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Working with ionising radiation

What types of ionising radiation are there?

Ionising radiation is emitted by natural radioactive radiation sources but can also be generated artificially.

The following types of radioactive particles are distinguished

  • alpha radiation (helium nuclei);
  • beta radiation (electrons from the nucleus);
  • positron radiation (positively-charged electrons from the nucleus);
  • neutron radiation and deuteron radiation;
  • gamma and X-ray radiation (electromagnetic radiation).

Enclosed and open sources

  • Enclosed radioactive sources are mounted on a carrier or encapsulated making the spread of radioactive substances almost impossible. Examples are calibration sources for contamination monitors and caesium sources for therapeutic purposes.
  • Open sources are radioactive sources that are not attached to a carrier. The risk of spread in the surroundings is large. Open sources are also used in research and in nuclear medicine. For use in laboratories specific requirements are imposed on the room worked in.

May I use ionising radiation myself?

According to the Radiation Protection Decree you may only work with ionising radiation under the supervision of a qualified radiation expert. His permission and consent are therefore always required.

Anybody who in their work with open sources or with equipment that emits ionising radiation has a chance of more than 1 millisievert (mSv) of exposure per year (over and above normal background radiation) is considered to be a radiological worker. The exposure standards for radiological workers are different than those for non-radiological workers (colleagues, members of the public).
Table 1 gives an overview of the dose limits per year for radiological and other workers and the surroundings according to the Radiation Protection Decree.

Table 1. Statutory dose limits (mSv) per year

Category

Radiological 
worker 
3)

Employees between
16 and 18 years

Other people within the location

Members of the public outside the location

Effective dose

20 1)

6

1

0.1

Eye lens

150

150

15

-

Skin

500 2)

150 2)

50 2)

-

Hands, forearms, feet and ankles

500

150

50

-

1) Additional limit values apply to pregnant staff.
2) Average over non-exposed skin surface of 1 cm.
3) Radiological worker is a:

  • Category A employee if there is a reasonable chance of the exposure being greater than 3/10 of the limit; 
  • Category B employee if the chance of the exposure being greater than 3/10 of the limit is very small. 

Please note: Separate regulations apply to category A and category B employees with respect to medical examination, medical supervision, dose registration and reporting.

What are the risks of ionising radiation?

If the body is exposed to radioactive radiation then tissue damage can occur. The damage increases as the quantity of radiation energy absorbed increases.

Dependent on the quantity and dosage rate, radiation can have two types of consequences:

  • the direct consequences: within several hours or weeks. Cell damage, burns or genetic mutations occur;
  • the later consequences: sometimes decades later abnormalities are expressed (genetic mutations, cancer) or abnormalities occur in the offspring.

Irradiation and contamination

  • Irradiation is understood to mean external exposure; this stops as soon as you remove yourself from the source.
  • Contamination is understood to mean internal exposure. The exposure stops as soon as the radioactive source is excreted from the body. This can proceed very slowly.

Which measures do I need to take?

Various points are important for maintaining optimum working conditions.

  • Keep the quantity of radiation used as low as possible.
  • Keep the exposure to a minimum (and/or work as quickly as possible).
  • Keep the distance to the source as large as possible.
  • Use shielding (for example, lead shielding when working with gamma emitters, Perspex screening for beta emitters).
  • Where prescribed use personal protection equipment (lead apron, lead gloves etc.).

How do I work safely with X-rays?

X-rays are produced when electrons or ions collide with the matter. In the case of constant intensity of the particle beam the dose rate strongly increases with increasing energy; for a accelerating voltage of several tens of kilovolts, a doubling of the accelerated voltage can lead to a thousand-fold increase in the dose rate.

Important to know

  • only experts may carry out X-ray measurements;
  • the readings of the various radiation monitors require interpretation;
  • in a vacuum an impermissible radiation intensity can develop at voltages higher than 5 kV and/or currents greater than 1 mA. If this situation could occur somewhere - think especially about new set-ups! - the radiation expert must be informed as soon as possible, so he can carry out an effective measurement;
  • experiments for which an impermissible radiation intensity might occur should be screened off appropriately, clearly marked and have a radiation monitor and warning lamps. Such experiments require a licence.

Tips

  • Make sure that the equipment is sufficiently screened off.
  • Let the equipment be maintained in the prescribed manner.
  • If in doubt let the radiation expert carry out measurements.
  • If the dose rates are high then wear lead aprons and/or other personal protection equipment.

How should I dispose of radioactive waste?

Strict rules apply to the disposal of radioactive waste. The radiation expert can inform you further about this. He will assume responsibility for transport of the waste to COVRA NV.

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