Accessory for Alpha sample counting system

Accessory for Alpha sample counting system -

Technical Data

Alpha Probe type AP165 manufactured by NUCLEONIX is meant to be used along with Radiation Counting System model RC 605A for counting alpha samples. Radiation Counting System along with Alpha Probe essentially works as an Alpha Counting System.

Alpha Probe of NUCLEONIX make is essentially an integration of ZnS (Ag) scintillator screen, optically coupled to a 2” PMT & covered by a pin hole free aluminized mylar foil to provide, sealing against ambient light. Scintillations received by PMT because of Alpha particles will be converted to electrical charge and inturn to voltage pulses. Each of these events after amplification in the RCS will be counted. The required high voltage is applied (which is typically 900V) through RCS to the Alpha Probe.

Probe has a drawer assembly which facilitates sample placement on sample tray for counting applications. The counting samples are usually deposited on planchets of 25mm diameter or filter paper upto 38mm diameter.

Detector material : Zns (Ag) Screen covered with Aluminized mylar foil.
Density : 10mg/cm 2
Efficiency : 25%
Background counts / 1 Hour: Less than 7 to 8 counts
Photomultiplier tube : PMT of ETL or Hamamatsu make or its equivalent.
Size : 50.8 dia (2″)
Operating Voltage Range : 700 to 900V
Drawer Assembly : Holds both 25mm dia SS planchets or 50mm dia filter paper.

SS and aluminium planchets are required to place the prepared environmental samples for counting. These planchets are of 25mm dia & have a depth of 2mm. These are designed to fit into the sample / source holder / drawer of the detector assembly.


Am241 alpha standard source can be supplied as an optional item. This is an electro deposited source on an SS planchet. Typical activity is in the range of 3000 to 5000 dpm.


(i) Count Net – RS485 based networking software (for multiple systems network).

(ii) Data Communication Software : for data downloading from a single system.

(iii) Dot Matrix Printer : Radiation Counting System has a built-in centronics printer port, it can be directly connected to a printer. Data readings stored in the unit can be downloaded onto the printer (Care should be taken while choosing the printers not all printers are compatible. Please cosult Nucleonix systems for choosing your printer).


The minimum detectable activity is that amount of activity under the same counting time gives a count which is different from the background by 3 times the standard deviation of the background counting rate.
MDA=BG (cpm) + {(3*(BG)1/2 )/t}
Where t is the time in minutes

Minimum Detectable Activity (MDA) calculations for Radiation Counting System (RC605A): For Counting samples:
Example (1) :
What is the MDA for a counter with background of 7 counts in 1 hour?
MDA = {0.1166+ {(3*(7)1/2)/60}
=0.1166+ {(3*2.645)/60}
=0.2488 CPM
=0.004146 CPS.

Thus any gross alpha counts over 0.2488CPM can be considered to be due to radioactivity. That is to say any gross counts above 15 counts per hour can be considered to be due to radioactivity. To calculate the MDA in terms of Bq, divide by the efficiency of the detector The lower the MDA, the more accurately the activity of samples with low counting rates can be determined. This can be statistically achieved by increasing the counting time and /or by decreasing the BG.

Example (2) :
What is the MDA (in Bq) for a counter with background of 7 counts in 60 minutes and an efficiency of 26% for the nuclide of interest?
MDA = {(3*(7)1/2)/60} =0.1322 CPM
=0.1322/0.26 (efficiency) =0.5084 DPM
0.5084 DPM=0.00847 DPS or 0.00847Bq.