LB Thesis Outline

Abstract

Photon Activation Analysis functions as a way to quantify isotopic concentrations in a certain material. This information is very useful when trying to find potential contaminants within a sample. Selenium, when ingested in large amounts, is harmful as it is a toxic substance. When applying PAA, one of the most important pieces of the investigation is ensuring that isotopes within a sample are detectable i.e. how active does a sample have to be to detect the isotopes of interest? Soil was gathered and targets were created with 50%, 10%, 1%, and 0.1% concentration by mass of selenium which was introduced to the soil during the target creation. The targets were irradiated using the Linear Accelerator at the Idaho Accelerator Center with a beam energy of 32 MeV. Once active, the spectral data was gathered using a high purity germanium detector.

• Give results of signal to noise ratio plot (Experimental MDA)*

Theory

LB Thesis Theory Section

Experimental Setup

Give beam parameters, include schematic of the experimental setup (xfig),include pictures of accelerator and W/Al Radiator. Give GPS coordinates for soil gathered.

Target Information

a schematic of the target is shown below:

Sample	Soil Mass (g)	Inner Se Mass (g)	Outer Se Mass (g)	Front Outer Nickel Foil (g)	Front Inner Nickel Foil (g)	Rear Inner Nickel Foil (g)	Rear Outer Nickel Foil (g)
50% Sample	0.4921	0.5145	0.0900	1.5535	0.3956	0.3050	1.6140
10% Sample	4.9921	0.5142	0.1245	1.3310	0.3592	0.2768	1.2196
1% Sample	10.2403	0.0954	0.0914	3.4274	1.8672	1.7220	3.4887
0.1% Sample	100.1242	0.1074	0.1042	1.3911	0.4467	0.2548	1.3804

DAQ

LB Thesis DAQ Writeup

Detector Efficiencies

LB May 2017 Det A Efficiency

LB May 2017 Det B Efficiency

Calibration Method

When using the HpGe detector, the energy isn't directly given due to the fact that the energy deposited by the photon into the crystal is converted into an ADC channel number. The energy calibration is quite simple. By using calibrated sources with known activities, dates of activation, and energy lines, one can place the calibrated source in front of the HpGe detector and find which channel number corresponds to the energy line of interest. This would be a single data point in your calibration. To ensure that the calibration is of a high quality, take several sources with several different energy lines that span the channel range of the detector and compare the channel number to the energy. Once this information has been found, simply make a file with the energy the line was supposed to be, the channel number, and the standard deviation from a Gaussian fit and plot the points. Once the points are plotted a linear fit can be done to find exactly how the energy lines deviate from the raw channel number.

Data/Error Analysis

LB Thesis Thin Window Analysis

Split Run Measurement Technique

Since there were other people present on the day of irradiation that were using the detectors, a more creative measurement approach was devised. It was known that potentially only 1 detector would be available for use, so a flagging system was implemented to distinguish how the sample type was changed over the time of the measurement. A Co-60 flag was used because it only has energy lines well above the selenium's lines of interest. This means that there would be no extra signal near the region of interest while taking data. For example, a run would be started on a detector with a pure selenium sample being counted. After some amount of time (usually a minimum of 5 minutes) the pure selenium sample was removed and the Co-60 flag was placed in front of the detector for roughly 1 minute to ensure that the Co-60 would be visible. It is worth noting that the time here is important as the detector has a much lower efficiency near the Co-60 lines, so a longer Co-60 measurement is advised to ensure a signal. Once the Co-60 lines are clearly visible in the spectrum, switch the Co-60 out for the selenium-soil mixture and continue counting. Once the mixture is done counting, reintroduce the Co-60 for roughly 1 minute, then swap it out with the pure selenium sample again. This can be repeated for the length of the entire runtime.

Appendices

• Include arrays of plots similar to analysis pages?

• Include ROOT macros?

• Include runlists?