoms there are in the second before the time equal to 0 seconds on the graph?

Find the proportion of atoms that remains after 1 second. Then increase the number of original atoms by the same proportion.

What kind of nuclear power is responsible for sunshine? Give an example.

Fusion: proton + deuteron produces helium-3

Which of these is electromagnetic radiation?

Gamma radiation

How does the mass per nucleon of an element change as the atomic number increases?

The mass per nucleon first decreases then increases.

How does the mass per nucleon in uranium compare with the mass per nucleon in its fission fragments?

The mass per nucleon is greater in uranium.

Which ions of like charge and equal speed are least deflected in a mass spectrometer?

The more massive ions

Which of these ejects into the atmosphere the greatest amount of dangerous radiation?

Coal-fired power plants

What change in atomic number occurs when a nucleus emits an alpha particle? A beta particle? A gamma ray?

-2, +1, 0

Suppose the half-life of a material is 10 days. You have one 1 kg of the material today. How much of the material would you have after 10 days and 20 days, respectively?

0.5 kg after 10 days, and 0.25 kg after 20 days

At the end of the fourth year?

1/16

If a sample of a radioactive isotope has a half-life of 1 year, how much of the original sample will be left at the end of the second year?

1/4

At the end of the third year?

1/8

A material has a half-life of 1 day. If 2 kg of this material is available today, how much of it was available yesterday, and how much the day before?

4kg yesterday, and 8 kg the day before

Which of these puts the greatest amount of pollutants into the atmosphere?

Coal-fired power plants

When thorium decays by emitting a beta particle, what is the atomic number of the resulting nucleus?

91

What is the other product of this reaction?

He-4

For helium to release energy, should it be fissioned or fused? What about uranium?

Helium should be fused; uranium should be fissioned.

Why is a chain reaction more likely to occur in a big piece of uranium than in a small piece?

In a big piece, the ejected neutrons are more likely to strike another nucleus before exiting the piece.

What is the long-range fate of all the uranium that exists in the world?

It will turn into lead

Do humans receive more radiation from artificial or natural sources of radiation? What fraction comes from this source?

Natural, about 80%

What is the role of neutrons in the atomic nucleus?

Neutrons contribute strong nuclear force attraction without adding in electric force repulsion, so they help hold the nucleus together.

What is the effect of placing small amounts of fissionable isotopes with large amounts of U-238?

Neutrons from the fission transmute U-238 to Pu-239, a fissionable fuel.

What isotope is produced when U-239 emits a beta particle?

Np-239

What two elements did Pierre and Marie Curie discover?

Polonium and radium

Which type of detector senses flashes of light produced by charged particles or gamma rays?

Scintillation counter

Why doesn't the repulsive electrical force of protons in the atomic nucleus cause the protons to fly apart?

The attractive strong nuclear force holds the nucleus together.

What is transmutation? Give one example.

The change of one chemical element into another, such as uranium to lead

What element has the lowest mass per nucleon?

The element with the lowest mass per nucleon is the element with an atomic number of about 25.

When a pair of hydrogen nuclei are fused to create helium, how does the mass of the resulting helium nucleus compare with the sum of the nuclear masses before fusion?

The mass of the helium nucleus is less than the sum of the masses of the hydrogen nuclei.

How does the rate of decay of a long-half-life material normally compare to the rate of decay of a short-half-life material?

The rate of decay is lower for a long-half-life material.

How does the time needed go from the original number of atoms to one-half of that number compare with the time needed to go from one-half of the number of atoms to one-quarter of the number?

The time needed to go from the original number of atoms to one-half of that is equal to the time needed to from one-half of the number of atoms to one-quarter.

Which will leak more neutrons: two separate pieces of uranium or the same pieces stuck together? Why?

The two separate pieces will leak more because smaller pieces have more surface area per volume.

In what way is a nuclear reactor similar to a conventional fossil-fuel plant?

They both boil water to make steam.

Rank from greatest to least the reduction of mass per nucleon that accompanies the fusion of the following pairs of nuclei. a. Two hydrogen nuclei b. Two carbon nuclei c. Two aluminum nuclei d. Two iron nuclei

Two hydrogen nuclei Two carbon nuclei Two aluminum nuclei Two iron nuclei

Which of these typically undergoes a chain reaction?

U-235

Name two isotopes that can undergo fission when they absorb a neutron.

U-235, Pu-239

What element reacts in a breeder reactor to breed nuclear fuel?

U-238

Why is lead found in all deposits of uranium ore?

Uranium undergoes radioactive decay, transmuting into lead.

Fission of a U-235, escape, absorbed by a U-238

What element reacts in a breeder reactor to breed nuclear fuel?

Is work required to pull a nucleon out of an atomic nucleus? Does the nucleon, once outside, have more energy than it did when it was inside the nucleus? In what form is this energy?

Yes, work is required; more energy; more mass per nucleon

An element that undergoes radioactive decay becomes _________.

an entirely different element

Which element(s) has/have a mass of exactly 1.000 amu per nucleon?

both carbon and astatine

Do today's nuclear power plants use fission, fusion, or both?

fission

Which type of radiation - alpha, beta, or gamma - predominates within an enclosed elevator descending into a uranium mine?

gamma

Rank these three types of radiation by their ability to penetrate a page of a book, from greatest penetration to least. A. Alpha particle. B. Beta particle. C. Gamma ray

gamma, beta, alpha

Which of these elements cannot produce energy by fission or fusion?

iron

All the uranium in today's deposits in the future will become _________.

lead

Suppose 2 kg of a material has a half-life of 1 day. After how long will NONE of the material remain?

never

What occurs when a nitrogen nucleus captures an extra neutron?

none of the above

If a certain isotope has a radioactive half-life of 10 years, how much of the isotope will remain at the end of 20 years?

one quarter

The strong force is one of the four fundamental forces in nature, and exists _________.

only between particles in the nucleus

Which of these two products fuels the explosive reaction?

tritium