Principles of Radiation Protection

What does the radiation protection acronym ALARA stand for?

As Low As Reasonably Achievable

What are the three core cardinal principles used to minimize external radiation dose?

Time Distance Shielding

How is external radiation dose related to the length of time spent in a radiation field?

It is directly proportional (minimizing time spent directly minimizes the cumulative dose).

An individual works in a $300mrem/hr radiation field for 15 minutes. What cumulative dose do they receive?

75 mrem (calculated as $300 mrem/hr \times 0.25\hr

What mathematical relationship governs radiation intensity (I )as a function of distance (D) from a point source?

The Inverse Square Law:

According to the inverse square law, how does doubling your distance from a radioactive point source affect radiation exposure?

Exposure is reduced to one-fourth of the original intensity.

A technologist working 2 m from a source measures an exposure rate of 2.5 mR/hr. What is the exposure rate if they move to 4 m?

0.625 mR/hr

An exposure rate is $0.68mR/hr at 5ft. To reduce the exposure rate to 0.25mR/hr, to what distance must a worker move?

8.25 ft

Which materials are primarily used to shield gamma rays and X-rays in nuclear medicine?

lead and tungsten.

Which materials should be used to shield pure beta-emitting radionuclides like 90 Y or 177 Lu?

Low-Z materials such as plastic, acrylic, glass, or aluminum (to minimize Bremsstrahlung radiation).

Why are high-atomic-number (high-Z) materials like lead avoided when primary shielding pure high-energy beta emitters?

cause high-energy beta particles to decelerate rapidly, creating penetrating Bremsstrahlung X-rays.

Which type of ionizing radiation is completely stopped by a single sheet of paper?

Alpha radiation

Which material is required to stop beta particles that pass through paper?

Aluminum

What is the Half-Value Layer (HVL) of a shielding material?

The material thickness required to reduce radiation to 50% of its original intensity.

What fraction and percentage of original exposure remains after radiation passes through 3 Half-Value Layers (HVLs)?

0.125(1/8) Percentage: 12.5%

What percentage of original exposure remains after placing 5 Half-Value Layers (HVLs) of shielding?

3.1% (or a fraction of 0.031)

What is the lead HVL thickness for Technetium-99m (140 keV)

0.27 mm of lead

What is the lead HVL thickness for Iodine-131 (364 keV)

3.0 mm of lead

What is the lead HVL thickness for Fluorine-18 (511 keV annihilation photons)?

4.1 mm of lead

What is the lead HVL thickness for Cesium (662 keV gamma photons)?

6.5 mm of lead

Rank lead, iron, concrete, and water in order of increasing thickness required to achieve equivalent gamma attenuation.

Lead < Iron < Concrete < Water (Lead is thinnest, water is thickest).

How does the required shielding thickness of iron compare to lead for gamma attenuation?

it takes twice as much iron as lead to achieve equal gamma attenuation.

If an unshielded source yields 35mR/hr, what is the exposure rate after placing 7 HVLs of shielding?

0.273 mR/hr

Unshielded dose rate is 1.88 mrem/hr. Reduced by 3 HVLs, how long will it take a worker to accumulate 4\mrem?

17 hours

An 18F source produces 50 mR/hr . What is the intensity behind 20.5 mm of lead shielding if 1 HVL = 4.1 mm?

1.5625 mR/hr

An 131 source (1 HVL lead} = 3.0 mm has an intensity of 150 mR/hr. What is the intensity through a 4.5 mm lead shield?

53.03 mR/hr

When is mandatory radiation monitoring required for adult occupational workers under NRC regulations?

When an adult worker is likely to receive in 1 year more than 10% of the NRC occupational dose limit.

Deep Dose Equivalent (DDE)

The external whole-body radiation exposure dose equivalent evaluated at a tissue depth of 1 cm (1000 mg/cm2

Committed Effective Dose Equivalent (CEDE)

An estimate of the 50-year internal radiation dose equivalent to a person resulting from inhalation or ingestion of radioactive material.

Lens Dose Equivalent (LDE)

The external radiation exposure dose equivalent to the lens of the eye evaluated at a tissue depth of 0.3 cm (300 mg/cm2.)

Shallow Dose Equivalent (SDE)

The external radiation exposure dose equivalent to the skin or an extremity evaluated at a tissue depth of 0.007 cm (7 mg/cm2.)

Total Organ Dose Equivalent (TODE)

The sum of Deep Dose Equivalent (DDE) and the maximum Committed Dose Equivalent (CDE) to the specific organ receiving the highest dose.

What is the annual NRC occupational dose limit for the Whole Body (TEDE)?

5 rem (5,000 mrem or 0.05 Sv / 50 mSv)

What is the annual NRC occupational dose limit for any individual Organ (TODE)?

50 rem (50,000 mrem or 0.5 Sv / 500 mSv)

What is the annual NRC occupational dose limit for Skin (SDE) and Extremities (SDE)?

50 rem (50,000 mrem or 0.5 Sv / 500 mSv)

What is the annual NRC occupational dose limit for the Lens of the Eye (LDE)?

15 rem (15,000 mrem or 0.15 Sv / 150 mSv)

What is the NRC dose limit for an embryo/fetus during the entire gestation period of a declared pregnant worker?

0.5 rem (500 mrem or 0.005 Sv / 5 mSv)

What is the monthly NRC dose limit for an embryo/fetus during pregnancy?

0.05 rem (50 mrem or 0.0005 Sv / 0.5 mSv)

What is the annual NRC dose limit for an individual member of the general public (EDE)?

0.1 rem (100 mrem or 0.001 Sv / 1 mSv)

Within what time window following radioiodine handling must routine bioassays (thyroid uptake tests) be performed?

24 to 72 hours after handling

What action is required if a routine thyroid bioassay reveals a radioiodine content exceeding 1 uCi

A repeat uptake test must be performed and an investigation initiated to take corrective action.

What action is triggered if a thyroid bioassay shows radioiodine uptake exceeding 5 uCi

The individual must be referred for medical consultation to consider removal procedures (e.g., thyroid-blocking agents).

What five main variables influence external radiation dose?

"1. Radiation type and energy 2. Dose rate 3. Duration of exposure . 4. Exposure geometry . 5. Tissue composition and depth"

What are the three essential components of a traditional film dosimeter badge?

the photographic film emulsion, the plastic holder (casing), and a set of diverse radiation filters.

What is the primary function of metal filters inside a film badge dosimeter?

They differently attenuate radiation to help determine the type, energy, and penetration of the exposure.

What is a major limitation of film dosimeters regarding minimum detectable gamma dose?

Exposures of less than 20 mrem of gamma radiation cannot be accurately measured.

Which environmental conditions degrade film badge dosimeter accuracy?

Excessive heat and humidity (which cause film fogging).

What detector material is utilized inside Optically Stimulated Luminescence (OSL) dosimeters?

Aluminum oxide

How are trapped electrons released to measure dose in an Optically Stimulated Luminescence (OSL) dosimeter?

By stimulating the aluminum oxide material with selected frequencies of laser or LED light.

What is the function of the plastic filter in an OSL dosimeter?

It eliminates beta particles and extremely low-energy photons from reaching the sensor.

What is the role of the copper (Cu) filter in an OSL dosimeter?

It removes lower and moderate-energy photons to evaluate exposure to high-energy radiation.

What active crystal sensing material is used in Thermoluminescent Dosimeters (TLDs)?

Lithium fluoride (LiF) crystals.

How are trapped electrons released to read radiation exposure in a Thermoluminescent Dosimeter (TLD)?

By heating the crystal material (thermoluminescence).

Where and how should a extremity TLD ring badge be worn during radiopharmaceutical handling?

Worn on the hand receiving the highest exposure, with the sensitive crystal facing the palm side, underneath protective gloves.

What is a major operational advantage of electronic personal dosimeters?

They provide immediate, real-time digital readouts of accumulated exposure and dose rate.

What physical vulnerability can cause a false-high exposure reading on an electronic personal dosimeter?

Mechanical shock from dropping the device, which causes electrical discharge.

What whole-body dose threshold defines ALARA Investigational Level I (10% of allowable limit)?

500 mrem/year (5 mSv/year)

What whole-body dose threshold defines ALARA Investigational Level II (30% of allowable limit)?

1,500 mrem/year (15 mSv/year)

What administrative actions are required when an employee exceeds ALARA Level II threshold?

employee must be notified in writing, an investigation generated, corrective actions proposed, and the document signed by the employee.

Which institutional official oversees the personnel badge monitoring system and reviews all dosimetry reports?

The Radiation Safety Officer