SECTION 6: Dose Limits and Personal Monitoring

• Annual Radiation Dose Limits
• The ALARA Principle
• External Monitoring
• Internal Monitoring
• Declared Pregnant Worker Program
• Research Involving Radiation Work at Other Institutions or Companies

Annual Radiation Dose Limits (top)

Each worker who is monitored for external or internal radiation exposure at the University is notified about the doses he or she receives. For example, a worker using NRC-licensed radioactive materials (as most workers at the University do) who is notified that that he or she received a whole body dose of 50 millirems (mrem) and a shallow skin dose of 150 mrem during a quarter will note that this constitutes 1% and 0.3%, respectively, of the appropriate annual limits. (See the table below for a listing of the dose limits established by the Nuclear Regulatory Commission (NRC) and the state of New Jersey.

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, Environmental Health & Safety (EHS) will investigate to determine causes of the dose and to recommend practices to minimize radiation exposure in the future.

Further information about radiation exposure from radioactive materials taken up internally is provided in Appendix B in the listings of Annual Limits of Intake (ALI), the amount of a specific radioisotope taken internally which will produce a whole body dose of 5000 millirems. For example, Appendix B states that the ALI for H-3 is 80 mCi. If a worker is notified that he or she has had an intake of 80 mCi of H-3 with a resulting dose of 5 mrem, then the table below indicates this dose to be 0.1% of the annual radiation dose limit.

Organ	NRC Limit (mrem/year)	State Limit* (mrem/year)	University Investigation Level (mrem)	Comments
Whole Body	5,000	5,000	100	Includes dose from both external and internal sources
Lens of the Eye	15,000		300
Extremities	50,000	75,000	1000	The extremities include the arm or leg below the elbow or knee
Skin	50,000	30,000	1000
Embryo/Fetus	500 (for the entire pregnancy)		50	Applies only when a Declaration of Pregnancy has been submitted
Occupational exposure of a minor	10% of the limits above	10% of the limits above	50	Applies to anyone under 18 years of age
Member of the General Public	100	500	50

*State of New Jersey dose limits apply to workers who use state-licensed radioactive materials and x-ray machines.

The ALARA Principle (top)

Although the University must keep doses of students, staff and visitors below the relevant NRC or state dose limits, the University is further required by NRC 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 readily be achieved. Consequently 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.

External Monitoring (top)

Required Monitoring

Monitoring of external radiation exposure is required for the following persons:

• Any person using an x-ray diffractometer
  
• Persons using radioactive materials in the following amounts and types of use:

Types of use	Examples	Amounts for which monitoring is required
Use of Open sources of B-emitters with energies > 250 keV*	P-32	5 mCi or more
Use of Open sources of g-emitters with energies < 0.1 MeV*	Cd-109, I-125	1 mCi or more
Use of Open sources of g-emitters with energies > 0.1 MeV*	Cr-51, Co-57, Fe-59, Zn-65	0.5 mCi or more
Use of sealed sources containing energetic B/g-emitters	Co-60, Cs-137, Ra-226	0.1 mCi

* Monitoring is not required for operations which only involve aliquoting from a stock vial and do not involve any other manipulation of radioactive materials.

• Declared pregnant workers who work in labs using gamma emitters or high-energy beta emitters (>250 keV)
  
• Other persons may be issued monitors at the discretion of the Radiation Safety Officer (RSO).

Optional Monitoring

External monitoring can be requested by any person working in a laboratory in which gamma emitters or energetic beta emitters are used, even if that person does not meet the criteria for required monitoring. In such a case, EHS meets with the worker initially to discuss any concerns the worker has and will then initiate radiation monitoring for the next year. After providing dosimetry for a year, EHS meets with the worker again to review doses for the past year and to discuss whether monitoring should be continued.

Monitoring is not generally provided for persons working in laboratories in which only alpha emitters or low energy beta emitters (< 250 keV) are used.

How to Request a Monitor Badge

Contact EHS to request radiation monitoring services, and supply the following information: name, social security number, department, name of the laboratory in which the primary radiation exposure occurs, purpose of request (i.e., new service, replacement for a lost/damaged badge, etc.), the source of radiation exposure (radioisotopes, x-ray machines, etc.), length of time for which monitoring service is needed, and the urgency of the request.

The Rules of Monitor Badge Wear

• Wear badges so the name label faces toward the source of radiation.
  
• Wear the ring badge under gloves to avoid contaminating the badge (but be careful not to throw out the ring badge with the gloves when discarding the gloves as radioactive waste.)
  
• Store badges in low radiation background areas.
  
• Do not expose badges to elevated temperatures (e.g., don’t store badges on hot sunny surfaces or near radiators).
  
• Notify EHS immediately if you suspect you may have received an unusual exposure.
  
• Do not wear your badges when you receive medical x-rays or are exposed to other medical sources of radiation.
  
• If your badges become contaminated, damaged or lost, call EHS immediately to request replacements.
  
• Badges are generally exchanged once a quarter, although badges for declared pregnant workers are exchanged once a month. Turn in your old badges to your badge exchange contact promptly at the end of the wear period, after you receive your new set of badges.

How to Find Out Monitoring Results

Monitoring reports are received by EHS approximately six weeks after the end of a monitoring period and forwarded to each Authorized User shortly thereafter. An individual can request his/her radiation exposure history any time by contacting EHS.

Internal Monitoring (top)

Radioactive materials can be taken up internally when volatile or other airborne radioactive materials are inhaled and when radioactive materials are absorbed through skin or ingested. Internal uptakes may occur when lab personnel unknowingly handle contaminated objects, when permeation occurs through highly contaminated gloves, or when spills occur. To determine the dose resulting from an intake, bioassays must be performed. For the radioisotopes commonly used at Princeton University, bioassays usually involve urinalysis or external thyroid counting.

When are Bioassays Required?

EHS may request bioassays when widespread contamination has occurred in a laboratory, and when skin contamination has occurred. A worker can request a precautionary bioassay at any time. A bioassay is required under the following circumstances:

• When a person uses H-3 exceeding the amounts listed below (which are the amounts a person handles at any one time or the cumulative activity handled by that person during one month):

Nature of Use	Form	Activity
In an open room	HTO* and other forms, including nucleotide precursors	100 mCi
	H-3 gas in a sealed vessel	100 Ci
In a chemical fume hood	HTO and other forms, including nucleotide precursors	1 Ci
	H-3 gas in a sealed vessel	1000 Ci

* HTO is tritiated water

• When a person uses I-125 exceeding the amounts listed below (which are the amounts a person handles at any one time or the cumulative activity handled by that person during any three month period)

Nature or Use	Form	Activity
In an open room	As NaI or other volatile form	1 mCi
	Bound to a non-volatile agent	10 mCi
In a chemical fume hood	As NaI or other volatile form	10 mCi
	Bound to a non-volatile agent	100 mCi

How to Arrange for a Bioassay

Thyroid counting is performed at the EHS office and requires no more than ten minutes. Contact EHS to schedule an appointment. Supplies and instructions for urine bioassays are provided by EHS.

Declared Pregnant Worker Program (top)

The NRC’s Fetal Dose Regulations

The two most important aspects of the NRC’s fetal dose regulations are:

• The 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.

How to Submit 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:

1. Provide an opportunity to submit a Declaration of Pregnancy. A Declaration of Pregnancy form is included in Appendix E or may be obtained from EHS. 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.

2. Provide information concerning risk of fetal radiation exposure.

3. Evaluate the worker’s dose history and exposure potential. For the type of radiation work performed at Princeton University, it is rarely necessary to recommend reassignment or changes to job duties.

4. Make recommendations for reducing radiation exposure.

5. Monitor the worker’s radiation dose with regard to worker and fetal dose limits.

Research Involving Radiation Work at Other Institutions or Companies (top)

Any Princeton University employee or student who plans to do radiation work at other institutions must notify EHS before visiting the other institution. The radiation exposure of visitors from Princeton University will be monitored by the host institution, using badges supplied by that institution. However, Princeton is required to keep track of the total radiation exposure received by its employees and students. EHS will contact the host institution and request radiation exposure records.