BERTHOLD TECHNOLOGIES LB 124 Scint Series - Measured Quantities

LB 124 Scint 1. The Principle of Operation of the LB 124 Scint
3
1.3 What’s Being Measured?
a) Counts per second (cps)
The Contamination Monitor is used to measure the radiation ac-
tivity on the surface of persons or objects in counts per second.
With this measuring method, all alpha, beta and gamma counts
are then counted and displayed every second (cps). Since the
count rate registered each second is subject to statistical varia-
tions, the average is calculated on a continuous basis, so that
the displayed result is adapted to the count rate and the dis-
played results is less and less subject to statistical variations af-
ter a very short measuring time.
b) Area activity (Bq/cm
2
)
When you choose to measure the contamination in Bq/cm
2
(i.e.
the radiation area activity), the count rate has to be converted
into surface activity. There is a different conversion factor for
each nuclide. The individual factors are stored in the LB 124
Scint. It is therefore necessary to select the nuclide or nuclide
compound to be measured at the device before each meas-
urement. An alpha nuclide can be set for the alpha channel and
a nuclide with beta or gamma radiation can be set for the beta-
gamma channel. The types of radiation are distinguished during
measurement. The measurement takes place simultaneously.
This does not mean, however, that the contamination monitor is
able to measure this particular nuclide selectively; but the moni-
tor just values the contamination (i.e. the count rate measured)
as if it was caused by the respective radio nuclide.
The conversion is based upon calibration factors determined for
each nuclide and for your monitor. They do not only depend on
the
- radiation type,
- radiation energy and
- decay scheme of the respective nuclide;
but other factors are of importance as well, such as the:
- detector sensitivity,
- measuring geometry,
- self-absorption in the calibrating source.
The calibration factor thus indicates the value with which the
counts per seconds have to be multiplied to obtain a result dis-
play in Bq/cm
2
.
Accordingly, a measurement in Bq/cm
2
is only correct if the se-
lected nuclide and the measured nuclide are one and the same.