Measuring Device Key to Astronaut Safety
Two TEPC’s (Tissue Equivalent Proportional Counter) measure the amount of radiation on Space Station Alpha. A stationary TEPC measures how much radiation the astronauts would absorb if they are moving around and not shielded from the radiation. The portable TEPC stays with the astronauts while they are working and shielded. The readings from the TEPC’s are expressed in rems. 

Rad and Rem
When working with radiation, scientists use two terms to describe the amount of radiation. The two terms are “rad” and “rem.”

A rad---“Rad” is the term used to describe one unit-measure of an amount of radiation. One-thousandth (1/1,000) of a rad, or a millirad, is the unit often used to describe how much radiation an astronaut’s body is exposed to while on Space Station Alpha.

A rem (Roentgen equivalent man) is the term used to describe the number of rads of radiation that the body absorbs and the approximate damage caused by the dose of radiation. A rem is the number of "rads" multiplied by a quality factor. The quality factor takes into account the potential effects of different types of radiation. One-thousandth (1/1,000) of a rem, or a millirem, is the unit often used. The relation between rad and rem depends on the kind of particle emitting the radiation. On Earth 1 rad of gamma rays = 1 rem; one rad of beta = 10 rems; one rad of alpha particle = 30 rems.

Describing the Rad / Rem Relationship
One way to describe the Rad / Rem relationship is to compare rads of radiation to ounces of chocolate. If we compare one ounce of Hershey’s chocolate to one ounce of the finest gourmet, Belgian chocolate, you would have one ounce (rad) of each. But which is more chocolaty? The more chocolatey tasting chocolate would have more chocolatey taste (Rems) for each ounce (rad) of chocolate. The more the taste (rems) the better the quality.

One more factor is needed to determine the amount of rems, and that factor is time. Rems of radiation are absorbed over time. The measure of rems absorbed in a period of time is called a “dose.”

Dose---“Dose” is the total amount of radiation that a person receives over a period of time. The units used are rems. A dose rate is the speed at which the person receives radiation at any given time. For example, if a person is exposed to a dose rate of 50 millirem per hour, then in one hour the total dose is 50 millirem. At this same dose rate, then in one half hour the total dose is 25 millirem.

There are two types of radiation in the electromagnetic spectrum, non-ionizing and ionizing.   
Examples of non-ionizing radiation would be ultraviolet light, radio waves, TV waves, the spectrum of visual light, and microwaves.  Examples of ionizing radiation are x-rays and gamma rays. The sun also ejects ionizing particles, called proton particles. These are called ionizing protons. Ionizing protons also cause serious radiation damage to the body.  The TEPC measuring devices used on the space station detect both ionizing radiation and ionizing protons.

Earth-bound Radiation versus Solar Proton Events
On Earth, alpha and beta particles are extremely dangerous forms of radiation and do a great deal of radiation damage to the human body. An equivalent rad of x-rays or gamma rays does less rem of damage than an alpha or beta particle. Alpha and beta particles are not part of solar proton ejections. But ionized protons are, and these travel farther and carry very dangerous levels of radiation (higher rems) for each rad that is received by the astronauts. Ionized protons are as dangerous, or more dangerous, than Alpha and Beta particles on Earth.

[Alpha and Beta particles are very short-lived phenomena on Earth. They can travel only very short distances. I believe that they are, in some cases, what is called “secondary radiation,” an idea which we edited from the original materials of Sherri’s because of the concrete/water/ balloon detour. They are not part of the “events,” per se, but they may be part of the results of the event as the ionized protons hit the sides of the space station. That is my understanding at this point.]

The Importance of Accuracy
Measuring radiation is very important. It must be performed with accuracy and precision. The astronauts will count on you to use the correct terminology and calculate the correct amount of exposure. The Acute Effects of Radiation Exposure Chart describes in rems, the effects of different amount of radiation upon the astronauts.

[If you want to move reference to Chart, it’s fine with me. I don’t have a conceptual overview of how this unit will play out. You asked a question in the “Radiation: Friend or Foe” essay, at the end, about the references of the last paragraph. You asked: “Do we mention here or in later article.” It was my understanding that you had no article sequence in mind. The technical nature of this stuff, it seems to me, necessitates sequencing of some sort. How else will the students construct a baseline vocabulary that lets them conceptually construct the information as they proceed from one essay to another. The gradual introduction of terminology builds of necessity. I still don’t think we can let students tackle the complexity of “radiation” any other way.]