Radioactivity

Radiation

Radiation: The process of emitting �energy in the form of waves or particles.�

Where does radiation come from?

Radiation is generally produced when particles interact or decay.��A large contribution of the radiation on earth is from the sun (solar) or from radioactive isotopes of the elements (terrestrial).�

Radiation is going through you at�this very moment!

Isotopes

Review: What’s an isotope?

Two or more varieties of an element �having the same number of protons but �different number of neutrons. Certain �isotopes are “unstable” and decay to �lighter isotopes or elements.��Deuterium and tritium are isotopes of hydrogen. In addition to the 1 proton, they have 1 and 2 additional neutrons in the nucleus respectively*.

Another prime example is Uranium 238, or just ²³⁸U.

Radioactivity

By the end of the 1800s, it was known that certain �isotopes emit penetrating rays. Three types of radiation �were known:�

• Alpha particles (α)�
• Beta particles (β)�
• Gamma-rays (γ)�

Where do these particles come from ?

• These particles generally come �from the nuclei of atomic isotopes �which are not stable.�
• The decay chain of Uranium �produces all three of these forms�of radiation.�
• Let’s look at them in more detail…

Alpha Particles (α)

88

Radium�Ra²²⁶

88 protons

138 neutrons

86

Radon�Rn²²²

Note: This is the�atomic weight, which�is the number of�protons plus neutrons

86 protons

136 neutrons

+

n

n

p

p

α (⁴He)

2 protons

2 neutrons

The alpha-particle (α) is a Helium nucleus. ��It’s the same as the element Helium, with the �electrons stripped off !

Beta Particles (β)

6

Carbon

C¹⁴

6 protons

8 neutrons

7

Nitrogen

N¹⁴

7 protons

7 neutrons

+

e^-

electron

(beta-particle)

We see that one of the neutrons from the C¹⁴ nucleus “converted” into a proton, and an electron was ejected. The remaining nucleus contains 7p and 7n, which is a nitrogen nucleus. In symbolic notation, the following process occurred:

​

n 🡪 p + e ( + ν )

This is a neutrino. It has no charge and travels at near the speed of light

Gamma particles (γ)

In much the same way that electrons in atoms can be in an �excited state, so can a nucleus.

Neon

Ne²⁰

10 protons

10 neutrons�(in excited state)

10 protons

10 neutrons�(lowest energy state)

+

Gamma and often x - rays

Neon

Ne²⁰

A gamma is a high energy light particle.�

It is NOT visible by your naked eye because it is not in �the visible part of the EM spectrum.

Gamma Rays

Neon

Ne²⁰

+

The gamma from nuclear decay�is in the X-ray/ Gamma ray �part of the EM spectrum�(very energetic!)

Neon

Ne²⁰

Health effects alpha (α) radiation are:

• Most alpha (α) radiation travels only a short distance (a few inches) is not able to penetrate clothing or human skin.
• Alpha-emitting materials can be harmful if inhaled (Radon gas), swallowed, or absorbed through open wounds.

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Examples of some alpha emitters: radium, radon, uranium, thorium.

Some of the health effects of beta (β) radiation are:

• Beta (β) radiation may travel several feet in air and is moderately penetrating clothing provides some protection
• Beta radiation can penetrate human skin to the "germinal layer," where new skin cells are produced. If high levels of beta-emitting contaminants are allowed to remain on the skin for a prolonged period of time, they may cause skin injury.
• Beta-emitting contaminants may be harmful if ingested. �

Examples of some pure beta emitters: strontium-90, carbon-14, tritium, and sulfur-35. �

Some health characteristics of gamma (γ) and X radiations are:

• Gamma (γ) radiation and x rays are able to travel many feet in air and many inches in human tissue. They readily penetrate most materials and are sometimes called "penetrating" radiation.
• Dense materials are needed for shielding from gamma radiation. Clothing provides little shielding from penetrating radiation, but will prevent contamination of the skin by gamma-emitting radioactive materials.
• Gamma radiation and/or characteristic x rays frequently accompany the emission of alpha and beta radiation during radioactive decay. �Examples of some gamma emitters: iodine-131, cesium-137, cobalt-60, radium-226, and technetium-99m.

Radium Girls cartoon

Radium Girls

Nail Salons

Where do we find radioactive material

• Radon Gas

US radon Map

What’s your Dose?

• https://www.epa.gov/radiation/calculate-your-radiation-dose

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Half-Life

The “half-life” (h) is the time it takes for half the atoms of a radioactive substance to decay.

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For example, suppose we had 20,000 atoms of a radioactive substance. If the half-life is 1 hour, how many atoms of that substance would be left after:

10,000 (50%)

5,000 (25%)

2,500 (12.5%)

1 hour (one lifetime) ?

2 hours (two lifetimes) ?

3 hours (three lifetimes) ?

Rate of Decay

• Beyond knowing the types of particles which are emitted�when an isotope decays, we also are interested in how frequently�one of the atoms emits this radiation.�
• A very important point here is that we cannot predict when a�particular entity will decay.�
• We do know though, that if we had a large sample of a radioactive �substance, some number will decay after a given amount of time.�
• Some radioactive substances have a very high “rate of decay”,�while others have a very low decay rate.�
• To differentiate different radioactive substances, we look to�quantify this idea of “decay rate”