X-ray diffraction (XRD) and x-ray fluorescence (XRF) analysis equipment both generate high intensity ionizing radiation that can cause severe and permanent injury if any body is exposed to the primary beam even for a few seconds. All persons using x-ray diffraction and analytical devices must register with the Radiation Safety Office and be instructed on the following information.

Production and characteristics of x-rays

  • X-rays are produced by bombarding a focus of high speed electrons on a metal target. As the rapidly moving electrons are suddenly stopped by the metal target, x-rays are produced. (this takes place in an x-ray tube, see attached diagram)
  • X-rays are a penetrating form of electromagnetic energy of short-wavelength photons that originate from the electron orbitals.
  • Interaction of electrons with the metal target produce 2 main types of x-rays:
    • Characteristic
    • Bremsstrahlung

Units of Radiation

milliRoentgen (mR) is a unit of exposure in air

  • 1 R = 87.7 ergs/gm of air
    • 1 R = 2.08 x 109 ion pairs/cc of air
  • millirem (mrem) is a unit of radiation dose
    • 1 R (of low energy x-rays) = 1 rem of radiation dose to tissue

Hazards of Excessive Radiation Exposure:

Symptoms of large amounts of acute whole body radiation exposure;

  • 0 - 25 rem ---- no observable effect
  • 25 - 50 rem ---- possible blood changes - no serious injury
  • 50 - 100 rem -- blood changes - some injury

Dose vs. Effect curve

  • threshold vs. non-threshold
  • linear vs. non-linear

Clinical Symptoms of Acute Radiation Over-exposure: (greater than 300 rem)

  • 1 to 3 weeks after over-exposure - erythema, ulceration and blisters
  • this may heal during the first month
  • then skin may atrophy over the next few months
  • after a year - ulceration and blistering may occur because of sun or heat burn
  • Amputation may be necessary at dose greater then 10,000 rem

Methods for Controlling Radiation Exposure

  • Time ---- decrease time, decrease radiation dose (proportional)
  • Distance ---- increase distance, decrease radiation dose (inverse square)
  • Shielding ---- increase shielding, decrease radiation exposure (proportional)
  • Signs and labels ---- decrease accidental radiation exposure

Dosimetry

Exposure Limits:

NRC annual limit;

  • 5 rems - effective dose equivalent (whole body)
  • 50 rems - shallow dose equivalent (skin or to each extremity)
  • 15 rems - eye dose equivalent (lens of the eye)
  • 0.5 rem - dose to embryo/fetus during entire pregnancy

ALARA; As Low As Reasonably Achievable
UVM Dose limits; 10% of the NRC annual limits
Background and other dose levels;

  • 295 mrem (millirem) - average background dose in U.S.
  • 300 mrem - average dose from 1 abdomen radiograph
  • 200 mrem - average dose from 1 dental radiograph
  • 20 mrem - average dose from 1 chest radiograph
  • 3 mrem - average dose to UVM personnel in 1 year

Radiation monitoring devices;

  • film badge (exchanged every month)
  • room monitor (exchanged every month)
  • pelvic badge (pregnant radiation workers, exchanged every 2 weeks)

Emergency procedures

Working hours call the Radiation Safety Office at ext. 62570 After working hours or on weekends call UVM Police Services at ext. 114

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