UNIVERSITY OF CALIFORNIA, IRVINE
ENVIRONMENTAL HEALTH & SAFETY OFFICE
RADIATION SAFETY DIVISION
RADIATION AND ELECTRICAL
SAFETY SYLLABUS FOR NEW
USERS OF X-RAY MACHINES
UNIVERSITY OF CALIFORNIA, IRVINE
RADIATION SAFETY SYLLABUS (X-RAY MACHINES)
TABLE OF CONTENTS
Page #
I. DEFINITIONS: RADIATION 3
II. ATTENUATION OF X-RAYS IN MATTER 3
III. X-RAY DETECTION AND MEASURMENT 4
IV. RADIATION EXPOSURE AND DOSE UNITS 5
V. BIOLOGICAL EFFECTS OF IONIZING RADIATION 6
VI. METHODS TO MINIMIZE RADIATION EXPOSURE 8
VII. RADIATION DOSIMETRY 11
VIII. EXTERNAL RADIATION DOSE LIMITS 12
IX. GENERAL RADIATION SAFETY PROCEDURES 14
X. ELECTRICAL SAFETY 18
XI. MACHINE TYPE-SPECIFIC SAFETY PROCEDURES 22
XII. MOST COMMON CAUSES OF EXCESSIVE 24
RADIATION EXPOSURES
2
RADIATION SAFETY
I. DEFINITIONS: RADIATION
A. Radiation: The emission and transport or energy in the form of electromagnetic waves or high-energy
subatomic particles.
B. Ionizing Radiation: Radiation that contains enough energy to dislodge electrons from atoms.
C. Photon: Packet of electromagnetic radiation which contains a discreet quantity of energy. Photons
8
travel at the speed of light (3 x 10 m/sec). Radio waves, microwaves, infrared radiation, visible light,
ultraviolet radiation, x-rays and gamma rays are all forms of photon radiation.
D. X-rays: Penetrating photon radiation emitted during energy level transitions of orbital electrons, or by
the rapid deceleration of electrons as they traverse matter. X-rays are frequently produced for industrial,
research and medical applications by bombarding a metallic target with fast moving electrons under a
high vacuum.
E. Energy: The capacity to do work. The energy of an x-ray is the electromagnetic energy contained in
the x-ray photon. Such energies are frequently measured in units of electron volts (eV). One electron
-19 3 6
volt is equal to 1.602 x 10 joules. Note: 1 keV = 10 eV; 1 Mev = 10 eV.
F. Attenuation: The reduction in the quantity of radiation during its passage through matter resulting from
interactions with the matter.
G. Useful x-ray beam: That part of the x-ray radiation that passes through the machine aperture. This is the
radiation which is useful for conducting experiments, taking medical or dental x-rays, etc.
H. Leakage radiation: All radiation, except the useful beam, coming from an x-ray machine.
II. ATTENUATION OF X-RAYS IN MATTER
X-rays of the same energy are absorbed in an exponential manner:
-µx
I = I0e
3
where I0 is the original x-ray intensity, I is the x-ray intensity transmitted through an absorber of
thickness x, e is the base of the natural logarithm system, and µ is the slope of the absorption curve (the
-1
linear attenuation coefficient with units cm ). The linear attenuation coefficient is related to the half-
value layer (HVL), which is the thickness of a radiation absorbing material which will reduce the
photon (gamma ray or x-ray) intensity by 1/2, in the following way:
HVL = 0.693/µ
Inserting this expression into the equation above yields:
-(0.693x/HVL)
I = I0e
For a thickness of 2 HVLs, the photon intensity is reduced to 1/4 the original value. For a thickness of 3
HVLs, the photon intensity is reduced to 1/8 the original value, and so on. A shielding thickness of 7
HVLs is needed to reduce the photon intensity to less than 1% of the original value. This is a good rule
to remember when you need to determine the amount of shielding to use to properly attenuate x-ray
radiation.
III. X-RAY DETECTION AND MEASUREMENT
The basic requirement for a radiation detector is that the instrument’s detection medium interacts with
the radiation in such a manner that the magnitude of the response of the instrument is proportional to the
radiation property being measured. The instruments commonly used to detect x-rays are described
below.
A. Geiger-Mueller (GM) Counters:
GM counters are used to detect low levels of x-ray radiation, and they can often be used to provide
estimates of x-radiation dose rates, providing they have been properly calibrated for the energy of
the x-rays detected.
Major advantages of GM counters: Principle of operation very simple, relatively inexpensive, easy
to use, reasonably small in size, reliable, durable, and very versatile. Thin window GM counters are
very useful for locating leaks of x-rays through shielding, or from an experimental x-ray setup.
Major disadvantages of GM counters: Because any ionization event which occurs in the sensitive
volume of the detector produces a pulse of the same magnitude, a GM counter cannot be used to
measure radiation exposure directly.
4
The sensitivity of a GM counter is dependent upon the energy of the incident radiation in a non-
linear fashion. They are much less sensitive to radiation at very low photon energies (leading to an
under-response of the detector); however, the response of most GM counters is approximately linear
for photon energies above 100 keV.
Before each use, the batteries should be checked by the operator of the GM to ensure that they
have sufficient charge. Most GM counters have a simple battery test feature, generally in the form
of a button to press or incorporated into the range adjustment switch.
B. Ion Chambers:
Ion chambers are generally used to detect high levels of x-rays, and they are capable of measuring
radiation exposure and radiation exposure rates directly.
Principal advantages: Capable of measuring very high radiation levels. As was mentioned, ion
chambers can be used to directly quantify the magnitude of an ionizing radiation field.
Major disadvantages: Not useful in measuring the low radiation levels, except for a few specific
instruments which have electron multiplication in the sensitive volume of the detector.
IV. RADIATION EXPOSURE AND DOSE UNITS
A. Roentgen (R): Unit of radiation exposure. This unit is related to the number of ion pairs produced
by x-rays in air. The radiation exposure rate is generally measured in milliroentgens per hour (0.001
R/h). Most GM counters are scaled in units of mR/h. [Some are scaled in counts per minute.]
B. Rad (radiation absorbed dose): Unit of radiation dose. This unit is related to the quantity of energy
actually deposited in a medium (1 rad is equal to the deposition of 100 ergs of radiant energy per
gram of medium). It turns out that if air is exposed to 1 R of x-ray radiation, the equivalent energy
deposition in the air would be about 0.87 rad.
C. Rem: unit of radiation dose equivalent. The factor used for gauging the relative biological
effectiveness of a given type of radiation is known as the Quality Factor (QF). For x-rays, the
Quality Factor is equal to 1.
When the absorbed dose in rads is multiplied by the Quality Factor, the resulting value is the dose
equivalent expressed in rems. Thus,
dose equivalent (in rems) = dose (in rads) x QF (= 1 for x-rays) = dose (in rads)
5
Note: For simplicity, an x-ray radiation exposure of 1 R is assumed to be approximately equal to
a dose of 1 rad and a dose equivalent of 1 rem.
The radiation exposure/dose units above are the "traditional" units which have been used for
many decades. These units are still commonly used in the United States. However, a new system of
units [termed the Systeme International (SI)] was introduced in the early 1980s and has been
widely adopted, especially outside of the United States. When communicating with individuals from
other countries, SI units should always be used. The following two units are from that system.
D. Gray: The Gray (Gy) is equal to an absorbed dose of 1 joule of energy per kilogram of medium.
The relationship between the gray and the rad is as follows:
1 gray = 100 rads
E. Sievert: The Sievert (Sv) is a unit of radiation dose equivalent:
sieverts = dose (in grays) x QF
1 sievert = 100 rems
V. BIOLOGICAL EFFECTS OF IONIZING RADIATION
There are two types of exposure to ionizing radiation: a) acute exposure -- a single, often accidental
exposure to a high dose of radiation during a relatively short period of time, which may produce severe
biological effects very soon after exposure; and b) chronic exposure -- long-term exposure to a level of
radiation higher than the normal background level (which is on the order of about 150 mrem/y in
southern California), but much lower than that needed to produce acute effects. The observable
biological effects of chronic exposure, if they occur, may not be apparent until many years (often more
than 20 years) after the period of exposure.
Some of the major biological effects produced by acute exposures and chronic exposures to penetrating
forms of ionizing radiation such as x-rays are discussed below. [Less penetrating forms of radiation,
such as alpha and beta particles, primarily affect the skin (providing the emitting radioisotopes are not
inhaled or ingested), and do not produce many of the effects mentioned here.]
6
A. Acute effects:
Acute exposure of the human body to x-rays may affect all of the organs and systems of the body.
However, since the organs are not all equally sensitive to radiation, the pattern of response (disease
syndrome) of a severely over-exposed individual depends upon the magnitude of the dose received.
To simplify the classification process, the acute radiation syndrome is subdivided as follows:
1. Hemopoietic (blood system) syndrome
Changes in the blood cell count are the most sensitive biological indicators of acute
radiation exposure. Radiation doses on the order of 50-100 rads (rads ~ rems here) or more
damage the radiosensitive cells in the bone marrow and the lymphatic system, thereby producing
reductions in the numbers of certain blood cells (including white and red blood cells, and
platelets) in the circulatory system. The symptoms of this syndrome include anemia, fatigue,
some gastrointestinal effects, and an increased likelihood of infection.
Acute exposure of your body to x-radiation in quantities below about 500 rads will not
produce any immediate physical manifestations (headache, tingling, etc.). Therefore, you
cannot judge the safety of a particular radiation field on the basis of biological warning
sensations!!!
2. Gastrointestinal syndrome
Penetrating radiation doses on the order of 500-1000 rads produce severe effects on the
radiation-sensitive cells which line the stomach and intestines. All of the symptoms of the
hemopoietic syndrome occur, with the addition of severe nausea, vomiting and diarrhea
(sometimes bloody) which begin very soon after the radiation exposure. Secondary effects
include infection and nutritional impairment. Death within 1-2 weeks after the exposure is quite
possible.
3. Central nervous system syndrome
Radiation doses on the order of 2000 rads or more damage the less radiosensitive central nervous
system, as well as most of the other organ systems of the body. Extreme confusion, followed by
unconsciousness, is observed within minutes of the exposure, and death occurs in a matter of
hours to several days.
B. Chronic effects:
The following effects are possible for individuals exposed to moderate levels of radiation (much
higher than standard background levels) for extended periods of time (often many years), or for
those who survive acute high-level exposures to radiation:
1. Cancer (including leukemia)
Exposure to ionizing radiation has been found to increase the likelihood of developing cancer,
including bone cancer, skin cancer and leukemia, years (sometimes as many as 20 years!) after
the exposure.
7
2. Cataracts
Exposure of the eyes to ionizing radiation over an extended period of time may produce cataracts
(clouding of the lenses of the eyes). This occurs for types of radiation capable of penetrating
human tissue to a depth of about 0.3 cm – the depth of the lens of the eye; this includes x-
radiation.
3. Genetic effects
Radiation exposure of the DNA in human sperm or eggs, or of the cells which produce them,
may produce genetic damage leading to mutations. Consequences of this include the increased
likelihood of miscarriage or birth defects. Geneticists have estimated that the "doubling dose",
which is the dose of radiation that would eventually lead to a doubling of the mutation rate, is on
the order of 50-250 rads.
Considering the safety controls employed in laboratories in which x-ray machines are
used on the UC Irvine campus, the radiation safety training of x-ray machine operators,
and the results of radiation dosimetry monitoring of exposed individuals (very few
individuals receive detectable radiation doses while at UC Irvine), it is very unlikely that
anyone here will suffer any harmful biological effects from exposure to radiation,
providing that the proper radiation safety precautions continue to be followed!!!
C. Effects of skin exposure:
Because of its physical location (lining the exterior of the body), the skin is subjected to a higher
radiation exposure than other tissues, especially in the case of very low-energy x-rays. An acute skin
dose on the order of about 300 rem of low-energy x-rays can result in erythema (redness of the skin
due to inflammation, much like a sunburn). Higher skin doses might cause changes in pigmentation,
hair loss, blistering, ulcerations, and a predisposition to skin cancer. Chronic exposure to low levels
of x-rays can also lead to an increased likelihood of skin cancer later in life.
Inflammation of the skin due to exposure of the hands and face to x-rays was a common problem for
th
radiologists during the early 20 century.
VI. METHODS TO MIMIMIZE RADIATION EXPOSURE
The radiation produced by x-ray machines can be very dangerous, and this danger should not be
played down. On the other hand, there is no reason to be afraid to operate these machines after
receiving proper training and instructions, and implementing appropriate safety precautions.
8
A variety of safety devices are incorporated into x-ray machines, in accordance with regulations for
manufacturers of this equipment and EH&S requirements. However, the user should not depend too
heavily on these devices and fail to exercise due caution. If one of these safety devices should fail and
not be noticed, as serious injury can result. Adequate safeguards must be provided, but these can never
replace alertness to possible hazards. Proper training in the operation of x-ray machines needs to include
the nature of these hazards so that the user can be cognizant of them and be on the lookout for potential
problems.
The major goal of the Radiation Safety Division of the EH&S Office at UC Irvine is to ensure the
radiation exposures of the faculty, staff, students, visitors, and the general public are reduced to levels
which are as low as reasonably achievable (ALARA). The three primary means at our (and your)
disposal to reduce radiation exposures are discussed below:
A. Time: It is readily apparent that the less time one spends working with, or in the vicinity of, x-ray
machines, the lower will be the potential for radiation exposure. Therefore, it is recommended that
individuals working with x-ray machines only operate them as long as is necessary to perform the
needed procedures. When somebody else is operating the machine, if you don’t have to be nearby,
leave the area.
This does not mean that experiments should be performed in a hurried manner, since the
likelihood of accidents increases substantially in such cases. However, by following established
protocols, and seeking advice from other knowledgeable colleagues, it is possible to greatly improve
the efficiency of studies, and thereby reduce the radiation exposure time. Also, if individuals who are
performing the studies are concentrating on their work (as opposed to talking with friends, etc.),
experiments can be completed more quickly and efficiently.
B. Distance: The greater the distance between the researcher and the source of radiation, the lower will
be the radiation exposure. The x-ray intensity follows the inverse square law in that the radiation
exposure rate falls off as 1/d2, where d is the distance between the researcher and the radiation
source. If you double your distance from an x-ray source, the radiation intensity falls to one-fourth of
the original value!
C. Shielding: One of the easiest means of protecting laboratory personnel from radiation exposure (for
radiation sources located outside of the body) is to place appropriate shielding between the
researcher and the radiation source. Due to its high density (11.3 grams/cm³), lead is an ideal
material for shielding against high-energy photon radiation such as x-rays (and also gamma rays).
However, for low-energy x-rays, less dense materials (aluminum, safety glass, leaded glass, even
wood) are sometimes used.
Shielding for protection against x-rays falls into two categories:
1. Source shielding
Source shielding is usually supplied by the manufacturer of the x-ray machine as a lead shield
within which the x-ray tube is housed. It is needed to protect against leakage radiation, which is
all radiation except the useful beam coming from the tube housing.
9
2. Structural shielding
Structural shielding is designed to protect against the useful x-rays, leakage radiation, and
scattered radiation (scattered by materials within the x-ray beam). It encloses both the x-ray tube
and the space in which the object being irradiated is located. This shielding may be in the form
of a lead-lined box in the case of an x-ray tube used by a biologist to irradiate small organisms,
or it may be shielding in the walls of a room in which x-ray procedures are performed. In any
event, structural shielding is used to protect people in occupied areas outside of an area of high
intensity x-radiation.
In some cases only the x-ray machine itself is shielded. In other cases, it is necessary to
incorporate lead shielding into walls, floors and ceilings of facilities.
The wavelengths of the x-rays used most commonly in x-ray diffraction fall in the range from
-9
approximately 0.05 nm (1 nm = 10 m) to 1 nm, corresponding to an energy range of 1keV up to
20 keV. These are so-called “soft” x-rays which are readily absorbed in matter. A thickness of
only several millimeters or less of aluminum, iron or lead is required to reduce the intensity of
the transmitted beam to 1/10 that of the initial intensity.
Research facilities in which medical-type or dental-type x-ray machines are housed will often
require more shielding than x-ray diffraction facilities, since higher energy x-rays are often
generated (up to hundreds of keV). In such cases, up to an inch or more of lead shielding is often
used.
The half-value layers (HVL) and tenth-value layers (TVL - quantity of structural shielding
required to reduce the intensity of an x-ray beam to 10% of its initial value) of lead are listed
below for commonly used x-ray tube kilovolt potentials (kVp). Normally, at least a TVL of
shielding would be required for the walls of an x-ray facility, depending upon the factors listed
above. Source shielding is, of course, considerably thicker!!!
X-RAY HALF-VALUE AND TENTH-VALUE LAYERS
(Millimeters of lead shielding)
Max. kV HVL TVL
50 0.06 0.17
70 0.17 0.52
100 0.27 0.88
125 0.28 0.93
150 0.30 0.99
200 0.52 1.7
250 0.88 2.9
10
VII. RADIATION DOSIMETRY
Radiation dosimeters are devices which are capable of measuring an accumulated absorbed dose of
ionizing radiation. Dosimeters are distributed by the EH&S Office to all individuals on campus
who have a reasonable likelihood of receiving measurable doses, including all individuals who work
with x-ray machines.
There are several types of dosimeters used on the UC Irvine campus:
A. Film badges:
A film badge consists of a packet of dental-sized film wrapped in light-tight paper and worn in a
plastic holder. Depending upon the type(s) of film used, film badges are capable of quantifying doses
due to high-energy beta particles, x-rays, gamma-rays, and neutrons.
Film badges are often used to measure the deep dose equivalent (DDE – for exposure of the body to
penetrating radiation [measured at a depth of 1 cm of tissue]) and the shallow dose equivalent (SDE –
for skin exposure to less penetrating radiation [measured at a depth of 0.007 cm of tissue]). They are
normally worn on the front of the body, somewhere between the waist and the neck.
Film badges must be stored well away from sources of radiation when they are not being worn, since a
film badge is intended to measure the dose to the person to whom it is assigned, and it must not be
exposed to radiation when he/she is not being exposed. Film badges are usually issued for month-long
periods only, since the darkened images tend to fade if they are worn for longer durations.
B. Thermoluminescent dosimeter (TLD) badges and rings:
Many crystals emit light if they are heated after having been exposed to radiation. Therefore, they are
called thermoluminescent (heat – light) crystals. Absorption of energy from the radiation excites the
electrons in atoms in the crystal lattice. Heating the crystal releases the excitation energy as light. The
total amount of light emitted is proportional to the number of excited electrons, which is in turn
proportional to the dose of ionizing radiation received.
Thermoluminescent dosimeters respond to high-energy beta particles, protons, x-rays, and gamma-rays.
Due to their small size, they are often used in dosimeter rings that are intended to measure the
shallow dose equivalent (SDE) to the hands and fingers. TLD rings should always be on the hand
which is more likely to receive the greater dose. TLD body badges are also assigned, when appropriate.
TLD ring and body badges are generally issued for 3 month periods, since the crystals retain the stored
radiation dose information for that long without any significant losses.
11
Note: Radiation dosimeters assigned at UC Irvine must only be used on the UC Irvine campus.
They are not to be worn at other facilities (including the UC Irvine Medical Center, which has its own
dosimetry program). In addition, dosimeters may only be worn by the person to whom they are
assigned (the person whose name is stamped or written on the dosimeter). Never intentionally expose
your dosimeters to radiation fields just to see if they work!! Since dosimetry results constitute legal
records, such actions cause serious problems for you and the University. Make sure that nothing (such
as a liquid) is spilled onto the dosimeters, and that they are not exposed to extremes in temperature.
Remember that a recorded radiation dose for a dosimeter assigned to you will be considered an exposure
to you, even if you have not been wearing it. Store your dosimetry well away from areas in which
radiation sources, such as x-ray machines, are present!!!
VIII. EXTERNAL RADIATION DOSE LIMITS
The U.S. government and the California Department of Health Services (DHS) have established external
radiation dose limits which may not be exceeded under most circumstances (some provisions for higher
doses during extreme radiation-related emergencies are also written into the regulations). In an effort to
reduce all radiation exposures to levels as low as reasonably achievable (ALARA), the UC Irvine
campus’ administrative guidelines have been set at levels equivalent to 10% of the legal limits for
adults and 20% for minors. A brief, simplified listing of the legal limits and the associated UC Irvine
guidelines is provided below. More detailed information can be found in the UC Irvine Radiation Safety
Manual.
DOSE EQUIVALENT LIMITS FOR ADULTS
Federal/State Campus
Dose Equivalent Measured Legal Limit Guideline
Category Using (rems/year) (rems/year)
Total effective* Body badge 5 0.5
Shallow (skin) Body badge 50 5
Shallow (hands/fingers) TLD ring 50 5
12
DOSE EQUIVALENT LIMITS FOR MINORS (<18 years of age)
Federal/State Campus
Dose Equivalent Measured Legal Limit Guideline
Category Using (rems/year) (rems/year)
Total effective* Body badge 0.5 0.1
Shallow (skin) Body badge 5 1
Shallow (hands/fingers) TLD ring 5 1
Body badges can be either film badges or TLD badges. For x-ray users who do not have any intakes of
radioactive materials into their body by ingestion or inhalation, the total effective dose equivalent is the
deep dose equivalent from radiation which can penetrate 1 cm of tissue.
In addition, dose limits and guidelines have also been established which are related to the exposure of
the embryo/fetus of a Declared Pregnant Woman. A woman who becomes pregnant (and who works
with radioisotopes or a radiation-producing machine on campus) needs to inform the UC Irvine
Radiation Safety Officer, in writing, of her pregnant status and the estimated date of conception in order
to become a Declared Pregnant Woman. This would ensure that all necessary precautions are followed
for the protection of her developing embryo/fetus. Briefly stated, women in this category may only
receive on the order of 10% of the body radiation dose allowed for other adults (i.e., the UC Irvine
guideline dose would be 0.05 rem during the pregnancy); skin and hand dose limits and guidelines are
not affected.
Before starting to work with an x-ray machine, all women of child-bearing age are required to be
instructed regarding the risks attendant to prenatal exposure to radiation. Refer to the policy on
“Prenatal Radiation Exposure” (available from EH&S) for more information on this subject.
It must be noted that substantial safety factors are incorporated into the dose limits/guidelines
given above. For example, the legal limit body dose for an adult is 5 rem/year. Even if an adult
received this dose from a single (acute) exposure to penetrating x-ray radiation, he/she would not
demonstrate any clinically/medically-observable effects. In fact, it would normally take an acute body
dose of about 100 rems (~ 100 rads) to produce observable effects on the human body (in this case,
effects on the blood cell-forming system, perhaps leading to an increased susceptibility to certain
illnesses).
If you should receive a radiation dose greater than the federal/state legal limit, you will be
required to discontinue your use of x-rays for the remainder of the calendar year. If you receive a
lower, but still substantial, dose (perhaps on the order of 100 mrem or more), an EH&S Health
Physicist will contact you and your Responsible Principal Investigator to determine how the
elevated dose occurred, and how to avoid such doses in the future (additional shielding, etc.)
13
IX. GENERAL RADIATION SAFETY PROCEDURES FOR RESEARCH LABORATORIES WITH
X-RAY MACHINES
There are many laboratories on campus in which x-ray machines are used in research studies.
It is the responsibility of the EH&S Office, the Responsible Principal Investigators in the
laboratories, and the persons involved in the studies to make sure that they are used safely. This is
not a difficult task, as long as the campus’ radiation safety rules, regulations and recommendations are
understood and followed.
An introduction to some of the basic x-ray safety procedures which should be used in research
laboratories is provided below. More information can be obtained in the UC Irvine Radiation Safety
Manual.
A. Radiation Use Authorizations (RUAs): Responsible Principal Investigators (RPIs) on the UC
Irvine campus may apply for the authorization to use x-ray machines by applying to the UC Irvine
Radiation Safety Committee (through the EH&S Office) for a Radiation Use Authorization (RUA).
[RUAs are only valid for research conducted on the UC Irvine campus; UC Irvine Medical Center
has its own radiation safety program]. The following information must be included in an RUA
application:
1. Description of machine (type of machine, manufacturer, model number, serial number, year
of manufacture, and maximum operating parameters {kVp, mA}).
2. Operating protocol and typical operating parameters. Provisions for “use log book”
(and routine radiation safety monitoring).
Use logs are valuable resources with regards to determining how elevated radiation
exposure incidents occurred. Entries in this log book must reflect the user’s name, the
date of use, the procedure performed, operating parameters, dates of safety checks of
safety devices, and information related to functional checks and inspections, radiation
surveys, findings, corrective actions taken, and emergency notification. Daily entries
must be made for each operation of the x-ray equipment. If operating parameters are
to change, EH&S must be notified before the equipment is operated with the new
parameters!
3. Health and safety provisions such as shielding, interlocks, and access control.
14
All x-ray generating equipment must have operational interlocks (except for unenclosed
medical machines, etc.), activation (x-ray on) indicators, and a keyed switch that controls the
main power to the x-ray generator. Access to this key must be controlled!
An RUA gives the Responsible Principal Investigator approval to use specified x-ray
machines in particular experiments performed by authorized, trained individuals in
specific locations (rooms), while taking specified radiation safety precautions. The
authorization to use radioisotopes is not implied by the authorization to use an x-ray
machine!!! Deviations from the conditions spelled out on the RUA are not allowed unless
EH&S is first notified and the Radiation Safety Committee approves the changes. All
correspondence related to an RUA must include the name of the RPI.
A. Radiation safety training: All individuals who will be working with x-ray machines or other
ionizing radiation-producing machines on the UC Irvine campus must be trained in the related safety
procedures. Prior to starting the work, such individuals must come over to the EH&S Office at
specific times (on a Monday or Tuesday morning at 10 am; or on a Thursday or Friday afternoon at
2 pm – one day only!) to complete an open-book quiz (based in part on this Syllabus), and to fill out
the necessary paperwork.
In order to document that all individuals are adequately trained in the safety aspects related to the
specific procedures that they will be performing in the course of their research studies, all
individuals who will be working with ionizing radiation sources must complete, in conjunction with
their Responsible Principal Investigator, an On-the Job Training Form. The form must then be
returned to the EH&S Office.
B. Security: Rooms in which x-ray machines are stored must not be left unlocked and unattended.
At least one authorized individual (listed on the RUA) must be present in such rooms at all times that
the rooms are unlocked. Alternatively, the machines may be securely locked.
C. Posting and labeling: Each door to a room in which an x-ray machine is located must be labeled
with a sign which reads “Caution -- X-rays” in order to alert personnel that they are entering a room
in which exposure to radiation is possible.
All x-ray machines must be prominently labeled (“This equipment produces radiation when
energized”). In most cases, an additional warning device (visual or audible) which indicates when
radiation is being produced is required. The operating protocol for the machine needs to be
prominently posted near it.
D. Dosimetry: In order to monitor the exposure of personnel working with x-ray machines, radiation
dosimetry is distributed to individuals who have a reasonable likelihood of receiving measurable
doses. [Those operating cabinet-type machines generally do not need dosimetry.]
When the UC Irvine Radiation Safety Committee requires dosimetry for operation of an x-ray
machine, all personnel must wear an appropriate dosimeter whenever they work with or near the
operating machine. Remember that dosimeters not in use must be stored away from the machine in
an area where they will not be exposed to radiation.
All dosimeters are individually assigned. Use by someone else would make individual dose
assignment impossible. Dosimeters must be exchanged at required times (at the beginning of
15
the month for every third month, in most cases) to facilitate timely EH&S follow-up of rare
high measured doses. Film badges are exchanged monthly.
Body dosimeter badges should be worn on the chest, belt, or collar; TLD rings should be worn on
the index finger with the label on the palm side of the hand most likely to be exposed to radiation.
It should be remembered that a low-energy x-ray beam can be substantially attenuated while passing
through a hand or finger.
A personnel dosimeter must never be intentionally irradiated. The resulting dose may be
credited to the person to whom the dosimeter is assigned, resulting in a needless investigation, a
medical examination for the “exposed” individual, and possible work restrictions.
E. Safety devices (interlocks, etc.): Certain safety devices for x-ray machines are required by state
and federal agencies. Examples are warning lights, beam enclosures, interlocks, and shielding
(usually lead). All safety devices must be maintained in good working order, and must not be
replaced or modified without EH&S approval.
Note: An interlock is a device for precluding access to an area of radiation hazard by
either preventing entry or by terminating the hazard (in the case of x-ray machines, this would
involve stopping the production of x-rays) if the enclosure is opened.
No safety device is absolutely fail-safe or foolproof, and none is more important than the use of
caution and common sense.
If a key is provided to bypass an interlock, access to that key must be carefully restricted
to prevent routine use of the interlock bypass.
A safety device must never be intentionally defeated without very good reasons and without
notifying EH&S in advance! If the design of a device makes a certain desired operation
inconvenient or impossible, another device affording the same measure of protection must be
substituted and approved by EH&S prior to operation. High radiation exposures have occurred when
one person has tampered with a safety device, while the next user relied upon it. If a required safety
device becomes nonfunctional, the machine must not be operated until it is repaired and
subsequently checked by EH&S.
G. Machine location: An x-ray machine needs to be located in an area that is not in the main traffic
pattern of the laboratory or near other commonly-occupied work areas. A room devoted solely to the
machine is desirable, since it may be locked when not in use or during unattended operation.
The machine must be situated so that scattered radiation or stray beams will be directed away from
the operator and toward an unoccupied area, preferably towards an outside wall. Any change in the
location of an x-ray machine must have prior approval by EH&S.
H. Radiation monitoring: When required by an RUA, an appropriate radiation survey meter (GM
counter, ion chamber) must be available for use when an x-ray machine is operated. Since many
machines emit low-energy x-rays, a thin-window probe is usually required. Metal-window probes will
not respond adequately to x-rays with energies of less than 50 keV. The probe should be small enough
16
to fit into cramped areas without disturbing delicate machinery. EH&S can recommend appropriate
survey meters for specific applications.
Personnel must be adequately trained in the operation of radiation monitoring equipment. X-ray
machines should be routinely monitored to assure that shielding, interlocks, seals, etc., are in
good working order. Whenever a procedure or system parameter is changed, the unit should be
monitored. Listen to your intuition!! If something seems to be different or wrong regarding the
operation of a machine, make sure that the matter is thoroughly investigated to ensure that everything
is functioning as it should be.
Any significant increase in radiation level, or discovery of significant scattered radiation in an
accessible area, must be immediately reported to EH&S. [EH&S generally monitors x-ray
machines on an annual basis.]
After any repairs or modification of an x-ray machine interlock or shielding, EH&S must be consulted
before operation is resumed. A radiation safety survey may be required by EH&S before operations
can resume.
I. Safe operating procedures: An appropriate x-ray machine operating procedure is well thought-out,
and makes use of installed safety devices and radiation safe techniques. In a research situation, new
personnel and experimental procedures are constantly being introduced. Each operator (in
consultation with the Responsible Principal Investigator) must carefully analyze and plan new
procedures prior to performing them. Written operating and safety instructions are required.
Before using an x-ray machine, personnel must be familiar with campus requirements for the machines
they will be operating. EH&S should be used as a resource for explanation of regulations and advice
regarding the safety of the new procedures planned.
J. Radiation exposure incidents: If you know or suspect that you or a co-worker has been exposed to a
high level of radiation, notify the EH&S Office as soon as possible.
Note: When serious incidents occur after-hours or on weekends, call the campus police
(x911, 949-824-5222 from a cell phone), who will in turn call appropriate EH&S personnel at
their homes.
The procedure performed and the machine parameters and configuration during the incident must be
carefully noted and preserved so that the scenario can be recreated later with radiation measuring
devices in place.
In the case of a highly-collimated x-ray beam, personnel dosimeters may not give an accurate account
of the maximum radiation dose to the affected area of the body. Hand dosimetry (TLD ring badge),
however, can give a good indication of whether or not an exposure to the beam has occurred.
Therefore, it is important to give the dosimetry to EH&S for immediate processing if an elevated
exposure is suspected. Prompt notification may prevent additional over-exposures.
17
X. ELECTRICAL SAFETY
Since x-ray machines are equipped with high voltage power supplies, considerable care must be
taken during the operation, maintenance and repair of these machines in order to prevent
electrical shock, which can have lethal consequences. In addition, faulty electrical equipment and
wiring can cause serious fires.
Although campus records do not indicate that electrical shock is a major cause of injury on the campus,
it is nonetheless common knowledge that people receive small shocks in the course of their work with
electrical equipment. People who have been accustomed to working with this equipment for long
periods of time sometimes become willing to take what seems to be a small chance of electrical shock.
It should not take a serious accident to make everybody aware of the high potential risk to life and
property caused by electric current!
The physiological responses to electrical shock, as a function of current, are described below (AC =
alternating current; DC = direct current):
Current in Milliamperes Physiological Effect
2 (AC), or 10 (DC) Threshold of sensation; a strong
tingling
10 (AC), or 60 (DC) Let go current, above which one
freezes due to muscular contraction;
a very painful and hazardous shock
100 (AC), or 500 (DC) Death due to heart fibrillation and
paralysis of breathing
Equipment and circuits operating at 25 volts or less under normal conditions present a negligible shock
hazard. However, the current passing through the body is the key factor in any electrical shock, not
voltage per se, although the voltage does provide the driving electrical potential.
Most of the over 1000 electric shock fatalities which occur in the U.S. every year are due to problems
with low voltage equipment, and therefore, it is imperative that respect be given to low voltage
equipment and circuits, as well, and that adequate precautions be taken regardless of voltage.
18
A. Electrical Safety Precautions:
There are a number of safety precautions which must be observed when working with, or around,
electrical equipment. Included among these are:
3
The typical resistance of the human body is on the order of 10 ohms. Keep your body’s resistance high
by making sure your hands and feet are dry when working with electrical equipment. Never handle
electrical equipment when your hands, feet or body are wet (due to perspiration, blood, etc.), or
when standing on a wet floor, or working at a sink.
Shoes must be worn in the laboratory (rubber-soled shoes are preferable). Regard all floors as
conductive and grounded unless they are covered with well-maintained, dry rubber mats of a type
suitable for electrical work.
The removal of jewelry (rings, etc.) and watches is strongly recommended when working with
electrical or mechanical equipment.
Know the location of all circuit breakers and off-switches on all equipment. Assume all electronic items
are potentially lethal. Kill the power and pull the plug before working on electrical equipment.
Permanent equipment cannot be cord-connected, but must be hard-wired with a clearly labeled lock-out
safety switch installed at the device, or a clearly labeled quick-disconnect safety switch panel with lock-
out located within sight.
There must be a minimum of 75 cm of clearance between a switch panel and any nonconductive object,
and a minimum of 105 cm clearance to any grounded object. Keep storage and furnishings away from
these panels. Allow sufficient work space between equipment items to provide for adequate isolation.
Report all electrical shock incidents and defective equipment. A shock means something is wrong!
The slightest shock when operating an electrical appliance in one situation might, in another situation,
result in instant death or serious injury if conditions change (more of the body in contact, your body
better grounded, hands wet, etc.).
The Golden Rule of Electrical Safety is: Rely on qualified electrical technicians to perform
repairs, and consult Facilities Management or EH&S when in doubt. Discourage “do-it-yourself”
wiring.
Never overload electrical circuits!
Capacitors rated as low as the microfarad range are capable of delivering painful shocks.
If an electrical component burns out and releases smoke or noxious gases, the room must be well
ventilated immediately, since the compounds released may be toxic.
Be certain that all high voltage x-ray equipment is grounded, and that all live studs, power units, etc.,
(i.e., anything “hot”) are protected, preferably via completely grounded enclosures with interlocks to
disconnect the electric power and ground the high voltage when the enclosure is opened.
19
An effort should be made to provide interlock protection for all live circuits within cabinetry. Do not
defeat the safety interlocks on the equipment. Operations, including tests, should be conducted
remotely from outside the interlocked enclosure. Equipment must be designed to preclude live male
connectors, wires, terminals, or studs which are open to the touch. Be certain capacitor banks and
other sources of high voltage are grounded before hooking up components, replacing fuses, etc.
Caution signs to warn of hazards are helpful, but alone are not considered to be reasonable protection.
Never take the attitude that nobody is brazen or “dumb” enough to enter the lab and proceed to touch a
hot line or stud. Hazards must be physically isolated from persons who may inadvertently,
unknowingly, or casually encounter live current.
Power driven appliances, metal laboratory equipment (even metal table lamps), and plastic or other non-
conductive items having exposed metal parts are required to be grounded. Check for 3-wire cords and
3-pronged plugs. Basic exceptions to the requirement for electrical grounding exist for devices utilizing
a Cal-Rod and for double insulated plastic cases approved by U.L.
Frequently inspect all electrical cords, and replace those that are frayed or damaged. Use the proper cord
for the particular appliance or equipment. Two-wire extension cords and adaptor plugs are not
permitted, since equipment is not grounded when connected to them. Such devices merely fault the
grounds that are provided with the equipment. Pig-tail grounds on two-prong plugs are not
acceptable. Plugs on cord-connected equipment must conform to the National Electrical
Manufacturers’ Association (NEMA) configuration for applicable voltage and ampere ratings.
Extension cords should be short (2 m maximum length), limited to temporary use, and should never
cross frequently-traveled pathways unless suitably protected to avoid damage and the creation of
tripping hazards. Never tack cords to the walls, etc., and keep cords away from pinch-points and hot or
wet surfaces. Never string cords across the ceiling, over water pipes, or near sinks, and never place
cords and plugs under physical stress or tension. Check the area on the cord where it joins the plug or
device for proper installation and any evidence of wear.
“Octopus” electrical plug connections, such as cube taps, invite trouble and are not acceptable.
Power bars must be compatible with the circuit load being used, be U.L. approved, and be individually
fused. Usually the EH&S Office will request that additional outlets be installed within the room instead
of resorting to the use of power bars. Power bars must never be “ ganged” (one bar plugged into another
bar)!
Provide clear instructions on the hazards and safe use of electrical equipment, have wiring diagrams
available, provide adequate space for installation, clearly identify terminals, circuits, and controls, and
maintain the equipment well. Design and direction of operation of all controls must be uniform, with
“off” and “on” switches clearly marked.
Test probes must only be used by qualified individuals, and such probes must be entirely insulated
and have recessed or short tips. Equipment must be tested before being made operational.
Only double or triple-pole switches which disengage all power lines should be used. Safety switches or
unit circuit breakers that disconnect all lines must also provide for locking in the “off” position so that
no one can inadvertently energize the system or equipment with which another person is working.
20
B. Preparation for electrical health-related emergencies:
The following safety guidelines related to electrical hazards must be followed when working with high-
voltage x-ray equipment:
Use the buddy system (have another person present) when working with high voltage
equipment, especially outside of normal working hours or in isolated areas. Remember that
only trained, experienced personnel are to service such equipment.
Do not perform electrical work when you are fatigued or hungry, or when under the influence of
medications which may cause disorientation or drowsiness (antihistamines, etc.).
Do not work when your mental attitude, whether through emotional or chemical stimulus, would
induce risk-taking.
All personnel working with high voltage and/or high current sources should be trained in
CPR, and a CPR instruction chart should be conspicuously posted. Contact EH&S ( 949-824-
6200) for more information.
Make sure that you understand all operational safety precautions. Query your supervisor.
Read the safety section of the manual for the x-ray equipment. Be familiar with the RPI’s
safety requirements. Post instructions and frequently review procedures and improve them,
when indicated.
Study the manuals supplied by the manufactures of the equipment being installed or used, and do not
deviate from the instructions regarding the safe use of the equipment without first contacting the
manufacturer.
Make sure that a fire extinguisher suitable for fighting electrical fires is immediately available
for use. Most extinguishers on the UC Irvine campus are designated as “ABC” extinguishers,
with the “C” indicating the appropriateness of the device for fighting electrical fires. Never
use water to fight such a fire!!!
C. Response to health emergencies:
Learn rescue procedures for helping victims of apparent electrocution: Kill the circuit, if
possible; remove the victim with a non-conductor if he/she is still in contact with an energized
circuit; initiate cardiopulmonary resuscitation (CPR) immediately, and continue until relieved by
emergency medical personnel; have someone call for emergency assistance as soon as possible after
discovering the medical emergency ( x 911 from a campus phone, or 949-824-5222 from a cell
phone).
Note: Only individuals trained in CPR should administer it!! It is possible that well-intentioned
but untrained individuals may actually do more harm than good by attempting the procedure (in
some cases, injured people have had their ribs broken by the pounding of over-zealous first
responders!!!
21
XI. MACHINE TYPE-SPECIFIC SAFETY PROCEDURES
A. X-ray diffraction/fluorescence machines:
X-ray diffraction machines, which usually have tube voltages ranging from 25 to 50 kV, put out a
highly-collimated x-ray beam with characteristic peaks from 5 to 17 keV. The primary beam
constitutes the most hazardous radiation, often capable of producing an exposure rate on the order of
5
10 rems/minute near the port.
After the beam passes through an open area and strikes the sample to be irradiated (the crystal, etc.),
the diffracted radiation is scattered in a characteristic manner (which is a function of the crystal
structure) at particular angles with intensities of up to 100 rems/h. The diffraction pattern is
measured with a radiation detector or photographic film. General scattering of the primary beam off
structures such as the sample holder, beam stop, etc., may be as high as 10 rems/h.
In the case of operation of the machine in the x-ray fluorescence mode, the primary x-ray beam
strikes the sample inside of a shielded enclosure, and only scattered (as opposed to diffracted)
radiation and secondary radiation excited in the sample as a result of the irradiation emerges from
the machine for analysis. Consequently, external radiation levels are usually much lower in the
fluorescence mode than in the x-ray diffraction mode.
Several types of radiation warning systems, which indicate whether the x-ray tube is activated and if
the shutters are open, are required. Usually the machine must be enclosed inside an interlocked
chamber, although some operations may be permitted with an accessible beam. A beam stop, which
is designed to block the path of the primary beam, must always be in place, and should be located as
close to the port as possible. Lead-glass windows on alignment ports should always be double
checked to make sure they are in place. In fact, it is recommended that regular maintenance checks
be performed to ensure that all safety devices are in proper working order.
Whenever the area of the beam path must be entered, the operator must do more than check warning
lights or rely on interlocks. The power must be turned off, and the system lockout (power, or
“on/off) key removed. The voltage and current indicators must be checked each time. An open-
beam system must never be left unattended. Never trust automatic shutters or beam enclosure
interlocks. It is recommended that the beam enclosure be in place at all times when the tube is on,
and that in certain cases glasses be worn during operation in some cases (even ordinary lenses can
attenuate low-energy x-rays by a factor of 5-10).
Whenever an x-ray system is modified or realigned, radiation scatter needs to be checked with a
radiation survey meter. Leakage from the side of the shutter-collimator area is common and is
usually directed toward the operator. Wide beam collimators are especially prone to scatter. The
tops of goniometers usually need shielding; EH&S can assist in determining the necessary quantity
of shielding. TLD finger dosimeters are required for all operators.
22
B. Cabinet x-ray machines:
A cabinet x-ray machine usually employs a wide beam of x-rays inside a shielded, interlocked box.
Tube potentials of up to 150 kV are used. Radiation exposure levels inside the enclosure may be as
4
high as 10 rems/minute at 30 cm from the tube over a wide arc. Scatter is not normally a problem,
since the enclosure must limit outside radiation levels to less than 0.5 mrem/h at 5 cm from the
exterior surface of the enclosure.
Fail-safe indicators are used to indicate when the x-rays are being produced, and the entry door must
be interlocked. When changing samples, the tube power must be turned off, and the system lockout
key removed. Voltage and current meters must be monitored prior to opening the door. Never rely
solely on the door interlock to inactivate the tube. A survey meter with its audio speaker left on
near the door will serve as a back-up warning device. Dosimetry is not generally required.
X-ray systems designed for inspection of carry-on baggage at airports are examples of cabinet-
type x-ray machines.
C. Electron microscopes:
X-ray tubes in transmission electron microscopes usually operate at potentials of around 100 kV.
The route of personnel radiation exposure (although extremely rare) is usually by way of x-ray
leakage caused by improper beam alignment, poor shielding design, or improperly maintained
equipment. The leakage usually occurs near the electron gun, but can also occur at the specimen
chamber and viewing chamber.
High-voltage power supplies can also emit radiation if they are improperly shielded. Levels of up to
100 mrems/h have been measured on campus, and higher levels are possible. Built-in shielding,
lead-glass ports, and other protective devices must not be removed.
If there is to be a special mode of operation which may increase beam size, EH&S must be notified
so that a radiation survey may be made.
Dosimeters are not normally issued to electron microscopists, since most modern machines have
demonstrated no leakage on routine surveys.
Microscopes not capable of tube potentials greater than 30 kV, such as scanning scopes, do not
present a radiation hazard, since the x-rays cannot penetrate the housing.
D. Medical x-ray machines used in research:
Requirements for x-ray machines used in research are presented in the handbook entitled “California
Radiation Control Regulations,” which is essentially a reproduction of Title 17 of the California
Administrative Code.
23
Doses for typical medical-type radiographic x-ray machines range between 10 mrem up to more
than 1 rem per exam. Scatter doses are around 1 mrem per exposure at 30 cm from the beam.
Normally the system operator will be behind a lead-lined shield during exposures. If not, a lead
apron must be worn. Lead sheets or aprons must be used to reduce unnecessary exposure to the
patient. The beam must be collimated to restrict exposures to the area of clinical interest.
Fluoroscopy dose rates of up to 10 rem/min in the beam are possible. Scatter to the operator can be
several hundred millirem per hour. The operator must wear a lead-lined apron, lead-lined gloves,
and may use other shielding devices to protect himself/herself and the patient. Body dosimeter
badges must be worn on the outside of the aprons by all operators.
Rooms that house medical-type x-ray machines must be shielded according to State requirements.
All operators of x-ray equipment must wear body dosimeter badges.
If an x-ray machine is modified in any way, EH&S must be notified so that a radiation survey
can be conducted to ensure safety.
E. Other x-radiation-generating machines:
Any high-voltage generator operating in excess of 15 kV may leak x-rays. Examples of such
machines on campus are ion-implant machines, some high power lasers, Van de Graaff accelerators,
and projection television units. EH&S should be contacted if there is concern that such a piece of
equipment may be leaking x-radiation, thus exposing personnel. EH&S can perform a radiation
survey, assign dosimetry, and require special precautions, when necessary.
X-ray generating devices used in plasma physics research often emit x-rays in very short pulses,
usually with minutes or hours, or in some cases weeks or months, between pulses. Personnel in the
vicinity of these machines can usually stand behind shielding or be evacuated from the general area
during each pulse. Electrical circuits and equipment associated with most of these devices can be
very hazardous.
XII. MOST COMMON CAUSES OF EXCESSIVE RADIATION EXPOSURES
The most common causes of excessive radiation exposures of operators of x-ray machines are:
1. Safety precautions not followed (interlocks defeated, protective housing removed, etc.).
2. Chatting, thinking about other matters; carelessness; fatigue.
24
3. Failure to follow procedures as described by the Responsible Principal Investigator (taking
inappropriate shortcuts).
4. Failure to properly train new personnel.
5. Failure to anticipate possible accidents before they occur, and to take steps up-front in
order to avoid them.
Remember that the use of x-ray machines is very safe as long as appropriate
precautions are taken, and common sense is used. Biohazardous agents and certain chemicals
used on the UC Irvine campus present much more substantial health risks to the personnel
handling them than do the x-ray machines properly used on the UC Irvine campus.
If you have any questions related to the safe operation of x-ray machines, please contact
EH&S at 949-824-6098 or 949-824-6904.
25