In Vivo Monitoring
The scheduling and measurement process for obtaining in vivo measurements is
usually straightforward. Workers are scheduled for the measurements and results are
available shortly after the measurement is completed. Counting times for in vivo
241Am measurements range from about 15 minutes to an hour or more, depending on
the type of measurement and sensitivity required. The long counting times can
impose limitations on the throughput of workers through a measurement facility,
making scheduling an important issue. Procedures should be in place to assure that
workers arrive for scheduled measurements and that follow-up occurs when a
measurement is not completed or a worker fails to show.
Occasionally, workers are found who are claustrophobic when placed inside in vivo
counter cells. Leaving the cell door partially open may help reduce some of the
anxiety, but will also likely compromise the low background for which the system is
Many workers want to know the results of their measurements. While a simple
statement by the in vivo measurement technician may be adequate, a form letter
stating that results were normal (or showed no detection of any of the nuclides of
concern) can provide permanent verification. If results are not normal, a form letter
can also be used to explain what happens next.
An important aspect of any in vivo measurement program is the calibration and
verification testing of the measurement equipment. In vivo measurement results are
highly dependent on the determination of a background result. Likewise, calibration
using known activities in appropriate phantoms is also important. Phantoms are
available commercially or by loan from the USDOE Phantom Library, operated by
the Pacific Northwest Laboratory.(1)
Urine sampling programs can be effectively administered using either workplace or
home collection protocols. Workplace sampling protocols must assure that adequate
precautions are taken to prevent external contamination of the sample by levels of
activity well below the detection capabilities of friskers and workplace monitors.
Home collection protocols have the advantage of being sufficiently removed from the
workplace to render as essentially nonexistent the potential of very low-level
minor external contamination of the samples is extremely important due to the
dosimetric implications of plutonium in urine.
(1) For information on or to request loans from the USDOE Phantom Library, contact In Vivo Radioassay Research Facility, at the
Pacific Northwest Laboratory, telephone (509) 376-6102.