Table of Contents
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Introduction
When X-
Handheld XRF:
Radiation Safety Guide
Manual Information
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Author(s):
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A. Armstrong & N. Lawler
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Reviewer(s):
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H. Barnes
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Supervisor Approval:
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D. Houpt
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Origination date:
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2017 371T
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Current version:
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V378P | V371T
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Revised:
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Domain:
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X-Ray
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System:
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XRF
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Keywords:
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Elemental analysis
In This Manual
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Introduction
When X-ray radiation from the handheld XRF (pXRF) excites atoms in the sample, the atoms release fluorescent X-rays. The energy level of each fluorescent X-ray create is characteristic of the element excited; as a result, one can tell what elements are present. The Olympus Delta pXRF detects and determines the fluorescent X-ray energies produced. As the pXRF emits radiation (from 8-40keV), a comprehensive knowledge of radiation safety and procedures is needed.
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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 (see Figure 1, below):
- Alpha particles
- Beta particles
- Gamma rays and X-rays
- Neutron Particles
The penetrating power for each of the four basic radiations varies significantly.
Figure 1. Types of Ionizing Radiation and Their Sources
Radioactivity-Emitting Materials
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- 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 an RPD
- Ionize atoms by interacting with electrons
Distance
Because X-rays (and gamma rays) have no charge or mass, they are highly penetrating and can travel quite far. Range in air can easily reach several hundred feet. Figure 2 reflects this graphically.
Figure 2. Penetrating Power of Radiation
Shielding
X-rays interact with matter and lose energy because of that interaction. Therefore, the best shielding materials are dense, such as concrete, steel, or lead.
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- 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. By learning to respect and work safely around radiation, we can limit our exposure and continue to enjoy the benefits it provides.
Table 1a and 1b., below summarize the risks associated with various activities; note the low loss associated with occupational radiation exposure (when proper controls are in place).
Table 1a (left) and 1b (right). Average estimated days lost by occupation and daily activities.
Radiation Dose Limits
To minimize the risks from the potential biological effects of radiation, the state health departments and the Nuclear Regulatory Commission (NRC) have established radiation dose limits for occupational workers as shown in Table 2a and 2b, below.. The limits apply to those working under the provisions of a specific license or registration.
Table 2a (left) and 2b (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 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. Table 3 lists the exposure limits for different regions of the body.
Type of Body Area | Description | Allowable Limit (rem/year) |
Whole Body | The whole body is measured from the top of the head to just below the elbow and just below the knee. The limit is the sum of both internal and external exposure | 5 |
Extremities | The hands, arms below the elbows, the feet, and legs below the knees | 50 |
Skin | The entirety of the skin | 50 |
Organs or Tissues | All organs and tissues, including the brain | 50 |
Lens of the Eye | The cornea (the internal eye and retina are included in organs or tissues) | 15 |
Declared Pregnant Worker | If a worker declares their pregnancy (formally and in writing), their radiation exposure limits are reduced by a factor of 100; the exposure limit for the embryo/fetus is as shown | 0.5 |
Table 3: Dose Limits by Body Area
Additional Note: Pregnancy
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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, 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
The inverse square law does not apply to sources of greater than a 10:1 ratio (distance: source size), or to the radiation fields produced from multiple sources.
Shielding
The third (and 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. 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.
Although shielding may provide the best protection from radiation exposure, there are still several precautions to keep in mind when using the Olympus Delta Handheld XRF:
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The pXRF analyzer generates spectrum data by analyzing the specific X-ray energies that get 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 XRF 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 light or thin samples that do 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! Discrete samples, including powders mounted in plastic cups, should only be analyzed in the Olympus pXRF Test Stand. The walls of the Test Stand are lead-lined. When the pXRF is secured in the Test Stand and the lid is closed, the radiation emission is considered negligible.
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 handheld XRF, in order to better understand and apply the practices of ALARA doses (using time, distance and shielding).
Radiation Profile
Figure 4, below, states the Olympus DELTA Series pXRF measured doses of scattered radiation, based on pXRF target and position.
Figure 4. Olympus DELTA Series Measured Doses Chart
Handheld XRF Analyzer Safety Design
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- WARNING: No one but the operator should be allowed to be closer than 3 feet from the pXRF, particularly the beam port. Ignoring this warning could result in unnecessary exposure.
- WARNING: The operator should never defeat the IR sensor in order to bypass this part of the safety circuit. Defeating this safety feature could result in over-exposure of the operator.
- Do not allow anyone other than trained personnel to operate the pXRF
- Be aware of the direction that the X-rays travel when the red light is on and avoid placing any part of your body (e.g., eyes, hands) near the X-ray port to stabilize the instrument during operation.
- Never hold a sample up to the X-ray port for analysis by hand; hold the instrument to the sample.
- Establish a no-access zone at a sufficient distance from the instruments measurement window, which will allow air to attenuate the beam.
- Enclose the beam working area with protective panels (e.g., >3.0 mm stainless steel).
- Wear an appropriate dosimeter (see the Laboratory Officer for more information on when a dosimeter is called for).
- The operator is responsible for the security of the handheld XRF. 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).
- Always store the instrument in a secure location when not in use.
- During transport to and from the set up location, store the instrument in a cool, dry location.
- 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. Credits for subsequent changes to this document are given in the page history.
Archived Versions
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