Analytical X-ray GuideMassachusetts Institute of Technology

Environmental Health and Safety: Radiation Protection ProgramBusiness Hours: Mon-Fri 8am-5pm (617)-452-3477

After Hours/Weekends/Holidays: Call MIT Operations Center (617)-253-4948 (x100 from MIT Landline)Email: environmental@mit.edu

URL: ehs.mit.edu

Roles and Responsibilities

Massachusetts Department of Public HealthRadiation Control Program

MIT Radiation Protection Committee

MIT EHS Radiation Protection Program

Principle Investigator/Laboratory Supervisor

Radiation User

9 Traits of a Positive Safety Culture

Radiation Doses in Our Daily Lives (mrem)

Regulatory Dose Limits

Lens of the Eye

Whole Body

Skin and Extremities

Declared Pregnant Worker

Minor

General Public

15,000 mrem/year

5,000 mrem/year

50,000 mrem/year

500 mrem per gestation period (9 months)

500 mrem per year

100 mrem per year

What are X-rays?

X-rays are a form of electromagnetic radiation that is highly energetic and has a short wavelength.

Bremsstrahlung X-rays “braking radiation”: Produced when a high speed electron traverses a target material and undergoes a change in velocity causing it to decelerate due to the strong positive forces of the target atom’s nucleus. The energy lost by the electron in this process is radiated in the form of X-rays (conservation of energy and momentum).

Characteristic X-rays: Produced when outer-shell electrons fill vacancies in inner shells of an atom’s electron cloud resulting in the emission of X-rays in a spectrum that is “characteristic” to each specific element.

Biological Effects

Prompt Effects- Occur shortly after receiving large doses of radiation.- Skin reddening, hair loss, and radiation burns.- No concern for genetic effects.

Delayed Effects- Occur due to receiving continuous low-level radiation dose from either internal or external exposure. - Cataracts: Induced when a radiation dose exceeding 500 rad is delivered to the lens of the eye for photon radiation.- Cancer: Risk of cancer induction associated with high radiation doses may occur.- Other effects include leukemia and hereditary effects.

X-ray HazardsRadiological Hazards

Primary Beam: Most hazardous region due to very high exposure rates emitted directly from the port.

Leakage or scatter radiation through cracks, defective equipment, inadequate shielding, irregularly shaped samples.

Other Hazards

Electrical shock, chemicals, and/or biological materials

As Low As Reasonable AchievableALARA

Minimize Time- Work efficiently

Maximize Distance- While system is in use, if you are not required to be near the system, move away!

Shielding- Operate system with all shielding and safety components in place. Use additional engineering controls if necessary.- NEVER tamper with system interlocks

X-ray Safety Features

Safety Interlocks- Prevent access to primary beam or potential hazards

Warning lights- Lights labeled with “X-RAY ON”- Indicate x-rays are being generated

Unit labeling- “Caution – High Intensity X-ray Beam” or - “Caution – This equipment produces radiation when energized”

Source housing- Shielding for X-rays

Potential Exposure Pathways

Aligning X-ray beam visually

Violation of procedures – over riding interlocks, by-pass safety features designed by manufacturer.

Modification of shielding

Failure to realize X-rays are emitted from several ports

Equipment failure – shutter, warning light, interlock sensor

Know location and/or presence of primary and diffracted beams at all times.

Inspect shielding – cracks

Do not perform maintenance without permission.

Perform routine survey to check for leakage.

Do not by-pass any safety device or interlock.

Do not leave the unit unattended when operational.

Know what you are doing and where to expect problems.

Don’t put your fingers/body parts in the beam!

Radiation Exposure (Dose) Units

Roentgen (R)- Charge from photons deposited per kilogram of air (STP)- 1 R = 2.58 x 10-4 C/kg

Absorbed Dose (rad or Gray)- Energy deposited per unit mass of material- 1 rad = 0.01 J/kg- 1 Gy = 1 J/kg- Therefore, 1 rad = 0.01 Gy or 1 Gy = 100 rad

Quality Factor (QF)- Weighting Factor for taking into account the biological risks of a radiation type and energy for causing stochastic effects (which are based on population statistics) such as cancer and genetic effects.- Does not apply to acute (short term effects) of radiation- QF for photons (X-rays) and electrons = 1

Absorbed Dose Equivalent (rem or Sievert)- Equal to the absorbed dose multiplied by the radiation weighting factor (which is particle and energy dependent)- 1 rem = 1 rad x QF- 1 Sv = 1 Gy x QF

Radiation Survey and Monitoring

Inverse Square LawInverse Square Law: The dose rate R2 at distance d2, decreases from a point source at d1 with dose rate R1, as the inverse square of distance d2.

2

2

112

ddRR

Survey Meter Controls & Operation

Fast / SlowNeedle

Response

Portable Radiation Survey Meter- Use Geiger Mueller (GM) probe - Check instrument for damage - Check battery level- Check detector response with source on side of unit- Perform background measurement- Scan area with probe slowly (1-2 inches / second) at a distance of ~2 inches from surface- Note: audio off does not mean the instrument is off

Area Monitoring- Monthly area monitoring badge(s) available- No measurable dose / background levels- No more than 2.0 mR/hr @ 5 cm from any surface

- If >2.0 mR/hr contact your PI/Supervisor and Radiation Protection

- Check for leakage radiation outside the X-ray cabinet beam enclosure- Check that radiation is not present when changing samples (this will ensure that the shutter is working)

AudioOn / Off

NeedleReset (Zero)

BatteryTest

Decade Selector Knob

Counts perminute (cpm)

milli-Roentgen per hour(mR/hr)

BatteryTurn Screw

Geiger Muller (GM)

Detector