Teachers: Please request permission to use these materials in your courses. These courses are only published on the web. Please support this free publishing effort by registering your use. Educational users may download and edit these tutorials to suit their needs provided that the original author is given credit. Any comments or suggestions you may have to improve these tutorials will be greatly appreciated.

Tutorials developed at UTMB:

• Methods in X-ray Crystallography Course
• SMART (Bruker CCD) software tutorial
• SAINT (Bruker) software tutorial

• RasMol Tutorial (Gale Rhodes)
• Structure Factor Tutorial (Keven Cowan)

• UCSF X-ray Diffraction Safety (Go To UCSF)
• CAL Tech X-ray Generator Safety (Go To CALTEC)
• Radiation Safety for X-Ray Diffraction Equipment National Bureau of Standards Handbook 111 (ANSI N43.2)
• Hazards in the Use of X-Ray Analytical Instrumentation R. Jenkins and D.J. Haas, Philips Instr.
• The Interaction of X-Rays with Matter and Radiation Safety James R. Connolly, EPS400-002
• The SCSB Radiation Safety Test (Required for all users)

Radiation Safety For X-ray Diffraction

RADIATION SAFETY FOR X-RAY UNITS

NATURE OF ANALYTICAL X-RAYS

Analytical x-ray machines produce intense beams of ionizing radiation that are used for diffraction and fluorescence studies. The most intense part of a beam is that corresponding to the K emission of the target material and is called characteristic radiation. In addition to the characteristic radiation, a continuous radiation spectrum of low intensity is produced ranging from a very low energy to the maximum kV-peak setting. This is referred to as 'bremsstrahlung' or white radiation. Undesirable wavelengths may be filtered out using a monochromator.

X-ray diffraction wavelengths (w) are selected so as to roughly correspond to the inter-atomic distances within the sample, and to minimize fluorescence. Wavelengths commonly used are 1.54 Å (Cu targets), 0.71 Å (Mo targets), 0.56 Å (Ag targets), and 2.3 Å (Cr targets). The relationship between wavelength and x-ray photon energy is determined by the equation

E = hc/w

where
E = energy in ergs (1eV = 1.6E-12 erg)
h = Planck's constant = 6.614E-27 erg-sec
c = velocity of light = 3E10 cm/sec
w = wavelength in cm (1Å = 1E-8 cm)

X-rays emitted from an open, uncollimated port form a cone of about 30 degrees. The x-ray flux can produce a radiation field at one meter on the order of 10,000 R/hr. A collimator reduces the beam size to about 1 millimeter diameter.

X-RAY HAZARDS AND BIOLOGICAL EFFECTS

X-rays produced by diffraction machines are readily absorbed in the first few millimeters of tissue, and therefore do not contribute any dose to the internal organs of the body. However, the lens of the eye can receive a dose from x-rays of this energy. Overexposure of lens tissue can lead to the development of lens opacities and cataracts.

Absorbed doses of a few hundred rad may produce a reddening of the skin (erythema) which is transitory in nature. Higher doses -- 10,000 rad and greater -- may produce significant cellular damage resulting in pigment changes and chronic radiation dermatitis. Exposure to erythema doses may not result in immediate skin reddening. The latent period may be from several hours to several days.

(Note: X-rays used for medical diagnosis are about one order of magnitude shorter in wavelength. Diagnostic rays are designed for tissue penetration and are carefully filtered to avoid x-ray damage to the skin caused by the longer, more readily absorbed wavelengths).

SOURCES OF IONIZING RADIATION

The primary beam is not the only source of ionizing radiation. Any high voltage discharge is a potential source of x-rays. Faulty high-voltage vacuum-tube rectifiers may emit x-rays of twice the voltage applied to the x-ray tube. Other sources of ionizing radiation are:

• Secondary emissions and scattering from the sample, shielding material, and fluorescent screens.
• Leakage of primary or scattered x-rays through gaps and cracks in shielding.
• Penetration of the primary beam through or scattering from faulty shutters, beam traps, or collimator couplings.

SAFETY PRECAUTIONS AND NOTES

The shielding, safety equipment and safety procedures prescribed for x-ray diffraction equipment are applicable only for up to 75 kV-peak x-rays. Additional or greater precautions are necessary for machines operating at higher voltages.

The PI has the basic responsibility for providing a safe working environment by ensuring that equipment is operationally safe and that users understand safety and operating procedures.

The equipment operator is responsible for his own safety and the safety of others when using an analytical x-ray machine.

Prior to removing shielding or working in the sample area, the operator must check both the warning lights and the current (mA) meter on the console. Never trust a warning light unless it is on! Always use a survey meter to check that the shutters are actually closed if current is still being supplied to the tube. It is possible for a shutter to be stuck partially open even when the indicator shows that it is shut. The best way to avoid an accidental exposure is to turn the machine off before working in the sample area.

Never put any part of the body in the primary beam. Exposure of any part of the body to the collimated beam for even a fraction of a second may result in damage to the exposed tissue.

A person not knowledgeable about x-ray equipment should not attempt to make repairs or remedy malfunctions. If you suspect a machine is malfunctioning, turn it off or unplug it. Place a note on the control panel and inform the PI or his designated representative.

Repairs to the high voltage section must not be made unless the primary leads are disconnected from the high voltage transformer and a signed and dated notice is posted near the x-ray ON switch. Turning off a circuit breaker is not sufficient.

Bare feet are not permitted in the laboratory or around electrical equipment. Even slightly moist skin is an excellent electrical conductor and contact with faulty, ungrounded equipment may result in severe injury or death.

Do not attempt to align x-ray cameras without first consulting an experienced person. Alignment procedures require special training and knowledge.

Special care is required when one power supply is connected to more than one x-ray tube.

EYE PROTECTION

The use of safety glasses or prescription lenses is encouraged when working with analytical x-rays. While glasses cannot be depended upon to provide complete protection to the eyes, they can reduce x-ray exposure. Glass provides about 10 times the protection of plastic. Neither, however, will adequately protect the eye from direct exposure to the primary beam.

FLUORESCENT SCREENS

It is unsafe to inspect an x-ray beam with a fluorescent screen without special precautionary measures. Notify the Safety Office before performing a procedure using a fluorescent screen.

TUBE STATUS INDICATORS

There must be a visual indication located on or near the tube head to indicate when x-rays are being produced This is usually an assembly consisting of two red bulbs, wired in parallel and labeled X-RAYS ON. If one of the lights is burned out, the operator should either replace it before leaving the room, or leave a note on the light assembly indicating that the bulb is burned out. An unlit warning bulb does not necessarily mean that x-rays are not being produced. Always check the control panel.

SAFETY DEVICES

Interlock switches are used to prevent inadvertent access to the beam. They should not be bypassed. Interlocks should be checked periodically to insure that they are functioning properly.

Interlocks and other safety devices and warning systems are not foolproof or fail-safe. A safety device should be used as a back-up to minimize the risk of radiation exposure -- never as a substitute for proper procedures and good judgment.

Detector Type

DIP2030H-VLM

SMART 2k-CCD

Detector Size image

30 cm diameter (x2)

9 cm square

Cycle time

7 minutes

3-20 sec.

Crystal-Det distance

50 - 450 mm

50 - 300 mm

X-Ray Source

MX06HF 1.2 kW Cu 100 micron ultra-fine focus

MX06CE 1.2 kW Cu 100 micron ultra-fine focus

X-Ray Optics

MSC Blue Confocal

XENOCS Fox-2D

Cooling system -170 C

100°K CryoCooler-II

100°K CryoCooler-I

On-line training

(Data Collection How-to.)

On-line Guide

Other Shared Instruments supported by the SCSB

Protein Solutions Dynamic Light Scattering (Bolen Lab MRB 5.154)

MALDI Mass Spectrommeter (Lee Lab MRB 5.138)

Data Collection

See the X-ray Data Collection How-to.

Instrument scheduling is available online.

Data Collection

See the SMART/SAINT/XPREP on-line how-to.

Instrument scheduling is available online.

Instruction Manual

See the X-ray Data Collection How-to.

Cryo-Loops

See the Cryo-Loops How-to.