Radiology Lab #3
MakeAdeal
ActivatedAluminumexperiment.docx
Activated Aluminum Half-Life Measurement
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Abstract
The GM detector is among the economical and simple to use detectors that exist. The GM plateau is of significance since it gives a range of voltages which allow the device to work correctly. The right plateau voltage at the begging ensures that the GM counter operates. When the voltages as well as the counts are plotted, the result is similar to the one given by Knoll. In the experiment, the system efficiency and dead time were of interest. The dead time is said to be the time when the GM counter can’t produce any pulse since it needs multiplication process in order to reverse itself. In the GM counter, the dead time is in micro-seconds. For the dead time to calculated, two sources are required where one source is counted then the other source, and lastly the sum of the two sources obtained. In order to determine the dead time, the values can be subjected into an algebraic expression.
Introduction
The GM counter is the most economical, simplest and the oldest detector that is used to detect radiation. The device is mostly used in the detection of a radiation field. The gases that are used to detect radiation through gas multiplication are helium and argon. GM counter works at very high voltages that cause adequate gas multiplication which makes pulses to have equal height. Due to the high voltage, the GM counter can’t make radiation type or spectroscopy distinction.
The plateau voltage is of significance when setting up the GM counter for the purposes of gas
multiplication. For the gases to multiply to enough high heights, the GM counter should be set to
high voltages. The voltage is usually placed in the GM region. The plateau voltage will be in the
GM counting plateau.
Fig 1: Detection Regions Radiation graph
Before the GM counter reaches the plateau region, it must reach the starting voltage. The starting
voltage is said the high electric fields which can allow the GM counter to begin reading the pulses
since there is high gas multiplication. The knee is the transition from the starting voltage to the
plateau voltage. An increase in voltage will make the GM detector enter the area of continuous
discharge and this will make the detector to be overwhelmed with pulses. This may damage the
device if not corrected. The GM detector disadvantage is that it has a large dead time. In the GM
counter, the dead time is the measure of the time from the fist pulse to the next pulse while
disregarding the pulse height. Recovery time is the time elapsed when the GM detector discharges the pulse that has the same amplitude like the first full pulse height and it is longer than the dead time.
Fig 2: GM Regions
Fig 3: Recovery Time and Dead Time
Absolute efficiency and intrinsic efficiency is given by:
Experiment Setup
Activated Aluminum was given. The GM counter with its supporting electronics was set up for use as a scalar or counter. The GM counter was tested if it was working. The counter to the aluminum was set up to the aluminum lab counting time. The following sequence was used to set up the counter. “Config Module” to “recall” to “AL-LAB” to “Oper” mode (Bentsman, 2016). The readings were recorded every 12 seconds for 15 trials.
Experimental Results
From the values recorded, the graph below was plotted where the horizontal axis is the time in seconds and the vertical axis is the NET CPM. A trendline was plotted on the same graph and the gradient obtained. The gradient was -627.8 and the decay constant was stated to be 627.8 since the negative sign is as a result of the graph direction which shows the decay of Aluminum.
Fig 4: Graph of Times vs. NET CPM
The half life is given by T(1/2)= 0.69/627.8 which is given as 1.1*10-3.
Y= 1106319296, and Z= 0.473868932.
Thus
= 1.84e-4
Results Discussion
The effects of dead time were included due to the random nature of the radioactive decay which means that there exists a probability that a true event is lost since it happens too fast following a preceding event.
From the calculations, the decay constant was found to be -627.8 while the half life calculated was 1.1*10-3 s. Also, the dead time calculated was 1.84e-4. The known half life of radio Aluminum is 7.17*105. The estimates intrinsic efficiency was 0.074% and the estimated absolute efficiency was 0.66%. The dead time was 1.84e-4 s. The dead time is far much smaller than the 100microseconds of knoll book.
Conclusion
The experiment was a success to a greater degree. The errors that occurred during the experiment are: the background radiation, statistical errors and particle coincidence errors.
REFERENCES
Bentsman, J. (2016). Introduction to signal processing, instrumentation, and control: An integrative approach
Kuehn, K. (2016). A student's guide through the great physics texts: Volume IV
Leroy, C., & Rancoita, P.-G. (2016). Principles of radiation interaction in matter and detection.
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