Re: Source Expiration Dates

["Tom O'Dou" <tom_dixie@email.msn.com>]

OK, This is what I think.

Radioactive sources have expiration dates on their calibration if it is
associated with a traceablity from a certifying organization such as NIST.

>What exactly does the expiration date mean? (There is some indication
>that it refers to the integrity of the source encapsulation.)

Typically the reason for this expiration date is to ensure that the dominant
radionuclide(s) measured in the source continue to be dominant and no
daughter in-growth or other radionuclide(s) which may be 'in the background'
cause a change to the properties of the source.

For some radionuclides with long half lives decaying to a singe
non-radioactive nuclide, the concept does not make a lot of sense, the
source should continue to provide service if it is properly cared for.

Many radioactive check sources or 'calibration check sources' are
continuously checked each day, as you count your standards to determine your
efficiency.  As such, the traceability of the standard is continuously
re-evaluated.

If you have data to show that based on your information, the source still
provides its intended purpose, then the source is still traceable and YOU
CAN PROVE IT.

If on the other hand, the source has changed in time and no longer provides
you with satisfactory calibration data, then it has shown you that you can't
trust it - toss it out.

Regarding the issue of source encapsulation, for an electroplated source -
if it is well taken care of, the source will last for many years without
concern for the plating coming off of the substrate.  If you are worried
about this, then check the box that you store it in.

For sources that are in a plastic disk configuration, it is my experience
that plastic will deteriorate over time and the source enacpsulation may
break if dropped.

>
>Can sources be used past this date? Why or why not? (ANSI standards,>etc.)

As described above, if you have the data, the date does not mean much.  If
you don't, a regulator could say that you are not meeting the intent of the
regulation to provide a traceable calibration of the devices that you are
calibrating with the traceable source.

You may want to ask a regulator about this.

>
>If sources are used past this date, are there any precautions needed,
>such as leak checks?


I have a general rule about calibration standards.  If you wipe the surface
many times, you are doing more damage to the source than if you don't.  For
alpha emitters you will remove activity - how much did you remove, and can
you still call that source traceable?  In my opinion - NO.

Remember, if you are using calibrated sources to comply with some
regulation, then be sure to consult with your local regulator before
listening to me.

Have a happy day!

Tom O'Dou, CHP, RRPT
tom_dixie@msn.com




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