LB Se-79 Soil Analysis

Below is a description of how the activity of the Se-79 in the May 2017 soil/Se was determined.

Activity of Se-79m

First, find the activity of the Se-79m state which has a half life of 3.92 [math] \pm [/math] 0.01 minutes. The line of interest here is 95.73 [math] \pm [/math] 0.03 keV

Histogram analysis

The most active sample was the 10% Se/soil mixture's pure selenium witness pellet, so let's analyze that first. The histogram for the sample from 615<t<1115 s is shown below.

The line in the stats box labeled "integral" represents the total number of counts in the window, which is

I = 7787 [math] \pm [/math] 88.24 Counts

and the background is

B = 5053.2 [math] \pm [/math] 60.6 Counts

Now subtract the background from the total number of counts in the window

N = 2733.8 [math] \pm [/math] 107.05

Now divide by the runtime to get the activity

[math] A_{Measure} [/math] = [math] \frac{2733.8 \pm 107.05}{500} = 5.5 \pm 0.2 [/math]

Note this is the measurement some time after the beam was turned off, so we can correct this back using the known half life of Se-79m ([math] \lambda [/math] = 0.0029 [math] \pm [/math] 0.00008 [math] s^{-1} [/math])

[math] A_{Beam Off} = A_{Measure} e^{\lambda t} [/math]