Who can benefit from a gamma sample changer?
The number of gamma spectroscopy samples showing up in count rooms
seems to be growing geometrically. People doing gamma spectroscopy in
bioassay, NAA, waste characterization, sediment analysis or environmental
radiation monitoring with either germanium or sodium iodide detectors can
often benefit from a gamma sample changer that automates routine counting
procedures. Regulatory requirements and
QA programs can easily add another 30-40% more count load. Homeland
security events could potentially generate large number of priority screening
samples for many labs. Historically most labs have responded to this
increasing number of samples by adding more detectors -- which in turn
required more shields, more MCAs and more floor space. Add to
this the increased work required for routine calibration and QA and you
just have more of everything. If things really get backed up you can always add a second shift
with still more people to hire, train and pay.
When detectors were smaller and the count times longer, you could effectively arrange samples so that the shorter
counts were done during
the day with human intervention to change samples. The 8hr plus counts
could be counted over night. This would keep total available detector time deployed
relatively efficiently. Several factors including higher efficiency
detectors, the ability for the MCA systems to preset on an MDA, and the emergence of screening samples have
all conspired to generate shorter average count times. Unless you have at
least some samples that you know will require an 8-12 hr count time,
keeping the detectors busy overnight with a single shift operation becomes
The cost effective solution to this problem may be to use an automatic
gamma sample changer. Fortunately the computer power in commercially
available MCA systems is well suited to this task. The objective is to
leverage the existing detector and MCA system investment by making
overnight and weekend hours productive counting hours. There is
substantial experience where laboratories using automatic gamma sample
changers have been able to increase the production of a specific detector
by as much as a factor of 2-3 relative to their historic average on a
manual system. This is based on 2-4hr count times with a 35-40% detector
and a single shift, 5 day-per-week staffing level.
The benefit to your laboratory will depend on your specific samples,
equipment, and operating methods. The purpose here is to raise questions
that will help you define those factors in your count room's operation
that effect the benefit you can derive from a gamma sample changer. You
will have to think through the details of how you want to operate to determine the
implications and benefits for your lab.
General rules for benefiting from a gamma sample changer
- Sample sets with short (~1/2hr) count times benefit a lot during the
daytime hours from a sample changer simply because the operator is freed
up to do other things without frequent interruptions.
- Regardless of the count times much of your benefit comes from the
overnight and week end hours. This means that you must be able to handle
enough samples in a single load to run at least overnight and, preferably,
over the week end.
- Make sure that the sample changer is capable of handling several
different counting protocols in a single load so you can have mix sample
- The closer and more flexible the integration with your MCA and analysis
software of choice the better.
- Can the machine work with existing MCA systems and detectors? Will a
special detector requirement cost me dearly in the future?
- Samples near or over 24hr count times have minimal benefit. You
probably should just buy more detectors.
Questions for internal review
Lab Staffing ____________Hr/day ___________Days/week
Number of samples ____________ Heavy week ___________ light week
Will turn around commitments allow averaging busy and light weeks
Sample count times
Most common __________ Average _______________
||#/ wk - must be day counts, lots of
||#/ wk - must be day counts, lots of
||#/ wk - these can help soak up
overnight hours , minimal help over week ends
||#/wk - efficient overnight – not much
help over week ends
||#/wk - sample changer not of much
Average hours/week the detector is currently actively counting
(potential hours =168hr from 24hr x 7days)
current backlog _________ # samples _________ total hours of count time
________ revenue $$
Will improved turn around generate more revenue and/or good will?