20
Built in Isotope Efficiencies
The Inspector has a number of built in efficiencies for specific isotopes. If you know the isotope being
surveyed, then you can select one of the pre-programmed isotope efficiencies to calculate the activity of your
known source. The activity
(DPM and Bq)
is different from the rates of exposure
(mR/hr, µSv/hr, CPM, and CPS).
Activity is the number of disintegrations of a radioactive substance in a given unit of time, which is specific to
the isotope being detected. The efficiencies programmed into the Inspector USB are based on the geometry of
our wipe test plate, which places samples 1cm from the end window of the detector.
Caution: Do not use the
built in efficiencies unless you are surveying a known isotope, as doing so will give you inaccurate results.
Decay
When an atom emits an alpha or beta particle or a gamma ray, it becomes a different type of atom. Radioactive
substances may go through several stages of decay before they change into a stable, or non-ionizing, form. For
example; U-238 has 14 different stages of decay before it stabilizes.
An element may have several forms or isotopes. A radioactive isotope of an element may be called a
radioisotope. However, the more correct term is radionuclide.
Selecting a Built-In Isotope Efficiency
Enter the Utility Menu and scroll to the USE menu item and press SET on the end panel of the unit to select
the isotope efficiency you want to use for your survey. For example, if you know you are surveying Iodine-131,
then you would select I131 from the menu. Once you have selected the cooresponding isotope, press the SET
button to select it. Press SET again to begin normal operation of the Inspector.
You can select from any of the following isotope efficiencies built into the Inspector:
35
Sulfur (S-35),
90
Strontium
(Sr/y-90),
137
Cesium (Cs-137),
32
Phosphorus (P-32),
14
Carbon (C-14),
131
Iodine (I-131),
60
Cobalt (Co-60), and
Alpha.
Selecting Between DPM and Bq
Enter the Utility Menu and scroll to the UNIT menu item and press SET on the end panel of the unit to change
the units of measurement between DPM (when mR/hr and CPM are selected) and Bq (when µSv/hr and CPS
are selected).
Chapter 9: Built in Isotope Efficiencies
