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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 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.
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 2: Dose Limits by Body Area
Additional Note: Pregnancy
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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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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
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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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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
A solid Solid orange light 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 the Tracer 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 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. It should not be set down or carried in this state.
Infra-Red Sensor
The Tracer has aninfra-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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