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RADIATION SAFETY MANUAL
Section 8: X-Ray Radiation

INDEX
8.1 X-Ray Analysis Equipment
8.2 Diognostic X-Ray Equipment

8.1 X-RAY ANALYSIS EQUIPMENT
8.1.1 Introduction
Various itemised X-ray equipment are used in universities for the analysis of various materials. This equipment makes use of the phenomena of X-ray diffraction, absorption and fluorescence. In this manual such equipment will be referred to in general as X-ray analysis units or equipment. The dose rate in the X-ray beams from such equipment may be very high and even a brief exposure of any part of a person's body to such a beam could be harmful. Equipment of modern designed incorporates safety features which makes it unlikely that a person using it in the proper manner will be exposed to the intense X-ray beams. Older units still in use may have fewer safety features and may not comply with the requirements of this NH&MRC Code of Practice. All X-ray analysis units, where improperly used, are potential sources of exposure to limited areas of the body (i.e. eye, skin of the face, fingers and hands) particularly while sample or detector adjustments are made, or when equipment is altered or component parts are replaced.

Reports are occasionally received of actual or suspected over-exposure to limited areas of skin or to the eye by older types of units or due to the practice of inactivating safety features on more recent units. Some workers have had repeated episodes of actual over-exposure. In several cases, the victim was not the person who inactivated the safety feature, but an unsuspecting co-worker.

Exposure to a primary beam from an X-ray analysis unit is considered to be avoidable by using a combination of instrumental safety features, working rules and radiation monitoring.

This Manual lays down some general working rules safety features and some monitoring requirements that should become automatic when using X-Ray Analysis Units. However users must also make themselves familiar with the NH&MRC Code of Practice and the operating manual and safety aspects applying to particular pieces of equipment.

8.1.2 Warning Signs, Lights & Labels

  1. Every X-ray analysis unit shall be fitted with an illuminated sign or a combination of a sign and a light which is activated only if the X-ray tube is energized and which then indicates that the X-ray tube is operating. This sign shall be legible and readily discernible for at least two metres on all accessible sides of the X-ray analysis unit.
  2. Each shutter shall be linked with an illuminated sign or light which is illuminated only when that shutter is open and indicates without ambiguity which shutter is open.
  3. Each room, cubicle or area in which an X-ray analysis units is operated shall have a sign at each entrance stating that an X-ray analysis unit is in that room, cubicle or area.
  4. Each room, cubicle or area in which a unit, other than an enclosed unit, is operated shall have at each entrance an illuminated sign or a sign combined with a light which is activated only when the X-ray tube is energized and which then indicates that the X-ray tube is operating.
  5. The lights specified in this Code shall be designed to be 'fail safe' (i.e. to de-energize the X-ray if a light fails); alternatively, adequate warning that a light has failed shall be indicated in a clear and unambiguous manner.
  6. Partly enclosed units which incorporates fixed shields and/or barriers shall be designed to give a clear and positive warning if the barriers or shields are incomplete. A clear and unambiguous notice shall also be displayed on or near the unit indicating the hazards of operating the unit while barriers or shields are incomplete.
  7. Partly enclosed units which are partly enclosed by the interlocked or fixed barriers and/or shields shall have displayed on or near them a prominent notice which warns of the hazard of placing any part of the body, such as the hand, inside the barriers or shields.
  8. Each X-ray analysis unit shall be clearly labelled to indicate whether it is an enclosed unit, or a partly enclosed unit.

8.1.3 General Working Rules for all X-ray Analysis Units

8.1.3.1 Each person who uses an X-ray analysis unit shall avoid exposing any part of the body to a primary X-ray beam. If actual or suspected exposure has occurred the appropriate course of action (see Section 9) should be taken.
8.1.3.2 No person shall allow the X-ray tube of an X-ray analysis unit to remain energized unless all warning lights, as required by this Code, are operating correctly.
8.1.3.3 No X-ray tube shall be energised:
 
1. while outside its protective tube housing, or
2.

with an unshielded aperture in the tube head or protective barrier.
8.1.3.4 No sample, collimator or analysing crystal shall be changed or adjusted while a primary X-ray beam passes through that collimator or is incident on that sample crystal unless:
 
1. the sample, collimator or crystal, during and after the change or adjustment, is within a shielded enclosure, and
2. the change or adjustment is done by remote means from outside the enclosure.
8.1.3.5 Immediate measures shall be taken to remove potentially hazardous situations arising from X-ray beams that may be emitted due to equipment defect, misalignment or any other reason.
8.1.3.6 A list of additional working rules shall be drawn up for each X-ray analysis unit where necessary to ensure safety. This is of particular importance for units which do not meet the requirements of this Code for enclosed or partly enclosed units. A suggested pre-use safety checklist follows. The checklist could be posted on the outside of the instrument.
  • Visual check of the instrument and signage
  • Availability of a survey meter of suitable range
  • Checking of interlock switches
  • Checking for security of moving parts
  • Monitoring of cabinet at full energy setting.
8.1.3.7 The necessary operations of the X-ray analysis equipment shall not be performed by inexperienced persons unless under direct supervision of an experienced operator.
8.1.3.8 Alignments or adjustments shall not be carried out visually while the X-ray tube is energized, unless a viewing system is used which is shielded or designed to prevent exposure of the eye or other parts of the body to the primary beam.
8.1.3.9 The X-ray analysis unit shall not be operated, by inactivation of an interlock or with part of its enclosure removed without prior approval of the Radiation Branch of the EPA (NSW) or unless the X-ray rube is wholly enclosed by the tube housing with all apertures completely covered by interlocked shutters and/or fixed covers.
8.1.3.10 If under prior approval of the Radiation Branch of the EPA (NSW) the X-ray analysis unit is operated with an interlock inactivated or part of its enclosure removed exposing the primary beam, the following rules shall be applied.
 
1. The number of persons who carry out the alignment of a camera or sample in an X-ray beam, or who make any adjustment or alteration to the analysis equipment while the X-ray tube is energized, shall be the minimum necessary to carry out the operation safely.
2. An experienced person not engaged in the operations specified in 6.2.10.1 and observe the procedures and warn each operator doing them of any operation which might lead to any part of the body being exposed to a primary beam or any excessive level of leakage radiation or scattered radiation.
3. When the X-ray tube is energized, access of non-essential personnel to the room containing the unit shall be prevented by physical barriers. A sign warning of the operations in progress shall be placed at each entrance to the room containing the unit.

8.1.4 Monitoring
Radiation monitoring is an essential aid in the control of radiation hazards in the vicinity of X-ray analysis units. However, the accurate measurement of radiation from these units is often difficult and a person seeking to do such a measurement needs specialized equipment, careful technique, and an understanding of the principles involved. The performance of measurements following an accidental exposure of a person to a primary beam is important as a realistic assessment of the dose received is needed to assist in the prediction and treatment of radiation injury. However, radiation monitoring required during use of X-ray analysis units need not be as accurate. In this case simple measurements directed towards prevention of exposure to primary beams and reduction of leakage and scattered radiation to suitably low levels are adequate. The following rules should apply:

8.1.4.1 Accurate measurements of radiation exposure or dose, or their rates, in primary, scattered or leakage beams should only be attempted by, or under the supervision of, a person competent to perform such measurements.
8.1.4.2 Personnel Monitoring
  Localised personal monitors are usually inadequate indicators of exposure to the narrow beams of radiation which may be emitted from X-ray analysis units. However, personal monitors have been found useful in the discovery of some cases of exposure of persons to primary beams from X-ray analysis units and in the assessment of whole body dose due to exposure of leakage and scattered radiation from such units. The following requirements for personal monitoring are therefore recommended:
 
1. Each person working in the vicinity of X-ray analysis equipment should wear a suitable personal monitoring device on the chest throughout all exposures made with the unit.
2. Additional personal monitoring devices should be worn on a wrist or finger of all persons using X-ray analysis equipment, other than enclosed units except when an enclosed unit is operated with an interlock inactivated or part of an enclosure opened.
8.1.4.3 Monitoring of Equipment
  The user of each X-ray analysis unit shall ensure that regular radiation monitoring of the unit is carried out to detect unintended radiation emissions and to assist in preventing such emissions. The following requirements shall apply to such radiation monitoring:
 

Each instrument used for dose rate monitoring shall comply with the following requirements:

  • Its indication shall be accurate to within ±50% for incident radiation over the particular energy range of the X-ray analysis unit to be monitored. More than one monitor or detector may be used to meet this requirement provided their individual energy responses are known for the particular X-ray spectrum of interest.
  • Its sensitivity shall be adequate to give a positive indication with a time response of not more than 20 seconds for a true dose rate of 10 m Gyh-1 when measured in a field of radiation uniform over the sensitive volume of the detector and having an effective energy within the range specified above.
8.1.4.5 If provided with meter indication, the meter shall be either:
 
1. calibrated in arbitrary units only, and the appropriate method of conversion from these units to exposure rate or dose rate for a radiation field uniform over the sensitive volumes of the detector indicated on the instrument, or
2. calibrated in units of exposure rate or dose rate, with a statement clearly displayed on the instrument that its calibration is correct only for a radiation field uniform over the sensitive volume of the detector.
8.1.4.6 Each of these radiation surveys shall be conducted with the X-ray tube of the analysis unit operated at the maximum rated voltage and the maximum rated current for that voltage, and with no filtration in the primary beams other than the inherent filtration.
8.1.4.7

Periodical radiation monitoring shall be carried out on each X-ray analysis unit that is operated on a regular basis. The frequency of monitoring should be not less than that given in the following schedule, but some variation of this schedule may be warranted with certain units or periods of use:

Monitoring

Type of Unit

  • Enclosed; or
  • Partly Enclosed.
Frequency of
  • Quarterly
  • Monthly
In addition, partly enclosed units should be examined for hazardous situations and all safety features checked at least once in each week. For units that do not comply with Section 5 of this Code see 6.4.8.2.
8.1.4.8

Special radiation monitoring shall also be conducted in the following circumstances:

(a) installation of the X-ray analysis units,
(b) replacing an X-ray tube,
(c) any modification or reassembly of any shielding component.
(d) any actual or suspected over-exposure, and
(e) after any extended period of non-use.

This monitoring should include the use of radiographic film or collimated detector to determine accurately the location and extent of any cracks or defects in the shielding.
8.1.4.9 Adequate records shall be kept of all radiation monitoring and examinations for hazards and each entry should include a description of the equipment arrangement and any action taken as a result of the monitoring or examination.

8.2 DIAGNOSTIC X-RAY EQUIPMENT
8.2.1 Introduction
8.2.2 Licensing of Operators
The above units are housed and operated under the auspices of the Discipline of Medical Radiation Technology apart from the animal x-ray unit housed in the MSB Animal Rooms. Only members of this Discipline and the University Veterinarian with the appropriate licences may operate these units or supervise the operation of these units.

8.2.3 Warning Signs and Labels
All the warning signs (both visual and audible) as recommended by the NH&MRC Codes of Practice must be in place and operating. Specifically, each unit should be fitted with a combination of warning sign and light which is illuminated when the unit is energised and an alarm audible when the unit is energised and the shutter open. There should be a fail-safe system in operation in which the unit will fail to energise if either the warning light or alarm fail to operate.

There should be a warning sign and light outside the room housing the x-ray units which is illuminated when any of the units are in operation.

8.2.4 Shielding
There shall be appropriate shielding and clothing (e.g. lead aprons) available for the protection of operators of all diagnostic x-ray machines. This applies to staff and students on site and students on placement as part of course requirements.

8.2.5 Staff & Students
Staff and students operating diagnostic x-ray machines are required to wear personal radiation monitors and be part of an organised badge system (see Section 3).

8.2.6 Protective Barriers
The equipment shall be housed such that:

(a) The controls of the apparatus are located behind a fixed protective shield, situated within the room where the radiation apparatus is housed. The shield shall be not less than 2.1m in height and arranged so that the radiation emitted by the radiation apparatus has scattered at least twice before it enters the area behind that screen occupied by the operator.
(b) The control area should not be situated in the direction of the primary beam, or part thereof, and it should be a minimum distance of 2 metres from the x-ray tube assembly.
(c) The exposure switch shall be arranged so that it cannot be operated outside the shielded area.

8.2.7 Other Protective Barriers

(a) A protective apron and protective gloves with a shielding value of not less than 0.3mm lead equivalent at 150kVp shall be provided for the operator’s use if the operator is not able to stand behind the protective barrier.
(b)

All protective clothing shall be clearly and indelibly marked with the following information:

  • manufacturers’ name or trademark;
  • lead equivalence at a stated potential difference;
  • date of manufacture;
  • single or laminated material;
  • size.
(c) Handling and storage of protective clothing shall be in strict accordance with the manufacturer’s recommendations. Most shall be provided to ensure that aprons may be hung to prevent cracking of the protective material.

8.2.8 Exposure Indication Warning Signs

(a) A radiation warning sign must be displayed on the outside of the entry doors to the room in which the apparatus is installed.
(b) The radiation warning sign must conform with those requirements of Australian Standard AS1319-1983 “Safety Signs for the Occupational Environment” published by the Standards Association of Australia relating to caution (warning) signs.
(c) The sign shall be illuminated whenever the x-ray tube is placed in the preparation mode prior to exposure.

8.2.9 The X-Ray Assembly and Support

(a) The x-ray tube assembly shall be supported and remain stationary when placed in position for radiography, except tomography and other procedures in which it is a requirement that the x-ray tube assembly move in a predetermined manner.
(b) Markings on tube assemblies and beam limiting devices shall be in English and clearly visible.
(c)

X-ray tube assemblies shall bear the following markings on the outer side of the tube housing in a visible position:

  • name or trademark of manufacture of x-ray tube
  • type of model number and serial number of x-ray tube insert
  • name or trademark of x-ray tube housing
  • type number and serial number of x-ray tube housing
  • maximum potential difference of x-ray tube housing
  • nominal value of inherent filtration and any added filtration of the tube housing expressed in equivalent aluminium thickness at a specific kVp
  • size of nominal focal spot(s)
  • position of focal spot(s)
  • position of anode

8.2.10 The Beam Limiting Device

(a) An adjustable multi-leaf collimator shall be fitted to the x-ray tube assembly, and the extent of the diagnostic radiation beam shall be defined by a light beam.
(b) The area illuminated by the light beam collimator shall be effectively coincident with the irradiated area. The total misalignment of any edge of the light field with the respective edge of irradiated field shall not exceed 1% of the distance from the focus to the image receptor. This shall be so for both broad and fine focus.
(c) The light beam collimator should be capable of rotation of not less than ± 45o from the central position.
(d) The centre of illuminated area shall be indicated.
(e) The adjustable area selectors of the light beam collimator shall be provided with scales that relate the selected area to the focal spot-film distance.
(f)

Beam limiting devices shall bear the following markings:

  • name or trademark of the manufacturer or supplier
  • type of model number and serial number of device
  • nominal value of inherent filtration of the collimating device and any added filtration expressed in equivalent aluminium thickness at a specific kVp

8.2.11 Radiation Leakage

(a) The x-ray tube shall be enclosed in a housing in such a manner that their air kerma from leakage radiation measured at a distance of 1 metre from the focus of that tube in one hour, averaged over an area not larger than 100cm2, shall not exceed 1.0mGy.
(b) Diaphragms, cones or collimators used to limit the primary beam to the area of clinical interest shall be constructed so that, in combination with the tube assembly, they comply with the leakage radiation limits set out in paragraph 8.2.7 (a).

8.2.12 The Exposure Switch

(a)

The exposure switch shall have a circuit closing contact which:

  • can be maintained only by continuous pressure
  • makes it impossible to make repeat exposures without releasing the switch
  • makes it possible to interrupt the exposure at any stage of a programmed exposure
(b)

The exposure switch shall:

  • be designed so that it is protected against accidental operation and
  • be arranged so that it cannot be operated outside a shielded area.

8.2.13 Indication of Exposure Factors
The exposure factors which have been set by adjusting the control setting shall be provided and clearly indicated at the control panel.