NCRP 116: Limitations of Exposure to Ionizing Radiation
Background
Released in 1993, NCRP 116 is an update to the NCRP 91 (released 1987). NCRP 91 was largely based on study of atomic bomb survivors completed by the Radiaton Effects Research Foundation (RERF). Three important factors were recognized as result of RERF’s work. First, excess cancers continued to be observed in atomic bomb survivors into the latest study period, at time of writing. Second, cancer incidence appeared at a rate consistent with a multiplicative projection model. Third, revised risk-dose estimates became available. However, because the risk assessment was incomplete, the limits set by NCRP 91 were considered upper limits rather than radiation safety design goals. NCRP 116 was created upon completion of risk assessments from several national and international bodies and generally increases the reported risks of radiation exposure.
Definitions
- Deterministic vs Stochastic Effects
- Deterministic Effect: a somatic effect which increases in severity with increasing radiation dose above a threshold dose.
- Stochastic Effects: health effects which occur randomly and for which the probability of the effect, rather than the effect’s severity, is related to dose.
- “For radiation-protection purposes, the risk of a stochastic effect is proportional to dose without threshold, throughout the range of dose and dose rates of importance in routine radiation protection.”
- As Low As Reasonably Achievable (ALARA): making every reasonable effort to maintain exposures to radiation as far below the dose limits as is practical
Tables
Group | Risk Factor | NCRP Report 91 | ICRP Publication 60 | NCRP Report 116 |
Workers | Fatal cancer | 1.25% per Sv | 4% per Sv | 4% per Sv |
Workers | Non-fatal cancer | – | 0.8% per Sv | 0.8% per Sv |
Worker | Severe genetic effects | 0.4% per Sv | 0.8% per Sv | 0.8% per Sv |
Members of the Public | Fatal cancer | – | 5% per Sv | 5% per Sv |
Members of the Public | Non-fatal cancer | – | 1% per Sv | 1% per Sv |
Members of the Public | Severe genetic effects | – | 1.3% per Sv | 1.3% per Sv |
Embryo/fetus | – | 20% per Sv | – | ~10% per Sv |
NCRP Report 91 | ICRP Puclication 60 | NCRP Report 116 | |
Based on Stochastic Effects | 50 mSv annual effective dose limit
10 mSv × age (y) cumulative effective dose limit for workplace | 50 mSv annual effective dose limit
100 mSv in 5 year cumulative effective dose limit | 50 mSv annual effective dose limit
10 mSv × age (y) cumulative effective dose limit for workplace |
Based on Deterministic Effects | 150 mSv annual dose equivalent limit to lens
500 mSv annual dose equivalent limit to all other organs (e.g. red bone marrow, breast, lung, gonads, skin, extremities) | 150 mSv equivalent dose limit to lens
500 mSv annual equivalent dose limit to skin, hands, and feet | 150 mSv annual equivalent dose limit to lens
500 mSv annual equivalent dose limit to skin, hands, and feet |
Annual Limits of Intake (ALI) | [50 mSv]/[HE (50) Bq-1] | [20 mSv]/[HE (50) Bq-1] | – |
Annual Reference Levels of Intake | – | – | [20 mSv]/[HE (50) Bq-1] |
NCRP Report 91 | ICRP Publication 60 | NCRP Report 116 | |
Based on Stochastic Effects | 1 mSv annual for continuous exposure
5 mSv annual for infrequent exposure | 1 mSv annual
A higher value may be acceptable if average annual over 5 years is less than 1 mSv | 1 mSv annual for continuous exposure
5 mSv annual for infrequent exposure |
Based on Deterministic Effects | 50 mSv annual limit to lens, skin, and extremities | 15 mSv annual limit to lens
50 mSv annual limit to skin, hands, and feet | 50 mSv annual limit to lens, skin, and extremities |
Embryo/fetus | 5 mSv annual limit
0.5 mSv per month once pregnancy is known | 2 mSv limit to woman’s abdomen once pregnancy is declared
Limit intake of radionuclides to 1/20 of ALI | 0.5 mSv limit per month once pregnancy is known |
Negligible Individual Dose (NID) | 0.01 mSv annual per source or practice | – | 0.01 mSv annual per source or practice |
Organ | NCRP Report 91 | ICRP Publication 60 | NCRP 116 |
Gonads | 0.25 | 0.20 | 0.20 |
Red bone marrow | 0.12 | 0.12 | 0.12 |
Colon | – | 0.12 | 0.12 |
Lung | 0.12 | 0.12 | 0.12 |
Stomach | – | 0.12 | 0.12 |
Bladder | – | 0.05 | 0.05 |
Breast | 0.15 | 0.05 | 0.05 |
Liver | – | 0.05 | 0.05 |
Esophagus | – | 0.05 | 0.05 |
Thyroid | 0.03 | 0.05 | 0.05 |
Skin | 0.01 | 0.01 | 0.01 |
Bone surface | 0.03 | 0.01 | 0.01 |
Remainder | 0.30 | 0.05 | 0.05 |
SUM | 1.01 | 1.0 | 1.0 |
Radiation Type | NCRP Report 91 (Q) | ICRP Publication 60 (wR) | NCRP Report 116 (wR) |
X and γ-ray, electrons, positrons, and muons | 1 | 1 | 1 |
Neutrons |
|
|
|
Protons > 2 MeV | – | 5 | 2 |
Alpha particles, fission fragments, nonrelativistic heavy nuclei | 20 | 20 | 20 |
Related Pages
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