A pdf version of this document can be found on the D-tect
Systems website, here.
Background radiation: ~ 3 mSv/yr (300 mrem/yr) in North America and slightly higher in Asia. 88% of background radiation comes from natural sources (half of this from radon gas), almost all the remaining radiation comes from medical sources.
Background radiation: ~ 3 mSv/yr (300 mrem/yr) in North America and slightly higher in Asia. 88% of background radiation comes from natural sources (half of this from radon gas), almost all the remaining radiation comes from medical sources.
 |
| World Nuclear Organization |
Safety Levels: American regulatory limit for occupational exposure: 50 mSv/yr (5 rem/yr). This limit was chosen because it is the lowest rate at which there is evidence of cancer being caused in adults. Pregnant women and children should have no more than a 10th of this (5 mSv/yr or 500 mrem/yr). A lethal full-body dose for a man is around 4-5 Sv (400-500 rem) in a short time period.
Radiation Sickness Threshold: 1000
mSv (1 Sv or 100 rem) in a short time period. Symptoms: nausea, hair
loss, weakness, skin burns
Long-term Radiation Exposure:
cancer, cell mutation, birth defects. The danger of continued
overexposure to radiation is that symptoms can appear after 20 years
after exposure.
Radiation Exposure vs. Distance:
if you double the distance, you reduce the exposure by a factor of 4.
Ionizing Radiation Types
Alpha
Penetration: stopped by skin or paper, dangerous when ingested
or breathed in.
Beta
Penetration: stopped by aluminum plate or 1 cm of human flesh,
heavy clothing may be needed.
Gamma & X-rays
Penetration: easily passes through most matter, shielding
requires concrete, lead or water.
Neutron
Penetration: Just like gamma rays, shielding requires concrete
or water. Neutron radiation only comes from cosmic rays and nuclear
reactions, and although it isn’t ionizing, it can cause other materials
to become radioactive and is often accompanied by other radioactive
materials.
Protection from
Radiation
Limiting Time: For people who are exposed to radiation in addition to
natural background radiation through their work, the dose is reduced by
limiting exposure time.
Distance: In the same way that heat from a fire is less the further
away you are, the intensity of radiation decreases with distance from
its source.
Shielding: Barriers of lead, concrete or water give good protection from
penetrating radiation such as gamma rays. Radioactive materials are
therefore often stored or handled under water, or by remote control in
rooms constructed of thick concrete or even lined with lead.
Containment: Radioactive materials are confined and kept out of the
environment. Radioactive isotopes for medical use, for example, are
dispensed in closed handling facilities, while nuclear reactors operate
within closed systems with multiple barriers which keep the radioactive
materials contained. Rooms have a reduced air pressure so that any leaks
occur into the room and not out from the room.
Radiation Exposure Units
of Measurement
Exposure: measure of the strength of a radiation field at some point
in air. Basic unit: “roentgen” (R).
Dose: absorbed dose is the amount of energy that ionizing
radiation imparts to a given mass of matter. Basic units: “gray” (Gy)
and “radiation absorbed dose” (rad). 1 Gy = 100 rads. In human tissue, 1
R of gamma radiation = 1 rad of absorbed dose.
Dose Equivalent: relates to the absorbed dose to the biological effects of
that dose. Basic units: “sievert” (Sv) and “roentgen equivalent in man”
(rem). 1 Sv = 100 rem.
Dose
Rate: a measure of how fast radiation a
radiation dose is being received. Basic units: mSv/yr, mrem/yr, etc.
Half-life: The time it takes for half the nuclei in a specific isotope
to undergo decay.
Radiation Examples
Air travel: measured dose during air travel
is 5 µSv/hr (43.8 mSv/yr or 4380 mrem/yr) according to the FAA. This is
about 15 times background radiation.
Watching TV: 4 hours a day adds up to 2
mSv/yr (200 mrem/yr)
Allowable short-term dose for workers on the
Fukushima accident: 250 mSv (25 rem)
Radiation Measurement on the
perimeter of the Fukushima Nuclear Plant: 1-3 mR/h (about 10-30 µSv/h)
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| U.S. Environmental Protection Agency |
Atomic Shorthand
Example: “Iodine-131” =
53I131
Radioactive Iodine
Iodine concentrates in the thyroid. Because
of this, radioactive iodine (a byproduct of nuclear reactions)
contributes to thyroid cancer more than other types of cancer. For this
reason, potassium iodide tablets are given to increase the amount of
safe iodine in the body, as this limits the amount of radioactive iodine
the body will absorb.
The most common kind of radioactive iodine
(Iodine-131) has a half-life of only 8 days.
Nuclear Plants
There are over 440 commercial
nuclear power plants operating in 30 countries which accounts for about
14% of the world’s power. The US has 104 operating reactors, the most
of any nation. Japan previously had 56.
 |
| International Atomic Energy Agency |
Alarm
Levels for the MiniRad-D Radiation Detector
Alarm Level
|
µrem/hr
|
mrem/hr
|
µSv/hr
|
mSv/hr
|
1
|
35
|
0.035
|
0.35
|
0.00035
|
2
|
40
|
0.04
|
0.4
|
0.0004
|
3
|
55
|
0.055
|
0.55
|
0.00055
|
4
|
65
|
0.065
|
0.65
|
0.00065
|
5
|
100
|
0.1
|
1
|
0.001
|
6
|
200
|
0.2
|
2
|
0.002
|
7
|
350
|
0.35
|
3.5
|
0.0035
|
8
|
600
|
0.6
|
6
|
0.006
|
9
|
1100
|
1.1
|
11
|
0.011
|
D-tect Systems
The radiation facts and protection information in this
post were published by the World Nuclear Association
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