X-ray Sources

Copyright of Pickering Enterprises

X-Ray Sources

Characteristics of X-rays

X-ray Safety for Medical Personnel

Analytical X-ray Systems

Basic x-ray Safety Requirements

Characteristics of X-rays• Produced when high

speed electron is slowed down and/or stopped

• External hazard– Time– Distance– Shielding– Engineered controls– Monitoring– Administrative controls

What are x-rays?• X-rays are produced when accelerated electrons

interact with a target, usually a metal absorber, or with a crystalline structure. This method of x-ray production is known as bremsstrahlung.

• The bremsstrahlung produced is proportional to the square of the energy of the accelerated electrons used to produce it, and is also proportional to the atomic number (Z) of the target (absorber).

Ionizing Radiation

X-RAY AND GAMMA ( ) RAY PROPERTIES

Charge: None

Mass: None

Velocity: 3 x 108 m/s

Origin:

Rays: Nucleus

X Rays: Electron Cloud & Bremsstrahlung

• Primary Beam•The critical radiation exposure problem with analytical X-ray •Can cause localized acute exposure •Never intentionally place any part of their body in the primary beam •The maximal energy deposition in epithelial tissues •Erythema or reddening of the skin can occur when skin is acutely exposed to 300 R (much less than a second) •Radiation burns may occur from longer exposures.

• Scattered Radiation•Some of the radiation is scattered out of the primary beam. •These radiation fields are less intense than the primary beam •They still represent a potential hazard •Scattered radiation fields can be measured by the analytical operators with a survey meter.

• Leakage•Some radiation may leak around the rube housing structure.

Three Regions of High Exposure Concern

1. Primary Beam

2. Scattered Radiation

3. Leakage

Rotating Anode Systems:What are the danger areas?

1. Primary Beam

2. Scattered Radiation

3. Leakage

Sealed Tube Systems:What are the danger areas?

Sealed Tube/Microfocus Systems:What are the danger areas?

1. Primary Beam 2. Scattered Radiation

3. Leakage

X-Ray Burns vs. Thermal Burns

• 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

Exposure Effects

• 1000 rad - second degree burns

• 2000 rad - intense swelling within a few hours

• 3000 rad - completely destroys tissue

• 400 rad acute whole body exposure is LD 50/30

• LD 50/30 - lethal to 50% of population within 30 days if

not treated

Hazards of Exposure to X-rays

Accident Case Study

• Case Study - A radiation accident at an industrial accelerator facility Health Physics, Vol. 65, No. 2, August 1992, pp. 131-140. Reproduced by permission.

• 3MV potential drop accelerator. 40 rad/s inside victim’s shoes, 1300 rad/s to hands.

• 3 days after exposure•Note erythema and swelling

•1 month after

• Note blistering and erythema

• 2 months after

Bioeffects- X-rays and Skin

• 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.

Common Cause of Accidents

• Rushing to complete a a job– Overriding safety features

• Boredom• Fatigue• Illness• Personal Problems• Working on unfamiliar equipment• Complacency (Attitude Accumulation)• 2 people working 1 job• Frustration

Four Main Causes of Accidents• Poor equipment configuration

– Ex. Unused beam ports not covered

• Manipulation of equipment when energized– Adjustment of samples or alignment of cameras when x-

ray beam is on

• Equipment failure– Shutter failure

– Warning light failure

• Inadequate training or violation of procedure– Incorrect use of equipment

– Overriding interlocks

Common Cause of Accidents

• Rushing to complete a ajob– Overriding safety features

• Boredom• Fatigue• Illness• Personal Problems• Working on unfamiliar equipment• Complacency (Attitude Accumulation)• 2 people working 1 job

Preventing Accidents• Know location and/or presence of primary and

diffracted beams AT ALL TIMES• Provide and inspect shielding• Do not perform maintenance (without confirming

that the tube is not energized)• Perform check of safety devices at least once per

month• Survey unit whenever moved or reconfigured.• DON’T PUT YOUR BODY PARTS IN THE

BEAM!!

Exposure EstimatesAt 5 cm from Tube Port

50 x (40) x (20) 29 = 279 R/sec (7.5)2 74

50 x (36) x (20) 42 = 363 R/sec (7.5)2 74

50 x (40) x (20) 47 = 452 R/sec (7.5)2 74

50 x (50) x (20) 74 = 889 R/sec (7.5)2 74

Exposure Rate:

50 x (kV) x (mA) Z = R/sec (cm)2 74

Characteristic Intensity:

Proportional to: (kVp - kVc)1.6

Radiation Safety Training for X-Ray Diffraction

•Designated Responsible Operator

•User Training

•Operating Procedures/Instructions

•Engineered Protection Systems

•Surveillance Programs

Open Beam XRD• Example of an

unenclosed (open) x-ray diffractometer (Geology Department).

• The open x-ray beam of such an instrument can be extremely hazardous, and it is far preferable to enclose the entire x-ray apparatus.

XRD (tin/polycarbonate enclosure)• Properly enclosed and

interlocked x-ray diffrac-tometer. The enclosure is made of tin-impregnated polycarbonate. – Leaded glass enclosures are

also used.

• If a panel is opened while the XRD is being used, the interlock should either shut off the x-ray or close the shutter, preventing accidental exposure to personnel.

AFC8 & Mercury CCD

AFC7 & Mercury CCD

RAXIS RAPID

DMAX RAPID

MULTIFLEX

Siemens for powder

Electron Microscope

Direct Drive RAXIS/Jupiter

Belt Drive Rotating Anode AFC6/IV++

Multiflex

Safety DevicesAnalytical units shall have the following safety devices as

required by State Regulations. Unused ports shall be secure in a manner which will prevent accidental

opening. Open beam units shall have a shutter over the port which cannot be opened unless a collimator or coupling has been connected.

Safety interlocks shall not be used to de-activate the X-ray beam except in an emergency or during testing of the interlock system.

Warning Devices All units with an open beam configuration shall have an easily identified

device located near the radiation source housing and labeled what gives a clear, visible indication of the X-ray generation status (on-off)

Safety interlocks shall not be used to de-activate the X-ray beam except in an emergency or during testing of the interlock system.

Warning Labels

A label which bears the following or similar words shall be placed on the X-ray source housing:

CAUTION - HIGH INTENSITY X-RAY BEAM A label which bears the following or similar wording shall be placed on

the control console of each unit near any switch which energizes the source:

CAUTION - RADIATIONTHIS EQUIPMENT PRODUCES

RADIATION WHEN ENERGIZED

Warning Lights An easily visible warning light labeled with these or similar words “X-

RAY ON” shall be placed near any switch that energizes an X-ray source, and shall be illuminated only when the generator is energized, and have fail-safe characteristics.

Shutters Each port shall be equipped with a shutter that cannot be opened unless

a collimator or a coupling device has been connected to the port.

Radiation Surveys

The Radiation Safety Office will perform a survey annually and following major repairs and/or system modifications. This survey will include inspection of all safety systems and a radiation exposure survey. The results of the survey will be kept on file in the Radiation Safety Office.

Users of analytical equipment should also routinely perform radiation surveys. The surveys should include monitoring for stray radiation in the immediate vicinity of the X-ray apparatus.

When the Operator Should Perform a Radiation Survey

1. Upon installation of your instrument.

2. After any major changes in equipment configuration or minor system maintenance to insure that no unanticipated exposure hazards exist.

3. Following any maintenance requiring the disassembly or removal of local components.

4. During the performance of maintenance and alignment procedures.

5. When visual inspection of the local components in the system reveals an abnormal condition.

Survey Meter Instrumentation

Survey should be performed with a portable Geiger-Mueller survey instrument although the results are not necessarily quantitative. If accurate measurements are desired, the instrument should be calibrated with the source of low energy X-rays. Consideration should also be given to possible monitoring errors due to the cross-sectional area of the monitored radiation beam being smaller than the sensitive area of the survey meter.

General Precautions Only Trained personnel shall be permitted to operate an analytical unit. Be familiar with the procedure to be carried out. Never expose any part of your body to the primary beam. Turn the X-ray beam OFF before attempting to make any changes to the

experimental set-up (except for beam alignment) While the beam is on DO NOT attempt to handle, manipulate or adjust

any object (sample, sample holder, collimator, etc.) which is in the direct beam path (except for beam alignment procedures).

Examine the system carefully for any system modifications or irregularities.

Follow the operating procedures carefully. DO NOT take short cuts! Never leave the energized system unattended in an area where access in

not controlled.

General Precautions Survey the area frequently to evaluate scatter and leakage radiation

fields. Never remove auxiliary shielding without authorization from the owner

of the analytical equipment or Radiation Safety Officer. Never bypass safety circuits, such as interlocks. Report all unusual occurrences to the owner of the analytical unit for

possible corrective actions. Only authorized, trained individuals as specified by the unit’s owner and

the Radiation Safety Office may repair, align or make modifications to the X-ray apparatus.

Designated Responsible Operator

• Authorized by the Health Physics Committee

• Ensures that only qualified individuals use the equipment

• Maintains the equipment in compliance with safety requirements

Limited Open X-ray Systems

• Accessible area have exposure rates not exceeding 2 mR/hr (any area outside of the barrier or shield routinely occupied by personnel).

• Maintain a log book of major changes to the system shielding, enclosures, and configurations.

• Engineered protection system shall be maintained– Failsafe interlocks on removable protective barriers– Exposure rate below 2 mR/hr at 5 cm form any surface– Key control on the production of x-rays– A console power on indicator (must be operational and used)– Warning light adequate to warn anyone present in the room that x-rays

are being produced.

Exposure Potential

• Fingers are at risk.– Significant injuries

have occurred with diffraction x-rays.

• Large exposures may occur.

• Skin and eyes may receive exposures.

General Methods of Protection

• Time

• Distance

• Shielding

Protective Devices & Procedures

• Devices– Interlocks

– Key control

– Shielding

• Procedures– Operating instructions

– Training

– Surveys

– Exposure monitoring

How to recognize failures

• Interlocks don’t work.• Radiation is observed

during surveys.• Unqualified people

operating the system.• Redness of the skin,

normally to the hand.• Warning light is not

operational.

Survey procedures & limitations

• Perform the pre and post operational checks.

• Record the results.• Make sure warning

lights are working.• Wear your dosimeter.• Instruments record low

readings.

Use of radiation dosimetry

• If you don’t use it, it will not provide useful information.

• Wear it properly.• Don’t wear another

persons film badge.• If you need additional

devices, contact the RSO.

• Decrease dose to patient and the operator

• Time– Determines total dose

• Voltage– Determines penetration

• Current– Determines dose rate

Radiation Exposure from Diagnostic Medical X-ray Examinations in the U.S. (1980)

Examination Type Effective Dose Equivalent (mrem) per Examination

CT (head and body) 111

Chest 8

Skull 22

Cervical Spine 20

Biliary 189

Lumbar Spine 127

Upper Gastrointestinal 244

Abdomen (kidneys, ureters, bladder) 56

Barium Enema 406

Intravenous Pyelogram 158

Pelvis 44

Hip 83

Extremeties 1

Reference: NCRP Report No. 100, Exposure of the U.S. Population from Diagnostic Medical Radiation (1989).

Filtration removes low-energy x-rays from the primary beam.

Collimation limits the beam to a useful area.

Compliance testing performed periodically.

Registration of sources with regulatory agency.

Medial X-ray Shielding

Structural Shielding Design

Patient

Employee-1

Employee-2

Secondary Barrier

Primary Barrier

X-ray Tube

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