Table of Contents

Introduction

When X-ray radiation from the portable XRF (pXRF) excites atoms in the sample, the atoms release fluorescent X-rays. The energy level of each fluorescent X-ray created is characteristic of the element excited; as a result, one can tell what elements are present. The Bruker Tracer 5 pXRF detects and determines the fluorescent X-ray energies produced. As the pXRF emits radiation (from 4 to 50 kV), a comprehensive knowledge of radiation safety and procedures is needed.

Radiation

What is Radiation?

The term radiation is used with all forms of energy: light, X-rays, radar, gamma rays, microwaves, and more. For the purpose of this manual, radiation refers to invisible waves or particles of energy emitted from any X-ray tube. Radiation if received in too large a quantity, can have an adverse health effect on humans. There are two distinct types of radiation: non-ionizing and ionizing radiation.

Non-ionizing Radiation

Non-ionizing radiation does not have the energy necessary 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, such as a sunburn, it is generally considered less hazardous than ionizing radiation.

Ionizing Radiation

Ionizing radiation has enough energy to remove electrons from neutral atoms. 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.
There are four basic types of ionizing radiation, emitted from different parts of the atom (Fig.1):

• Alpha particles
• Beta particles
• Gamma rays and X-rays
• Neutron Particles

Figure 1. Types of ionizing radiation and their atomic sources

The penetrating power for each of the four basic radiations varies significantly (Fig. 2).

Figure 2. Penetrating power of the four basic radiation types.

Alpha and beta particles have little ability to penetrate the skin, so alpha- and beta-radiation sources are more dangerous when they are taken into the body; this is called radiation poisoning. X-ray, gamma ray, and neutron sources are able to penetrate the skin, so this external risk is both direct (radiation burn or acute radiation exposure) and indirect (radiation poisoning).

Radiation Producing Devices

The pXRF is a radiation producing device (RPD); X-rays are generated by a cathode-ray tube. If current is applied to the tube in sufficient voltage (>4 kV) to generate X-rays, radiation is produced. If no current is flowing, no radiation is produced. Therefore, the pXRF is completely safe from a radiation standpoint when it is unpowered.
Note: The Bruker Tracer 5 pXRF emits only X-rays. For this reason, this manual will preferentially focus on x-rays from this point on.

X-Rays

• Electromagnetic waves or photons of pure energy that have no mass or electrical charge
• X-rays are emitted from the inner electron shells of atoms, or from a radiation producing device
• Ionize atoms by interacting with electrons

Biological Effects of Radiation

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. The most sensitive cells are those that are rapidly dividing.

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.

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 (i.e. months). 

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 of radiation better than acute doses because only a small number of cells need repair at any one time. Because 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. Acute doses of radiation can result in reduced blood count and hair loss. Radiation sickness occurs at acute doses greater than 100,000 mrem. 
Note: Acute dose to a part of the body most commonly occurs in industry (use of X-ray machines), and often involve exposure of extremities (e.g., hand, fingers). The prevention of acute doses to part of the body is one of the most important reasons for proper training of personnel.

Biological Damage Factors

Biological damage factors are those factors, which directly determine how much damage living tissue receives from radiation exposure, and include:

• 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 is exposed, the greater the biological effects.
• Cell sensitivity: Rapidly dividing cells are the most vulnerable.

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. Using other occupational risks and hazards as guidelines, nearly all scientific studies have concluded the risks of occupational radiation doses are acceptable by 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.

For every risk there is some benefit, so as the operator, you must weigh these risks for yourself and determine the if the risks are worth the benefit for you. By learning to respect and work safely around radiation, we can limit our exposure and continue to enjoy the benefits it provides. 

Radiation Dose Limits

To minimize the risks from the potential biological effects of radiation, regulatory agencies and authoritative bodies have established radiation dose limits for occupational workers (Table 1A, 1B). The limits apply to those working under the provisions of a specific license or registration.

Table 1A (left) and 1B (right). Typical radiation doses from selected sources and average occupational doses.

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 the main body area 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. Table 2 lists the exposure limits for different regions of the body.

Table 2: Dose Limits by Body Area

Additional Note: Pregnancy

The JRSO does not permit pregnant women to sail on the R/V JOIDES Resolution. The environmental controls and list of hazardous materials, including radioactive materials and radiation-producing devices, on board the ship are not designed with pregnant women in mind. If a woman determines that she is, or has become, pregnant, inform the ship's doctor immediately to prevent potential harm to the embryo/fetus.

Measuring Radiation

Measuring Devices

Several devices are employed for measurement of radiation doses, including ionization chambers, Geiger-Mueller tubes ("Geiger counter"), pocket dosimeters, thermoluminescence devices (TLD's), optically stimulated luminescence dosimeters (OSL) and film badges. On the ship, the JRSO has an ion chamber, film badges and finger rings.

Ion Chamber

An ion chamber is the simplest detector for measuring radiation. It consists of a cylindrical chamber filled with air and a wire running through its center with voltage applied between the wire and outside of the cylinder. When radiation passes through the chamber, ion pairs are extracted and build up a charge. This charge is used as a measure of the exposure received. This measurement, however, is not as efficient or sensitive as a traditional Geiger Counter.

Dosimeters

Since we cannot detect radiation through our senses, some regulating agencies require special devices for personnel operating a pXRF in order 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. These are two common types of dosimeters: whole body and extremity.

• Wear an appropriate dosimeter that can record low energy photon radiation
• Dosimeters with a wear period of three months may be used
• Each dosimeter will be assigned to an individual and is not to be used by anyone else
• If your dosimeter is damaged or lost, notify the X-ray technician, Assistant Lab Officer or Lab Officer.

Film Badge (Whole Body Dosimeter):

A whole body dosimeter is used to measure both shallow and deep penetrating radiation doses. It is normally worn between the neck and waist.

Finger Ring (Extremity Dosimeter):

A finger ring a film dosimeter in the shape of a ring, which is worn by workers to measure the radiation exposure to the extremities. Finger rings are the appropriate tool for pXRF use, since the hands are the most likely body part to be in proximity to the X-ray source.

Reducing Exposure

ALARA

Natural and man-made background radiation is ubiquitous, providing an average annual radiation dose of 0.620 rem to every U.S. citizen. Subsequently, any radiation dose received occupationally would be in excess of the background radiation dose received and can therefore be assumed to carry with it additive risk of deleterious effect.
State and federal regulations therefore establish a system of dose limitation and minimization. Individual doses are limited to ensure that deterministic effects (such as cataracts) are avoided and that total lifetime risks of stochastic effects (such as cancer and hereditary effects) do not exceed overall health risks for those persons working in safe industries. However, regulations also require that licensees further minimize radiation doses to individuals and to groups of individuals to the extent practical, social, economic and technological factors taken into account.
This concept or philosophy is given the special name ALARA which is an acronym for As Low As is Reasonably Achievable. That is the safety standard for working with all types of radioactive sources and radiation-producing devices, and it means that exposure should be as low as possible, within a reasonable limit.
While dose limits and administrative control levels already help ensure very low radiation doses, it is possible to reduce these exposures even more. The main goal is to reduce ionizing radiation doses to a level that is ALARA. There are three basic practices to maintain external radiation:

• Time
• Distance
• Shielding

Time

The first method of reducing exposure is to limit the amount of time spent in a radioactive area: the shorter the time of exposure, the lower the amount of exposure. The effect of time on radiation could be stated as:

Dose = Dose Rate X Time

This means the less time you are exposed to ionizing radiation, the smaller the dose you will receive, which is directly proportional to the time of exposure. Half the time means half the dose, and vice versa.

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; as distance is increased, the amount of radiation received is reduced.
This method can best be expressed by the Inverse Square Law, graphically represented below in Figure 3. The inverse square law states that doubling the distance from a point source reduces the dose rate (intensity) to ¼ of the original. Tripling the distance reduces the dose rate to 1/9 of its original value.
C X (D₁)²/ (D₂)² = I
C = the intensity (dose rate) of the radiation source
D₁ = the distance at which C was measured
D₂ = the actual distance from the source
I = the new level of intensity at distance D₂ from the source

Figure 3. Graphical Representation of the Inverse Square Law

Shielding

The third 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. Different materials are more effective against certain types of radiation than others. The shielding ability of a material also depends on its density, therefore, materials such as lead, concrete, or steel are the most effective.
Although shielding may provide the best protection from radiation exposure, there are still several precautions to keep in mind when using the Bruker Tracer 5 pXRF:

• Persons outside the shadow cast by the shield are not necessarily 100% protected. Note: All persons not directly involved in operating the pXRF should be kept at least three feet away.
• A wall or partition may not be a safe shield for persons on the other side. Note: The operator should make sure that there is no one on the other side of the wall.
• Scattered radiation may bounce around corners and reach an individual, whether directly in line with the test location or not.

Radiation from a pXRF

The user and anyone working in the area of the pXRF should always take reasonable precautions when using and working around the device. That means keeping body parts out of and away from the nose of the instrument (where the source is) and keeping a distance between the active source and themselves if not working directly with the instrument.

Radiation Scatter

Radiation scatter is produced whenever an absorbing material is directly irradiated from a nearby source. X-rays produced through fluorescence are randomly distributed in all directions. Scattering, however, is not uniform and is dependent on the sample being tested, the energy of the radiation, and other factors.
The X-ray tube within the pXRF is used to irradiate a chosen material at very close range with a narrow, collimated beam. The X-rays from the tube excite the atoms of the material, which then produce K- or L-shell X-rays. These fluorescent X-rays, the main beam, and scattered radiation can be contained inside the instrument if the sample is sufficiently dense and thick. For example: according to the manufacturer, a U.S. quarter can effectively contain the radiation inside the instrument; a plastic lid, in comparison, cannot. The main beam is much stronger than the fluorescence or scattered radiation and should be avoided.

Backscatter

The pXRF analyzer generates spectrum data by analyzing the specific X-ray energies that are scattered back to the detector. Because the X-rays travel in all directions, it is possible for an X-ray to miss the detector and be scattered in the direction of the operator. This is referred to as backscatter. Although the pXRF is specifically designed to limit backscatter reaching the operator, there is always the possibility that a small number of X-rays may scatter beyond the detector. In the case of a light or thin sample that does not contain the main beam, the main beam may then be scattered back towards the operator. In this case, a shield around the sample should be used.

Important! No additional shielding is deemed necessary by the manufacturer if the measurement window is fully covered and flat against a sample. However, JRSO highly recommends the use of additional shielding. Section half measurements should be performed using the shielded device holder that fits on and around the section half liner. Discrete samples, including powders mounted in plastic cups, should be analyzed using the small stage with the shielded cup or using the benchtop chamber whenever possible.

Radiation Profile

To ensure safe operation of the system, it is vital that the operator understand the radiation field. The radiation profile contains measurements of the radiation field. The profile should be studied carefully by anyone that operates the pXRF, in order to better understand and apply the practices of ALARA doses (using time, distance and shielding).

Figure 4, below, states the Bruker Tracer 5 pXRF measured doses of scattered radiation, based on pXRF target and position, provided by the manufacturer for our specific pXRF (serial number 900G7838). Distance and shielding minimize these potential exposures (Table 3).

Figure 4. Bruker Tracer 5 pXRF Radiation Profile.

Table 3. Calculated exposure based on onboard leak testing with an ion chamber. Background radiation detected as 2-10 µrem/hr. Measurements were performed in the direction of highest exposure based on the manufacturer's provided radiation profile of Tracer 5 serial number 900G7838 (positions H and I). 

Bruker Tracer 5 pXRF Safety Features

To control X-ray emissions, and thereby minimize the possibility of accidental exposure, the Bruker Tracer 5 pXRF analyzer has multiple standard safety features listed below. Be sure to understand how these safety features work before operating the device.

Software Password Protection

Once powered on, the requires a password be entered. This prevents the operation or generation of x-rays without a valid password. The password is only shared with authorized individuals trained in the operation of the Tracer. The x-ray will not arm unless the operator is logged into the software via the touch screen, or if using the laptop connection, through Bruker RemoteCtrl software application. Additionally, after 5 minutes of inactivity, the Tracer's software automatically times out and logs out the user (whether using the Tracer itself or Bruker RemoteCtrl). This will disarm the x-ray tube until the operator logs back in.

X-ray Warning

Once the password is successfully entered, an X-ray radiation warning is displayed. The operator cannot generate X-rays without pressing and releasing the trigger to acknowledge this statement.

Indicator Lighting

Lights indicate to the operator when the tube is in a powered state ready to measure and when X-rays are being actively emitted from the analyzer through the measurement window. The indicator lights are located along a light bar just below and on each side of the attachment rail on the top of the device.

No indicator lights visible

This signifies that the X-ray tube is disarmed and that there is no possibility of radiation exposure to you or bystanders. The instrument can be carried or set down safely in this condition. This also indicates the trigger is not active.

Orange indicator lights

Solid orange lights signifies that the X-ray tube is armed and ready to measure. In this state there is still no radiation exposure to you or bystanders until the trigger had been pressed. The Tracer can be repositioned, taking care not to push the trigger, but should not be carried in this condition.

Red indicator lights flashing

In addition to the solid orange lights, red lights will flash along the light bar along each side of the rail when the device is measuring. This signifies that the X-ray tube is actively emitting X-ray radiation through the measurement window. In this condition, the analyzer must be pointed toward a sample or surface and never at a human being.

Infra-Red Sensor

The Tracer has an infra-red sensor next to the measurement window that detects the presence of an object in front of the measurement window. X-rays can only be generated if the sensor detects an object or sample surface. If the device is pulled away from a sample, the X-ray tube will be disarmed.

Backscatter Detector

During each measurement, the X-ray count-rate is continuously monitored. If the count-rate drops below the allowable threshold, as it would in the absence of a sample, X-ray generation is discontinued, minimizing potential exposure. If the device is pulled away from the sample while a test is in progress, testing will stop and X-rays will shut off.

Warning Labels

Warning labels identify the analyzer as a radiation producing device.  The manufacturer's plate underneath contains regulatory information. Do not tamper with or remove these labels.

Radiation Safety Tips and Precautions

All operators should follow minimum safety requirements discussed below. When handled properly, the amount of radiation exposure received from the pXRF will be negligible. However, the following safety tips are provided to help ensure safe and responsible use:

1. Prior to using the instrument, undertake radiation safety training and proper operation of the Tracer.
2. WARNING: No one but the operator should be allowed to be closer than 3 feet from the pXRF, particularly of measurement window. Ignoring this warning could result in unnecessary exposure.
3. WARNING: The operator should never defeat the infra-red sensor in order to bypass this part of the safety circuit. Defeating this safety feature could result in over-exposure of the operator.
4. Do not allow anyone other than trained personnel to operate the pXRF.
5. Be aware of the direction that the X-rays travel when the red light is on and do not place any part of your body (e.g., eyes, hands) near the measurement window to stabilize the instrument during operation.
6. Never hold a sample up to the measurement window for analysis by hand; hold the instrument to the sample.
7. Establish a no-access zone at a sufficient distance from the instruments measurement window, which will allow air to attenuate the beam. Ideally, this is at least 1 meter (3ft).
8. Wear an appropriate dosimeter (see the Laboratory Officer for issue of a dosimeter).
9. The operator is responsible for the security of the Bruker Tracer 5 pXRF. When in use, the device should be in the operator's possession at all times (i.e., either in direct sight or a secure area). Do not leave the device without first logging out of the device software.
10. Always store the instrument in a secure location when not in use.
11. During transport to and from the set up location, store the instrument in its designated, cushioned, Pelican case.
12. WARNING: Pregnant women should not use the pXRF or work in proximity to it. See 'Additional Note: Pregnancy', above, for more information. Radiation exposure can be harmful to an embryo or developing fetus!

Credits

This document originated from Word document XRF_Safety_374.doc (see Archived Versions below for a pdf copy) that was written by N. Lawler and A. Armstrong and heavily adapted from Bruker Radiation Safety documentation. Credits for subsequent changes to this document are given in the page history.

Archived Versions

pXRF Safety - September 27, 2022

LMUG-pXRFSafety-230220-2005-194.pdf

XRF_Safety_374.pdf