X-ray Laboratory Safety

Additional Local Rules
for
System of Work in Powder X-ray Laboratory 313

Last updated 7 November 2008

Other web pages provide information on
Departmental Health and Safety (Chemistry UCL)

Contents:

1. Current Status
2. Critical Examination
3. New User Training
4. X-ray Safety Monitoring
5. Procedure for Open Beam Work within Controlled Radiation Area 312
6. Low Oxygen Alarm Testing

1. Current Status

The IMG X-ray laboratory currently has two X-ray generators, one supplied by Siemens, now Bruker, for a Siemens D500 Bragg-Brentano diffractometer, and one made by Spellman and supplied by Stoe for a Stoe refurbished STADI-P powder diffractometer. Both systems are equipped with non-walk-in safety radiation enclosures. The latter are fully interlocked. The opening of the shutter is only by positive user action and with the shielding correctly in place (i.e. doors closed). Accidental opening of the safety enclosures with the beam open results in a trip of the beam shutter which remains closed even when the enclosure doors are re-closed.

2. Critical Examination

1. Siemens D500
2. Stoe STADIP

3. New User Training

All new users of the X-ray powder diffractometers must be trained in person either by the laboratory research manager, Martin Vickers, or by the senior academic, Jeremy Karl Cockcroft, responsible for the PXRD laboratory.

Users will be given instruction on:

• The meaning of all hazard/warning signs and lights
• The normal status of the instruments (e.g. generator power levels)
• How to electrically isolate the X-ray generators in the event of emergency (e.g. burst water pipe)
• Accessing the sample areas of the diffractometers (e.g. opening and closing access doors)
• How to mount samples on the diffractometers
• How to align capillary samples on the Stoe diffractometer (e.g. use of the telescope)
• How to run standard samples for checking instrument alignment (e.g. quartz standard on the D500)
• How to acquire data via computer control of the diffractometer (i.e. use of either VAX and/or PC as required)
• How to display the acquired data

In addition, users are made aware of the local rules concerning X-ray laboratory safety.

Everyday users of the equipment must not touch or adjust any part of the diffractometer concerned with alignment. If misalignment is suspected (e.g. after a long power shutdown), users must contact Martin Vickers or Jeremy Karl Cockcroft as soon as possible. In the event of warning bulbs not functioing correctly, one of the above persons must be informed so that dead bulbs can be replaced.

In the event of non-ambient sample environments being used, these will be setup by Martin Vickers or Jeremy Karl Cockcroft and specific training will be given for their use.

4. Regular X-ray Safety Monitoring

The following procedures must be carried out during the year (typically every 2-6 months depending on active use of the equipment). Tests must be carried out with a calibrated and functioning Geiger X-ray monitor, and the results are to be recorded in the hardback IMG laboratory safety book. Before the specific tests below are started, the warning light bulbs of the X-ray generators should be checked for correct functioning. (The X-ray generators will normally function with one dead bulb, but not with two dead bulbs. Note that the Spellman generator has an additional single bulb in the safety box behind the generator.)

• Radiation Safety Tests on Siemens D500 Setup

  The following tests are done with the generator switched on and set to 45kV and 30mA for the Cu anode X-ray tube:

  1. Check that shutter opens and closes correctly using the manual open and close buttons on the control panel on the outside of the diffractometer. The warning lights should display both green and orange when the shutter is closed and the green light should swop to red when the shutter is open. The action of opening and closing the shutter should result in an audible sound.
  2. With the shutter in an open state, check that the safety system operates correctly when the front door is pulled open. The shutter should close and not reopen when the door is re-closed. (Note: prior to the improvement in the X-ray safety circuit, this could result in complete shutdown of the generator if the door was pulled open hastily.)
  3. With the door closed and the shutter open, use the Geiger monitor to test for leaks around edges of doors and panels. Note that this test is particularly important after the removal of any panels for whatever reason, rare though this instance may be.
  4. With the door open and the shutter closed, check that the shutter is not leaking radiation by carefully putting the Geiger tube in the path of the direct X-ray beam.
  5. Finally, test around the tube housing for X-ray leaks. (Note: prior to improvements of the tube housing, low level radiation leaks had been observed. The housing was improved by the addition of additional brass blanking plates in the shutter housing space of the tube housing.) This test is particularly important whenever the X-ray tube is changed.

• Radiation Safety Tests on Stoe STADI-P Setup

  The following tests are done with the generator switched on and set to 40kV and 30mA for the Cu (or Co) anode X-ray tube:

  1. Check that the shutter opens and closes correctly via the computer interface. When the shutter is open, the red light above the shutter should be illuminated. (In addition, when the X-rays are on, the red light on the front of the generator will also be illuminated.) Note that this test can be done with the X-rays on or off since the shutter interlock safety circuit is separate to the state of the X-ray generator (though the latter must be on) in contrast to the Siemens D500 setup.
  2. There are 8 glass doors on the safety shielding each equipped with 2 magnetic controlled microswitches. With the shutter open, check that opening each door results in closure of the shutter and that re-closing the door leaves the shutter closed. Again, this test may be done with the X-rays on or off.
  3. With the Geiger monitor and X-rays on (not off), check that there are no leaks around the X-ray tube housing (particularly at the anode end where the flat seal gives potential for leaks after the X-ray tube is moved or changed. This test must be done whenever the X-ray tube is changed.
  4. With the X-rays on and the shutter indicating closed, check that the shutter is fully closed and not leaking radiation by carefully placing the Geiger tube directly in the main beam.
  5. Finally, with the X-rays on and the shutter open, check with the Geiger monitor that there are no X-ray leaks through the glass shielding. This check is particularly important for the glass window that lies in the path of the main X-ray beam.

  Note that failure to remove the sample alignment telescope with result in a failure for test number one above.

5. Procedure for Open Beam Work within Controlled Radiation Area 312

From time to time it may be necessary to bypass the security interlocks on the Stoe system so as to re-align the diffractometer. (In extremely rare circumstances, open beam diagnostic work may be required for the Siemens system. In this case, a similar procedure to that described below should be adopted). This requires access to the bypass key that is kept in the key-cupboard. During open beam work, the following procedures must be followed:

• The working area must be temporarily re-designated as a controlled radiation safety area;
• Notices to this effect must be displayed on the entrance doors to 312;
• Access to the controlled radiation area must be restricted to authorized persons. The following persons are authorized:

  Dr Jeremy Karl Cockcroft
  Mr Martin Vickers

• Two persons should be in attendance: one to carry out the actual alignment procedure and the second to "shadow" so as to ensure that correct procedures are done with due regard to safety;
• The person carrying out the alignment work should wear the finger badge provided. Finger badges should be changed each month together;
• In the event of a suspected accidental exposure to the X-ray beam, the departmental safety officer should be informed and the relevant personal dosimeters should be returned for immediate dose assessment;
• Once the alignment procedure is completed, the override key should be returned immediately to the locked cupboard and the notices declaring the area as a controlled radiation area must be removed.

6.Low Oxygen Alarm Testing

The following procedures must be carried out on an ad-hoc basis (depending on active use of both liquid nitrogen and liquid helium dewars). The test may be carried out by blowing an inert gas over the oxygen sensors: in practice, expired air blown through a rubber tube and directed at the sensor should be sufficient to trigger the alarm system.

The alarm system consists of the main control box in 312 plus two oxygen level sensors, one positioned near floor level and the other positioned near ceiling level, plus 4 alarm units. Normal reading for oxygen level is 20.9% (though in practice the sensors may display a reading in the range 20.8% to 21.0% due to drift in the calibration as a function of time). If the level of oxygen drops to an unsafe level (< 18.5%) for either sensor, the audio-visual alarm box in 312 will produce a red flashing light and siren-style noise.

When the oxygen level returns to safe (i.e. both sensors reading > 18.5%), the alarms will automatically switch off. The current system does not record that the alarms have been triggered: it simply shows whether the oxygen level in the room is safe or unsafe.

• The following tests are performed:
  1. Test that the read out for the high-level sensor decreases when expired air is blown across the sensor. It should decrease sufficiently for the alarm to activate.
  2. Repeat the above test for the low-level sensor. Again, the alarm should activate.
  3. Check that the audio alarm within 312 sounds during either of the above tests.
  4. Check that the visual alarm within 312 flashes red during either of the above tests.