X‐RAY RADIATION SAFETY Operator Training Manual Bruker

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OperatorTrainingManual

X‐RAYRADIATIONSAFETY

030.0011.03.2

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1. Training Objectives ............................................................................................................... 3

2. What is Radiation? ................................................................................................................ 3

3. Radiation Terminology .......................................................................................................... 3

4. Types of Radiation ................................................................................................................ 5

4.1. Non-ionizing Radiation ................................................................................................ 5

4.2. Ionizing Radiation ........................................................................................................ 5

4.3. Penetration .................................................................................................................. 6

5. Units for Measuring Radiation .............................................................................................. 6

5.1. Rad (Radiation Absorbed Dose) .................................................................................. 6

5.2. Rem ............................................................................................................................. 6

5.3. Dose and Dose Rate..................................................................................................... 7

6. Significant Doses ................................................................................................................... 7

7. Biological Effects of Radiation ............................................................................................... 8

7.1. Cell Sensitivity.............................................................................................................. 8

7.2. Acute and Chronic Doses of Radiation ........................................................................ 8

7.3. Biological Damage Factors......................................................................................... 10

8. Putting Risks in Perspective ................................................................................................ 10

8.1. Risk Comparison ........................................................................................................ 10

8.2. Radiation Dose Limits ................................................................................................ 11

8.2.1. Declared Pregnant Worker ............................................................................... 12

9. Measuring Radiation ........................................................................................................... 12

9.1. Dosimeters ................................................................................................................ 13

9.2. Survey Meters ........................................................................................................... 13

10. Exposure Reduction (ALARA) .............................................................................................. 15

11. Production of X-Ray Radiation ............................................................................................ 17

12. Radiation Exposure Potential .............................................................................................. 19

13. Rights and Responsibilities ................................................................................................. 20

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1. Training Objectives

 Describe occupation radiation worker rights and responsibilities

 Describe Ionizing Radiation

 Describe the nature and properties of X-Ray radiation and its associated hazards

 Describe how X-Rays are produced

 Describe the biological effects of exposure to X-Rays

 Describe the X-Ray exposure potential of the Bruker Handheld XRF Analyzer

 Identify and describe personnel monitoring devices

 Identify and describe radiation survey instruments

 Describe the principles of radiation protection and ALARA

 Describe the designed safety features in the Bruker Handheld XRF Analyzer

 Describe the proper operating procedure for the Bruker Handheld XRF Analyzer

 Identify failure of designed safety features or other unusual conditions

 Describe XRF Analyzer user responsibilities

 Describe the Federal Regulatory Dose Limits

 List the common sense rules for safely operating the Bruker Handheld XRF Analyzer

The Bruker Handheld XRF Analyzer user’s training consists of this manual, the User Guide, the Basic

Operation Training Video, and the Radiation Safety Video. A PowerPoint presentation and the

instructor may also supplement these training materials. Proper training is vital for compliance, safe

operation, and understanding of the responsibilities of the user of handheld XRF analyzers. Some local

regulatory agencies require that training be documented and a demonstration of sufficient knowledge

through an examination be performed.

Bruker recommends that local regulatory requirements in regards to training be determined,

understood, and followed.

2. What is Radiation?

The term radiation is used with all forms of energy—light, X-rays, radar, microwaves, and more. For

the purpose of this manual, however, radiation refers to invisible waves or particles of energy from

radioactive sources or X-ray tubes. High levels of radiation may pose a danger to living tissue because

it has the potential to damage and/or alter the chemical structure of cells. This could result in various

levels of illness (mild to severe).

The user of a Bruker XRF analyzer must understand the nature of radiation and how to safely use XRF

analyzers.

3. Radiation Terminology

Before examining the subject of radiation in more detail, there are several important terms to be

reviewed and understood.

Bremsstrahlung: The X-rays or “braking” radiation produced by the deceleration of electrons, namely

in an X-ray tube.

Characteristic X-rays: X-rays emitted from electrons during electron shell transfers.

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Fail-Safe Design: One in which all failures of indicator or safety components that can reasonably be

anticipated cause the equipment to fail in a mode such that personnel are safe from exposure to

radiation. For example, if the red lamp indicating “X-RAY ON” fails, the production of X-rays would be

prevented.

Ion: An atom that has lost or gained an electron.

Ion Pair: A free electron and positively charged atom.

Ionization: The process of removing electrons from the shells of neutral atoms.

Ionizing Radiation: Radiation that has enough energy to remove electrons from neutral atoms.

Isotope: Atoms of the same element that have a different number of neutrons in the nucleus.

Non-ionizing Radiation: Radiation that does not have enough energy to remove electrons from

neutral atoms.

Normal Operation: Operation under conditions suitable for collecting data as recommended by

manufacturer, including shielding and barriers.

Primary Beam: Ionizing radiation from an X-ray tube that is directed through an aperture in the

radiation source housing for use in conducting X-ray fluorescence measurements.

Radiation: The energy in transit in form of electromagnetic waves or particles.

Radiation Generating Machine: A device that generates X-rays by accelerating electrons, which strike

an anode.

Radiation Source: An X-ray tube or radioactive isotope.

Radiation Source Housing: That portion of an X-ray fluorescence (XRF) system, which contains the X-

ray tube or radioactive isotope.

Radioactive Material: Any material or substance that has unstable atoms, which are emitting

radiation.

System Barrier: That portion of an area, which clearly defines the transition from a controlled area to

a radiation area and provides the necessary shielding to limit the dose rate in the controlled area

during normal operation.

X-ray Generator: That portion of an X-ray system that provides the accelerating voltage and current

for the X-ray tube.

X-ray System: Apparatus for generating and using ionizing radiation, including all X-ray accessory

apparatus, such as accelerating voltage and current for the X-ray tube and any needed shielding.

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4. Types of Radiation

As stated earlier, radiation consists of invisible waves or particles of energy that could have a health

effect on humans if received in too large a quantity. There are two distinct types of radiation: non-

ionizing and ionizing.

4.1. Non-ionizing Radiation

Non-ionizing radiation does not have the energy needed to ionize an atom (i.e. to remove

electrons from neutral atoms). Sources of non-ionizing radiation include light, microwaves,

power lines, and radar. Although this type of radiation can cause biological damage, like

sunburn, it is generally considered less hazardous than ionizing radiation.

4.2. Ionizing Radiation

Ionizing radiation has enough energy to remove electrons from neutral atoms in a process

called ionization. An atom having either a

positive or negative charge is an ion. A free

electron is also an ion. Ionizing radiation is

of concern due to its potential to alter the

chemical structure of living cells. These

changes can alter or impair the normal

functions of a cell. Sufficient amounts of

ionizing radiation can cause hair loss, blood

changes, and varying degrees of illness.

These levels are approximately 1,000 times

higher than levels that the public or workers

are permitted to receive.

The four basic types of ionizing radiation are emitted from different parts of an atom, as

shown in the image to the right.

NOTE: Bruker handheld XRF devices only emit X-rays.

Alpha Particles have a large mass, consisting of two protons and two neutrons, and a positive

charge. They ionize by stripping away electrons (-) from other atoms with its positive (+)

charge, and are generally only considered a radiation hazard if ingested or inhaled.

Beta Particles are high-energy, high-speed electrons or positrons which form ionizing

radiation also known as beta rays. They ionize other atoms by stripping electrons out of their

orbits with their negative charge, and are primarily a radiation hazard only to the skin and

eyes.

Gamma Rays and X-rays are electromagnetic waves or photons of pure energy that have no

mass or electrical charge. They ionize atoms by interacting with electrons, and are best

shielded by use of dense materials, such as concrete, lead, or steel. Bruker handheld devices

produce X-rays.

Neutron Particles are ejected from the nucleus of an atom during the normal operation of a

nuclear reactor or particle accelerator, as well as the natural decay process of some

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radioactive elements. They can split atoms by colliding with their nuclei, forming two or more

unstable atoms and cause ionization as they try to become stable. They are best shielded by

materials with a high hydrogen content (water, concrete or plastic).

4.3. Penetration

The penetrating power for each of the four basic radiations varies significantly, as shown

below.

5. Units for Measuring Radiation

The absorption of radiation into the body, or anything else, depends upon two things: the type of

radiation involved and the amount of radiation energy received. Internationally, the units for

measuring radiation are the Gray and Sievert; in the USA, the units are the rad and rem.

5.1. Rad (Radiation Absorbed Dose)

A rad is:

 A unit for measuring the amount of radiation energy absorbed by a material (i.e.,

dose)

 Defined for any material (e.g., 100 ergs/gm)

 Applied to all types of radiation

 Not related to biological effects of radiation in the body

 1 rad = 1000 millirad (mrad)

o The Gray (Gy) is the System International (SI) unit for absorbed energy

o 1 rad = 0.01 Gray (Gy) and 1 Gray = 100 rad

5.2. Rem

Actual biological damage depends upon the concentration as well as the amount of radiation

energy deposited in the body. The rem is used to quantify overall doses of radiation, their

ability to cause damage, and their dose equivalence (see below).

A rem is:

 Is a unit for measuring dose equivalence

 Is the most commonly used unit of radiation exposure measure

 A term that pertains directly to humans

 Takes into account the energy absorbed (dose); the quality of radiation; the

biological effect of different types of radiation in the body and any other factor.

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For gamma and X-ray radiation all of these factors are unity so that for these

purposes a rad and a rem are equal.

 1 rem = 1000 millirem (mrem)

o Sievert is the SI unit for dose equivalence

o 1 rem = 0.01 Sievert (Sv) and 1Sv = 100 rem

5.3. Dose and Dose Rate

Dose is the amount of radiation you receive during any exposure.

Dose Rate is the rate at which you receive the dose.

Example:

Dose rate = dose/time = mrem/hr

Dose = dose rate x time = mrem

6. Significant Doses

NCRP Report No. 160, Ionizing Radiation Exposure of the Population of the United States, published in

2006, summaries the effective dose per individual in the U.S. population as 625 mrem annually. This

number has increased over the previous value of 360 mrem primarily due to the increased radiation

exposure from medical procedures.

Typical Radiation Doses from Selected

Sources (Annual)*

Average Occupational Doses

Exposure Source

mrem per year

Occupation

Exposure

(mrem per year)

Background (50%)

311

Airline flight crewmember

1000

Medical (48%)

300

Nuclear power plant worker

700

Consumer (2%)

13

Grand central station worker

120

Occupational (0.1%)

0.5

Medical personnel

70

Round trip US by air

5

DOE/DOE contractors

44

Building materials

3.6

Worldwide fallout

<1

Natural gas range

0.2

Smoke detectors

0.0001

* Based on 2006 U.S. data only

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As previously stated, the general public is exposed daily to small amounts of radiation. However, there

are four major groups of people that have been exposed in the past to significant levels of radiation.

Because of this we know much about ionizing radiation and its biological effects on the body. The

earliest radiation workers, such as radiologists, received large doses of radiation before biological

effects were recognized. Since then, safety standards have been developed to protect such

employees.

The more than 100,000 people who survived the atomic bombs dropped on Hiroshima and Nagasaki,

those involved in accidents like Chernobyl, and those who have received radiation therapy for cancer

are examples of large groups that have received significant doses of radiation.

7. Biological Effects of Radiation

7.1. Cell Sensitivity

The human body is composed of billions of living cells. Groups of these cells make up tissues,

which in turn make up the body’s organs. Some cells are more resistant to viruses, poisons,

and physical damage than others. Rapidly dividing cells are the most sensitive cells, which is

why exposure to a fetus is so carefully controlled. Radiation damage may depend on both

resistance and level of activity during exposure.

7.2. Acute and Chronic Doses of Radiation

All radiation, if received in sufficient quantities, can damage living tissue. The key lies in how

much and how quickly a radiation dose is received. Doses of radiation fall into one of two

categories: acute or chronic.

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Acute Dose

An acute dose is a large dose of radiation received in a short period of time that results in

physical reactions due to massive cell damage (acute effects). The body can't replace or

repair cells fast enough to undo the damage right away, so the individual may remain ill for a

long period of time. Acute doses of radiation can result in reduced blood count and hair loss.

Recorded whole body doses of 100 – 250 mSv (10 - 25 rem) have resulted only in slight blood

changes with no other apparent effects.

Radiation Sickness

Radiation sickness may occur at acute doses greater than 1 Sv (100 rem.) Radiation therapy

patients often experience it as a side effect of high-level exposures to singular areas.

Radiation sickness may cause nausea (from cell damage to the intestinal lining), and

additional symptoms such as fatigue, vomiting, increased temperature, and reduced white

blood cell count.

Acute Dose to the Whole Body

Recovery from an acute dose to the whole body may require a number of months. Whole

body doses of 5 Sv (500 rem) or more may result in damage too great for the body to recover.

Example: 30 firefighters at the Chernobyl facility lost their lives as a result of

severe burns and acute radiation doses exceeding 8 Sv (800 rem.)

Only extreme cases (as mentioned above) result in doses so high that recovery is unlikely.

Acute Dose to Part of the Body

Acute dose to a part of the body most commonly occur in industry (use of X-ray machines),

and often involve exposure of extremities (hand, fingers, etc.). Sufficient radiation doses may

result in loss of the exposed body part. The prevention of acute doses to part of the body is

one of the most important reasons for proper training of personnel.

Chronic Dose

A chronic dose is a small amount of radiation received continually over a long period of time,

such as the dose of radiation we receive from natural background sources every day.

Chronic Dose vs. Acute

The body tolerates chronic doses better than acute doses because only a small number of

cells need repair at any one time. Also, since radical physical changes do not occur as with

acute doses, the body has more time to replace dead or non-working cells with new ones.

Genetic Effects

Genetic effects involve changes in chromosomes or direct irradiation of the fetus. Effects can

be somatic (cancer, tumors, etc.) and may be heritable (passed on to offspring).

Somatic Effects

Somatic effects apply directly to the person exposed, where damage has occurred to the

genetic material of a cell that could eventually change it to a cancer cell. It should be noted

that the chance of this occurring at occupational doses is very low.

Heritable Effects

This effect applies to the offspring of the individual exposed, where damage has occurred to

genetic material that doesn't affect the person exposed, but will be passed on to offspring.

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To date, only plants and animals have exhibited signs of heritable effects from radiation. This

data includes the 77,000 children born to the survivors of Hiroshima and Nagasaki. The

studies performed followed three generations, which included these children, their children,

and their grandchildren.

7.3. Biological Damage Factors

Biological damage factors are those factors that directly determine how much damage living

tissue receives from radiation exposure, including:

 Total dose: the larger the dose, the greater the biological effects

 Dose rate: the faster the dose is received, the less time for the cell to repair

 Type of radiation: the more energy deposited the greater the effect

 Area exposed: the more body area exposed, the greater the biological effects

 Cell sensitivity: rapidly dividing cells (e.g., eyes) are the most vulnerable

 Individual sensitivity: some individuals are more sensitive than others

Individuals sensitive to ionizing radiation:

 Developing embryo/fetus is the most sensitive

 Children are the second most vulnerable

 The elderly are more sensitive than middle-aged adults

 Young to middle-aged adults are the least sensitive

Bruker analyzers, if used in accordance with manufacturer’s instructions, do not pose any

significant threat of exposure to the operator. Because an embryo/fetus is most susceptible

to ionizing radiation, special rules have been developed for pregnant workers. See

Section 8.2.1.

8. Putting Risks in Perspective

Acceptance of any risk is a very personal matter and requires that a person make informed judgments,

weighing benefits against potential hazards.

8.1. Risk Comparison

The following summarizes the risks of radiation exposure:

 The risks of low levels of radiation exposure are still unknown.

 Since ionizing radiation can damage chromosomes of a cell, incomplete repair may

result in the development of cancerous cells.

 There have been no observed increases of cancer among individuals exposed to

occupational levels of ionizing radiation.

 Using other occupational risks and hazards as guidelines, nearly all scientific studies

have concluded the risks of occupational radiation doses are acceptable by

comparison.

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Average Estimated Days Lost

By Industrial Occupations

Average Lifetime Estimated Days Lost

Due to Daily Activities

Occupation*

Estimated

Days Lost

Activity*

Estimated

Days Lost

Mining/Quarrying

328

Cigarette smoking

2250

Construction

302

25% Overweight

1100

Agriculture

277

Accidents (all types)

435

Transportation/Utilities

164

Alcohol consumption (U.S. avg.)

365

5 rem radiation dose per yr for 30 years

150

Driving a motor vehicle

207

All industry

74

Medical X-rays (U.S. avg.)

6

Government

55

1 rem Occupational Exposure

1

Service

47

1 rem per year for 30 years

30

Manufacturing

43

* Note: based on US data only

Trade

30

The comparison of health and industrial risks illustrates the fact that no matter what you do

there is always some associated risk. For every risk there is some benefit, so you as the

worker must weigh these risks and determine if the risk is worth the benefit. Exposure to

ionizing radiation is a consequence of the regular use of many beneficial materials, services,

and products. By learning to respect and work safely around radiation, we can effectively

manage our exposure.

8.2. Radiation Dose Limits

To minimize risks from the potential biological effects of radiation, regulatory agencies and

authoritative bodies have established radiation dose limits for occupational workers. These

limits apply to those working under the provisions of a specific license or registration.

In general, the larger the area of the body that is exposed, the greater the biological effects

for a given dose. Extremities are less sensitive than internal organs because they do not

contain critical organs. That is why the annual dose limit for extremities is higher than for a

whole body exposure that irradiates the internal organs.

Your employer may have additional guidelines and set administrative control levels. Each

employee should be aware of such additional requirements to do their job safely and

efficiently. The limits described below have been developed based on information and

guidance from the International Commission on Radiological Protection (ICRP-1990), the

Biological Effects of Ionizing Radiation (BEIR) Committee, the US Environmental Protection

Agency (EPA), and the National Council of Radiation Protection (NCRP). For an XRF analyzer

using an X-ray tube as the source, any requirement on dose limits for the operators would be

established by the appropriate regulatory agency.

Annual Occupational Dose Limits

Exposed Area

International

U.S.

Whole Body

20 mSv*

5 rem

Extremities

500 mSv

50 rem

Organs or Tissue

(Excluding lens of the eye and skin)

500 mSv

50 rem

Lens of the Eye

150 mSv

15 rem

*Averaged over 5 years

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8.2.1. Declared Pregnant Worker

A female radiation worker may inform her supervisor of her pregnancy, in

writing, at which time she becomes a Declared Pregnant Worker. The employer

should then provide the option of a mutually agreeable assignment of work

tasks, without loss of pay or promotional opportunity, such that further

radiation exposure will not exceed the dose limits as shown in the following

table for the declared pregnant worker.

Radiation Limits for Visitors, Public, and Pregnant Workers

International and US Limit

1 mSv (100 mrem) per year

Pregnant Worker

(International Limit)

2 mSv (200 mrem) to abdomen during remainder of

gestation period after declaration

Pregnant Worker (US Limit)

Declared Pregnant Worker (embryo / fetus) - 0.5 rem / 9

months ( 0.05 rem / month)

The radiation produced by the hand-held XRF analyzer from the primary beam

is low energy X-Rays (4 to 50 keV) in a narrow collimated beam. The radiation

exposure to the user is primarily from scattered radiation from the objects

being analyzed and a small amount of radiation that passes through the

housing. When correctly using the XRF Analyzer, its engineered safety features

ensure radiation exposure will be significantly less than the annual limits.

9. Measuring Radiation

Because we cannot detect radiation through our senses, special devices may be required in some

jurisdictions for personnel operating an XRF Analyzer to monitor and record the operator’s exposure.

These devices are commonly referred to as dosimeters, and the use of them for monitoring is called

dosimetry.

The following information may apply to personnel using hand-held XRF analyzers in jurisdictions where

dosimetry is required:

 Wear an appropriate dosimeter that can record low energy photon (X-ray) radiation.

 Dosimeters wear period of three months may be used, subject to local regulation.

 Each dosimeter will be assigned to a particular person and is not to be used by anyone

else.

 Whole body dosimetry should be worn on the upper portion of your body between the

neck and waist.

 Extremity dosimeters should be worn on the fingers or wrist closest to the XRF analyzer

and is most importantly used on the hand not holding the analyzer.

 Do not intentionally expose a dosimeter to the primary beam.

 Do not expose you dosimeter to radiation outside of work (e.g., medical facilities and

dentist offices).

 Do not put you dosimeter in checked or hand carried luggage when traveling through

airports.

 If your dosimeter is damaged or lost, notify your supervisor and/or RSO.

Bruker recommends that local regulatory requirements in regards to occupational radiation

monitoring be determined, understood, and followed.

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9.1. Dosimeters

While there is variation between dosimeters, and from one type to another, most dosimeters

operate in a similar way. Exposure to ionizing radiation is absorbed by a material contained

within the dosimeter and, when processed, provides a measured dose. Regulators require

that processing of dosimeters be performed by a company that is NVLAP accredited.

Monitoring radiation exposure with dosimeters provides an indication of the working habits

and working conditions of the XRF user and may be a way to identify whether the XRF

analyzer is being properly used. Remember: a dosimeter does not protect you against

radiation exposure; it is simply a passive device that measures the amount of radiation

exposure received where the dosimeter was worn. The figure below shows various types of

dosimeters available.

Whole Body Dosimeter

A Thermoluminescent Device (TLD) or Optically Simulated Luminescence (OSL) whole-body

dosimeter may be used to measure both shallow and deep penetrating radiation doses. It is

normally worn between the neck and waist. The measured dose recorded by this device may

be used as an individual's legal occupational exposure.

Finger Ring

A finger ring is a TLD in the shape of a ring, which is worn by workers to measure the radiation

exposure to the extremities. The measured dose recorded by this device may be used as the

worker's legal occupational extremity exposure.

Wrist Dosimeter

A wrist dosimeter is a whole-body type dosimeter that is designed to be worm on the wrist

similarly to a wrist watch. Processing of the dose takes into account where the dosimeter is

worn and measures the radiation exposure to the extremities. The measured dose recorded

by this device may be used as the worker's legal occupational extremity exposure.

9.2. Survey Meters

Some jurisdictions require the measurement of radiation emitted or scattered from handheld

analyzers by the use of a survey meter, which detects radiation in real time. Survey meters

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generally consist of a detector and a read-out display. Commonly used survey meters are the

ionization chamber, Geiger-Mueller (GM) tube, and photomultiplier tube scintillation

detector. It is important to select a suitable instrument that is capable of monitoring the

type, energy, and intensity of ionizing radiation produced by the hand-held XRF analyzer. The

hand-held XRF analyzer produces low energy X-ray ionizing radiation. The energy of the X-rays

produced by the analyzer will be between 4 keV and 50 keV, with the average energy near 20

to 30 keV, and most of the X-ray energy being less than this due to effects of scattering which

significantly reduces the X-ray energy.

The GM tube instrument has the advantage of being economical and sensitive to low levels of

radiation. This instrument is good at identifying and isolating hot spots. However, an

instrument using a GM tube detector usually does not do well in providing accurate dose rate

measurements, unless specifically designed to do so. In such cases, a specially designed filter

is used to flatten out the energy response.

The ionization chamber is often a preferred instrument. The detector response is relatively

flat across its entire measurement range. The disadvantage is these instruments are often

more expensive and do not read out in the desired or useful measurement ranges. Their large

detector volumes can be challenging because the measurement results are usually affected

by geometry factors and the displayed dose rate is often much less than the actual field at

close distances.

The low energy plastic scintillator dose rate instrument uses a plastic detector that is nearly

tissue equivalent. This type of instrument has the advantage of being sensitive and providing

accurate results. One disadvantage is this type of instrument is typically more expensive than

the other instrument types.

If your jurisdiction requires the use of a survey meter, we recommend that you work with

your preferred instrument provider to identify a suitable survey meter for your application.

Survey instruments are used to provide information to assure that doses are kept ALARA and

to verify the integrity of the XRF Analyzer designed shielding has not been compromised. The

following characteristics should be used to assist in selecting an appropriate instrument.

 Radiation type: X-rays

 Energy range: 4 to 50 keV

 Measurement threshold: 0.01 mem/hr to 200 mrem/hour

 Accuracy: ± 10% of reading or better

Consult the meter’s user guide for proper calibration. Remember the instrument should be

calibrated to the type and energy of the radiation being monitored. The manufacturer may

require the use of correction factors to obtain accurate results for the energy of the X-rays

produced by the XRF analyzer.

We recommend that primary beam measurements never be attempted. Our safety

representatives will work with you to provide information about the primary beam should

you need more information than is provided in our manuals.

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10. Exposure Reduction (ALARA)

While dose limits and administrative control levels already ensure very low radiation doses, it is

possible to reduce these exposures even more. The main goal of the ALARA program is to reduce

ionizing radiation doses to a level that is As Low As Reasonably Achievable (ALARA). ALARA is designed

to prevent unnecessary exposures to employees, the public, and to protect the environment. It is the

responsibility of all workers, managers, and safety personnel alike to ensure that radiation doses are

maintained ALARA.

There are three basic practices to maintain external radiation ALARA: Time, Distance, and Shielding.

Time

The first method of reducing exposure is to limit the amount of time spent in a radioactive

area. Generally, the shorter the time, the lesser the amount of exposure.

The effect of time on radiation could be stated as

Dose = Dose Rate x Time

Example: If 1 hour of time in an area results in 1 mSv (100 mrem) of

radiation, then 1/2 an hour results in 0.5 mSv (50 mrem), and 1/4 an

hour would result in 0.25 mSv (25 mrem), and so on.

Distance

The second method for reducing exposure is by maintaining the maximum possible distance

from the radiation source to the operator or member of the public. The principle of distance

is that the exposure rate is reduced as the distance from the source is increased. The greater

the distance, the amount of radiation received is reduced. This method can best be

expressed by the Inverse Square Law.

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The inverse square law states that doubling the distance from a point source reduces the dose

rate (intensity) to 1/4 of the original. Tripling the distance reduces the dose rate to 1/9 of its

original value. Expressed mathematically:

I

D

D

C2

2

2

1

Where:

 C is the intensity (dose rate) of the radiation source

 D1 is the distance at which C was measured

 D2 is the distance from the source

 I is the new level of intensity at distance D2 from the source

The inverse square law does not apply to sources of greater than a 10:1 (distance: source size)

ratio, or to the radiation fields produced from multiple sources.

Shielding

The third, and perhaps most important, method of reducing exposure is shielding. Shielding is

generally considered to be the most effective method of reducing radiation exposure, and

consists of using a material to absorb or scatter the radiation emitted from a source before it

reaches an individual.

As stated earlier, different materials are more effective against certain types of radiation than

others. The shielding ability of a material also depends on its density, or the weight of a

material per unit of volume.

Example: A cubic foot of lead is heavier than the same volume of

concrete, and so it would also be a better shield.

Although shielding may provide the best protection from radiation exposure, there are still

several precautions to keep in mind when using handheld XRF devices:

 Persons outside the shadow cast by the shield are not necessarily 100% protected. Note:

All persons not directly involved in operating the XRF should be kept at least three feet

away.

 A wall or partition may not be a safe shield for persons on the other side.

 Scattered radiation may bounce around corners and reach nearby individuals, whether or

not they are directly in line with the test location.

WARNING: To avoid inadvertent exposure to others, the

operator should ensure that there is no one on the other

side of the wall or barrier when using an XRF analyzer.

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11. Production of X-Ray Radiation

X-rays are produced by two separate processes:

 Bremsstrahlung: continuous energy spectrum, process = acceleration of electron

 Characteristic: single energy line, process = electron shell transition

Bremsstrahlung is the German term for "braking" and was originally used to describe the unknown

penetrating radiation (X-rays) released when high-speed electrons were stopped by sudden impact with a

metal target. X-ray tubes are designed to use this process to create X-rays.

A modern miniature industrial X-ray tube consists of a ceramic container that is under vacuum. The

major components of a miniature X-Ray tube is the cathode and anode housed in a vacuum ceramic

tube. High voltage bias is applied between the anode (+) and the cathode (-). The picture below is

representative of the type of X-Ray tube used in the hand-held XRF analyzer.

A current passed through a miniature coiled tungsten filament raises the temperature of the wire to

approximately 1000°K, causing the thermionic emission of electrons. Typical currents of 5 to 100 µ

amps of current are used depending on the type of analysis being conducted.

The electrons emitted from the tungsten filament passes through the vacuum of the tube and are

accelerated as they are attracted to the positive charge of the anode. The large voltage potential of 40

to 50 keV transfers a large amount of energy to the electrons.

The electrons having gained a huge amount of kinetic energy impact the X-ray producing target. The

targets are usually made of Rhodium (Rh) or Silver (Ag) in the X-ray tubes used for handheld XRF

analyzers. The impaction of electrons on the target knocks a lower orbit electron from the target

atoms lower shell creating a void. A higher shell electron moves to fill the void, releasing its extra

energy in the form of an X-ray photon. This produces the X-rays required to conduct XRF analysis. The

figure below provides a diagram of a typical X-ray tube used in our application.

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The current applied to the filament changes the intensity of the X-ray by changing the number of

electrons emitted from the miniature coiled tungsten filament. More current means more electrons.

The voltage controls the energy of the X-rays. More voltage means higher energy X-rays.

A typical hand-held XRF analyzer X-ray tube will emit x-rays from 8 keV to 50 keV with the maximum

intensity occurring at about one-half the maximum keV. The X-ray spectrum will be distributed across

a continuum of energies. The figure below provides an example of a typical X-ray spectrum.

X-Ray production voltage and current settings in the handheld XRF Analyzer has been programmed to

produce the energy and intensity required to obtain the best analysis results for a particular

application. The user does not make any voltage or current adjustments in operating the XRF analyzer.

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12. Radiation Exposure Potential

Note

The following section uses the S1 TITAN as an example. The dose rate is typical of handheld XRF

instruments. For specific information on a particular instrument, see the instrument’s User Guide.

The potential for exposure to ionizing radiation is primarily from scattered radiation from the objects

being analyzed and small amounts of radiation from the analyzer’s housing. The potential exists for

exposure to the primary beam if the XRF analyzer is not operated properly, with the greatest potential

being to the operator’s fingers and hands. Table 1 provides the exposure potential of the S1 TITAN

when operated at its maximum voltage setting.

Table 1

Distance (cm)

Rad/hr

Deep Dose

(Rem/hr)

Shallow Dose

(Rem/hr)

Beam Port

4610

3642

5071

5 cm

398

314

438

10 cm

126

99.5

139

30 cm

18

14.2

19.8

100 cm

1.01

0.80

1.11

Table 2 lists the amount of time that it would take to reach the annual limits if the S1 TITAN is

operated with the beam port against a body part at its maximum power setting. The time to

reach these annual limits is quite short.

Table 2

Organ

Eye

Skin

Annual Limit

15 Rem

50 Rem

Time (minutes)

0.17

0.59

Table 3 lists the biological effects and typical dose and time to see the effects from exposure to

the primary beam.

Table 3

Skin Effect

Dose (Rad)

Time (minutes)

Erythema (Redding of Skin)

300

3.9

Dry Desquamation

1000

13.0

Wet Desquamation / Blistering

1500

19.5

Ulceration and Necrosis

3000

39.0

The effects of ionizing radiation exposure to the skin may only appear days or weeks after the

exposure. This is because the radiation damages the developing cells below the skin surface. The

damage cannot be observed until the top layers of the skin slough off.

 Erythema is redness of the skin, caused by hyperemia of the capillaries in the lower

layers of the skin.

 Dry Desquamation also called skin peeling is the shedding of the outermost membrane

or layer of a skin.

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 Wet desquamation is where the skin thins and then begins to weep because of loss of

integrity of the epithelial barrier and decreased oncotic pressure.

There have been no documented radiation related injuries from hand-held XRF analyzer operations.

The potential exists for injury to the fingers or hands if safety features are disabled and/or proper

operating instructions are not followed. There have been documented injuries which have occurred

from not following proper operating procedures and bypassing safety features on cabinet analytical

systems.

It is important to note that although the annual limits could be reached fairly easily through accidental

exposures through improper use of the XRF analyzer, the skin effects caused by exposures would take

significant more time than might occur through a momentary lapse of proper operation.

13. Rights and Responsibilities

Individuals who work with ionizing radiation producing equipment, such as the handheld XRF analyzer,

have certain rights and responsibilities. These rights and responsibilities are usually specifically defined

by the jurisdiction that the XRF analyzer is registered under.

If you are required to wear a dosimeter, you have the right to be informed of the occupational

exposure you receive. Typically, your employer is required to provide a report of your previous year’s

exposure during the 1st quarter of the next year

Users of handheld XRF analyzers have the responsibility to obey warning labels and follow the

operator training. You are required to follow the rules and regulations governing the operation of a

portable XRF. This is for your protection and the protection of co-workers, clients, and the public.

Typically, you are required to report concerns and violations to your supervisor and regulatory

authorities

Most jurisdictions require that individuals working under their rules and regulations never deliberately

cause a violation of any related rule or regulation. Deliberate violations usually are subject to

enforcement action. Mistakes and unplanned action usually do not apply.

Prior to using the handheld XRF analyzer, carefully read the instrument’s user guide.

As the operator of the handheld XRF analyzer, you are responsible for your safety and the safety of

others. The following are important responsibilities:

 Before pulling the trigger, be aware of the direction that the X-rays travel.

 Do not place any part of your body (especially the eyes or hands) near the examination area

during measurement.

 Do not hold a sample to the window for analysis by hand. Instead, hold the window to the

sample. The infrared (IR) sensor located on the nose is designed to prevent the emission of

X-rays in the absence of an object.

 Do not defeat the IR sensor in order to bypass the safety circuit. Defeating this safety

feature could result in unnecessary exposure of the operator. Occasionally, a sample may

not be reflective enough to trigger the IR sensor. In these cases, place a piece of white

paper or other reflective material between the sample and IR sensor.

 Use the optional safety shield or benchtop stand accessory for testing small or thin samples

or low-density materials, such as plastic, wood, soil, paper, or ceramics.

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 Wear an appropriate dosimeter if required by a regulatory agency when operating the

analyzer.

 Pregnant women should be aware that improper handling or improper use of the

instrument could result in radiation exposure.

 The operator is responsible for the security of the analyzer. When in use, the device should

be in the operator's possession at all times.

 Do not allow anyone other than trained and certified personnel to operate the analyzer.

 Always store the instrument in a secure location when not in use.

 If you suspect the analyzer is damaged, remove the battery pack and disconnect all power

sources.

14. Backscatter with Low Density Samples

Be aware that when using a handheld XRF analyzer, some radiation is scattered back towards the

operator. The amount of scatter is dependent on the density of the sample – with low density

samples, such as plastics, scattering more than high density samples, such as metals – and the shape of

the sample – with flat surfaces containing more of the backscatter and curved and irregular surfaces

containing less of the backscatter. The operator must keep hands and eyes away from the analyzer

nosepiece.

Further, it should be noted that low-density (LD) materials, such as plastic, wood, soil, paper, or

ceramic, will not attenuate higher energy X-rays as efficiently as high-density materials, such as metal

alloys. Thus a greater amount of the radiation is transmitted through the sample, which can cause a

higher dose rate to the operator. The operator should keep hands and eyes away from the analyzer

nosepiece. If LD samples are measured frequently, the use of a bench-top stand is recommended to

minimize scattered radiation. If the LD samples are small enough, the Small Sample Safety Shield is

adequate.