X-ray Device Safety
Annual course for users of
analytical X-ray devices
Ralf Haiges
Office: ACB 201, Lab: ACB 212
Phone: (213) 740-3197
Email: haiges@usc.edu
A copy of this presentation can be found at
crystallography.usc.edu
Introduction
Analytical X-ray devices are important tools in
various areas of modern research. X-ray
crystallography and X-ray fluorescence
spectrometry rely on X radiation.
But, X-ray diffraction equipment [XRD] can be
very dangerous, and operators of this equipment
must not become complacent or overconfident
about the potential danger of the X-ray beam.
What are X-rays ?
X rays are Electromagnetic waves generated by
the electron clouds of atoms.
• No charge
• No mass
• Travel at the speed of light
• Categorized in two groups depend on the energy
Low energy------ Non-ionizing radiation
High energy----- Ionizing radiation
Can cause “ionization”
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Electromagnetic Waves
Low
ENERGY
Microwaves
Radio
waves
Radar
High
Ultra-violet
Visible
light
Infrared
X ray
γ ray
Non-ionizing radiation
Ionizing radiation
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How are X rays produced ??
X-ray tube
X ray
Anode (+)
Cathode (-)
Target Electrons
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How are X rays produced ??
Most X-ray devices emit electrons from the cathode,
accelerate them with a voltage (vacuum), and let them
bombard a target (anode). As a result of interactions
between atoms of the target elements and electrons,
X rays are produced.
The energy of the X rays show a distribution that is
depending on the target material.
During this process, the device emits two different
types of radiation.
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Where do X rays come from ?
Atom of the target element
Bremsstrahlung
Nucleus
Electrons
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Where do X rays come from ?
Atom of the target element
Nucleus
Electrons
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Where do X rays come from ?
Atom of the target element
Characteristic Radiation
Nucleus
Electrons
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X-ray spectrum
Relative Intensity
Characteristic X rays
Continuous X ray
(Bremsstrahlung)
X-ray energy
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Radiation Units
R (Roentgen)
- The unit of radiation exposure in air.
•R (Roentgen)
Defined as the amount of X-ray or γ-ray
that will generate 2.58·10-4 coulombs/kgair (STP).
Note: this unit is only applicable to X- or
γ-ray
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Radiaton Units
Rad (Radiation absorbed dose)
• Definition: 1 Rad is the amount of radiation that will
deposit 0.01 J of energy in a kilogram of material
(tissue, air, shielding material …etc). This unit can be
used for any kinds of radiation.
• Rad is a traditional unit for absorbed dose.
International Unit (SI unit) for absorption dose is Gy
(gray). Conversion: 1 Gy = 100 rad.
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Radiaton Units
Rem (Roentgen equivalent man)
• It can be obtained from Rad with a weighting
factor. Different weighting factor is given for
different types of radiation.
For X-rays, weighting factor is 1. Thus, for X-rays,
1 rem = 1 rad.
• Rem is also traditional unit. SI unit used for rem
is Sv (sievert).
Conversion: 1 Sv = 100 rem
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Units
1 R = 0.93 rad (tissue) =
0.97 rad (bone) = 0.87 rad (air)
For a quick estimation of
exposure, it is often
approximated that
1 R = 1 rad = 1 rem.
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Background radiation
Exposure rate of the average U.S. resident is
360 mrem /year.
Terrestrial -8%
Cosmic - 8%
Internal- 11%
Natural
82%
Radon - 55%
Medical - 15%
Fallout - 0.3%
Reactor - 0.1%
Others - 2.6%
Man-Made
18%
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Occupational Exposure Limit
Whole Body – 5rem/year
Extremities – 50rem/year
Eye – 15rem/year
Pregnant workers – 0.5rem/gestation period
General public
Limited to 0.1 rem/year (in addition to the background radiation)
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Typical X-ray Beam Intensities
(XRD)
Primary beam
50,000-500,000 R/min
X-ray
Producing
Unit
Collimator/slit
Secondary beam
Leakage 0.5 - 5 R/hr
Scatter < 10 – 300 mR/hr
Sample
Diffracted beam
80 mR/hr
Primary beam
5,000 – 50,000 R/min
Note: whole body
occupational exposure limit
is 5 Rem/year
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Interaction of Xrays with Matter
Radiation interacts with matter by transfer of energy.
Main processes are:
– Absorption (energy transferred)
– Scattering (energy redirected)
Absorption is of most concern in x-ray interaction with
tissues
Types of Energy Transfer:
– Ionization
 Involves reaction with orbital shell electrons
 Involves multiple reactions until all energy is spent
 Highest potential for damage to target.
– Excitation
 Some of th incoming x-ray energy is being transferred to the target
 Typical result is release of heat and a rise in temperature
Biological Effects
Radiation
chromosome
Cell
Chemical bonds break
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Biological Effects
Sensitivity
Low
Typically, young and rapid growing cells
are more sensitive to the radiation than
grownup cells.
Muscle, Joints, Central nerves, Fat
Skin, Inner-layer of intestines, Eyes
Bone marrow, Lymph system, Reproductive organs
High
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Bioeffects on Surface tissues
• Because of the low energy (10-50 keV) of analytical
X-rays, most energy will be absorbed by the skin or
other exposed tissue.
• The threshold of skin damage is usually around 300
R resulting in reddening of the skin (erythema).
• Longer exposures can produce more intense
erythema (i.e., “sunburn”) and temporary hair loss
• The eye tissue is particularly sensitive – if you are
working in an area where diffracted beams could be
present, eye protection should be worn.
Biological Effects of Radiation
Effect
Dose
Primary beam
exposure time
Erythema
500–800 Rem
0.08-0.12 s
Epilation (temporary)
350 Rem
0.05 s
Epilation (permanent)
1200 Rem
0.18 s
Acute dermatitis
3000-4000 Rem
0.45-0.60 s
Chronic dermatitis
thousands of Rem in many
small doses over several
years
N/A
Skin Cancer
Small doses over a long
period of time to receive a
large total dose
N/A
WARNING
Very serious injuries
have resulted from the
use of XRD equipment.
Large doses of
radiation have caused
burns and permanent
injuries to workers.
Sources of Exposure
• The primary beam
• Leakage of primary beam through cracks in
shielding (e.g. tube housing, shutter)
• Penetration of primary beam through shutters,
cameras, beam stops, etc.
• Secondary emission (fluorescence) from a
sample or shielding material
• Diffracted rays from sample
• Radiation generated by rectifiers in the high
voltage power supply of older units
Accident cause
Manipulation while X-ray is in operation
- adjustment or alignment of samples/cameras while beam is on
Safety features of the device not used
- interlocks, shielding of unused port …etc.
Unauthorized use
- untrained user, unsupervised operation
Safety feature failure
- Shutter, warning light …etc.
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Accident Prevention
Know X-ray beam status at ALL TIMES !
Use safety features (shielding, shutter, warning sign, etc.)
Do not place any part of your body in the beam.
Make sure the beam is off when maintaining the
device or adjusting sample/camera locations.
Do not forget to shield (or cap) unused ports.
Do not operate the device if you are not trained by
an administrator.
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ALARA
ALARA = As low as reasonably achievable
- Main objective of Radiation protection
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Safety Basics
• Time – minimizing time around a radiation
source will reduce total exposure
• Distance – maximize distance from a radiation
source to reduce total exposure
“Inverse Square Law”
• Shielding – material used to attenuate radiation
and reduce occupational exposure. For x rays,
shielding is most often lead.
Inverse Square Law
Radiation exposure varies inversely with
the square of the distance from the source
E
∞ 1 / d2
Safety Features of Devices
Interlock/Shutter
Shutter will not open when enclosure doors are
open. (Avoids accidental exposure while changing
samples)
Safety key
To prevent unauthorized use, x-ray machine
operation requires several steps (key(s) to be in
place to switch on the device, etc.)
Warning sign
Indicates on-off status of the X-ray machine
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Interlocks
Do not use the Safety Interlocks to
deactivate the X-ray beam, except in
emergencies.
Warning Lights
Each port must have a readily discernible
indication of shutter status [opened or
closed]. There must be a warning light
that is illuminated when the X-ray tube is
energized. The light must be near the
X-ray tube housing or port and be in
the operator’s field of view.
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Who May Use the Instruments?
• Only trained, authorized persons may use
X-ray diffraction equipment.
• All such persons must have received a
Radiation Safety Training.
Dosimetry
• A regular badge dosimeter and a ring dosimeter
should be worn during maintenance procedures of
X-ray diffraction devices.
• Dosimeters only monitor radiation but do not
protect from it!!!!!
Important Notes About
Dosimetry
• Due to the small cross sectional area of
the primary X-ray beam, ring badges may
not accurately record the maximum dose
received by the XRD user.
• Dosimeters should be exchanged every
quarter year.
• Wear only your own badge/ring.
General Precautions
•
•
•
•
•
•
•
•
Only trained personnel is permitted to operate an analytical X-ray 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 setup.
While the shutter is open DO NOT attempt to handle, manipulate or
adjust any object (sample, sample holder, collimator, etc.) which is in
the direct beam path.
Examine the system carefully for any system modifications or
irregularities.
Follow the operating procedures carefully. DO NOT take shortcuts!
Never leave the energized system unattended in an area where access
is not controlled.
Unauthorized repair or
modification
Do not remove shielding, or tube housing.
Do not modify shutters, collimators or
beam stops.
Individuals may not operate an XRD unit
in a manner inconsistent with SOPs and
safe operating standards.
Equipment Problems
If there are any questions or concerns about the
functioning of an XRD unit:
• Turn off the instrument immediately.
• Post a sign on the unit.
• Make a note in the log book.
• Report immediately to the unit supervisor.
Be aware that shutter mechanisms can fail.
Warning lights can fail.