Newsletter 28


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S. Neumaier1, H. Dombrowski1, K-H. Motzkus2, U. Häusler2
1 Physikalisch-Technische Bundesanstalt, Braunschweig, Germany
2 Bundesamt für Strahlenschutz, Berlin, Germany

Abstract

The German X-ray Ordinance lays down the basic requirements for type approvals of X-ray devices. In Germany, type approvals according to the Radiation Protection Ordinance and the X-ray Ordinance are issued by the Federal Office for Radiation Protection (Bundesamt für Strahlenschutz, BfS). The type testing of X-ray devices is carried out by the Physikalisch-Technische Bundesanstalt (PTB), the German National Metrology Institute and the highest technical authority of the Federal Republic of Germany for the field of metrology and certain sectors of safety engineering. In 2010, a new X-ray Ordinance is to come into force in Germany. This ordinance will introduce a new category of type-approved X-ray devices, called “basic-protection devices”, in addition to the existing five categories. In general, type approvals shall ensure high safety standards in radiation protection. In particular, the exposure of operators due to ionising radiation shall be kept “as low as reasonably achievable” (“ALARA principle”).

In the following sections, the technical requirements for basic-protection devices as well as the type-test procedures for this new category of X-ray devices will be outlined.

1. Introduction

The basic safety standards for the protection of the health of workers and the general public against the dangers arising from ionising radiation are laid down by European Council Directive 96/29/EURATOM [1]. This Directive applies to all practices which involve a risk from ionising radiation, namely (according to article 2):

  • (a) the production, processing, handling, use, holding, storage, transport, import to and export from the European Community and the disposal of radioactive substances;
  • (b) the operation of any electrical equipment emitting ionising radiation and containing components operating at a potential difference of more than 5 kV;
  • (c) any other practice specified by the Member State.
Some exceptions to the requirement of reporting or authorisation are listed in article 3. In particular, those practices, where type-approved devices are used and the ambient dose equivalent rate does not exceed 1 µSv h-1 at a distance of 0.1 m from any accessible surface of the device, require no authorisation, which facilitates the use of such devices, especially for industrial applications, considerably.

In Germany, these basic standards are implemented through the Radiation Protection Ordinance [2] (the current version came into force in 2001) and the X-ray Ordinance [3] (considerably amended in 2002). The Radiation Protection Ordinance (Strahlenschutz-Verordnung) provides regulations for the handling, use, storage, transport and disposal of devices containing radioactive substances. In addition, this ordinance governs the operation of accelerators or X-ray devices with high voltages exceeding 1 MV, whereas the X-ray Ordinance (Röntgen-Verordnung) provides regulations for the operation of X-ray devices with acceleration voltages between 5 kV and 1 MV and the operation of sources of stray radiation.

In general, an authorisation by the local supervisory authority is needed for practices which involve a risk from ionising radiation emanating from an artificial source. However, practices regulated by the German Radiation Protection Ordinance do not require an authorisation nor reporting, when a type-approved device is operated. On the contrary, according to the German X-ray Ordinance, the operation of type-approved X-ray devices in general requires reporting to the responsible authority. For that reason, the “1 µSv h-1” concept of Article 3 No. 2 of Council Directive 96/29/EURATOM is not applicable in Germany, as far as X-ray devices are concerned. As a consequence, the dose rate limits defined by the German X-ray Ordinance differ considerably from 1 µSv h-1 and vary strongly with the kind of X-ray device and its application. A more detailed description of the various categories of type-approved X-ray devices, as defined by the German X-ray Ordinance, follows below.

2. Type approvals in Germany

BfS is responsible for issuing German type approvals according to the Radiation Protection Ordinance and the X-ray Ordinance. In accordance with these ordinances, prior to issuing a type approval BfS initiates a type test by PTB. Concerning devices containing an encapsulated radioactive source a further technical authority, the Federal Institute for Materials Research and Testing (Bundesanstalt für Materialforschung und -prüfung, BAM), is involved in issues concerning leakage, materials chosen and the design of the encapsulation of the radioactive substance and quality assurance. Both ordinances mentioned do not constitute a claim for type approvals. This means that only devices or X-ray tube assemblies which assure a high safety standard according to the state of the technology can get a type approval.

2.1 Type testing of X-ray devices

The amended version of the German X-ray Ordinance of 2002 distinguishes between the following categories of type-approved X-ray devices:

  • X-ray tube assemblies (Röntgenstrahler) - Combinations of an X-ray tube with a protective tube housing. In some cases, the high voltage (HV) generator is included in the housing.
  • High-protection devices (Hochschutzgeräte) - X-ray devices which completely enclose the sample to be investigated, with the exception of small openings which allow only a hand to be entered.
  • Full-protection devices (Vollschutzgeräte) - X-ray devices which can be operated only when the sample to be investigated is completely enclosed by the protective housing. This has to be safeguarded by two independent safety circuits.
  • School X-ray devices (Schulröntgeneinrichtungen)  - Full-protection devices with additional safety requirements. They are used for educational purposes in schools.
In addition, sources of stray radiation like electron microscopes, which do not include an X-ray tube, but emit X-rays unintentionally, can obtain a type approval, if the requirements of the X-ray Ordinance are fulfilled and they pass a type test.

A new category of X-ray devices called “basic-protection devices” will be implemented by the forthcoming amended version of the X-ray Ordinance, which is expected to come into force in 2010:

  • Basic-protection devices (Basisschutzgeräte) - This new category will comprise cabinet X-ray systems which fulfil special requirements described below in section 2.3.
The dose rate limit for this new category, as well as the current and future dose rate limits of the existing categories (defined by Annex 2 of the X-ray Ordinance), are compared in Table 1. In Table 2, the organisational requirements for the operation of these X-ray devices are summarised.

Table 1. Dose rate limits for type-approved X-ray devices and sources of stray radiation

Category of type-approved system
Dose rate limits at the specified distance
Distance
According to current X-ray Ordinance [2]
According to X-ray ordinance of 2010
X-ray tube assemblies

2.5 mSv.h-1 (V ≤ 200 kV)
10 mSv.h-1 (V > 200 kV)

2.5 mSv.h-1 (V ≤ 200 kV)
10 mSv.h-1 (V > 200 kV)		1 m from the focal point
Basic-protection devices
n/A
10 µSv.h-10.1 m from any accessible surface
High-protection devices
25 µSv.h-1
10 µSv.h-10.1 m from any accessible surface
Full-protection devices
7.5 µSv.h-13 µSv.h-10.1 m from any accessible surface
Sources of stray radiation
1 µSv.h-11 µSv.h-10.1 m from any accessible surface

Table 2. Organisational requirements for the operation of type-approved X-ray devices and sources of stray radiation

Category of type-approved system
Report of authorised expert prior to start-up
Local radiation protection regime
Report of authorised expert every 5 years
X-ray tube assemblies
X
X
X
Basic-protection devices
-
X
X
High-protection devices
-
X
X
Full-protection devices
-
-
X
Sources of stray radiation
-
-
-

Full-protection devices are the only kind of type-approved X-ray devices which may, after prior reporting to the local authorities, be operated without having a pronounced radiation protection regime (i.e. without being investigated by an authorised expert prior to start-up, without the supervision of a radiation protection officer during the operation and without requiring any technical or radiation protection qualifications of the operator). Therefore, high technical safety standards have to be fulfilled in order to achieve a type approval for full-protection devices.

2.2 Technical requirements for type-approved devices

According to the X-ray Ordinance, high-protection devices, full-protection devices and school X-ray devices must meet the requirement that the X-ray tube or the X-ray tube assembly can only be operated if the protective casing is completely closed, which for the latter categories must be guaranteed by two independent safety circuits (exceptions are regulated in Annex 2 to the X-ray Ordinance). Detailed technical specifications regarding the implementation of this requirement have been established by a decision of the German Federal States of March 28, 2002:

  • The safety protection system used must comply with the safety degree of "category 3" specified in standard EN 954-1 [4]. In addition, the relevant regulations of standard DIN 54 113, part 2, are to be met [5]. This ensures that the failure of a component is detected at the latest when the operator tries to restart the device, so that the switching-on of the X-ray tube is electronically prevented.
  • Full-protection devices, school X-ray devices and high-protection devices must be provided with a time-delay function so that opening of the casing will be possible only if the acceleration voltage of the X-ray tube is less than 5 kV.

2.3 Technical requirements for the new type “Basic-protection devices”

Frequently, automatic X-ray scanners are used in industry and in safety applications for a variety of purposes: analysing the composition of food or technical materials, checking packages for foreign objects, checking the correct filling of non-transparent packages or cans, inspecting luggage for illicit items, just to list some examples. These systems are typically used in automated production lines of for example the solid-state industry, the food industry and during luggage inspections at airports or other facilities. A type test of the included X-ray tube on its own is not appropriate, because this test would merely guarantee, that the ambient dose equivalent rate at 1 m from the focal point of the tube would be lower than 2.5 mSv h-1 or 10 mSv h-1, depending on the operating voltage. This value is much too high if personnel or members of the public stay close to an X-ray scanner, as is typically the case for luggage inspection devices. An adequate category was, however, not defined in the X-ray Ordinance, so that these scanners could not be type tested appropriately in the past. Thus, a new category, named "Basic-protection devices", had to be defined.

What are the common characteristics of basic-protection devices? For practical reasons, the protective casing of this type of device cannot be completely closed. Usually, the protective casing has two apertures connected to a transport system; one for the insertion of goods and another for the removal of goods after they have been inspected. The apertures are sometimes covered by a flexible protective curtain to limit leakage radiation. The automatic transportation systems for the inspected goods are a protection against unwanted irradiation of human beings, but in some cases cannot prevent people from entering a transport belt completely. Therefore, the protective level of these kinds of devices is lower than that of full-protection or high-protection devices.

The following requirements for basic-protection devices will be introduced:

  • It has to be ensured that the protective casing encloses the X-ray tube and the object to be examined completely while the X-ray tube is in operation. Apertures are merely admissible for the automatic transportation of inspected goods and their dimensions have to be adapted to that purpose.
  • The dose rate limits for type-approved basic-protection devices at a distance of 0.1 m from the surface of the protective casing and at a distance of 0.1 m from the apertures may not exceed 10 µSv h-1 under maximum operating conditions.
  • If a continuous operation of the X-ray emitter is required, its operation without completely closed protective casing is allowed only if the dose rate inside the protective casing does not exceed 10 µSvh-1.
The background to these requirements is that the requirements for high-protection devices were extended so that openings for a conveyor belt or another automatic transportation system for inspected goods are admissible so that luggage inspection devices, food scanners or other X-ray scanners can obtain an adequate type approval, which supports the radiation protection of personnel or members of the public staying close to such devices.

3. Summary and conclusions

In Germany, type testing and type approvals are an important basis for the high safety standards, that protect workers and members of the public against avoidable exposures to ionising radiation. Certain categories of devices or apparatus are defined by law. This categorisation system defines different safety levels with increasing technical requirements, in order to allow for a stepwise reduction of organisational radiation protection. Therefore, type approvals help:

  • to keep the exposure from X-ray devices under normal operation conditions to human beings "as low as reasonably achievable" (“ALARA”),
  • to minimise the risk of failure that may cause harmful exposures, by state-of-the-art technical means and
  • to minimise the administrative expenditure for operators of X-ray devices and authorities (no individual authorisation for type-approved devices needed).
In order to maintain the high level of safety standards, the German legislation is adapted to the current state of the technology from time to time. The next version of the X-ray Ordinance will include a definition of basic-protection devices (a kind of cabinet X-ray system), which can be granted a type approval in the future. Some admissible limits of the ambient dose equivalent rates near X-ray devices will be lowered. These new limits will ensure that even for long exposure times close to an X-ray device the admissible effective dose limits will be met.

References

[1] European Commission, “Basic safety standards for the protection of the health of workers and the general public against the dangers arising from ionizing radiation”, Council Directive 96/29/EURATOM of 13 May 1996, Official Journal of the EC L159, Vol. 39 (Luxembourg: Office for Official Publications of the European Communities) (1996).

[2] “Verordnung über den Schutz vor Schäden durch ionisierende Strahlen” (Radiation Protection Ordinance - Strahlenschutzverordnung - StrlSchV) of 20 July 2001, BGBl. I S. 1714, latest revision on 13 December 2007, BGBl. I S. 2930 (2007).

[3] “Verordnung über den Schutz vor Schäden durch Röntgenstrahlen“ (X-ray Ordinance - Röntgenverordnung - RöV) of 8 January 1987, published as amended on 30 April 2003, BGBl. I S. 604 (2003).

[4] European Committee for Standardization (CEN), “Safety of machinery – Safety-related parts of control” (EN 951-1:1997-03) (Brussels: CEN) (1997).

[5] Deutsches Institut für Normung (DIN), “Non-destructive testing- Radiation protection rules for the technical application of X-ray equipment up to 1 MV“ (DIN 54113-1 to -3) (Berlin: DIN) (2005).