Dossier on the radioactivity


Radioactivity

Matter is made up of atoms. Each atom consists of a nucleus composed of protons and neutrons. The nucleus is surrounded by electrons which gravitate around it like satellites. Radioactive materials spontaneously emit gamma or X rays and/or beta or sometimes alpha particles.

Beta particles are electrons. Because of their charge, they react very strongly to matter. They cover a distance of a few centimeters to a few meters in the air. A sheet of aluminium can stop them.

Alpha particles are helium nuclei (2 neutrons and 2 protons). They can cover a distance of a few centimeters in the air. A sheet of paper can stop them.

Gamma rays are electromagnetic rays which are formed by physical phenomena occurring within the nucleus of the atom. Gamma rays can produce ions (atoms or molecules which have an electrical charge which is not nil) directly or indirectly when they pass through matter. They can cover a distance of dozens of meters in the air. They can penetrate quite far. A thick layer of lead or concrete can effectively diminish their power of penetration.

X rays are similar to gamma rays but are formed by physical phenomena occurring within the electronic structure of the atom. They are used for medical purposes and are rarely found in nature.

Threshold levels of radioactivity


There is no threshold under which radioactivity is harmless. Any dose, even a very slight one, causes a health hazard. The greater the dose is, the greater the risk of cancer or genetic anomaly. The relation between the risk and the dose is considered to be linear. Indeed, the International Commission on Radiological Protection (ICRP) proposed in 1990 that the equivalent of the maximum dose should be of one millisievert per year, that is to say 11.4µRem/h in average. This norm concerns doses other than those due to medical examinations or natural radioactivity. The former norm which is still occasionally used was of 5 millisieverts per year but it included all of these different types of radiation.

The ICRP estimates that each millisievert is responsible for 60 extra cancers (50 of which are lethal) and 13 genetic anomalies per million persons.

Calculation of average doses


You must take into account the radiation levels corresponding to the places you are usually in and the amount of time you usually spend there in order to calculate an average dose.

Example :

Dwelling: 20µRem/h, 12 hours a day,
Work place: 30µRem/h, 8 hours a day,,
Other places: 10µRem/h, 4 hours a day.

Average dose = (20x12) + (30x8) + (10x4) = 520 µRem for 24 hours.

So

520 ÷ 24 = 21,6 µRem/h.

Effects of radioactivity


The ionization of molecules in the human body can cause disorders capable of causing cancerous tumours and genetic mutations likely to create hereditary abnormalities.

Parts of the body most sensitive to radiation (in decreasing order):

  • The reproductive glands of both sexes (hereditary abnormality)
  • Breasts (cancer)
  • Red bone marrow (leukaemia)
  • Lungs
  • Thyroid gland
  • Bones
  • Muscle tissue
  • Skin

Natural irradiation


Source Level
Sedimentary soil 4µRem/h in average (according to the region)
Granitic soil 20 times more than sedimentary soil (radioactivity of 8000Bq/kg)
Radon This gas is a product of uranium which migrates through the soil and stagnates in dwellings. It emits alpha particles and some gamma rays.
Cosmic rays (*) 3.4µRem/h at sea level (10.3 to 3000m)
Human body 2.3 to 17.7 µRem/h (linked with ingestion and inhalation)
Water and food 5,7 µRem/h (non contaminated products)
(*) Cosmic rays are reduced by the atmosphere, their effects are thus increased with altitude. The level can reach 300µRem/h in an plane at an altitude of 10000 m, especially near the North or South Pole.

Artificial irradiation


Source Level
Medical 11.4 µRem/h average/year (X rays, radiotherapy)
TV screen 0,11 µRem/h
Nuclear tests 51.3 µRem in 50 years (average diluted atmospheric fallout)

Contamination and concentration






The following diagram illustrates very well how radioactive elements are propagated and how they can be concentrated in food.

Beware, game such as migrant birds (ducks, woodcocks.) can be radioactive as most of them come from eastern Europe where numerous contaminated zones are to be found. (see Radex RD1503 user’s manual for their detection).

Radioactivity contamination and concentration

Contacts


Common radioactive objects


Alarm clocks and watches

Twenty years ago the hands of an alarm clock or watch were luminescent. The substance used were usually radium or other radioactive substances. Measurements taken next to the face of an alarm clock or watch can reach 600µRem/h. It is best to avoid wearing such a watch.

Sleeves gas lamps

When camping you might have used gas lamps. A mantle is adapted to the lamp and once heated by the gas, it will emit light by incandescence. Levels measured vary from 15 to 360 Rem/h when in direct contact. At distances exceeding 50 cm, rays are no longer detected. You can protect yourself from radiations by keeping at a distance of more than 50 cm from a mantle. Avoid putting a mantle in your pocket.

The risk of contamination is much greater than the risks of radiation. There are indeed sleeves that contain thorium 232. Besides the direct effects of radiation these sleeves present another danger: thorium emits high levels of radiation, a few breathes are enough to reach the limit of tolerable risk. Also the dissemination of radioactive micro particles when the sleeve is heated to incandescence is not yet known. There are also risks when handling these sleeves after use. Fibers and dust increase the risk of breathing or inhaling radioactive particles. To manipulate the old sleeves, it is recommended to use gloves and if possible avoid breathing.

Lightning conductors

Fifty years after Benjamin Franklin discovered the lightning conductor in 1760, a Hungarian thought of placing a radioactive source at the tip of a lightning conductor. He thought that the radioactivity would ionize the air around the tip of the lightning conductor and make it conductive and that thunder bolts would in consequence be directed there. Although the efficiency of this method was uncertain, it was patented and commercialized in 1932.

It is thought that approximately 30 000 radioactive lightning conductors still stand on our roofs in France. In 1983 a decree forbade the use of radioactive elements in the manufacture of lightning conductors, leaving a period of 4 years for manufacturers to comply. In 1986 a new decree also forbade the import and sale of such lightning conductors.

Main radioactive isotopes


Atomic number Isotope (radio nuclide) Energy in MeV Main Rays Half life (half value period)
Alpha (α) Beta (β) Gamma (γ)
2 Tritium (He3) 0,019 β 12 year
6 Carbone-14 0,155 β 6.000 year
19 Potassium-40 1,46 β γ 1.300.000.000 year
27 Cobalt-60 0,318 β γ 5 year
37 Rubidium 87
38 Strontium-90 0,546 β 29 year
43 Technetium-99 0,292   β γ 212.000 year
53 Iode-123 0,16 γ 13,2 hours
53 Iode-125 0,03 γ 59,4 Days
53 Iode-129 0,194 β 15.700.000 year
53 Iode-131 0,971 β γ 8,02 Days
55 Cesium-134 2,06 β 2,06 year
55 Cesium-135 0,26 β 2.300.000 year
55 Cesium-137 1.17 β 30,07 year
57 Lanthane 138
62 Samarium 147
78 Platine 190
81 Thallium 204 0.764 β γ 3,78 year
81 Thallium 206
81 Thallium 207
81 Thallium 208 β γ 3,1 min
81 Thallium 210
82 Plomb 202 2,598 α 52 500 year
82 Plomb 204 2,186 α > 1,4×1017 year
82 Plomb 205 0,051 γ 1,53×107 year
82 Plomb 210 3,792 γ 22,3 year
82 Plomb 212 γ 10,6 hours
82 Plomb 214 β 27 min
83 Bismuth 207 2,399 β γ 31,55 year
83 Bismuth 208 2,88 γ 368.000 year
83 Bismuth 209 ? α 1.9 x 1019 year
83 Bismuth 210 α 5,01 Days
83 Bismuth 212 6,84 α β γ 61 min
83 Bismuth 214 β 20 min
84 Polonium-208 5.215 α β 2,898 year
84 Polonium-209 4.979 α β 103 year
84 Polonium-210 5.407 α 138 Days
84 Polonium-212 8.78 α 3 × 10-7 s
84 Polonium 214 7,7 α 1,6 × 10-4 s
84 Polonium 216 α 0,15 s
84 Polonium 218 α 3,1 min
85 Astate 210 5,631 α β 8,1 hours
85 Astate 215 α 7,21 hours
85 Astate 216 α 3 10- 4 s
85 Astate 217 α 32 ms
85 Astate 218 α
86 Radium 223 5.99 α 11,43 Days
86 Radium 224 5.789 α γ 3,6319 Days
86 Radium 226 4.78 α γ 1.600 year
86 Radium 228 0.046 β 6,7 year
87 Francium 221 6.457 α 4.8 min
87 Francium 222 2.033 β 14.2 min
87 Francium 223 5.430 α β 22 min
88 Radon 220 α 55,6 s
88 Radon 221 5,965 α 14,6 hours
88 Radon 222 5,49 α 3,8 Days
89 Actinium 224 1,403 α β γ 2,9 hours
89 Actinium 225 5,935 α 10 Days
89 Actinium 226 5,536 α β 29,4 hours
89 Actinium 227 5,536 α β 21,773 year
89 Actinium 228 2,127 β γ 6,15 hours
90 Thorium 228 5,52 α γ 1,9 year
90 Thorium 229 5,168 α 7.340 year
90 Thorium-230 4,68 α 75.380 year
90 Thorium 232 4,083 α 1,4 × 1010 year
90 Thorium 233 1,24 α 22,3 min
90 Thorium 234 0,199 β 24,1 Days
91 Protactinium 229 5,58 α β 1,4 Day
91 Protactinium 230 0,563 β 17,4 Days
91 Protactinium 231 5,149 α 32.760 year
91 Protactinium 232 0,31 β 1,31 Day
91 Protactinium 233 0,571 β 26,96 Days
91 Protactinium 234m 2,29 β 1,17 minute
91 Protactinium 232 0,23 β 6,75 hours
92 Uranium-232 5.4 α 68,9 year
92 Uranium-233 4.9 α 159.200 year
92 Uranium-234 4,85 α 244.500 year
92 Uranium-235 4,39 α 704 Millions of years
92 Uranium-236 4,57 α 23,42 Millions of years
92 Uranium-238 4,27 α 4.468.800.000 year
94 Plutonium-238 5,5 α 87,75 year.
94 Plutonium-239 5,24 α 24.000 year.
94 Plutonium-240 5,17 α 6.560 year.
94 Plutonium-241 5,17 α β 14.4 year
94 Plutonium-242 5,17 α 373.000 year
94 Plutonium-244 5,17 α 80.800.000 year
95 Americium-241 5,49 α γ 432 year (Smoke detectors)