How well do you know about the natural background radiation?

It looks like that the more we make measurements of the natural background radiation inside the Science Center Building the more questions are arising. How well does one know about the nature of the background radiation?

We should start posting new measurements with the shielded gamma counters.

Counts on different floors

Counts on different floors were measured using the two gamma detectors, SPA-3 and LEG-1. On each floor counts were measured with placing the detectors on the LEAD bricks and without LEAD bricks as shown in the following pictures.


Placing the detector on the LEAD bricks














Placing the detector on the cart without LEAD bricks














The following plots show gamma counts on each floor of NSC building of GSU. 1st and 6th floors are basement and roof respectively.

Taking measurements on different floors of NSC

Taking measurements on 4th floor of NSC

Taking measurements on 5th floor

Taking measurements on roof of NSC

Prabha (grad. student) is observing gamma counts

Operating high voltage for detectors

1.0 micro Ci Cobalt 60 source was used and placed near the detectors as showing in the following pics.

Threshold(R27) and Gain(R22) potentiometers (at side of the ESP-2) are adjusted to the maximum position in clockwise direction. However, I am not aware of the output values of both Threshold(R27) and Gain(R22). The nominal threshold value for both SPA-3 and LEG-1 detectors is 10mV which is given in the manual.

HV is changed from 700V to 1200V with a step size of 50V. The nominal HV for both detectors is 1000V which is given in the manual. However, the maximum HV which can be given for the detectors is not mentioned in the manual.

The following plots are made by reading the # of counts per minutes for different HV values. In fact, # of count per minute is calculated by taking counts for 10 minutes.

In the above plot it can be clearly found a plateau region. Hence, 1100V is selected as a suitable HV for LEG-1 detector.

In the above plot there is no plateau region. Since we don’t know the maximum HV for the detector, it is not suitable to increase the HV furthermore. However, 1100V is selected as a suitable HV for SPA-3 detector.

ESP High Voltage Measurements

The high voltage output of the ESP-2 is measured by connecting the Keithley HV probe. Measurements were taken using the HP multimeter. When the probe is connected all the readings are reduced by a factor of 1000.









This graph is plotted with set-HV in ESP on the “x” axis, and measured-HV on the “y” axis, when the probe is connected.


Since this shows a linear relation, we can use the Keithley HV probe for larger high voltage measurements.

Photoes of QuarkNet Detector

This picture shows the laptop which runs Labview to control the QuarkNet board.

The Labview program was developed by Mathes Kanishka Dayananda. He also worked on a Labview program to control the ESP detector through serial ports.

This picture shows the QuarkNet DAQ board. We mounted the board inside a small note card box which was bought from Office Depot. Out shop staff, Pete Walker, cut the box on the sides so that cables can be run through.

Here is a view of the downtown area in Atlanta. The picture was taken on the roof top of the Natual Science Center at Georgia State University. The dome in distance is the state capital of Georgia.

Here is a picture taken on the 5th floor in our Natual Science Center. The detector on right has been running for more than a month, which is a senior research project.

Kanishka was working on setting up his Labview program for taking cosmic ray rate measurement.

QuarkNet detector works with Labview

After a quick exercise, Kanishka Dayananda (my Ph.D. student) was able to operate the QuarkNet detector with Labview running on a laptop.

We took the detector to the roof of the Natural Science Center this afternoon and ran the DAQ for 10 minutes. We then took the detector down to the 5th floor and made a quick counting rate measurement at a location next to the two-paddle detector which has been taking data for over one month.