Chernobyl 1 - Radiation Released

By: Brink Harrison

Time: 2 class periods
Preparation Time: 10 minutes to photocopy

Radiation Plume #1 overhead
Chernobyl at the Time of Accident overhead
Teacher Background on units of radiation
Estimates of Radiation Released at Chernobyl Overhead
Table of Radionuclide Releases Overhead
Ionizing Radiation Exposure in the United States Guide Sheet
Homework sheet for Day 1

Calculating Your Personal Radiation Exposure Sheet

This lesson serves as the introduction to a set of lessons related to the horrific nuclear power plant disaster at Chernobyl in the Ukraine, part of the former Soviet Union. Students will review the process of unit analysis to convert between units of radioactivity and will examine the radiation released during the 10 days the fire at the power plant raged.


Students will be able to:

i. Apply unit analysis to convert between Curies (Ci) and Becquerels (Bq), which are units of radiation used to express the amount of radiation released.
ii. Use half-life data of radioactive nuclide material to demonstrate the use of an exponential function, specifically calculating the amount of material remaining after a given period of time.
iii. Covert from units of radiation curies or becquerels to units of mass to determine the scale of radioactive material release during the Chernobyl disaster.

Math Standards
• Use unit analysis to check measurement computations.
• Make decisions about units and scales that are appropriate for problem situations involving measurement.
• Recognize and apply mathematics in contexts outside of mathematics.

Teacher Background
On April 26, 1986, due to a combination of the construction of the power plant and human error, there was a melt down inside the reactor in Unit #4 of the Chernobyl Nuclear Power Plant. The subsequent steam explosion and fire blew the 1000-ton roof off the building and allowed radioactive material to escape. How much radiation were those workers in direct proximity exposed to? At the time of the explosion at Chernobyl, one source says that “on the roof of the destroyed reactor building, radiation levels reached a frightening 100,000 R per hour! “
(Source: http://www.agls.uidaho.edu/etoxweb/resources/Case%20Study/Chernob6.pdf)

The number above means little, unless you put it in terms of normal radiation exposure. According to a report from the National Council on Radiation Protection and Measurements (NCRP Report No. 93), the annual average effective dose equivalent received in the United States is approximately 360 mrem (millirems) per person.
(Source: http://epswww.unm.edu/xrd/xrclass/02-Rad-Safety.pdf or http://www.ocrwm.doe.gov/pm/program_docs/curriculum/unit_2_toc/47.pdf )

The total release of radionuclides to the environment has been approximated to be somewhere in the range of 1900 PBq of activity (in a Report to the US Department of Energy) and 12 EBq (in the assessment of the OECD Nuclear Power Agency). That is a range of about 51 million Ci to 324 million Ci
(Source: http://agls.uidaho.edu/etoxweb/resources/Case%20Study/Chernob6.pdf)

Related and Resource Websites


Chernobyl nuclear power station, Ukraine



1. Begin by telling your students the following story: On 4/28/86 at the Forsmark Nuclear Power Plant, which is 60 miles north of Stockholm, Sweden, suddenly signs of abnormally high levels of radiation were found. Up to five times the normal amount of radioactive emissions were found in the soil and greenery around the plant. Even further north in Sweden and Finland, where rain and snow were falling, the same disquieting signals were discovered. The original fear was that the Forsmark Plant was leaking radiation somehow. After extensive searches, the scientists decided that the plant was not losing radiation. It had to be coming from somewhere else!

Examining the wind patterns for those days, the wind had come up from the Black Sea, across the Ukraine, across the Baltic Sea and into Scandinavia. In other words, something terrible had happened in the Soviet Union, and the Soviet officials were not telling anybody about it. That disaster was Chernobyl.

2. Ask your students if they have ever heard of Chernobyl. Since most of them were not born when the Chernobyl disaster occurred, nearly 20 years ago in 1986, do not expect them to know much, if anything, about Chernobyl.

3. Next ask your students where in the world they think Chernobyl is located, considering how the winds carrying the radiation had swept across the Ukraine. Put up Radiation Plume #1 overhead (Source: http://agls.uidaho.edu/etoxweb/resources/Case%20Study/Chernob6.pdf figure #5) and mark the approximate location of Stockholm to show how far the wind had carried the radiation in just two days.

4. Share with the students the following:
On April 26, 1986, due to a combination of the construction of the power plant and human error, there was a melt down inside the reactor in Unit #4. The subsequent steam explosion and fire blew the 1000-ton roof off the building and allowed radioactive material to escape.

5. If possible, show the video, “Nowhere to Hide: A Look at Chernobyl”
(source: http://www.ucg-terrehaute.org/video/chernobylbb.rm) This 10-minute video gives a good picture of just how terrible Chernobyl was and some of the health problems caused by the radioactive materials released during this event. (Talking with an individual who lived in Kiev at the time of the accident, she says that the Geiger counters were recalibrated because they had been used in a different experiment and not by governmental decree)

If you can’t get the video, put up Chernobyl at the Time of Accident overhead (Source: http://www.agls.uidaho.edu/etoxweb/resources/Case%20Study/Chernob6.pdf figure #4) to show the damage to the reactor building and the huge hole through which radiation escaped. Firefighters battled the blaze, unaware of the terrible radiation, but it continued for ten days.

6. Before you can talk about how much radiation these workers and firemen were exposed to, you need to talk about the various ways of measuring radiation. Put up the Units of Radiation overhead and tell the students that radiation has several different units of measurement (see Teacher Background for further information).

a. The roentgen (R) is a unit of radiation exposure in air.

b. The rad (roentgen-absorbed-dose) is a unit of absorbed radiation or a unit of dose. A roentgen in air can be approximated by 0.87 rad in air, 0.93 rad in tissue, and 0.97 rad in bone. Doses are commonly expressed in rads/hr or mrads/hr or R/hr and mR/hr.

c. The rem (roentgen-equivalent-man) is a unit of dose equivalent. The rem is the absorbed dose in rads corrected for the equivalent absorption in living tissue. The rem is equal to the rad multiplied by a weighting factor depending upon the type of radiation.

d. For x-rays, the weighting factor is one. Therefore, for x-rays, one rem is equal to one rad.

7. Tell student that they will now calculate approximately how many mrems of radiation they are exposed to each year. Using the Ionizing Radiation Exposure in the United States guide sheet and the Calculating Your Personal Radiation Exposure sheet (Source: http://www.ocrwm.doe.gov/pm/program_docs/curriculum/unit_2_toc/47.pdf ), have students calculate approximately how many mrem they were exposed to this year. The average per capita US dose is 360 mrem per year. Tell the students that you can not assume a direct relationship between rads and rems for all radiation, but for x-rays it is a weighting factor of one. If they use this factor for their total exposure, how many roentgens where they exposed to?

8. Share with the students that at the time of the explosion at Chernobyl, one source says that “on the roof of the destroyed reactor building, radiation levels reached a frightening 100,000 R per hour! “
(Source: http://www.agls.uidaho.edu/etoxweb/resources/Case%20Study/Chernob6.pdf , page 2)
Students will use a ratio to calculate the factor that their personal exposure must be multiplied by to reach the level of exposure of the workers on the roof after the exposure. Point out that while their (the students’) exposure is over a year, the exposure of the fireman and other workers was per hour.

9. Share with the students that one of the areas of controversy about Chernobyl is the “source term” which refers to how much radioactivity was released from the exploded and burning reactor. Before we can approximate the amount of radioactivity released, we first need to deal with the units used for measuring the gross radioactivity in a substance that does not relate to doses or biological damage. These units are the Curie (Ci) and the Becquerel (Bq). These units both measure the rate at which radioactive material decays in disintegrations per sec (dps)

A curie, named after Madam Marie Curie, is the amount of radioactivity in one gram of radium. One gram of radium has 37,000,000,000 disintegrations per second (3.7x10^10 dps). This means that one curie of a different radioactive substance is the amount of that material that will have 3.7x10^10 dps. Thus, one curie of plutonium is a different number of grams from one curie of cesium.

A becquerel is the quantity of a radioactive substance that will have one disintegration per second (1 dps). One Ci =3.7x10^10 Bq.

In an atomic reactor there are many billions curies of radioactivity. The number four reactor at Chernobyl was believed to have 9 billion curies of radioactivity. To convert a large number of curies into becquerels, we need much larger units of becquerels, like petabecquerels (PBq) = 10^15 Bq or exabecquerels (Ebq )= 10^18 Bq.

10. Put up the Estimates of Amount of Radiation Released at Chernobyl overhead, showing each estimate separately. Ask students what they notice about these estimates and why they might vary so significantly depending upon the source.

a. 50 million curies of radioactive substances plus another 50 million curies of rare and noble gases was released (Russians and the International Atomic Energy Agency (IAEA), 1986 report)

b. 30% of the nuclear core, 3 billion curies of an estimated 9 billion curies was released (The US Argonne National Laboratory, 1986)

c. 50% of the core’s radioactivity, 4.5 billion curies, was released (The US Lawrence Livermore National Laboratory, 1986)

d. No less than 80 % of the reactor’s radioactivity, which amounted to 6.4 billion curies, was released. (Vladimir Chernousenko, chief scientific supervisor of the “clean up” for a 10-kilometer zone around the exploded reactor, 1991)

e. At the Union of Concerned Scientists Senior Energy analyst Kennedy Maize concluded that the “core vaporized – all 190 tons of fuel and all 9 billion curies.”

(Source: http://ratical.org/radiation/Chernobyl/Chernobyl@10p2.html)

As the Chairman of the Chernobyl Committee in Belarus said to Itar-Tass in Minsk on April 29, 1999, “No one knows how much fuel was left there (at Chernobyl)”

11. Tell the students they are now going to use unit analysis to convert from curies to PBqs and from PBq’s to Curies, given that and One Ci =3.7x10^10 Bq. Ask students how they would convert 50 million curies (Ci) into PBqs. To do this they need to draw upon the information about the relationship between Ci & Bqs, as well as the relationship between Bqs & PBqs. This exercise asks students to develop a unit analysis equation and be able to use scientific notation. (Teacher cheat sheet follows)

12. Then ask the students how they would convert 85 PBqs into Ci.

Teacher cheat sheet: Use the following conversion ratios to make it easier for you to check the students’ calculations when converting from Ci’s to PBq’s or from PBq’s to Ci’s:


1. Convert the estimated amounts of total radiation released at Chernobyl from Ci’s to PBq’s. (Answers are given below amount)

a) 3 billion Ci

b) 4.5 billion Ci

c) 6.4 billion Ci

d) 9 billion Ci

2. Convert the following estimated amounts of individual radioactive elements released at Chernobyl from Pbq’s into Ci’s (Answers are given below question. (You will need these numbers for a later homework assignment)

a)           1600 – 1920 PBq”s

Lower estimate:

Upper estimate:

b)           56 – 112 PBq’s

Lower estimate:

Upper estimate:

c)           8 – 12 PBq

Lower estimate:

Upper estimate:

d)           0.03 PBq

e)          0.042 PBq


Day 2

1. Ask the students if they think all of the radiation inside the reactor was released. Students will have to draw upon their understanding of radiation from science in answering this question.

2. Share with the students the fact that radiation is apparently leaking from the sarcophagus
built around the destroyed reactor. Ask the students “What does this imply?” Hopefully they will realize that there is still radiation inside.

3. Put up the Estimate of radionuclide releases overhead to show the approximate amounts of twenty important radionuclide released during the Chernobyl accident.
(Source: http://www10.antenna.nl/wise/index.html?http://www10.antenna.nl/wise/449-450/4.html or Source: Nuclear Energy Agency: 'Chernobyl, Ten Years On', Nov.'95, p.29.).

4. Notice that the estimated maximum release of these twenty important radionuclides totals a staggering 12,536 PBq. Ask the students to calculate how many times larger this number is than the original Soviet announcement of 50 million curies being released. (12,536 PBq is approximately 340 million curies, which is nearly 6.5 times the original Soviet estimate.)

For an analysis of the accident’s consequences, the most significant of the radionuclides released are radioactive Iodine (), radioactive Caesium (), and radioactive Strontium (). Radioactive Plutonium () and its various decay products, some which have a half-life of 24,000 years, causes concern about long-term contamination.

Hopefully all of the students have heard of the half-life of a radioactive substance. It is the amount of time it takes for one half of the original amount of a radioactive substance to decay.

But before we can use the half-life to determine how long the radioactive material will be radioactive, we need to calculate the number of grams of the material was originally released.
To do this we must first calculate the specific activity (SpA) of the particular radionuclide in units of disintegrations per unit time/ unit mass. The SpA is calculated from the basic formula:


If the students have done some chemistry, they should be able to derive the formula for SpA by using unit analysis and Avogadro’s number. If they don’t have the experience in chemistry, simply substitute the numbers into the formula to get:


This equation is satisfactory when the half-life of the nuclide is expressed in seconds. If however, the half-life is expressed in other units, such as days, then a separate time conversion is required. Have students use time conversion factors to arrive at the following equation:

*** Teacher cheat notes: Here are other formulas for the SpA of a radioactive element depending whether the half-life is in minutes, hours, or years. I’d recommend using just one formula so the students will become familiar with that particular formula.


Source: U.S. Department of Health, Education, and Welfare: Radiological Health Handbook: January 1970.

5. Looking at the SpA formula for a radioactive element whose half life is measured in days, ask students to think about how the specific activity of the radionuclide with a half life of 8 days () compares to the specific activity of the radionuclide with a half life of 30 years ()?

Teacher Cheat Sheet: To calculate the SpA of , which has a half-life of 8.0 days.

To Calculate the SpA of , which has a half-life of 30 years,

The students should notice that the radionuclide with the shorter half-life has a greater value of specific activity, SpA , than the SpA of the radionuclide with the longer half-life. This means that the shorter the half-life of a radionuclide, the more Curies given off per gram of the nuclide, and the more Curies given off per gram means the radionuclide decays faster.

Activity 2: Part 1: Simply by looking at the length of the half-life of each of the following radionuclides, arrange them in order from the radionuclide with the lowest SpA value to the radionuclide with the highest Spa value

1)   (Half-life:30 yrs)                2)   (Half-life:28 yrs)

3)   (Half-life:24,400 yrs)         4)   (Half-life:6,580 yrs)

Answer: , , ,

Part 2: Use the SpA formula for a half-life given in years,

to determine the SpA for each of the following radioactive elements.

1)     (Half-life:30 yrs)           answer:  

2)      (Half-life:28 yrs)           answer:

3)    (Half-life:24,400 yrs)     answer:

4)    (Half-life:6,580 yrs)       answer:

6. Ask the students how to determine the range of the number of grams of released at Chernobyl. (To do this, divide the estimated amount of Ci’s released, calculated in last night’s homework, by the SpA of )

Lower estimate:

Upper estimate:

An estimated range for the amount of released is

Activity 3:
Use the specific values of the SpA to calculate the number of grams of each of the following radionuclides released during the Chernobyl disaster. (These estimates will be used in the homework of this lesson)

1) 56 – 112 PBq’s            

Lower estimate:

Upper estimate:

2) 8 – 12 PBq’s                

Lower estimate:

Upper estimate:

3) 0.03 PBq                   


4) 0.042 PBq                 


Now that we know approximately how much of each radionuclide was released, we can calculate how long the radiation from that nuclide will remain in the environment, if it were all deposited in one location. To calculate the amount of time, we start with radiation decay equation:


But we want to know the time, t, it takes for the radionuclide to decay completely. The equation needs to be rewritten into the form (If the students are familiar with natural logarithms have them convert the half life equations to allow them to solve for the time t otherwise give them the formula):

Now do the calculation for . Remember that since the natural logarithm of zero does not exist, this means . Instead a small number like grams.

Lower estimate of 348.7 grams:   

Upper estimate of 418.5 grams:

Remember, these numbers are based upon estimations, and are meant to give approximate values. The “actual “reported values might be different.


Have the students use the modified radiation decay equation to determine how long it will take for each of the following radionuclides to decay “completely” if the total amount were deposited in one place. (Since you cannot use , choose a small value like grams)

1) 56 – 112 PBq      (half-life: 30 years)


2) 8 – 12 PBq      (half-life: 28 years)


3) 0.03 PBq      (half-life: 24,400 years)

4) 0.042 PBq      (half-life: 6,580 years)

Please make sure that you tell your students that the radiation was scattered and did not settle in just one location. However, there are still many “hot spots” where the radiation is too high for people to live.

By calculating the amount of radiation released and calculating an “approximate” length of time it will take for the radioactive materials to decay completely, the students should begin to realize the seriousness of the Chernobyl disaster.

Embedded Assessment

Students should be assessed throughout the lesson on their ability to use unit analysis to grasp the amount of radiation released upon the world by this single incident. The discussion that should follow the homework needs to deal with the health issues that are still occurring now and will continue to occur in the future.



















































































































































































































































PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:

NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award


Supported by NIEHS grant # ES06694

1996-2007, The University of Arizona
Last update: April 10, 2008
  Page Content: Rachel Hughes
Web Master: Travis Biazo