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  • A 51 TBq 137Cs teletherapy unit was left unsupervised.
  • Two people took it home and tried to dismantle it. In the attempt the source capsule was ruptured.
  • The caesium was highly soluble and readily dispersible.


A private radiotherapy institute moved to a new location, taking with it a 60Co teletherapy unit and leaving in place a 51 TBq 137Cs teletherapy unit. The licensing authority was not notified as required under the terms of the institute's licence. The former premises were partially demolished. As a result, the 137Cs teletherapy unit became totally insecure. Two people entered the premises and, not knowing what the unit was, but thinking it might have some scrap value, removed the source assembly from the machine. They took it home and tried to dismantle it. In the attempt, the source capsule was ruptured. The radioactive source was in the form of caesium chloride salt, which is highly soluble and readily dispersible. As a result, several people were contaminated and irradiated.

After the source capsule was ruptured, the remnants of the source assembly were sold for scrap to a junkyard owner. Fragments of the source the size of rice grains were distributed to several families. One of the exposed people took the remnants to the city public health department. This action began a chain of events, which led to the discovery of the accident. The authorities were informed, several sites of significant contamination were quickly identified and residents were evacuated. As a result of the event, eight people developed acute radiation syndrome, and four people died from radiation exposure.

INES procedure (click the highlighted flowchart items to follow the procedure)

Figure 4, page 145 of the Manual

Figure 5, page 146 of the Manual

Calculate D-value

Here's the calculation for the release from the radiation source:

2.E+01 = 20

51(137Cs)/20 = 2.55 times D2 value

Check the answer


The total release was 2.5 times the D2 value

Level 4 defines that the release should be:
“Greater than 250 times the D2 value”

Rating based on activity release is Below Scale/Level 0