iLab Projects - Radioactivity

Updated - 22 April 2008

Author: Len Payne

Overview
Learning
LabClient
Construction
Electronics

Overview

This Physics project is a simple experiment on radioactivity that examines some of the basic aspects of radioactivity processes such as the nature of radioactive decay and the inverse square law of the decrease of radioactive decay with distance.

Students use a Geiger counter to measure the radioactivity of a radioactive source as outlined in the Learning section below.

A table holding the radioactive source is rotated until the source is aligned with a hole in a thick lead plate. For the first part of the experiment the head holding the Geiger-Müller tube is set at a fixed distance from the source and many samples of the decay of the source is recorded. In the second part of the experiment the head holding the Geiger-Muller is moved to various distances from the radioactive source in order to examine the square law of radioactive decay.

The MIT iLabs Batch-mode architecture is used to run this experiment remotely over the internet.

Learning

Initially, this equipment will be used in an experiment that contain two parts:

Set the Geiger-Müller tube at a fixed distance from a Strontium-90 source. Measure the Geiger count over a period of four seconds and do this 300 times. A count of 200 to 300 should be achieved in a four second period. Then, investigate the statistical laws that describe radioactive decay.
Set the Geiger-Müller tube at various distances from the Strontium-90 source and measure the counts again. Then, investigate the inverse-square law that relates to the distance from a radioactive source.

Later on, either this equipment will be modified or a second unit will be built to allow various radioactive sources and absorbers to be used.

LabClient

The LabClient is a server-side graphical user interface web application using the Visual WebGui application development framework. The Batch-mode ServiceBroker is used.

The interface consists of three sections:

Lab Status - Displays information about the status of the Lab Experiment. Typically, the Lab Experiment will be online and the Message: field will show the number of experiments queued for processing. The Lab Experiment will be offline if the experiment application/service is not running, the LabServer is not responding, or the ServiceBroker is not responding. A link to this webpage is also provided.
Experiment Specification - The experiment specification is chosen and submitted here. The specification may be validated to ensure that it is sensible before submitting. The Validate button is not really necessary because the user interface will not allow an invalid specification, but it does provide the execution time of the experiment.
Experiment Result - The status of an experiment can be checked. The experiment may be waiting in a queue for processing, currently running, or have completed. If the experiment is queued or running, the estimated time to completion will also be shown. If the experiment has completed, the result may be retrieved and displayed in the Result: box. The result can then be saved (downloaded) as an Excel .csv file to the Client's computer for analysis. The experiment may be cancelled if it has not yet completed.

Lab Client Record

Creating a Visual WebGui LabClient record in the ServiceBroker (Batch-mode) is similar to creating an HTML LabClient record:

In the Loader Script box, type in the URL:
```
	http://localhost/RadioactivityLabClient/Post.LabClient.wgx
```
Replace "localhost" with the correct domain name and "RadioactivityLabClient" with the IIS virtual directory specific to your application.
The "Post." prefix is required to allow the SericeBroker-to-LabClient exchange of credentials.
Visual WebGui requires the ".wgx" extension be registered in the IIS. This is described in the Visual WebGui documentation.

Project Source Code

The code has been written to communicate directly with the LabServer during the development/debugging phase. It is useful the have the ServiceBroker out of the way during this phase. Removing the "USE_LABSERVER" conditional compilation symbol from the Project Properties->Build page disables the LabServer interface and enables the LabClient to communicate with the ServiceBroker when it is deployed.

LabClientVwg_20071115.zip (Visual Studio 2005)

Construction

The equipment was manufactured by Keith Lane and his team in the ITEE's Mechanical Workshop which is part of the EPSA's Technical Services Unit.

Question: There is one item missing in the 3^rd photo. What is it?

Electronics

A Faulhaber 12V DC micromotor with gear reduction and optical encoder is used to rotate the table holding the sources. A second Faulhaber 12V DC micromotor with gear reduction and optical encoder is used to move the head holding the Geiger-Muler tube up or down.

The Ocarina Analog Servo Drives provide a PWM ouput to power the DC micromotors. A differential current command input controls the Servo Drives.

A microswitch is used to determine the Home position of the table. Two microswitches are used as limit switches for the positioning of the head holding the Geiger-Müller tube.

A National Instruments NI-7340 motion controller card, which is installed in a PC, is used to control the Ocarina Analog Servo Drives. The controller card uses feedback from the encoders and microswitches to set the position of the table and the head.

Datasheets

Schematics

Circuit Board

Veroboard Circuit Layout

Answer: The assembly instructions.