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Open Source Training Modules


  Open Source Radiation Safety Training

Module 5: External & Internal Dose Limits

Overview of the Module

This module provides information about the following topics:

Annual Radiation Dose Limits

 The New Jersey Department of Environmental Protection (NJDEP) has established dose limits which are based on recommendations from national and international commissions.  The table below lists the limits set by the NJDEP:

University investigation level (mrem)
Whole Body
Includes dose from both internal and external sources.  The Whole Body limit applies to exposure of the torso and head when the radiation is penetrating enough to irradiate tissues at a depth of  1 cm where the deeper blood-forming tissues are located. 
Lens of the Eye
The Lens of the Eye limit applies to exposure of the eye to radiation penetrating enough to irradiate the lens, at a depth of  0.3 cm. 
The extremities include the arm or leg below the elbow or knee.  The Extremities limit applies to exposure of the extremities when the radiation is penetrating enough to irradiate tissues at a depth of  1 cm. 
The Skin limit applies to dose deposited in the skin when the radiation is penetrating enough to irradiate tissues at a depth of  0.007 cm. 
500 (for the entire pregnancy)
Applies only when a Declaration of Pregnancy has been submitted 
Occupational exposure of a minor
10% of the limits above
Applies to anyone under 18
 years of age
Member of the general public


Investigational Levels

The University has established investigational levels at doses considerably less than the dose limits. When a worker accumulates during any part of a year a dose at or above the investigational level, EHS will investigate to determine causes of the dose and to recommend practices to minimize radiation exposure in the future.

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As Low As Reasonably Achievable (ALARA)

Since the current model of radiation-induced cancer risk assumes that there is a risk no matter how low the radiation dose, it makes good sense to minimize radiation exposure. In fact, the University is required by NJDEP regulation to keep doses As Low As Reasonably Achievable (ALARA). This means that the University must work to keep doses as far below the dose limits as can reasonably be achieved.

To keep doses ALARA, the University has established investigational dose levels and will investigate any dose exceeding these levels in an effort to address causes of unnecessary radiation exposure.

In addition there are a variety of practical steps that you can take while working in the lab to minimize your radiation exposure.  These steps will be described in detail in the Radioactive Materials Safety Class.

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Annual Limits of Intake

Internal Exposure
Radiation exposure can occur both from radiation sources outside the body (external exposure) and from radiation sources within the body (internal exposure).  For example, internal exposure may occur through absorption through the skin when the skin becomes contaminated or when a volatile radioisotope, such as I-125, is inhaled.

Internal Dose Information for Common Radioisotopes
The NJDEP has defined a quantity, the Annual Limit of Intake (ALI), which is the amount of a specific radioisotope taken internally which will produce an annual Whole Body dose of 5000 millirems.  The following table below lists the ALIs for radioisotopes commonly used at Princeton University:

ALI for Ingestion 
ALI for Inhalation
H-3 80 80
C-14 2 2
P-32 0.6 0.9
P-33 6 8
S-35 10 20
I-125 0.04 0.06

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Declared Pregnant Worker Program

This section provides a general overview of the Declared Pregnant Worker Program.  More detailed information about the program is available in Section 6 of the Radiation Safety Manual for Laboratory Workers.

The NJDEP’s Fetal Dose Regulations apply only to a woman who has voluntarily informed her employer, in writing, of her pregnancy and the estimated date of conception.  The dose to the fetus resulting from occupational exposure of a declared pregnant woman may not exceed 500 mrem for the entire pregnancy.

Submitting a Declaration of Pregnancy
Any radiation worker who is pregnant or believes that she may be pregnant should contact EHS. All inquiries will be kept in confidence. EHS will take the following steps:

  • Provide an opportunity to submit a Declaration of Pregnancy.  (A Declaration of Pregnancy form is included in the Radiation Safety Manual or may be obtained from EHS.
  • Provide information concerning risk of fetal radiation exposure.
  • Evaluate the worker’s dose history and exposure potential.
  • Make recommendations for reducing radiation exposure.
  • Monitor the worker’s radiation dose with regard to worker and fetal dose limits.

For the type of radiation work performed at Princeton University, it is rarely necessary to recommend reassignment or changes to job duties.

If a written declaration of pregnancy is not submitted to EHS, then the worker’s dose continues to be controlled under the normal dose limits for radiation workers.

Go to detailed information about Princeton University's Declared Pregnant Worker Program

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This is the end of the Dose Limit Module, which is the fifth of the six Radiation Basics modules.

Go to Module 6 (Radiation Monitoring Badges)


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