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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.
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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 2a1A, 2b1B). The limits apply to those working under the provisions of a specific license or registration.
Table
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1A (left) and
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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 internal organs 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 3 lists 2 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
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2: Dose Limits by Body Area
Additional Note: Pregnancy
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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.
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Film Badge (Whole Body Dosimeter):
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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, which is directly proportional to the time of exposure. Half the time means half the dose, and vice versa.
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- 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.
Specific pXRF User Requirements
Radiation from
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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.
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Important! No additional shielding is recommended 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 plastic 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.
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Figure 4, below, states the Bruker Tracer 5 pXRF measured doses of scattered radiation, based on pXRF target and position.
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, 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.
Distance (cm) | Dose Rate (mrem/hr) | 672 Hour Expedition Exposure | 5 Hour Exposure | |
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| Without Shielding | < 5 | Up to 0.056 | 38 mrem (0.38 mSv) | 0.28 mrem (0.003 mSv) |
| 20 | Up to 0.03 | 20 mrem (0.20 mSv) | 0.15 mrem (0.002 mSv) | |
| 30 | Background | Background | Background | |
| With Shielding | < 5 | Up to 12 | 8 mrem (0.008 mSv) | 0.06 mrem (0.0006 mSv) |
| 20 | Background | Background | Background | |
| 30 | Background | Background | Background |
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.
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Lights indicate to the operator when the tube is receiving power 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.
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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
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lights
Solid red LED array. This orange lights signifies that the X-ray tube is enabled, and that armed and ready to measure. In this state there is still no radiation exposure to you or bystanders . The instrument can be carried or set down safety 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
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lights flashing
In addition to the solid orange indicator lightlights, red lights will flash along the light bar beneath along each side of the rail when the device is measuring. This signifies that the X-ray tube is actively emitting xX-ray radiation through the measurement window. In this condition, the analyzer must be pointed toward a test sample or surface and never at a human being. It should not be set down or carried in this state.
Infra-Red Sensor
The Tracer has aninfrared 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.
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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.
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