# radioactive decay as a measure of age

Radioactivity is the tendency of certain atoms to decay into lighter atoms, a process that emits energy. Radioactivity also provides a way to find the absolute age of a rock. First, we need to know about radioactive decay.

Some isotopes are radioactive; radioactive isotopes are unstable and spontaneously change by gaining or losing particles. Two types of radioactive decay are relevant to dating Earth materials (Table 1.1): Particle Alpha Composition 2 protons, 2 neutrons Beta 1 electron Effect on Nucleus The nucleus contains two fewer protons and two fewer neutrons. One neutron decays to form a pro- ton and an electron. The electron is emitted. The radioactive decay of a parent isotope (the original element) leads to the formation of stable daughter product, also known as daughter isotope. As time passes, the number of parent isotopes decreases and the number of daughter isotopes increases (Figure 1.1).

## halflives

Radioactive materials decay at known rates, measured as a unit called half-life. The half-life of a radioactive substance is the amount of time it takes for half of the parent atoms to decay. This is how the material decays over time (see Table 1.2). No. of half lives passed 0 1 2 3 4 5 6 7 8 Percent parent remaining 100 50 25 12.5 6.25 3.125 1.563 0.781 0.391 Percent daughter produced 0 50 75 87.5 93.75 96.875 98.437 99.219 99.609 Pretend you find a rock with 3.125% parent atoms and 96.875% daughter atoms. How many half lives have passed? If the half-life of the parent isotope is 1 year, then how old is the rock? The decay of radioactive materials can be shown with a graph (Figure 1.2). Notice how it doesnt take too many half lives before there is very little parent remaining and most of the isotopes are daughter isotopes. This limits how many half lives can pass before a radioactive element is no longer useful for Decay of an imaginary radioactive sub- stance with a half-life of one year. dating materials. Fortunately, different isotopes have very different half lives. Click image to the left or use the URL below. URL:

## instructional diagrams

The following diagram provides an example of Alpha Decay, where a Radium atom transforms or decays into a radon atom. Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into an atom with a mass number that is reduced by four and an atomic number that is reduced by two. Alpha decay only occurs in very heavy elements such as uranium, thorium and radium. The nuclei of these atoms are very neutron rich (i.e. have a lot more neutrons in their nucleus than they do protons) which makes emission of the alpha particle possible. After an atom ejects an alpha particle, a new parent atom is formed which has two fewer neutrons and two fewer protons. Thus, when Radium-226 decays by alpha emission, Radon-222 is created.

Gamma decay is the process by which the nucleus of an atom emits a high energy photon, that is, extremely short-wavelength electromagnetic radiation. It is one of three major types of radioactivity (the other two being alpha decay and beta decay). Gamma decay is similar to the emission of light (usually visible light) by decay in the orbits of the electrons surrounding the nucleus. In each case the energy states, and the wavelengths of the emitted radiation, are governed by the law of quantum mechanics. But while the electron orbits have relatively low energy, the nuclear states have much higher energy. Gamma decay is a process of emission of gamma rays that accompanies other forms of radioactive decay, such as alpha and beta decay. Nuclei are not normally in excited states, so gamma radiation is typically incidental to alpha or beta decay the alpha or beta decay leaves the nucleus in an excited state, and gamma decay happens soon afterwards. Gamma radiation is the most penetrating of the three kinds. Gamma ray photons can travel through several centimeters of aluminum.

The diagram below shows the beta decay of carbon 14. The carbon-14 nucleus has a neutron within it change into a proton Then we see both a beta minus particle (an electron with high kinetic energy) and an antineutrino ejected from the nucleus. Carbon 14 has two extra neutrons in its nucleus and that is a higher energy configuration and is a bit unstable, so it can release an electron and have a neutron turn into a proton-forming Nitrogen 14 instead, which is more stable.

## questions

radioactive isotopes are _ and spontaneously change by ___.

``````-->  a) unstable; adding or subtracting particles

b) unstable; keeping their particles

c) stable; gaining or losing particles

d) stable; keeping their particles
``````

radioactive decay of an isotope leads to the formation of a __ product.

``````a) unstable daughter

b) stable parent

c) unstable parent

-->  d) stable daughter
``````

if a radioactive isotope loses an alpha particle its charge changes by

``````a) the loss of two negatives.

-->  b) the loss of two positives.

c) the addition of one positive.

d) the loss of one negative.
``````

if two half-lives have passed, this percent of the parent isotope remains.

``````a) 100%

b) 50%

-->  c) 25%

d) 12.5%
``````

if 75% of the daughter is produced, this many half-lives have passed.

``````a) 0

b) 1

-->  c) 2

d) 3
``````

a half life is the time it takes for half of the parent isotopes to change into daughter isotopes.

``````-->  a) true

b) false
``````

``````-->  a) is exponential

b) is constant

c) plateaus

d) none of the above
``````

this team of physicists discovered the spontaneous emission of particles that they called radioactivity.

``````a) steno and sutton

-->  b) pierre and marie curie

c) watson and crick

d) darwin and wallace
``````

a radioactive isotope pair is only useful for as long as there is enough daughter to be able to count.

``````a) true

-->  b) false
``````

## diagram questions

What are the pink spheres in the diagram?

``````a. Radiaton

b. Energy

c. Atoms

-->  d. Particles
``````

What three elements make up a radioactive atom?

``````-->  a. Energy, radiation, particle

b. atom

c. ion

d. nucleus
``````

What is emitted when a Radioactive atom decays and loses a particle?

``````a. Radiation

-->  b. Energy

c. Particle

d. Atom
``````

How many by products does a radioactive atom release?

``````-->  a. 3

b. 4

c. 2

d. 1
``````

Radioactive atoms produce what type of Energy?

``````-->  a. Radiation

b. Mechanical

c. Chemical

d. Physical
``````

What is derived from a Radioactive Atom?

``````-->  a. Energy

c. Heat

d. Cells
``````

Where does the separated particle go after leaving the parent nucleus?

``````-->  a. daughter nucleus

b. a particle

c. parent nucleus

d. uranium-238
``````

Identify the phenomenon illustrated in the figure.

``````a. Radioactivity

b. Carbon-14 dating

c. Nitrogen-14 decay

-->  d. Carbon-14 decay
``````

How many nuclei are there?

``````a. 5

b. 3

c. 4

-->  d. 2
``````

What makes up the parent nucleus?

``````-->  a. daughter

b. alpha

c. particles

d. aplha particle and daughter nucleus
``````

A parent nucleus splits into which parts?

``````a. gamma and beta particles

b. muon and tau particles

c. gold and silver particles

-->  d. alpha particle and daughter nucleus
``````

The parent nucleus breaks down into a daughter nucleus and what?

``````a. ion

-->  b. alpha particle

c. gamma particle

d. beta particle
``````

What energy is released from radioactive alpha decay?

``````-->  a. gamma

b. nu

c. beta

d. chi
``````

How many elements are shown?

``````a. 2

b. 3

c. 4

-->  d. 1
``````

How many protons is in the alpha particle?

``````a. 1

b. 4

c. 3

-->  d. 2
``````

What does the red circle represent?

``````a. Electron

b. Neutron

-->  c. Proton

d. Gamma
``````

Which rays are given out by splitting of Uranium in the diagram?

``````a. Proton

b. Decay

c. Alpha

-->  d. Gamma
``````

This type of particle is produced from the process of alpha decay.

``````-->  a. Alpha particle

b. Proton

c. Nucleus

d. Gamma particle
``````

Nucleus comprises how many elements?

``````-->  a. 2

b. 1

c. 3

d. 4
``````

What makes up a nucleus?

``````a. nucleus with 2 fewer protons and 2 fewer neutrons

-->  b. neutron and proton

c. alpha partical

d. neurons and protons
``````

What is the Nucleus with the fewer protons and neutrons called?

``````a. Isotope

-->  b. Daughter

c. Proton

d. Alpha particle
``````

After alpha decay, Am-241 turns into alpha particle and what?

``````a. Rd-231

b. F-8

-->  c. Np-237

d. Th-225
``````

Am-241 combined with what forms an alpha particle?

``````a. none

-->  b. Np-237

c. neutron

d. proton
``````

What is an atom of neptunium 237 plus an alpha particle?

``````a. A beta particle

b. An atom of neptunium 239

c. Nothing

-->  d. An atom of americium 241
``````

How many stages are shown in the diagram?

``````a. 2

b. 1

c. 4

-->  d. 3
``````

What is expelled when Am-241 becomes Np-237?

``````a. delta particle

b. beta particle

c. god particle

-->  d. alpha particle
``````

How many elements are shown?

``````a. 5

b. 3

-->  c. 2

d. 4
``````

Nucleus is composed of how many elements?

``````a. 3

-->  b. 2

c. 1

d. 4
``````

What does the blue circle represent?

``````a. Radiation

b. Proton

-->  c. Neutron

d. Nucleus
``````

After the parent splits into the daughter and?

``````a. Daughter

b. Parent

c. All three

-->  d. The Alpha
``````

How is an element defined?

``````a. Number of electrons it contains

b. Number of neutrons it contains

c. Number of atoms

-->  d. Number of protons it contains
``````

What is daughter in the diagram?

``````a. proton

b. neutron

c. unstable isotope

-->  d. stable isotope
``````

How many alpha particles are produced by the decay diagram?

``````a. 3

-->  b. 1

c. 2

d. 4
``````

What is happens when an alpha particle leaves?

``````a. Neutron

b. Proton

c. Isotope

-->  d. The parent decays
``````

This process involves the release of energy from a high energy atom with no change in the number of protons or neutrons.

``````a. Alpha decay

b. I don't know

-->  c. Gamma Decay

d. Beta decay
``````

What is shown in the diagram?

``````a. Nuclear Energy

-->  b. Gamma Decay

c. Solar Power

d. Energy Release
``````

From the diagram, what happens to the energy in a high energy atom after gamma decay?

``````a. both high and low energy wave released

-->  b. high energy gamma wave released

c. no change to energy

d. low energy gamma wave released
``````

What element represents He?

``````a. Sodium

b. Titanium

c. Chlorine

-->  d. Helium
``````

During Alpha Decay, Ra breaks down into which one of two elements?

``````a. O

b. N

-->  c. He

d. H
``````

``````a. radon and carbon

c. carbon and helium

``````

How many protons are lost based on below diagram?

``````a. 88

b. 86

-->  c. 2

d. 4
``````

During this decay what happens to the atomic mass?

``````a. It increases

-->  b. It decreases.

c. It multiplys

d. It stays the same
``````

Ra becomes Rn and what after Alpha Decay?

``````a. Rb

b. Xe

-->  c. He

d. Ar
``````

What is the function of the upper left superscript beside the element?

``````-->  a. It shows the number of neutrons.

b. It shows the number of charge.

c. It shows the number of electons.

d. It shows the number of protons.
``````

What is the alpha particle produced when PU experienced radioactive decay?

``````a. O

-->  b. He

c. U

d. H
``````

How many elements are in this diagram?

``````a. 2

b. 1

-->  c. 3

d. 4
``````

How many elements are there?

``````a. 3

b. 5

-->  c. 2

d. 4
``````

What does the symbol He mean?

``````a. Neuron

b. Nucleus

-->  c. Helium

d. Proton
``````

What is alpha particle?

``````a. Potassium

-->  b. Helium

c. Sodium

d. Calcium
``````

``````-->  a. helium-4

b. carbon-14

c. hydrogen-2

d. oxygen-12
``````

How many gamma photon are there?

``````a. 4

b. 2

c. 3

-->  d. 1
``````

What kind of nucleus does one or more of the protons or neutrons occupy a nuclear orbital of higher energy than an available nuclear orbital of lower energy?

``````a. Relaxed Nucleus

b. Converse Nucleus

c. Diverse Nucleus

-->  d. Excited Nucleus
``````

What are the blue circles in the diagram?

``````a. protons

b. electrons

-->  c. neutrons

d. nucleus
``````

How many elements are involved in the decay of Uranium?

``````-->  a. 3

b. 1

c. 4

d. 2
``````

How many protons does helium have?

``````a. 90

b. 234

c. 4

-->  d. 2
``````

Uranium-238 becomes alpha particle and what after alpha decay?

``````a. krypton-132

b. carbon-14

-->  d. thorium-234
``````

How many products are formed during alpha decay?

``````a. 3

b. 4

-->  c. 2

d. 1
``````

Plutonium-240 becomes an alpha particle and what after alpha decay?

``````a. barium-46

-->  b. uranium-236

d. thorium-238
``````

Radium-228 becomes a beta minus particle and what after beta minus decay?

``````a. flourine-5

b. rubidium-214

-->  c. actinium-228

d. thorium-225
``````

What process is shown in the diagram?

``````-->  a. Beta minus decay of Ra

b. Beta minus decay of Ac

c. Nuclear fusion

d. Nuclear fission
``````

How many elements are shown?

``````a. 4

b. 5

c. 3

-->  d. 2
``````

Does this reaction satisfy the law of conservation of mass?

``````a. Data Insufficient

b. Can't say

c. No

-->  d. Yes
``````

How many protons are there in a Helium atom?

``````a. 86

-->  b. 2

c. 88

d. 4
``````

What does He represent?

``````a. Arsenic

-->  b. Helium

c. Sodium

d. Oxygen
``````

What is shown in the diagram?

``````a. Beta Decay of Atom

b. Beta Decay of Proton

c. Beta Decay of Electron

-->  d. Beta Decay of Neutron
``````

Which is the emitted product of a decay event?

``````a. Nitrogen

-->  b. Beta particle

c. Neutron

d. Alpha particle
``````

How many parts are produced by the beta decay of a neutron?

``````a. 2

b. 4

c. 5

-->  d. 3
``````

How many types of articles are shown in the diagram?

``````a. 1

b. 3

-->  c. 4

d. 2
``````

When a neutron undergoes beta decay, which of these do not form as a result?

``````a. beta particle

b. antineutrino

c. proton

-->  d. tau
``````

It consists or two protons and two neutrons bound together into a particle identical to a helium nucleus

``````a. Epsilon particle

-->  b. Alpha particle

c. Beta particle

d. Sigma particle
``````

What represents the symbol He?

``````a. Arsenic

b. Atom

-->  c. Helium

d. Sodium
``````

How many particles are in the diagram?

``````a. 1

b. 5

-->  c. 3

d. 4
``````

What does He represent?

``````-->  a. Helium

b. Sodium

c. Oxygen

d. Carbon
``````