SCSB Crystallography Facilities

The mission of the Sealy Center for Structural Biology and Molecular Biophysics X-ray Crystallography Laboratory is to provide access to state of the art X-ray diffraction instrumentation and the associated support facilities for Center crystallographers. 

The Center has recently installed new x-ray diffraction and solution scattering instrumentation for the lab. The new equipment starts with the Rigaku Ultimate Home Lab® which comprises the unsurpassed high-brilliance FR-E++DW Superbright x-ray generator, with the industry standard RAXIS-IV++ crystallography system with both Cu and Cr optics. In addition, we are acquiring the innovative Rigaku BioSAXS-1000, the first SAXS instrument dedicated to biological research in the southern mid-western states, once again marking UTMB as a leader in structural biology resources.

The SCSB X-ray Crystallography resources currently consists of two x-ray area detector systems. The first area detector is a Rigaku R-AXIS-IV++ dual 30cm Imaging Plate detector mounted on the Rigaku FR-E++DW Superbright x-ray generator. The second detector is a Bruker SMART 2K CCD, which can reach upto 0.84 Å resolution. For enhanced data we have available a choice of sample cooling systems. Both systems are equipped with a Cryo Industries of America CRYOCOOLER. A 4 °C Cold Air refrigerated cooling system is available for samples which cannot be frozen, or do not require freezing.

The Rigaku BioSAXS-1000 2D-Kratky camera is mounted on the left port of our Rigaku FR-E++DW Superbright x-ray generator. This camera offers unsurpassed solution scattering data for macromolecular samples. For more information visit our SAXNS site.

Instrument scheduling, for qualified users, is available online.

PROTOCOLS

These are a collection of documents from the SCSB X-ray Crystallography Center and our research groups.
X-RAY Policy
R-AXIS-IV Guide BioSAXS Guide General Rad Safety
R-AXIS-IV Logbook BioSAXS Logbook nbs111 Rad Safety Rules
CCD Logbook BioSAXS Manual Radiation Hazards
Cryo how to Data archive info Radiation Safety *Test*
Crystal Cryo Log DIP User Manual
ROBOTICS Policy
PHOENIX Quick Start Zetasizer QS Robotics *Test*
PHOENIX Manual ZS Logbook ZS Software Download
PHOENIX Logbook Olympus-DP20 Crystal Trak Trays
PHOENIX Sample Form Minstrel Use
Sealing DWBs Mass Spec. Cal. DIP Logbook
HPLC Column Care Nano Drop Log
Administrative Docs
Emergency Plan Faculty Use Form

Crystallographic Education

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.

Thank you,
Mark A. White

Tutorials developed at UTMB:

Links to Tutorials at other sites:

Radiation Safety

Table Of Contents

Radiation Safety For X-ray Diffraction


Safe Practices:

Telltale Lights: Users should check the Power and Shutter lights every time they walk into the room. Each light operates in an interlock circuit such that if the light is off, you are guaranteed that either the Power is off, or the Shutter is closed.
Beamstops: Beamstops serve two functions: to shorten the path of air scatter, and to protect the image plate. Users should check that the beamstop is in place whenever x-ray power is on, regardless of the shutter status. If you wish to remove the beamstop to check the direct beam position, you must remain in the room while you are doing the experiment. Protecting Your Fingers from the Direct Beam: Always CLOSE the shutters before working in the enclosures. When you manipulate anything in the vicinity of the goniometer, you should assume that the shutter is open and that there is no beamstop: therefore do not put your fingers in the path of the direct beam.
Generator Room Access: Do not work behind the X-ray Generators. Generator rooms are not shielded from air scatter.
Beam-confinement Labyrinths: Labyrinths are junctions between two pieces of equipment through which the beam passes. Any small disturbance of the x-ray optics can ruin the alignment, and reduce the beam intensity. In this event, call Mark White for assistance. Furthermore, if the equipment is severely distorted, dangerous amounts of x-rays can leak out. Visually check that the beam path is properly intact before opening the shutter.
Survey Meters: Users should know how to conduct radiation survey with portable meter.
X-ray Shutter: When data are not being collected the shutter switch should be closed. Before opening the shutter, double check that the beamstop and shields are in place, and that the labyrinths are properly aligned.
Visitors: Visitors must be escorted by an authorized user. It is considered to be a risk factor to bring visitors into the generator rooms.

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.

Crystallographic Facilities

    Detector Type

    SMART 2k-CCD

      Detector Size image

      30 cm square

      9 cm square

      Cycle time

      2 minutes

      3-20 sec.

      Crystal-Det distance

      102 - 450 mm

      50 - 300 mm

      X-Ray Source

      FR-E++DW 2.475 kW Cu/Cr 70 micron micro-focus

      MX06CE 1.2 kW Cu 100 micron ultra-fine focus

      X-Ray Optics

      MSC Varimax Confocal Cu/Cr

      XENOCS Fox-2D

      Cooling system -170 C

    100°K CryoCooler-II

    100°K CryoCooler-I

      On-line training

      Other Shared Instruments supported by the SCSB

    Malvern Zetasizer micro V Dynamic Light Scattering (Robotics Lab BSB 6.614)

    AUC (SBL MRB 5.148)

    BIACORE T100 (SBL MRB 5.148)

    MALDI Mass Spectrommeter (Solution Biophysics Lab MRB 5.148)

    THERMOFLUOR (SBL MRB 5.148)

Rigaku R-AXIS-IV++

Data Collection

See the R-AXIS-IV User Manual

Instrument scheduling, for qualified users, is available online.

Bruker SMART 2K CCD

Data Collection

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

Instrument scheduling, for qualified users, is available online.

CIA CRYO-COOLER

Instruction Manual

See the X-ray Data Collection How-to.


Cryo-Loops

See the Cryo-Loops How-to.