University Environmental Health & Safety
X-rays were discovered in 1895 when William Conrad Roentgen observed that a screen coated with a barium salt fluoresced when placed near a cathode ray tube. Roentgen concluded that a form of penetrating radiation was being emitted by the cathode ray tube and called the unknown rays, X-rays.
X rays are a form of electromagnetic radiation which arises as electrons are deflected from their original paths or inner orbital electrons change their orbital levels around the atomic nucleus. Like gamma rays, x rays require more shielding to reduce their intensity than do beta or alpha particles. X and gamma rays differ primarily in their origin: x rays originate in the electronic shell, gamma rays originate in the nucleus.
Type Radiowave Microwave Infrared Ultraviolet X-Ray Gamma Ray Photon Energy 1µ ev 1m ev 1 ev 4 ev 10 kev 1 MeV
X-rays are photons (electromagnetic radiation) which originate in the energy shells of an atom, as opposed to gamma rays, which are produced in the nucleus of an atom.
When fast-moving electrons slam into a metal object, x-rays are produced. The kinetic energy of the electron is transformed into electromagnetic energy.
High voltage electrons from cathode Boiled off by high temperature Electrons strike anode Electrons slow down in anode and convert to x-rays Called Bremsstrahlung
Highly penetrating Electrically neutral Wide range of energies Travel in straight lines at speed of light Cause ionization Cause fluorescence in crystals Cannot be focused by lens Produce photograph images Produce scattered radiation
Roentgen (R): The roentgen (R) is a unit of radiation exposure in air. It is defined as the amount of x-ray or g radiation that will generate 2.58E- 4 coulombs/kg of air at standard temp and pressure. RAD: RAD stands for Radiation Absorbed Dose and is the amount of radiation that will deposit 0.01 J/kg of material. Dose A roentgen in air can be approximated by 0.87 rad in air, 0.93 rad in tissue, and 0.97 rad in bone. The SI unit of absorbed dose is the gray (Gy), which has the units of J/kg. 1 Gy= 100 rad.
REM: REM stands for Roentgen Equivalent Man. The REM is a unit of absorbed dose and is equal to the rad multiplied by a weighting factor which varies according to the type of radiation. The weighting factor for x-rays is equal to 1. For x-rays, one rem is equal to one rad. The SI unit used in place of the rem is the sievert (Sv). 1 Sv = 100 rem.
*Declared pregnant women
Primary Beam Very intense exposures in beam Could be > 100,000 R/min Small beam diameter, <1 cm Scattered Radiation Low intensity Large area of exposure From housing leakage From any target material
X-ray leakage. Sky shine scattered x-rays Inadequate shielding Not following safety procedures Bypassing interlocks, etc. Not using or heeding radiation instruments Not using protective equipment Lead aprons, etc.
Primary Radiation Useful beam Wall, ceiling, floor or other structure that intercepts radiation from x-ray tube Secondary Radiation X-rays scattered from patient or other objects Leakage from x-ray tube housing Wall, ceiling, floor or other structure that intercepts radiation from scatter or leakage
Somatic (body) effects of whole body irradiation can be divided into "prompt" effects and "delayed" effects. Prompt effects that appear quickly Delayed effects that may take years to appear
Most nerve endings are near the surface of the skin High energy x-rays penetrate the outer layer of the skin that contains most of the nerve endings so one does not feel an X-Ray burn until the damage has been done X-rays penetrate to the deeper, basal skin layer, damaging or killing the rapidly dividing germinal cells, that are destined to replace the outer layers
Somatic Damage to genetic material in the cell May cause cell to become a cancer cell Probability is very low at occupational doses Heritable Passed on to offspring Observed in some animal studies but not human
Most radiation overexposures from analytical x-ray equipment are to the extremities. For x-rays of about 5-30 kev, irradiation of the fingers or hands does not result in significant damage to blood-forming tissue. At high exposures some general somatic effects to the skin can occur. Very high exposures may necessitate skin grafting or amputation of the affected extremity. Biological effects can be observed at 10 rem in special blood studies. Typically effects are visually observed at 50 to 100 rem.
Rapidly dividing cells are more susceptible to radiation damage. Examples of radiosensitive cells are Blood forming cells The intestinal lining Hair follicles A fetus This is why the fetus has an exposure limit (over gestation period) of 500 mrem (or 1/10 th of the annual adult limit)
Sensitivity of the unborn Rapidly dividing cells are radiosensitive Potential effects Low birth weight - (most common) Mental retardation Chance of childhood cancer
Incidental not wanted or used Computer monitors, electron microscopes TV, electron beam welders <0.5 mr/hour Intentional x-rays for specific use Fixed, interlocked, shielded room X-ray diffraction, fluorescence analysis Medical x-rays, industrial cabinet and non-cabinet installations
Used for radiography Measure thickness ANSI N43.3 three classes Cabinet, exempt shielded, shielded Safety requirements Area postings, control panel labels Surveillance, barrier, shielding, fail-safe interlocks, warning signals Visible, audible, emergency switches
For diffraction or fluorescence Enclosed beam and open beam Safety requirements Label Caution this equipment produces x-rays when energized Fail-safe light, X-rays On Fail-safe indicator, Shutter Open Fail-safe interlocks, doors/panels Beam stops, shielding
Tube is in a cabinet Enclosure contains sample, shielding, and exclusion for persons Such as baggage inspection Comply with 21 CFR 1020.40 Dose rate 0.5 mrem in an hour at 5 cm Safe in a non-controlled area
All x-ray paths are enclosed No part of body exposed to beam Safer than open-beam X-ray tube, sample, detector, etc. Enclosed in chamber Shutter or fail-safe interlock to prevent entry Dose rate <0.5 mrem in an hour at 5 cm from external surface
Faxitron Cabinet X-ray System
Ametek Spectro XEPOS X-ray Fluorescence
One or more x-ray beams open Human exposure possible Only use if: Need to make adjustments Need for frequent changes Motion of sample and detector Examination of large items
Bruker AXS X-ray Diffractormeter
Thermo Scientific NITON XL3t XRF analyzer
Time of exposure seconds Tube current (ma) Tube potential (kvp) Filtration (shielding) Distance (inverse square law)
Interlocks never bypass interlocks or other safety devices Warning Lights know the beam status whenever working with XRD or XRF Shielding Locked doors
Posting Black or magenta trefoil on yellow Yellow and magenta ropes, tapes, etc. to make boundaries Visible from all directions State dose rate and entry limits State when condition exists, i.e. red light on
Labels Caution this equipment produces x-rays when energized Warning Devices Warning signals status of x-ray tube Visible indicators of power on Current meter, warning light on panel Warning light near door Shutter open indicator
Interlocks Could use fail-safe interlocks on doors or panels to prevent x-rays when open. Testing Energize tube Open each door to panel Check warning light, current meter Record results
Quarterly Upon installation of equipment Upon changes Following maintenance requiring disassembly of a local component During maintenance and alignment procedures When abnormal conditions observed
Compliance with annual dose limits 5 rem per year total effective dose equivalent Check safety features Measurements Thin window GM or Nal for leakage radiation (to find where leakage occurs) Ion chamber for exposure rate (how much)
Expiration Renewal Report of changes Approval not implied Assembler obligation Reciprocal recognition Information for shielding plan Design of operators booth
If there are any questions or concerns about the functioning of an X-ray emitting instrument, it must be taken out of service immediately and reported to the University employee responsible for the equipment or the Radiation Safety Officer. [Be aware that shutter mechanisms can fail. Warning lights can fail.]
Thank You