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Typical doses received during diagnostic x-ray exams
Procedure Effective Dose (mSv)
Chest 0.02
Dental 0.01
Skull 0.07
Leg 0.02
Mammogram 0.40
Barium enema 7.0
Upper GI 3.0
CT head 2.0
CT abdomen 10.0

What mass of 137 Cs Escaped chernobyl?

The Chernobyl accident in Ukraine (formerly in the Soviet Union) exposed the surrounding population to a large amount of radiation through the decay of 137 Cs . The initial radioactivity level was approximately A = 6.0 MCi . Calculate the total mass of 137 Cs involved in this accident.


The total number of nuclei, N , can be determined from the known half-life and activity of 137 Cs (30.2 y). The mass can be calculated from N using the concept of a mole.


Solving the equation A = 0.693 N t 1 / 2 for N gives

N = A t 1 / 2 0.693 .

Entering the given values yields

N = ( 6.0 MCi ) ( 30.2 y ) 0.693 .

To convert from curies to becquerels and years to seconds, we write

N = ( 6.0 × 10 6 Ci ) ( 3.7 × 10 10 Bq/Ci ) ( 30.2 y ) ( 3.16 × 10 7 s/y ) 0.693 = 3.1 × 10 26 .

One mole of a nuclide A X has a mass of A grams, so that one mole of 137 Cs has a mass of 137 g. A mole has 6.02 × 10 23 nuclei. Thus the mass of 137 Cs released was

m = ( 137 g 6.02 × 10 23 ) ( 3.1 × 10 26 ) = 70 × 10 3 g = 70 kg .


The mass of 137 Cs involved in the Chernobyl accident is a small material compared to the typical amount of fuel used in a nuclear reactor. However, approximately 250 people were admitted to local hospitals immediately after the accident, and diagnosed as suffering acute radiation syndrome. They received external radiation dosages between 1 and 16 Sv. Referring to biological effects in [link] , these dosages are extremely hazardous. The eventual death toll is estimated to be around 4000 people, primarily due to radiation-induced cancer.

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Check Your Understanding Radiation propagates in all directions from its source, much as electromagnetic radiation from a light bulb. Is activity concept more analogous to power, intensity, or brightness?


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  • Nuclear technology is used in medicine to locate and study diseased tissue using special drugs called radiopharmaceuticals. Radioactive tags are used to identify cancer cells in the bones, brain tumors, and Alzheimer’s disease, and to monitor the function of body organs, such as blood flow, heart muscle activity, and iodine uptake in the thyroid gland.
  • The biological effects of ionizing radiation are due to two effects it has on cells: interference with cell reproduction and destruction of cell function.
  • Common sources of radiation include that emitted by Earth due to the isotopes of uranium, thorium, and potassium; natural radiation from cosmic rays, soils, and building materials, and artificial sources from medical and dental diagnostic tests.
  • Biological effects of nuclear radiation are expressed by many different physical quantities and in many different units, including the rad or radiation dose unit.

Key equations

Atomic mass number A = Z + N
Standard format for expressing an isotope Z A X
Nuclear radius, where r 0 is the radius of a single proton r = r 0 A 1 / 3
Mass defect Δ m = Z m p + ( A Z ) m n m nuc
Binding energy E = ( Δ m ) c 2
Binding energy per nucleon B E N = E b A
Radioactive decay rate d N d t = λ N
Radioactive decay law N = N 0 e λ t
Decay constant λ = 0.693 T 1 / 2
Lifetime of a substance T = 1 λ
Activity of a radioactive substance A = A 0 e λ t
Activity of a radioactive substance (linear form) ln A = λ t + ln A 0
Alpha decay Z A X Z 2 A 4 X + 2 4 H e
Beta decay Z A X Z + 1 A X + −1 0 e + v
Positron emission Z A X Z 1 A X + + 1 0 e + v
Gamma decay Z A X * Z A X + γ

Questions & Answers

as a free falling object increases speed what is happening to the acceleration
Success Reply
of course g is constant
acceleration also inc
photo electrons doesn't emmit when electrons are free to move on surface of metal why?
Rafi Reply
What would be the minimum work function of a metal have to be for visible light(400-700)nm to ejected photoelectrons?
Mohammed Reply
give any fix value to wave length
40 cm into change mm
Arhaan Reply
40cm=40.0×10^-2m =400.0×10^-3m =400mm. that cap(^) I have used above is to the power.
i.e. 10to the power -2 in the first line and 10 to the power -3 in the the second line.
there is mistake in my first msg correction is 40cm=40.0×10^-2m =400.0×10^-3m =400mm. sorry for the mistake friends.
40cm=40.0×10^-2m =400.0×10^-3m =400mm.
this msg is out of mistake. sorry friends​.
what is physics?
sisay Reply
why we have physics
Anil Reply
because is the study of mater and natural world
because physics is nature. it explains the laws of nature. some laws already discovered. some laws yet to be discovered.
is this a physics forum
Physics Reply
explain l-s coupling
Depk Reply
how can we say dirac equation is also called a relativistic equation in one word
preeti Reply
what is the electronic configration of Al
usman Reply
what's the signeficance of dirac equetion.?
Sibghat Reply
what is the effect of heat on refractive index
Nepal Reply
As refractive index depend on other factors also but if we supply heat on any system or media its refractive index decrease. i.e. it is inversely proportional to the heat.
you are correct
law of multiple
if we heated the ice then the refractive index be change from natural water
can someone explain normalization condition
Priyojit Reply
please tell
1 millimeter is How many metres
Darling Reply
1millimeter =0.001metre
The photoelectric effect is the emission of electrons when light shines on a material. 
Chris Reply

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