load resulting in a reduced beta intensity measured by the proportional

detector. From a continuously integrated count rate the mass on the filter

tape is calculated. During sampling, the mass on the filter spot is always

known and the rate of particulate accumulation is observed.

A continuous measurement of the flow rate determines the sample volume.

A proportional valve is used to maintain the sample flow rate at its nominal

value. From both integrated sample volume and mass detection the

particulate concentration is calculated. At any given time the output signal

delivers the concentration of particulate in actual or standard conditions.

The Model 5014i outputs particulate matter concentrations to the front

panel display, the analog outputs, and also makes the data available over the

serial or Ethernet connection.

Additionally, the Model 5014i proportional detector is sensitive to natural

alpha activity of the aerosol passing through the sampling system. The

additional alpha count rate is used to measure the presence of Radon gas

and infer the daughter nuclides of Radon gas. These daughter nuclides

create a small beta emission. This externally sampled beta emission is

perceived by the detector to be a higher count rate and the higher the count

rate, the less apparent mass detected. Therefore, by measuring the natural

alpha activity due to Radon gas, the proportional beta interference from the

daughter nuclide emissions are subtracted from the count rate to provide a

refined mass measurement. This potential error from Radon gas

interference may be (in lower strength radioactive devices; e.g.; <100 μCi)

as high as actual particle concentrations, especially after filter change or

when the natural activity concentration changes. The Model 5014i has

implemented this procedure to determine separately the natural activity in

the aerosol and to eliminate this error. This procedure further allows the

Model 5014i to provide a more stable reading at lower ambient particulate

concentrations compared to similar methods. Furthermore, from this

information the activity concentration of the natural noble gas Radon is

derived.

The measurement chamber houses an RTD temperature sensor. The Tsensor

directly measures the temperature of the incoming sample stream for

a continuous air mass compensation, and the flow system. The flow and

ambient sensor measurements are combined within a firmware algorithm to

maintain an accurate measurement and control of volumetric flow at the

inlet and through the differential orifice.

The Model 5014i also includes three pressure sensors to measure the

differential pressure across a subsonic orifice, vacuum under the filter tape,

and barometric pressure. The flow P-sensor is solely used for measurement

at the orifice for flow rate control. The vacuum sensor is used for air mass

compensation, as an indicator for clogging of the system and is included in