Here’s the first draft of the radiation FAQ. Comments and/or critiques anyone? Keep in mind it’s first draft and haven’t run spell check, etc. More detail? Less? No, can’t have less. This barely covers the subject.
/jim/japan/Understandingradiation/draft0.doc
Understanding Radiation
by Jim Carver
Understanding radiation is important in our study of the after effects of The Fukushima Dai-ichi Disaster that began on Mar. 11, 2011. There are basically two main types of radiation, ionizing radiation and non-ionizing. NASA defines the two types as follows:
“Ionizing radiation is radiation with sufficient energy to remove electrons from the orbits of atoms resulting in charged particles, and it is this type of radiation that is evaluated for purposes of radiation protection. Examples of ionizing radiation include gamma rays, protons, and neutrons. Ionizing radiation is different from ion formation that occurs in ordinary chemical reactions, such as the generation of table salt from sodium and chlorine. In such a reaction, only the outermost electron is removed to form a positively charged ion. With ionizing radiation, if the energy is sufficient, electrons other than those in the outermost orbits can be released; this process renders the atom very unstable, and these ions are very chemically reactive.
Non-ionizing radiation is radiation without sufficient energy to remove electrons from their orbits. Examples are microwaves, radio waves, and visible light."
srag-nt.jsc.nasa.gov
Other examples of radiation include alpha-rays or particles, which are accelerated helium nuclei, and beta-rays, high speed electrons.
<A disscussion of alpha, beta and gamma particles/rays will be placed here>
The ionizing effects of radiation can due considerable damage to human tissue depending upon the intensity and length of exposure. It is interesting to note that while ionization of atoms within the molecules in living tissue create free radicals or ions which may lead to cancerous cells, radiation is also used in the medical field to kill cancerous cells. Research has shown that cancerous cells are somewhat less resistant to radiation than normal cells. [citation needed]
Source intensity is based on the amount of atomic nuclei emitting a high energy particle or in the case of gamma rays, a photon. Bequerels (Bq) and Curies (Ci) are the most common measurements.
1 ray emitted in 1 second = 1 Bq
Bq’s have to have a volume or a mass so we know how much material is involved. To say that there are 1 000 000 Bq is meaningless since there is not a quantity specified. But, a reading of 1 000 000 Bq/cm3 , does have meaning, because we know that 1 million particles (I’ll just use particles, but you know, could be photon) are emitted every second for each cubic centimeter of material. Do be careful when interpreting the readings in terms of the quantity. They might be in cubic centimeters (cm3) or Kilograms (Kg), note that the former is volume and the latter is mass. One could say that there are 1000 cm3 of water in one Kg, so the cubic centimeter is 1000 less than the kilogram. WRONG! In reality, if we are dealing with a soil sample, which has a specific gravity (SG) of around 2.65, which is 2.65 times the weight of water, we need to multiply 2.65 x 1000 to get the equivalent intensity compared to our cubic centimeter of water, or (cc) if you like. Note that volcanic soils, such as those found on the Island of Japan, have a larger amount of Iron (Fe) and Magnesium (Mg), making them normally heavier than continental crust. The SG will be higher. [value needed]It is therefore very important to convert units very carefully for comparison purposes
Before I talk about Curies (Ci), I would like to review some metric definitions:
The Metric System
The Metric System of measurement is the standard used by most scientific disciplines. The system is based upon measures of distance (in meters), volume (in liters), and mass (in grams). Scales of measurements increase or decrease as multiples of ten which facilitates expression of measurement values using the decimal system. The table below shows the most common prefixes and their relative magnitudes. Note that web browsers do not support use of superscripts and subscripts very well, so the notation 10^2 means "10 to the power of 2, or 10 squared". Similarly, the notation 10-2 should be read as "10 to the power of -2".
Prefix Scientific Notation Decimal equivalents Example Units
tera- (T) = 10^12 1000000000000 terabyte
giga- (G) = 10^9 1000000000 gigabyte
mega- (M) = 10^6 1000000 megabyte (mb)
kilo- (K) = 10^3 = 1000 kilogram (kg);
kilometer (km)
centi- (c) = 10-2 = 0.01 centimeter (cm)
milli- (m) = 10-3 = 0.001 milligram (mg);
millimeter (mm)
micro- (u) = 10-6 = 0.000001 microgram (ug)
microliter (uL)
nano- (n) = 10-9 = 0.000000001 nanogram (ng)
nanoamperes (nA)
pico- (p) = 10-12 = 0.000000000001 picogram (pg)
picoamperes (pA)
abacus.bates.edu adapted by author
Marie Curie was a very brave, pioneering scientist in the study of radioactive elements and compounds, mainly dealing with Radium. She gave her life in the pursuit of science and the Curie (Ci) is named in her honor.
1 Ci = 3.7×1010 decays per second or Becquerels = 37GBq
Note that a Ci is a large amount of radiation and micro Curies (uCi) are often used.
The Bq is the SI unit and used more often throughout the world, even in the United States. [citation] u=Greek letter mu, meaning micro-
Units used to Define Biological Effects
“The sievert (symbol: Sv) is the SI derived unit of dose equivalent radiation. It attempts to quantitatively evaluate the biological effects of ionizing radiation as opposed to the physical aspects, which are characterised by the absorbed dose, measured in gray. It is named after Rolf Sievert, a Swedish medical physicist renowned for work on radiation dosage measurement and research into the biological effects of radiation.”
“The unit gray measures absorbed radiation which is absorbed into any material. The unit sievert specifically measures absorbed radiation which is absorbed by a person. The equivalent dose to a person is found by multiplying the absorbed dose, in gray, by a weighting factor (w). The weighting factor (sometimes referred to as a quality factor) is determined by a combination of: the radiation type, the tissue absorbing the radiation, and other pertinent factors.[1]
In terms of SI base units:
1 Sv = 1 Gy • w (where Sv=sievert, Gy=gray, w=weighting factor specific to each type of radiation and tissue).
1 Gy = 1 J / kg of absorbing material
therefore:
1 Sv = 1 J / kg of absorbing material • w
Except from:
en.wikipedia.org
[conclusion]