X-ray Laboratory Safety
Additional Local Rules
System of Work in Powder
X-ray Laboratory 313
Last updated 7 November 2008
Other web pages provide information on
Health and Safety (Chemistry UCL)
- Current Status
- Critical Examination
- New User Training
- X-ray Safety Monitoring
- Procedure for Open Beam Work within
Controlled Radiation Area 312
- 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
- Siemens D500
- 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
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
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:
- 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.
- 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.)
- 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.
- 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.
- 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:
- 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.
- 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.
- 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.
- 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.
- 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
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
- The following tests are performed:
- 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.
- Repeat the above test for the low-level sensor.
Again, the alarm should activate.
- Check that the audio alarm within 312 sounds during either of
the above tests.
- Check that the visual alarm within 312 flashes red
during either of the above tests.
Industrial Materials Group