Chapter IV - Personnel Dosimetry

4.1 TLD Badges
TLD badges are used at ASU to monitor personnel for exposure of the body to penetrating ionizing radiation such as gamma and x-rays, and exposure of the skin to less penetrating radiation such as beta particles. For most individuals, results of the TLD badge readings are also used as estimates for the exposure of the lens of the eye. TLD badges are required for operators of most analytical x-ray equipment at ASU. They are not required for some cabinet type equipment. The need for TLD badges is determined by the Radiation Safety Officer at the time of the initial radiation safety training.

TLD badges must be worn on the trunk of the body at or above the waist. Dosimetry devices must not be taken home or left in laboratory areas where they may be exposed to radiation or excessive heat. The badge is sensitive to heat and humidity.

4.2 Extremity Dosimetry
Ring dosimetry devices are used at ASU to monitor for radiation exposure to the hands are issued to most personnel using analytical x-ray equipment. Ring badges must be worn with the sensitive portion of the ring towards the source.

4.3 Dosimeter Exchange
The TLD badges and the rings are exchanged on a quarterly basis. ORS personnel hand carry TLDs and rings to department offices during the last few days of each quarter. Old TLDs and rings must be hand carried to the ORS. Campus mail must not be used. This policy has been established to avoid exposure of TLDs and rings to sources of radiation, heat, and humidity during transit and maintain the chain of custody.

Dosimetry should be returned to the ORS during the first 5 working days of the new quarter.

4.4 Lost or Damaged Dosimeters
Periodically, dosimetry devices are lost or damaged. This should be reported to ORS staff immediately so that replacement dosimeters can be issued.

4.5 Regulatory Dose Limits
4.5.1 Limits for Radiation Workers

ARRA has imposed limits on the dose of ionizing radiation which may be received by individuals working with sources of ionizing radiation. These limits are shown in Table 4-1.

Annual Limit, which is the more limiting of:

1. Total Effective Dose Equivalent

2. Sum of the deep dose equivalent and committed dose equivalent to any organ or tissue other than the lens of the eye

Annual Limit, which is the more limiting of: a. Total Effective Dose Equivalent b. Sum of the deep dose equivalent and committed dose equivalent to any organ or tissue other than the lens of the eye	5 rem (0.05 Sv) 50 rem (0.5 Sv)
Eye Dose Equivalent	15 rem (0.15 Sv)
Shallow Dose Equivalent to the skin or to each of the extremities	50 rem (0.5 Sv)

Table 4-1 Regulatory Dose Limits

4.5.2 Limits to the Embryo-Fetus of Declared Pregnant Workers

Due to concerns about prenatal radiation exposure (See Appendix C) ARRA regulations provide separate limits for the embryo/fetus of Declared Pregnant Workers. The limit is 0.5 rem dose equivalent to the fetus during pregnancy.

This limit applies only for workers who have formally declared pregnancy in writing. Declaration of pregnancy should be sent to the Radiation Safety Officer and include the estimated date of conception.

Individuals concerned about radiation and pregnancy should feel free to speak to the Radiation Safety Officer.

4.5.3. Limits for Members of the Public

The regulatory limit for members of the public is 0.1 rem total effective dose equivalent per year. This limit applies to all individuals who are not trained to work with sources of ionizing radiation. At ASU this includes most faculty, staff and students.

4.6 ALARA
In view of uncertainties that exist concerning the health effects of exposure to low doses of Radiation (see Appendix A), it is prudent to keep doses to personnel "as low as is reasonably achievable" (ALARA). Each user of radiation sources at ASU has the responsibility to incorporate shielding and protective devices, and to take any other steps required to keep doses ALARA.

4.7 Investigation Levels
In order to maintain doses ALARA, investigational levels have been established at ASU. These dose levels are shown in Table 4-2. The limits are evaluated on a quarterly basis.

Personnel exposures equal to or greater than Investigational Level I, are reviewed by the RSO, who reports the results to the RSC at their next regularly scheduled meeting. The RSC may require corrective actions on the part of the RSO or registrant.

Personnel exposures equal to or exceeding Investigational Level II are investigated in a timely manner by the RSO who takes immediate action if warranted. A report of the investigation, actions taken, and a copy of the individual's radiation dosimetry history are presented to the RSC at their regularly scheduled meeting following completion of the investigation. The RSC may impose restrictions on the user as warranted.

Investigational limits exceeding those listed in Table 4-2 may be established by the RSC for a worker or group of workers when the higher investigational levels are consistent with good ALARA practice for the work being conducted by the individual or group.

Limit	Level (rem/quarter)
	Level I    Level II
Total Effective Dose Equivalent	0.065  0.200
Eye Dose Equivalent	0.180  0.600
Shallow Dose Equivalent to the Skin or to each of the Extremities	0.625  2.000

Table 4-2 Investigational Dose Levels

4.8 Reports to Workers on Radiation Dosimetry
The ORS keeps careful records on results of radiation dosimetry for personnel on the ASU dosimetry program. These records are available for review by these personnel.

4.8.1 Review of Records in the ORS

Personnel issued dosimeter devices are welcome to review dosimetry results on file in the ORS. This review should be arranged with the ORS. The RSO requires positive identification of individuals seeking access to dosimetry results since these records are covered by state and federal privacy laws.

4.8.2 Annual Dosimetry Report

During the spring of each year, a report on dosimetry results for the previous calendar year is sent to each individual issued dosimeters at ASU. A summary of individual dosimetry results are also sent to the registrant responsible for supervising the work requiring dosimetry.

4.8.3 Notification of Results Exceeding Investigation Limits

Personnel are notified quickly of results which exceed Investigation Levels listed in Table 4-2. Personnel are not notified quarterly of routine dosimetry results which do not exceed the Investigation Levels.

4.9 Radiation Dosimetry Units
The following paragraphs explain the dosimetry units used in this chapter.

4.9.1 Absorbed Dose

The amount of energy absorbed by irradiated tissue is an important variable in the assessment of radiation risk and damage. The absorbed dose is defined as the energy absorbed per unit mass of tissue. The traditional unit for absorbed dose is the rad.

1 rad = 100 erg / gram

The rad is being replaced by a new unit based on the International System of Units (SI). The new unit is the Gray.

1 Gray = 1 joule / kg

Spending a little time with the units will reveal that

1 Gray = 100 rad

The SI units have not found widespread use in radiation protection in this country. It is the system of units which is used internationally, however, and will eventually replace the older units here.

4.9.2 Dose Equivalent

Alpha, beta, gamma/x-radiation, and neutrons differ in the damage produced for a given absorbed dose. Special units of dose equivalent are used to adjust the absorbed dose for this difference. The traditional unit of dose equivalent is the rem.

1 rem = 1 rad x Q

Q is called the quality factor and is assigned to radiation based on the relative risk for a given dose. Currently, a quality factor of 1 is used for photons, electrons, and positrons. A quality factor of from 2.3 to 10 is used for neutrons, depending on their energy, and a quality factor of 20 is used for alpha particles. The SI unit for dose equivalent is the Sievert.

1 Sievert = 1 Gray x Q

RADIATION TYPE	Q
x and gamma rays	1
beta particles	1
alpha particles	20
neutrons	2.3 to 10

Table 4-3 Radiation Quality Factors

4.9.3 Exposure

The energy absorbed by irradiated tissue is rarely measured directly. Most radiation detection instrumentation used in radiation protection measures the number of ion pairs produced in a volume of gas. The traditional unit used to measure ionization in air is the roentgen:

1 Roentgen = 2.58 x 10⁴ coulombs / kg air

The roentgen is defined only for x-rays and gamma rays. It is not used for beta, alpha, or neutron radiation.

Exposure of 1 roentgen of radiation results in an absorbed dose to tissue of 0.97 rad. For purposes of radiation protection and dosimetry, it is usually assumed that the roentgen, rad, and rem are numerically equivalent for gamma rays and x-rays.

4.9.4 Effective Dose Equivalent

The various organs and tissues in the body differ in their sensitivity to radiation. The bone marrow and other blood forming tissues of the body are much more sensitive to radiation than the skin. In order to quantify the risk from radiation exposure when the body is not irradiated uniformly (different doses are delivered to different organs or tissues) a unit called the effective dose equivalent has been developed. The effective dose equivalent is given the symbol H and is defined as:

 

Where DI is the dose equivalent received by the ith tissue or organ, and WI is a weighting factor which is assigned to the ith tissue or organ depending on its sensitivity to radiation. Weighting factors currently in use are listed in the accompanying table. The units of the effective dose equivalent are the rem and the Sievert depending on which is used for the individual tissue or organ dose equivalent.

TISSUE	WEIGHTING FACTOR
Gonads	0.25
Breast	0.15
Red Bone Marrow	0.12
Lung	0.12
Thyroid	0.03
Bone Surfaces	0.03
Remainder	0.30
Whole Body	1.00
The 0.30 for remainder results from 0.06 for each of 5 remaining organs, excluding the skin and the lens of the eye, that receive the highest doses.

Table 4-4 Effective Dose Equivalent Weighting Factors

4.9.5 Committed Effective Dose Equivalent

When radioactive materials are inhaled, ingested, or otherwise internalized, they may be retained in some tissues for a long period of time. In some cases a fraction of the material may remain in the body for years. The committed effective dose equivalent is the effective dose equivalent that will be received from an intake of radioactive material by an individual during the 50 year period following the intake.

4.9.6 Deep Dose Equivalent

The deep dose equivalent is the dose equivalent at a tissue depth of 1 cm.

4.9.7 Shallow Dose Equivalent

The shallow dose equivalent is the dose equivalent at a tissue depth of 0.0007 cm averaged over an area of 1 square centimeter.

4.9.8 Eye Dose Equivalent

The eye dose equivalent is the dose equivalent to the lens of the eye.

4.9.9 Total Effective Dose Equivalent

The total effective dose equivalent is the sum of the committed effective dose equivalent for all intakes of radioactive material and the deep dose equivalent to the whole body resulting from exposure to external sources of radiation.