PAA Selenium

Using PAA ro measure Selenium concentrations.

According to Krouse<ref name="Krous1962"> H.R. Krause and H.G. Thode,"Thermodynamic Properties and Geochemistry of Iosotopic Compounds of Selenium",.Can. J. Chem., vol 40, pg 367</ref> , the fractional concentration of Se-82/Se-76 in plant material is observed to be less than from primordial (meteoric) concentrations by as much as 1.2%. Anaerobic bacteria are known to reduce selenates and senelites in biological systems. This may be the reason plant material has fractionation of selenium isotopes. They also observe excess concentrations of up to 0.4% in soil.

Plant material appears to detect environmental selenium.

Can one perform PAA measurements of Se-82 and Se-76?

Neutron knockout of Se-82

If you knock a neutron out of Se-82 you produce the unstable isotope Se-81 which Beta emitts with half life of 18 min and a meta-state that emmits a 103 keV gamma with a 57 minute half life.

[math]{82 \atop 34\; }Se (\gamma,n){81 \atop \; }Se[/math]

Other prominent photons

260 & 276 keV for the 57 minute half life isotope

Neutron knockout of Se-76

If you knock a neutron out of Se-76 you produce the unstable isotope Se-75 which has a half life of 119 days.

[math]{76 \atop\; }Se (\gamma,n){75 \atop \; }Se[/math]

The prominent photons emitted have the following energies

136, 264, and 279 keV

The article below describes how plant material and soil contain Se-76 to Se-82 ratios that differ from other natural samples by 1.5%. They argue that it is due to the bacteria living in plant material.

File:Krouse CanJournChem 40 1962 p367.pdf

Plant material is a natural way to sample the selenium content to determine if there are difference isotopic ratios due to the impact of human activities on the environment.

Experiments

Chlorine

It looks like Cl-35 is abundant as you see photon energies of 146 keV and 2127 keV (you can barely see 1176 keV) from Cl-34's decay (neutron knocked out of Cl-35).

The half life is 32 minutes.

Should check the half life from the run AccOnAlInDetASe-AinDetD_001.root using the calibration

MPA->Draw("0.18063+0.960133*evt.Chan>> SeRun_008(8000,0.5,8000.5)","evt.ADCid==3");

Irradiation of Horse Mineral Supplement

Chlorine is a dominant signal

First, look at the peak around 146 keV https://wiki.iac.isu.edu/index.php/File:146_keV.png

Next I plotted the counts as a function of time to get an exponentially decaying graph. When doing an exponential fit here, the parameter "b" given by root will be the decay constant.

https://wiki.iac.isu.edu/index.php/File:Counts_vs_time_146kev.png

Root gives a value b = 3.83655x10^-4, which yields a half life of 30.11 minutes.

Now do the same for the 2127 keV line https://wiki.iac.isu.edu/index.php/File:2127_keV.png

Here are the counts plotted as a function of time https://wiki.iac.isu.edu/index.php/File:Counts_vs_time_2127keV.png

Root gives b = 3.31508x10^-4, which yields a half life of 34.8 minutes.

Possible Yb-167 in the Sample

Yb-167 has a half life of 17.5 minutes and can be produced by knocking a neutron out of Yb-168, which is stable.

I looked at the horse feed spectrum and compared the spectral lines for Yb-167, below is a table of those results:

Energy (keV)	Spectrum Energy (keV)	Half life (min)
90.84	89	18.23
106.18	105	18.0
112.88	113	18.86
132.02	137	19.2
161.29	161	17.3
203.75	204	17.27
280.5	281	17.0
290.89	289	16.7
323.5	322	16.6
354.0	354	16.7
375.9	378	15.5
387.0	388.4	19.1
398.1	402	16.1
688.5	691	15.6
733.2	736	17.1
920.32	922	16.6
977.9	980	16.9
1025.9	1028	16.9
1242	1245	17.5
1340.1	1341	16.5
1410.4	1413	18.6
1433.4	1437	16
1631.7	1630	19.6

The average of these half lives is 17.22 minutes, but it turns out this was just coincidental noise meaning we must overbin the spectrum.

Investigation of Se_B_002

Using the Se_B_002, I will investigate the peaks seen in the spectrum.

The first peak seen in the spectrum was at 74.1 \%pm%\ 2.947 keV. The half life was found to be 324.94 days. When doing the rad search I used a window from 69-79 keV and a half life window from 200-400 days.

Isotope	Energy (keV)	I(%)	Half life
153-Gd	69.67	2.419	240 days
254-Es	69.7	not given	275.7 days
254-Es	70.4	not given	275.7 days
153-Gd	75.4	0.0783	240.4 days

254-Es doesn't really have a mechanism to produce this isotope. The nearest stable isotope would have to have greater than a quadruple neutron knockout, or a triple proton knockout.

153-Gd could possibly be produce from 154-Gd by knocking out a neutron, but the half life is still far off. The hottest decay lines for 153-Gd are 97.4 and 103.2 keV with I = 29 and I = 21.11 respectively. Neither of these lines are seen in the spectrum.

First Observation of Se lines

Using the 44 Machine at 7 kW power and 44 meV incident electron energy to produce a bremsstrahlung spectrum with a mean energy of 15 meV.

All runs lasting less than 214 seconds have time stamp that gives real time if you divide by clock frequency of 20 MHz.  The first 32 bits are used for a real time measurement.

SeRun_01-11-16

SeRun_03-07-16

References

<references/>

MSDS

Selenium shot, amorphous, 2-6 mm, Puratronic, 99.999% Alfa Aesar product # 10603 File:AlphaAesarSelenium MDSD.pdf

Informative links

http://www.deq.idaho.gov/regional-offices-issues/pocatello/southeast-idaho-phosphate-mining/southeast-idaho-selenium-investigations/

https://inldigitallibrary.inl.gov/sti/3169894.pdf

http://giscenter.isu.edu/research/Techpg/sisp/index.htm

PAA_Research