Radiation DoseAssessment
in Nuclear Emergencies
Thomas Johnson, PhD, CHP, NRRPT, CLSO
Professor

Environmental and Radiological Health Sciences

Objectives• Radiation dose assessment immediately
following an emergency• Methods to determine radiation dose toindividuals after emergency

Immediately after Accident• Focus on preventing acute radiation effects toindividuals.
• Contamination issues are a secondary
concern, especially when the contaminatedincident site and number of evacuees islarge.
• Individuals with spot contamination greaterthan 2.2 × 106 dpm (37,000 Bq) should be apriority for decontamination

Immediately after Accident
Nausea and vomiting are the earliest clinicalsigns of acute radiation syndrome (ARS).
Nausea and vomiting are symptoms that
occur as whole-body absorbed doses
becomehigh [i.e., >100 rad (>1 Gy)].

Immediately after Accident

Criticality Accident
Radiation dose reading in armpit
after criticality accident neutron exposure

μGy
3.5 � 𝑥𝑥h
Dose in Gy =mass in kg

Example
Induced 24Na activity expected after
fast neutron exposure to 0.04 Gy offast neutrons
Mass in kg Count rate
Count rate 15
immediately following minutes after
exposure (cpm)
exposure (cpm)70275
13580310
15590
350
175
100400200

Criticality Accident
Fast neutron dose based on 32P activation inhair(See IAEA Technical Report Series 152 forsample preparation)
D = 0.55 A
A = 32P activity (dpm per gram of hair)D = dose in Gy

Rule of Sevens and Tens
• After exposure rates have begun to decrease,for every seven-fold increase in time after
detonation of a nuclear weapon, there is aten-fold decrease in exposure.

Example
Time inhours
1Fraction
decrease-Radiation
Intensity Gy/h1000

7

1/10

100

49

1/100

10343

1/10001

Example
50 Gy/h radiation dose rate at three hours afterdetonation
After 21 hours, radiation dose will be 5 Gy/hAfter 147 hours, radiation dose will be 0.5 Gy/h.

Distance to LD50 Initial Nuclear Radiation(INR), Residual Nuclear Radiation (RNR)

Dose in Gy in Frist Hour AfterDetonation
Detonation 1000 m 2000 m 10,000 myield (kt)
0.01

6.7

1.5

0.001

0.1

38

8.3

0.1

1210

47

0.6

1012002603.5

Radiation Dose by Injury

Radiation
Dose in Gy
3Time to Onset

Temporary hair loss

14-21 days

Skin ErythemaTransient thensecondary erythema,
14-21 d10-15

Skin Dry desquamation>21 days>20

NeurovascularMinutes (death in 24syndrome48 h)Skin wet desquamation 2-3 weeks

620-50Biological Radiation Dosimeters• Pseudo Pelger Huet Cell Anomaly– Still experimental– Thought to demonstrate linear response to alltypes of ionizing radiation exposure– Requires a blood smear– Can be used to quickly sort• Count lymphocyte acentric/dicentric in blood– Well established method– Measures >0.2 Sv

Inhalation Radiation Dose
• Nasal swabs – assume estimate 5-10% ofintake, may be as high as 25%– Not a good quantitative predictor, qualitative yes• Bioassay– In vivo using NaI or HPGe
– In vitro using urine or fecal analysis

Electron Spin Resonance (ESR)• Useful for external gamma ray doses above
0.5 Sv• Requires crystal matrix materials– Tooth, watch crystal, some building materials• Complex, time consuming

Inverse Square Dose Estimate• Photon measurements
𝐼𝐼 1𝑑𝑑12 = 𝐼𝐼 2𝑑𝑑22• I1 = Radiation intensity at location 1• I2 = Radiation intensity at location 2• d1 = distance from location 1 to radiation source• d2 = distance from location 2 to radiation sourceExample• The radiation dose rate from a radiation
sources is 0.05 Gy/h at a distance of 10meters. A person was standing at 2 metersfrom the source for 1 hour. What is theradiation dose?

Inverse Square Dose Estimate
𝐼𝐼 1𝑑𝑑12 = 𝐼𝐼 2𝑑𝑑22• I1 = 0.05 Gy/h
• I2 = Radiation intensity at location 2• d1 = 10 m
• d2 = 2 m
0.05 Gy/h (10 m)2= 𝐼𝐼 2 (2 m)2I2 = 1.25 Gy/h

1.25 Gy/h for 1 hour = 1.25 Gy

References•NCRP Commentary 19, Key Elements ofPreparing Emergency Responders for
Nuclear and Radiological Terrorism•IAEA Evaluation of Radiation Emergencies
and Accidents, Technical Report Series 152•Health Physics and Radiological Health 4thEdition