LMS Stability, Data Correction and the Radiation Accident

within the PrimEx Experiment

by

LaRay J. Benton

M.S. Nuclear Physics

May 2006 Graduate

North Carolina A&T State University

Thomas Jefferson National Laboratory

PrimEx Collaboration

Advised by Dr. Samuel Danagoulian

One issue that has had affect data analysis and calibration is the filter wheel position during data collection phase 2 of the experiment. During the experimental run, data collection was done in three phases; Phase 1: Pedestal Analysis, Phase 2: LMS Data, Phase 3: Production Runs.

Where as the phase of the experiment periodically changed throughout the experimental run. Hence, the current phase of the experiment depended on the type of data that was being collected at the time. Thus the filter would rotate, depending on the phase of the experiment, and it would either allow a signal to enter the LMS trigger, or not. During Phase 2 of the experiment, light was allowed in and LMS Data was collected. However, there are different settings of filter wheel position, and depending on the position of the filter wheel, we would record LMS data that was not collimated and corresponded to the filter wheel position in which it was recorded. Therefore you have some runs that had LMS data, and some that didn't.

This absence of LMS data is displayed on our graphs, bottom right, and is seen as wholes in the graphs. The larger the whole, the more consecutive runs that were taken with the filter wheel position being closed.

Missing LMS Data

There is a total of 332 runs without LMS data, equating to about 23.85% of the total run (1350 Runs), and I labeled these as bad runs in my analysis. This missing data is also confirmed and corresponds to wholes existent in Dr. Danagoulian's PMT ratio plots. This behavior is also seen in the actual data, as seen to the left, as ADC values that often deviate drastically from the mean, with a constant value that is the same for all runs where there is no LMS data. Hence, these bad runs are not initially included in my averaging technique to correct LMS data, but values for these bad runs will be filled in later in my analysis.

LMS Data

As you can see to the left, the actual LMS data for crystal ID W1005 displays a behavior that is directly proportional to the filter wheel position. Where as for every sequence of runs, they alternate between a High, Med, or Low ADC count readout. Hence, giving validity to the fact that there are 3 filter wheel positions in which light or a signal can enter into the LMS trigger. Thus, when we went to analyze the LMS data, particularly the stability of the data over all runs, we got graphs that looked like the one shown above. This graph displays 3 separate graphs, instead of one single graph. Hence, supporting the fact that our signal is being divided into three parts, instead of being collimate into one single signal. So to correct this problem we chose to collimate every three runs, take an average of the group, and redisplay the results. This was very possible to do and a very likely solution since each run was only giving us 1/3 of the total signal that we needed.

Averaged Data

As seen above to the left, when we average every 3 runs we get a single averaged ADC value, as well as a single run number to plot it against. Now when we averaged all the runs and plotted them, as shown above right, our graphs yield a single line data that is better descriptive of the LMS data and stability over the entire run, for this particular ID. However, we did encounter situations where not all of the averaged groups had1 Med, 1 High, and 1 Low data set. Some had 2 Med and 1 Low, 2 High and 1 Med, ect. . . This resulted in averaged values that were either above or below the mean for the averaged data set. This particular situation is shown above to the left, highlighted in red. Looking back at the previous slide, the averaged group of runs 4148, 4149, and 4150, yields an ave of 921.33 which is above the overall mean, and is displayed as the first point above the mean on the graph shown above. To correct these situations, different algorithms had to be devised and entered into the code to correct this problem.

As you can see above, my program does corrects the LMS data and fixes any data points that fall outside of the mean during the averaging of the data. I edited my program to correct all LMS data and handle all possible combinations of data. Where as my program is capable of handling various data sets such as; 2 High and 1 Low, 1 Low, 1 Med, and 1 Low, ect.. Hence now all incorrect data points will be collimated and corrected.

Corrected LMS Data

Instead of setting the value of the averaged group equivalent to a predetermined group, or value already calculated, which is a widely used way to correct data, I'm using the values given within the averaged group to correct its self. An example of the code used to correct the data is as follows;

if (fabs(((val[0]+val[1]+val[2])) - ((val[0]+val[1]+val[1]))) <= 3.0) // This works

{

if ((val[1]-val[2])==0.0 && val[0] < val[1]) // This fixes #1

{

val[2]= (val[0]-((val[1]-val[0])));

sum = val[0]+val[1]+val[2];

//	cout <<sum <<endl; // This prints out the Sum of 3 runs

cout <<sum / 3.0 <<endl; // This prints out the Average of 3 runs

k=0;

sum=0.0;

}

This is the code I used to correct the data point mentioned earlier, in which the data points were corrected and the averaged of the group went from 921.33, as mentioned on slide #4, down to a value of 914, which is well with in the mean. This was done by reassigning the value of the 3rd run in the set, and recalculating the average of the group. The following is an example of how I corrected of this group, and is equivalent to the code written above.

Run 3 = Run 1 - ( Run 2 – Run 1) = 914 - ( 925 – 914) = 903

New Average = (Run 1 + Run 2 + Run 3) / 3.0 = ( 914 + 925 + 903) / 3.0 = 914

How I Corrected the Data

Thus, my program collimates and corrects the data graphs, but does not correct all of the data points for every ID. There are some incidents were my program does improve the data, but doesn't correct it to the point were the graphs are linear and smooth as shown earlier. These particular ID's and graphs are a result of an over exposure to radiation of the crystals, during the experimental run. The graphs of one of these exposed ID's are as follow;

Radiation Accident

As shown in both graphs by the inverse spike in the data, the radiation accident happened around run 5050. What is even more interesting is as time passed from run to run, the crystal started almost repairing its self and rather re cooperated from the radiation damage done to it. To better understand this anomaly and others, the rate dependence of the LMS gain may need to be monitored and analyzed, to understand the effects from this radiation exposure in order to correct the data for all radiated ID's. This analysis is ongoing.

Other Anomalies

Other anomalies from graphs that are not yet explained are as follows;

Correction of Missing LMS Data

Data correction for all missing runs or runs without LMS data will occur as follows;

1) A complete list of all IDs having the same general plots must be made, and divided into groups of rather their plots are Linear, Exponential, etc...

2) For those plots that are Linear, a Mean value will be determined, and all ADC values for missing or bad runs will be set to a value equal to the mean. All Exponential plots and other plots will have to be fitted and a function will have to be calculated, and all missing or bad ADC values for these IDs will be set to that particular function in order to fill in all wholes present with in the data.

3) After all data is corrected and filled in, all data will be re-graphed and will hopefully display a single continuous line of data, depending on the ID, and will improve our stability plots, histograms, and overall data, such that calibration of HyCal can be performed.

In relation to statistics, when the LMS was developed and implemented into the PrimEx experiment, it was calculated that we would need a total of 2000 statistics of LMS data, for the total signal needed in order to properly calibrate the detector and it's associated instruments, and correctly calculate and record the short-term stability of the experiment it's self. However, upon analysis of the data, particularly analyzing the ADC spectrum of events, it was discovered that we were only accumulating about 700 statistics or events, instead of the 2000 initially determined. Where as in the set-up of the LMS, we 3 reference PMT's and 1 pin-diode that makes up the total LMS trigger. Thus giving us the following equation for the LMS trigger;

3 yap + 1 LED = LMS Trigger

Thus giving us a 3 to 1 ratio in relation to the 3 radioactive yap sources to the LED. Hence indicating that the data received by the LMS is only 1/3 of the total signal, every run gives us a signal of about 700 statistics instead of the 2000 needed.

2005-10-28T09:00:37