Chapter 19 Key Terms and Definitions, Rev. Qts 1-20, Exercises 1-10

Alpha Particle

A helium atom nucleus, which consists of two neutrons and two protons and is ejected by certain radioactive elements.

Why is lead found in all deposits of uranium ores ?

All uranium isotopes eventually decay to lead.

Why would you expect alpha particles to be less capable of penetrating materials than beta particles?

Alpha particles have a mass of 4 amu and a charge of +2, while beta particles have a mass of 1/1800 amu and a charge of -1. As a result, alpha particles are much more likely than beta particles to interact with matter, making it very difficult for them to penetrate anything.

Which type of radiation --alpha, beta or gamma-- results in the greatest change in mass number? The greatest change in atomic number?

Alpha radiation results in the greatest change to both mass number and atomic number.

How do the electric charges of alpha, beta, and gamma rays differ from one another?

Alpha: positive charge Beta: negative charge Gama: zero charge

The alpha particle has twice the electric charge of the beta particle but deflects less in a magnetic field. Why?

An alpha particle has about 8000 times the mass of a beta particle, so it is hard to accelerate the alpha particle and it does not deflect as much as a beta particle.

Beta Particle

An electron ejected from an atomic nucleus during the radioactive decay of certain nuclei.

Why is there more carbon-14 in living bones than in once-living ancient bones of the same mass?

Because it takes a long time for carbon 14 to decay therefore it starts earlier but it does not hurt you.

Why are alpha and beta rays bent in opposite directions in a magnetic field? Why is the path of gamma rays unaffected?

Because opposites repel force and the gamma rays are neutral (unaffected).

How is carbon-14 produced in the atmosphere?

By plants.

Why is carbon-14 dating useless for dating old coins but not old pieces of cloth?

Carbon dating only works with things that were once living,, The old coins were never alive, but the cloth came from something that was once living (i.e. plant).

Which is radioactive, carbon-12 or carbon-14?

Carbon-14 is radioactive.

What do cosmic rays have to do with transmutation?

Cosmic rays are involved because the earths atmosphere is continuously bombarded with these and cause many atoms in the upper atmosphere to transmute.

Which type of radiation--alpha, beta, or gamma--predominates in the interior of a high-flying commercial airplane? Why?

Gamma radiation because they can penetrate most materials (alpha particles cannot easily penetrate solid materials and beta particles caannot penetrate aluminum).

Which type of radiation--alpha, beta, or gamma-- results in the least change in atomic number? The least change in the atomic number?

Gamma radiationresults in the least change to both mass number and atomic number.

Which of the three rays has the greatest penertating power?

Gamma rays have the most penetrating power.

Gamma Radiation

High-energy radiation emitted by the nuclei of radioactive atoms.

What does the proportion of lead and uranium in rock tell us about the age of the rock?

It can tell the date that it was formed.

What is meant by radioactive half-life?

It measures the time it takes for a given amount of the substance to become reduced by half due to decay, and the emission of radiation. The half-life is the time for half the sample to decay to another element.

When the isotope bismuth-213 emits an alpha particle What new element results? What new element results if it instead emits a beta particle?

It reduces by 2. It becomes Thallium.

Why is a sample of radium always a little warmer than its surroundings?

Its atoms are continally being struck by alpha and beta particles

What role do neutrons play in the atomic nucleus?

Neutrons contribute strong nuclear force attraction without adding in electric force repulsion (because they are neutral/no electrical charge), so they help hold the nucleus together.

Is it possible for a hydrogen nucleus to emit in an alpha particle? Defend your answer.

No, because it does not contain enough nucleons

Is radioactivity on the Earth something relatively new? Defend your answer.

Radioactivity is as old as the earth. Radioactive elements have been deep within the earth since its beginning.

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

The atomic number is reduced by two in an alpha decay. The atomic number is increased by one in a beta decay.

Transmutation

The conversion of an atomic nucleus of one element to an atomic nucleus of another element through a loss or gain of protons.

Strong Nuclear Force

The force of interaction between all nucleons, effective, only at very, very, very close distances

What is the origin of most of the radiation you encounter?

The leading source of natural occurring radiation is radon-222, cosmic, ground and human tissue.

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

The naturally occurring isotopes U-238 and U-235 decay very slowly and ultimately become isotopes of lead.

Carbon-14 Dating

The process of estimating the age of once living material by measuring the amount of a radioactive isotope of carbon present in the material.

How does the decay rate of an isotope relate to its half-life?

The rate of decay is lower for a long-half-life material. The longer the half life, the slower the rate.

How are the strong nuclear force and the electric force different from each other?

The strong nuclear force acts between quarks (composite particles known as hadrons) at distances similar to the radius of an atomic nucleus. The electric force acts between charged particles, and its range is infinite. Also, the strong nuclear force is much stronger.

Radioactive

The tendency of some elements, such as uranium, to emit radiation as a result of changes in the atomic nucleus.

Half-Life

The time required for half the atoms in a sample of a radioactive isotope to decay.

Elements above uranium in the periodic table do not exist in any appreciable amounts in nature, because they have short half-lives. Yet there are several elements below uranium in the table that have equally short half-lives , but do exist in appreciable amounts of nature. How can you account for this?

These elements result from the radioactive decay of uranium; therefore, they can be found in among uranium decay.

What is the half-life of radium-226?

1620 years

When thorium, atomic number 90 , decays by emitting an alpha particle, what is the atomic number of the resulting nucleus?

88 protons. Emitting an alpha particle leads to the loss of two protons and two neutrons from the nucleus: atomic number (# of protons) diminishes by two, mass number (p + n) diminishes by 4 (2 p and 2 n).

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

91 protons. A beta particle is an electron, so the atomic number of the resulting nucleus is increased by 1 proton. The resulting element has 91 protons, Protactinium.