Guidance

Rapid screening for internal radioactive contamination: training resource

Training guide for NHS and emergency services staff on rapid screening of people for internal radioactive contamination.

Following an incident which releases radioactive material into the environment it may be necessary to monitor people for internal contamination. The immediate aim is to identify those with internal contamination levels high enough to require medical assessment. Monitoring should be carried out as soon as possible.

Internal contamination results when radioactive material is inhaled or ingested, while external contamination refers to radioactive material on skin and clothing. Monitoring for external contamination is not covered by this training.

This training package outlines the procedures to be followed for monitoring of internal contamination for 5 radionuclides using handheld radiation detectors and how these are used to identify people who require medical assessment. A comprehensive description of procedures can be found in the supporting guidance document HPA-CRCE-014: Guidance on screening people for internal radioactive contamination.

In the case of an event involving radionuclides that can not be detected using handheld radiation detectors other monitoring methods are available. These are not discussed in this training package, but details can be found in the guidance document.

This training guide is aimed at staff who have some experience of using a handheld radiation monitor. This includes NHS staff who have been trained to use the RAM GENE-1 monitor, staff from NHS medical physics departments and trained staff from other emergency services.

At the end of this guide there is a link to a short test, to gauge your level of understanding.

If you have any questions or comments about this training contact mike.youngman@phe.gov.uk.

Monitoring of internal contamination: by different radionuclides

The identification of people who require medical assessment cannot be performed until the radionuclides have been identified.

Radionuclide identification must only be carried out by a suitably qualified radiation expert such as a radiation protection advisor (RPA).

Call Public Health England (PHE) on 01235 834 590 for advice on radionuclide identification.

If a single radionuclide is present then monitoring can be performed using selected handheld monitors for certain radionuclides. The advantage of this is that suitable monitors should be available locally and so measurements can begin soon after the incident is confirmed.

monitoring of hand held detectors

The following radionuclides can be assessed using handheld monitors:

Radionuclide Radiation types emitted
Cobalt-60 (60Co) beta, gamma
Selenium-75 (75Se) gamma
Iodine-131 (131I) beta, gamma
Cesium-137 (137Cs) beta, gamma
Iridium-192 (192Ir) beta, gamma

If a mixture of radionuclides is present, or the radionuclide is not listed above, then seek expert help before proceeding with monitoring.

Monitoring for internal contamination: handheld monitors

Due to the differences in sensitivity the associated action levels are different for each handheld instrument. An action level is the net count rate which if exceeded indicates the person needs immediate medical assessment.

Instrument-specific action levels are provided for a number of the most commonly used handheld instruments within the UK. Monitoring with other instruments is not recommended unless separate guidance is available.

The number of days post incident that instruments can be used are given below, together with the radionuclides and age groups that they are capable of assessing.

A space means that the instrument is not suitable for that radionuclide.

APTEC-NRC ADM-300 with BSP-100 probe

APTEC-NRC ADM-300 with BSP-100 probe

This table shows the number of days that radionuclides are detectable.

Radionuclides Age 0 to 10 years Age 10 to 19 years Age over 20 years
60Co 6 7 7
75Se      
131I      
137Cs      
192Ir      

RADOS RDS 200 with GMP-11 probe

RADOS RDS 200 with GMP-11 probe

This table shows the number of days that radionuclides are detectable.

Radionuclides Age 0 to 10 years Age 10 to 19 years Age over 20 years
60Co      
75Se      
131I 8 20 20
137Cs      
192Ir      

ROTEM RAM Gene-1

ROTEM RAM Gene-1

This table shows the number of days that radionuclides are detectable.

Radionuclides Age 0 to 10 years Age 10 to 19 years Age over 20 years
60Co 4 4 5
75Se 30 30 30
131I 12 30 30
137Cs      
192Ir 3 6 8

Thermo Mini 900 with 44A probe

Thermo Mini 900 with 44A probe

This table shows the number of days that radionuclides are detectable.

Radionuclides Age 0 to 10 years Age 10 to 19 years Age over 20 years
60Co 6 6 30
75Se 30 30 30
131I 30 30 30
137Cs 6 14 30
192Ir 30 30 30

TSA stystems PRM-470CS

TSA stystems PRM-470CS

This table shows the number of days that radionuclides are detectable.

Radionuclides Age 0 to 10 years Age 10 to 19 years Age over 20 years
60Co 9 30 30
75Se 30 30 30
131I      
137Cs 5 7 20
192Ir 30 30 30

SAIC Exploranium GR-135

SAIC Exploranium GR-135

This table shows the number of days that radionuclides are detectable.

Radionuclides Age 0 to 10 years Age 10 to 19 years Age over 20 years
60Co 20 30 30
75Se 30 30 30
131I      
137Cs 6 7 30
192Ir 30 30 30

Monitoring for internal contamination: urine monitoring

For other radionuclides, where monitoring with handheld monitors cannot be used, alternative methods are available to identify people who may have inhaled or ingested radioactive material. These methods are not described in this training package. However, some radionuclides can be assessed through urine monitoring.

This table shows the radionuclides assessed through urine monitoring.

Radionuclide Radiation type emitted
Strontium-90/Yttrium-90 (90Sr/90Y) beta
Radium-226 (226Ra) alpha, beta, gamma
Thorium-228 (228Th) alpha, beta, gamma
Neptunium-237/Protactiunium-233 (237Np/233Pa) alpha, gamma
Plutonium-238 (238Pu) alpha
Americium-241 (241Am) alpha, gamma
Californium-252 (252Cf) alpha

More information on urine monitoring for radionuclides can be found in the guidance document HPA-CRCE-014: Guidance on screening people for internal radioactive contamination.

Monitoring location and precautions

Monitoring location

Monitoring of people for internal and external contamination would normally be carried out at a temporary radiation monitoring unit (RMU), set up close to the incident. The setting up of this unit is not a part of this training. Guidance on setting up an RMU can be found in the document HPA-CRCE-017 - Radiation Monitoring Units: Planning and Operational Guidance. A template RMU plan will be published in 2015.

In summary:

  • the RMU should be located in a covered area large enough to deal with the demand, providing adequate separation of people waiting for monitoring, being monitored, and awaiting transfer for further assessment
  • decontamination facilities should be made available if it’s possible that external contamination could be present on people
  • the monitoring should be carried out at a location where the levels of natural background radiation are not unusually high, and where levels have not been significantly enhanced by contamination from the incident

Monitoring precautions

The monitoring area in particular should be kept free of contamination. Chairs and floors should be covered so that they can be easily decontaminated.

Staff carrying out monitoring should wear suitable personal protective equipment (PPE). In all but extreme cases, the use of disposable coveralls, gloves and overshoes should provide adequate protection of staff carrying out monitoring of people.

Monitoring with handheld detectors

Reliable monitoring for internal contamination using handheld detectors is only possible where:

  • external contamination is not present
  • the radionuclide is known

Therefore, before internal contamination procedures can commence it will always be necessary to monitor for external contamination and to carry out decontamination procedures as required.

Where the radionuclide is initially unidentified, screening will enable identification of the most contaminated people, but it will not be possible to determine if the person needs medical assessment. As soon as the radionuclide is identified, the measurements previously made can be compared with appropriate action levels.

Radionuclide identification must only be carried out by a suitably qualified radiation expert such as a radiation protection advisor (RPA). Further advice on radionuclide identification can be provided by PHE.

Pre-measurement checks

Due to variations in sensitivity not all instruments can be used in all circumstances. Details of when particular instruments can be used is given in the ‘Monitoring for internal contamination section’.

Ensure that you are using a suitable instrument prior to proceeding with any measurements.

Before monitoring the following functional checks must be carried out:

  • battery check
  • background count
  • response to check source (if available)

Instruction on carrying out functional checks for each detector type are provided in the ‘using your local detector’ section.

Administrative requirements

Sufficient information should be recorded for each person monitored to allow them to be uniquely identified. This must include:

  • full name
  • date of birth
  • postcode

A complete monitoring record will include as a minimum:

  • the instrument used
  • background count rate (BCR)
  • net count rate (total count rate - BCR = net count rate)
  • whether the action level has been exceeded

Sample forms are available in HPA-CRCE-014: Guidance on Screening People for Internal Radioactive Contamination.

Monitoring with handheld detectors: procedure and action levels

Procedure

The procedure is as follows:

  • ensure adequate distance between person being monitored and people waiting
    • each person should be taken individually to the monitoring area maintaining a distance of at least 5 metres between the person being monitored and other potentially contaminated people
    • young children need not be separated from parents or guardians
  • position the detector
    • 131I: as Iodine accumulates in the thyroid the instrument being used must be placed close to the skin at the base of the front of the neck
A hand wearing purple nitrile gloves holding a handheld detector close to a man's neck
  • for all other nuclides the detector should be held 30 cm from the centre of the chest
A lab technitian wearing a white lab suit and purple nitrile gloves holding a handheld detector 30 cm away from a man being monitored
  • record the measurement
    • wait for about 10 seconds for the reading to stabilise and record the highest indicated detector count rate
    • some instruments take longer to stabilise. For these the reading should be observed until it is stable
    • note the units, counts per second (cps) or counts per minute (cpm). The BCR is subtracted from the total count rate measurement, to yield a net count rate

Action levels

The net count rate is compared to tables of action levels. If the action level is exceeded this means the person’s dose could exceed a threshold level.

Action levels are provided in the ‘using your local detector’ section, and are dependent on the:

  • instrument being used
  • age of the person being monitored
  • radionuclide being assessed
  • time between radionuclide intake and monitoring

If a net count rate exceeds the action level:

  • urgently refer the person for medical assessment
  • arrange for accurate measurements to be made

Accurate assessment will be performed using specialised transportable or laboratory based counting systems. Further details can be obtained from PHE.

Using your local detector

APTEC-NRC ADM-300 with BSP-100 probe

This table shows the radionuclides and maximum times between incident and measurement that this detector is suitable for.

Age group Cobalt-60 (60Co) Selenium-75 (75Se) Cesium-137 (137Cs) Iridium-192 (192Ir) Iodine-131 (131I)
Under 10 years 6 - - - -
10 to 19 years 7 - - - -
20+ years 7 - - - -

Pre-monitoring checks

The following procedure should be followed prior to using the detector:

  1. Remove the probe cover.
  2. Press and hold the POWER button until the instrument responds.
  3. Press ↑ to change the mode to ‘c/min B+G’. Response is given in cpm. This instrument requires a lengthy (~ 30 second) stabilisation time when changing from a low to high (or vice versa) count rate.
  4. Make sure that the battery low indicator is not shown. If it is, replace the batteries.
  5. Ensure that the BCR is approximately 180 cpm.
  6. Check response with a check-source if available.
  7. Instrument is now ready. The detector window should face the person being monitored.
  8. Press and hold the POWER button to switch the instrument off.

Action levels

The tables below outlines the action levels for this instrument for each radionuclide and age group. “-“ indicates that the detector is not suitable for that combination of radionuclide, time since incident and age group.

ADM-300 with BSP-100

This table shows the action levels for ADM-300 with BSP-100 probe (cpm).

60Co

Time between incident and measurement (days) under 10 years age 10 to 19 years age 20+ years
0 1400 2500 2700
1 1400 2400 2700
2 1300 2200 2500
3 1200 2100 2300
4 1100 2000 2200
5 900 1800 2000
6 480 890 1000
7 - 510 600
8 - - -
9 - - -
10 - - -
11 to 12 - - -
13 to 14 - - -
15 to 16 - - -
17 to 18 - - -
19 to 20 - - -
21 to 30 - - -

RADOS RDS 200 with GMP-11 probe

This table shows the radionuclides and maximum times between incident and measurement that this detector is suitable for.

Age group Cobalt-60 (60Co) Selenium-75 (75Se) Cesium-137 (137Cs) Iridium-192 (192Ir) Iodine-131 (131I)
Under 10 years - - - - 8
10 to 19 years - - - - 20
20+ years - - - - 20

Pre-monitoring checks

The following procedure should be followed prior to using the detector:

  1. Remove metal cover from connector at handle end and attach probe.
  2. Remove probe cover.
  3. Press the POWER button to switch on and wait until instrument automatically enters cps mode.
  4. Make sure that the battery low indicator is not shown. If it is, replace the batteries.
  5. Ensure that the BCR is approximately 1 cps.
  6. Check response with a check-source if available.
  7. Instrument is now ready for measurements.

Action levels

This table outlines the action levels for RADOS RDS200 with GMP-11 probe (cps), for each radionuclide and age group. “-“ indicates that the detector is not suitable for that combination of radionuclide, time since incident and age group.

131I

Time between incident and measurement (days) under 10 years age 10 to 19 years age 20+ years
0 5 18 17
1 10 32 30
2 10 34 32
3 9 32 30
4 8 29 28
5 8 28 26
6 7 26 24
7 6 23 22
8 5 22 21
9 - 21 19
10 - 18 18
11 to 12 - 16 15
13 to 14 - 13 13
15 to 16 - 12 11
17 to 18 - 10 9
19 to 20 - 8 8
21 to 30 - - -

ROTEM RAM GENE-1

This table shows the radionuclides and maximum times between incident and measurement that this detector is suitable for.

Age group Cobalt-60 (60Co) Selenium-75 (75Se) Cesium-137 (137Cs) Iridium-192 (192Ir) Iodine-131 (131I)
Under 10 years 4 30 - 3 12
10 to 19 years 4 30 - 6 30
20+ years 5 30 - 8 30

Pre-monitoring checks

The following procedure should be followed prior to using the detector.

  1. Turn instrument on. If it fails to start, change batteries and re-start.
  2. Perform a function test as follows:
    • turns instrument on
    • ensure that the audio sounds continuously for approximately 1 second
    • ensure that the RATE LED illuminates continuously for approximately 1 second
    • ensure that the liquid crystal display shows 8.8 : 8.8
  3. Set the instrument to the contamination mode – CAP OFF.
  4. Ensure that the CONTAMINATION LED is illuminated continuously.
  5. Observe for at least 10 seconds and ensure that the audio bleeps and the RATE LED illuminates intermittently.
  6. Ensure that the BCR is between 0 and 1 cps.
  7. Check response with a check-source if available.
  8. Instrument is now ready for measurements.

Action levels

These tables outline the action levels for ROTEM RAM GENE-1, for each radionuclide and age group. “-“ indicates that the detector is not suitable for that combination of radionuclide, time since incident and age group.

60Co

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 6 7 11
1 6 7 11
2 5 6 10
3 5 6 9
4 5 6 9
5 - - 8
6 - - -
7 - - -
8 - - -
9 - - -
10 - - -
11 to 12 - - -
13 to 14 - - -
15 to 16 - - -
17 to 18 - - -
19 to 20 - - -
21 to 30 - - -

75Se

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 120 180 440
1 120 180 430
2 110 170 410
3 110 160 390
4 110 160 380
5 100 150 360
6 100 150 350
7 100 140 340
8 100 140 340
9 90 140 330
10 90 130 320
11 to 12 90 130 310
13 to 14 90 120 300
15 to 16 80 120 290
17 to 18 80 110 280
19 to 20 80 110 270
21 to 30 65 100 230

192Ir

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 11 26 38
1 11 24 35
2 7 18 27
3 5 15 23
4 - 13 20
5 - 11 19
6 - 6 10
7 - - 7
8 - - 6
9 - - -
10 - - -
11 to 12 - - -
13 to 14 - - -
15 to 16 - - -
17 to 18 - - -
19 to 20 - - -
21 to 30 - - -

131I

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 9 32 30
1 17 55 53
2 18 59 55
3 15 55 52
4 13 50 48
5 12 48 45
6 10 44 42
7 9 40 39
8 8 38 36
9 7 36 33
10 6 32 31
11 to 12 - 27 26
13 to 14 - 23 23
15 to 16 - 20 20
17 to 18 - 17 17
19 to 20 - 14 14
21 to 30 - 6 6

SAIC Exploranium GR-135

This table shows the radionuclides and maximum times between incident and measurement that this detector is suitable for.

Age group Cobalt-60 (60Co) Selenium-75 (75Se) Cesium-137 (137Cs) Iridium-192 (192Ir) Iodine-131 (131I)
Under 10 years 20 30 6 30 -
10 to 19 years 30 30 7 30 -
20+ years 30 30 30 30 -

Pre-monitoring checks

The following procedure should be followed prior to using the detector:

  1. Protective ‘boot’ should be in place.
  2. Switch the instrument on by pulling the joystick back and hold it until TESTING appears on the display
    • use the joystick to navigate the menus: a quick movement of the joystick will move the cursor, but to select an option, ‘enter’, or ‘return’ pull the joystick back and hold briefly
  3. Select ‘Search and Dose’ from the main menu (the count rate in cps is displayed near the top of the display).
  4. Make sure that the battery low indicator is not shown. If it is, replace the batteries.
  5. Ensure that the BCR is approximately 50 cps.
  6. Check response with a check-source if available.
  7. For measurements of people the display screen should be held horizontally so that the end of the detector faces the person.
  8. Switch off by pushing the joystick forward and holding it until the countdown ends and the display is blank.

Action levels

The table below outlines the action levels for SAIC Exploranium GR-135 (cps), for each radionuclide and age group. “-“ indicates that the detector is not suitable for that combination of radionuclide, time since incident and age group.

60Co

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 340 530 750
1 330 520 750
2 300 460 680
3 300 430 630
4 270 420 610
5 210 380 560
6 110 190 290
7 60 110 160
8 40 73 110
9 35 61 95
10 30 55 85
11 to 12 30 50 80
13 to 14 25 47 75
15 to 16 25 45 75
17 to 18 23 42 68
19 to 20 23 40 66
21 to 30 - 36 59

75Se

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 12000 24000 42000
1 12000 23000 41000
2 12000 22000 39000
3 11000 21000 37000
4 11000 20000 36000
5 10000 20000 35000
6 10000 20000 33000
7 9800 19000 33000
8 9600 18000 32000
9 9400 18000 31000
10 9200 17000 31000
11 to 12 8900 17000 29000
13 to 14 8500 16000 28000
15 to 16 8200 15000 28000
17 to 18 7900 15000 26000
19 to 20 7700 15000 26000
21 to 30 6500 13000 22000

137Cs

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 150 260 320
1 150 250 320
2 130 230 290
3 130 210 270
4 120 210 260
5 120 200 250
6 100 170 230
7 - 110 170
8 - - 140
9 - - 130
10 - - 130
11 to 12 - - 120
13 to 14 - - 120
15 to 16 - - 120
17 to 18 - - 120
19 to 20 - - 120
21 to 30 - - 110

192Ir

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 1300 3300 4400
1 1200 3000 4000
2 860 2300 3100
3 650 1900 2600
4 560 1700 2300
5 500 1400 2200
6 360 740 1200
7 260 480 790
8 200 390 640
9 180 350 570
10 180 330 540
11 to 12 160 310 520
13 to 14 160 300 510
15 to 16 150 290 490
17 to 18 140 280 470
19 to 20 140 270 450
21 to 30 120 230 380

Thermo MINI 900 with 44A probe

This table shows the radionuclides and maximum times between incident and measurement that this detector is suitable for.

Age group Cobalt-60 (60Co) Selenium-75 (75Se) Cesium-137 (137Cs) Iridium-192 (192Ir) Iodine-131 (131I)
Under 10 years 6 30 6 30 30
10 to 19 years 6 30 14 30 30
20+ years 30 30 30 30 30

Pre-monitoring checks

The following procedure should be followed prior to using the detector:

  1. Remove cap.
  2. Turn rotary switch to first position ‘battery check’. If needle does not indicate in the green part of the display then replace battery and re-start procedure.
  3. Turn rotary dial to extreme clockwise position. Wait for a few seconds and ensure the background count rate is approximately 5 counts per second.
  4. Check response with a check-source if available.
  5. Instrument is now ready for measurements.

Action levels

The table below outlines the action levels for this instrument for each radionuclide and age group. “-“ indicates that the detector is not suitable for that combination of radionuclide, time since incident and age group.

60Co

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 35 60 140
1 35 60 140
2 30 55 130
3 30 50 120
4 30 50 110
5 25 45 100
6 10 20 55
7 - - 30
8 - - 20
9 - - 15
10 - - 15
11 to 12 - - 15
13 to 14 - - 14
15 to 16 - - 14
17 to 18 - - 13
19 to 20 - - 12
21 to 30 - - 10

75Se

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 4800 7600 18000
1 4800 7300 18000
2 4600 7000 17000
3 4500 6800 16000
4 4300 6500 16000
5 4200 6200 15000
6 4000 6200 15000
7 3900 5900 14000
8 3800 5700 14000
9 3700 5900 14000
10 3700 5400 13000
11 to 12 3600 5400 13000
13 to 14 3400 5100 12000
15 to 16 3300 4900 12000
17 to 18 3200 4900 12000
19 to 20 3100 4600 11000
21 to 30 2600 4000 9500

137Cs

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 20 35 70
1 20 35 70
2 20 35 65
3 15 30 60
4 15 30 60
5 15 25 60
6 12 25 50
7 - 15 40
8 - 10 30
9 - 10 30
10 - 10 30
11 to 12 - 10 30
13 to 14 - 10 30
15 to 16 - - 25
17 to 18 - - 25
19 to 20 - - 25
21 to 30 - - 25

192Ir

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 300 600 1300
1 300 600 1200
2 200 400 900
3 150 400 700
4 100 300 700
5 100 300 650
6 70 150 400
7 60 100 200
8 40 80 200
9 30 70 150
10 30 65 150
11 to 12 30 60 150
13 to 14 25 60 150
15 to 16 25 60 140
17 to 18 25 55 140
19 to 20 25 55 130
21 to 30 20 45 100

131I

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 400 1600 1600
1 800 3000 3000
2 900 3000 3000
3 800 3000 2500
4 700 2500 2500
5 600 2500 2000
6 600 2500 2000
7 500 2000 2000
8 400 2000 2000
9 400 2000 1500
10 350 1500 1600
11 to 12 300 1400 1500
13 to 14 200 1200 1200
15 to 16 200 1000 1000
17 to 18 150 800 800
19 to 20 120 700 700
21 to 30 40 300 300

TSA Systems PRM-470CS

This table shows the radionuclides and maximum times between incident and measurement that this detector is suitable for.

Age group Cobalt-60 (60Co) Selenium-75 (75Se) Cesium-137 (137Cs) Iridium-192 (192Ir) Iodine-131 (131I)
Under 10 years 9 30 5 30 -
10 to 19 years 30 30 7 30 -
20+ years 30 30 20 30 -

Pre-monitoring checks

The following procedure should be followed prior to using the detector:

  1. Press the POWER button to switch on.
  2. Allow the instrument to finish the auto background count, then press the ‘MODE’ button to enter search mode.
  3. Response is given in cps.
  4. Make sure that the battery low indicator is not shown. If it is, replace the batteries.
  5. Ensure that the BCR is approximately 70 cps.
  6. Check response with a check-source if available.
  7. For measurements of people the display screen should be held vertically so that the base of the detector faces the person.
  8. Press the POWER button to switch off.

Action levels

These tables outline the action levels for TSA Systems PRM-470CS (cps), for each radionuclide and age group. “-“ indicates that the detector is not suitable for that combination of radionuclide, time since incident and age group.

60Co

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 430 670 920
1 420 650 920
2 380 590 840
3 350 550 780
4 340 530 750
5 260 490 690
6 140 240 360
7 80 140 200
8 55 90 140
9 45 75 120
10 - 70 110
11 to 12 - 63 100
13 to 14 - 59 92
15 to 16 - 56 92
17 to 18 - 53 84
19 to 20 - 50 82
21 to 30 - 45 72

75Se

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 16000 28000 48000
1 15000 27000 47000
2 15000 26000 45000
3 15000 25000 42000
4 14000 24000 41000
5 14000 23000 38000
6 13000 23000 37000
7 13000 22000 37000
8 13000 21000 37000
9 13000 21000 36000
10 12000 21000 35000
11 to 12 12000 20000 34000
13 to 14 11000 19000 32000
15 to 16 11000 18000 31000
17 to 18 10000 18000 30000
19 to 20 10000 17000 29000
21 to 30 8600 15000 25000

137Cs

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 230 330 390
1 200 310 380
2 180 290 350
3 170 260 320
4 160 260 320
5 150 250 310
6 - 220 280
7 - 140 200
8 - - 170
9 - - 160
10 - - 150
11 to 12 - - 150
13 to 14 - - 150
15 to 16 - - 140
17 to 18 - - 140
19 to 20 - - 140
21 to 30 - - -

192Ir

Time between incident and measurement (days) Under 10 years Age 10 to 19 years Age 20+ years
0 1700 4300 5200
1 1600 3900 4800
2 1100 3000 3700
3 850 2500 3100
4 740 2200 2700
5 660 1800 2600
6 480 950 1400
7 340 620 930
8 270 510 750
9 230 460 670
10 230 420 630
11 to 12 210 400 600
13 to 14 200 390 580
15 to 16 200 380 550
17 to 18 190 360 540
19 to 20 180 350 520
21 to 30 160 300 450

Step by step guide for an example incident

This section outlines steps taken in the event that monitoring for individuals is required, 1 day after an event resulting in dispersal of 137Cs.

Decide on the monitoring method

Obtain expert help to positively identify the radionuclides.

Let us assume 137Cs has been positively identified.

The monitoring for internal contamination section states that the following radionuclides can be monitored using handheld radiation monitors:

  • Cobalt-60 (60Co)
  • Selenium-75 (75Se)
  • Iodine-131(131I)
  • Cesium-137 (137Cs)
  • Iridium-192 (192Ir)

Therefore in this case handheld radiation monitors will be used.

Other radionuclides will require different monitoring methods, such as measurement of urine sample. See guidance document HPA-CRCE-014: Guidance on Screening People for Internal Radioactive Contamination.

Additionally, you must ensure that handheld detectors capable of monitoring the radionuclide are available. These details can be found in the section Monitoring for internal contamination. In this case either of the following 3 instruments can be used:

  • SAIC Exploranium GR-135
  • Thermo Mini 900 with 44A probe
  • TSA systems PRM-470CS

Set up a monitoring facility

Monitoring is performed in the local RMU, as detailed in the monitoring location and precautions section.

People with contamination on their skin and clothing must be decontaminated prior to monitoring.

The person to be monitored should normally be at least 5 metres from other potentially contaminated people. However, it is not necessary to separate children from their parents.

Ensure record keeping procedures are in place

Obtain copies of the monitoring record form (see ‘administrative requirements’ section, as part of ‘Monitoring with handheld detectors’.

Assign a ‘unique person code’ to each person and ensure this is entered on the form.

Administrative personnel should be used to help each person to be monitored to fill in their personal details.

When monitoring is complete the results must also be entered on the form.

Perform pre-monitoring checks

Lets us assume a Mini 900 detector with 44A probe is locally available.

The monitoring instrument must be set up as shown in ‘using your local detector’ section.

A battery check must be performed and the instrument response should be checked if a suitable check source is available.

The background count rate in the general vicinity of the monitoring location must also be measured and recorded. Let us assume the background count rate is 5 cps.

Monitoring process

The measurement procedure is shown in the ‘monitoring with handheld detectors’ section.

As the radionuclide is not 131I the detector should be held 30cm from the person’s chest.

The reading is allowed to stabilise and the highest value seen recorded. Let us assume this value is 100 counts per second.

This value must be recorded on the monitoring record form.

Comparing results with action Levels

The net count rate is calculated as shown in the ‘monitoring with handheld detectors’ section.

In this case, the net count rate is 100 minus 5 which is 95.

Action levels are given in the ‘using your local detector’ section.

In this case, the Thermo Mini 900 with 44A probe has been used to monitor adults for 137Cs intake 1 day after the incident. The action level would therefore be 70 cps.

The action level is exceeded. You must urgently refer the individual for medical assessment. Arrangements must be made for more accurate measurements to be made.

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