[ RadSafe ] X-ray Generating Device Compliance

[Mark Ramsay]

HI Neil

A quick answer (but potentially requires a longer one!).

For the UK / EU the 'limit' is not a legal limit (at least not in the
UK). It is derived from a section of the EURATOM Directive which was
designed to basically allow exemption by member states of EU. The
interpretation of this, or more importantly the use of the 'limit',
differs to some extent (e.g surface dose rate / dose rate at 10 cm and
so on).

However, for all practical purposes it might as well be a legal limit
and it is this 'limit' (outside the US) that manufacturers will design
to. Furthermore, many US manufactures will also design to the EU 'limit'
for export etc etc...

" different survey techniques, different geometry, different survey
instruments and different interpretations" - I can quite believe it. In
the UK this would be done either by a Radiation Protection Adviser
(RPA), or by someone else who is able to consult the RPA. In this way
the checks would be deemed to have been done by a competent person to
ensure compliance with the Ionising Radiations Regulations 1999 (IRR99).
In the UK there is not a 'standard' approach, rather how it is done is
left to that competent person. That person (e.g. the RPA) should of
course have a standard / documented way of undertaking a survey which
may be subject to QA checks etc.

As for dose rates at the curtain etc - It seems your example was perhaps
not done by a 'competent person' ?! The key as you obviously know is
perhaps summed up as 'micro Sv-in-any-one-hour' (to use SI units). When
I look at such units I am interested in throughput (per minute / per
hour), spacing of articles being tested, number of curtains, how many
curtains can be open at any one time, size and shape of the objective
(long, short, wide), scatter potential, any shutters that open or shut
etc etc etc. This all yields the micro Sv-in-any-one-hour which is the
important criteria. Instantaneous dose rate it not ignored and there
might be reasons where it matters (e.g. some blockage which causes all
curtains to be open etc).

Hope this quick ramble makes some sense.

Rgs

Mark

www.ionactive.co.uk 

www.twitter.com/ionactive





-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Neil Walters
Sent: 20 October 2010 16:00
To: radsafe at health.phys.iit.edu
Subject: [ RadSafe ] X-ray Generating Device Compliance

Hi Radsafers!
Question about the radiation emission rates from devices used to scan
luggage and packages at airports, govt. buildings, etc...any comments,
logic, suggestions, experience or wisdom greatly appreciated.

These devices are manufactured to comply with US FDA emission rate limit
defined in 21 CFR 1020.40.(c) "...shall not exceed an exposure of 0.5
milliroentgen in one hour at any point five centimeters outside the
external surface".   For the UK and many other European countries that
exposure rate limit is 0.1 milliroentgen in one hour at any accessible
point.   I have yet to find a list comparing all country regulatory
limits for comparison.

However, with so many different regulatory bodies surveying these
devices for compliance to their specs and using different survey
techniques, different geometry, different survey instruments and
different interpretations, etc...I guess I am looking for some common
ground here.

I refer to a recent occurrence when a regulatory body (non-US) was
surveying a device when a package was entering the tunnel, as it passed
through the lead (Pb) curtains, obviously curtains open slightly and
they were able to measure greater than 0.1 milliroentgen per hour
emission rate in that area for that short time period, thus failing the
emission rate limit, but with no regard to cumulative measurements over
a 1 hour period.   I guess my question is are there any globally
recognized methods, techniques, guidance for regulatory agencies (AND)
certification / testing bodies to measure the emission rates of these
device and sign off that they are compliant, rather than using an
instantaneous rate that is not representative of the true exposure rate
during an actual hour?


Thoughts?


Very sincerely,
Neil Walters.

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