Abstract

This experiment was conducted to investigate the effect of small electromagnetic forces like the ones in ionic solutions could produce a noticeable effect on muon flux. To study this, detectors were placed above and below a cooler which held various solutions such as NaCl and CaCl₂. Water, corn oil, and an empty cooler were also used as bases for comparison. Due to time restraints, only one trial was conducted for each variable. While all liquids had lower flux rates than the empty cooler, CaCl₂ and corn oil did not produce the expected results. Muon flux when the cooler was filled with NaCl was lower than when the cooler was filled with water, and decreased when the concentration of the solution increased. Although it was not statistically significant, muon flux increased when molarity of CaCl₂ increased. Corn oil produced an average muon flux that was lower than both water and NaCl, which may be due to corn oil's high viscosity. Overall, the experiment produced promising results but did not lead to a concrete conclusion.

Introduction

This experiment investigated whether ions in solution could affect the flux rate of muons.

When primary cosmic rays interact with molecules in the Earth's atmosphere, they decay to smaller secondary particles such as kaons and pions, which then decay into muons. Muons are charged particles similar to electrons, but 200 times more massive. Their added mass leads to a greater inertia, which allows them to pass through matter unaffected. However, these particles can be detected using scintillators and photoelectric multipliers. Because muons have charges, they should experience some kind of electromagnetic interaction with other charged particles such as ions. 

While there have not been other e-lab posters documenting similar experiments, a 1977 experiment published in Hyperfine Interactions stated that there were calculations which predicted strong muon-capture effects, although a large effect was not observed experimentally.

We predicted that ions in solution would be able to capture muons, thus reducing their arrival rate on Earth.

Procedures

Materials and Equipment:

• H₂O
• NaCl
• Corn oil (or another nonpolar liquid)
• Cooler
• Cosmic ray detectors
• Computer and DAQ
• Shelves

Procedure:

1. Place cooler on a shelf and position detectors in sets of two, one stack above and one below the cooler.
2. Set detectors to four-fold coincidence
3. Run a flux study using the empty cooler
4. Fill cooler with 8 L of H₂O and run another flux study
5. Add 467.5 g NaCl to enough H₂O in the cooler to make 8 L of 1 M solution (making sure it dissolves completely)
6. Run a flux study
7. Add 2338. g NaCl to enough H₂O in the cooler to make 8 L of 5 M solution (making sure it dissolves completely)
8. Run a flux study
9. Fill cooler with 8 L of turpentine and run another flux study
10. Compare plots and analyze results

Results

As expected, the empty cooler had a higher average flux rate than any of the liquids and solutions tested. Using data from Figure 1, the average flux rate for the empty cooler was 477.828 events/m^2/min; 20 events more than the next highest, which was water with 457.28 events/m^2/min (Figure 2). Muon flux also decreased as the molarity of NaCl solution increased, from an average of 457.215 events/m^2/min at 1M (Figure 3) to 446.885 events/m^2/min at 5M (Figure 4). However, corn oil and CaCl₂ did not produce the expected results. When the concentration of CaCl₂ increased from 1M (Figure 5)to 5M (Figure 6), muon flux also increased, from an average of 424.126 events/m^2/min to 426.597 events/m^2/min. Muon flux with corn oil in the cooler (Figure 7) also did not yield the expected results, as it averaged to 449.647 events/m^2/min, lower than the flux for both 1M NaCl and water.

Discussions & Conclusions

Ions affect muon flux, but are not the only factor. While muon flux decreased as the ions in solution increased, this could be due to a variety of other factors, including viscosity (IMFs), molecule size, and environmental conditions such as temperature. A likely explanation for decreased muon flux is not that the ions deflect them, but rather the electrons in the outer shells of atoms. Large molecules have more electrons, which would explain why the trial using corn oil had a lower arrival rate than those using water and 1M NaCl. The large size of a corn oil molecule makes it more polarizable, creating greater IMFs and leading to less space for a muon to go through. 

Error Discussion

The trials in the experiment were not run on the same day for the same amount of time, so data could have been affected by temperature and pressure fluctuations. There also could have been systematic error, in which the paddles were shifted before one trial and then moved back for another. Furthermore, a greater volume of liquid could be used since the 8 L used in this experiment only filled about 10 cm of the cooler. 

Further Experimentation

In future experiments, it would be wise to test a greater range of molarities with smaller increments between them. The effects of different molecule sizes could also be investigated. If possible, gaseous and solid states should also be studied. 

Bibliography

Daniel, H., R. Bergmann, V. Dornow, F. J. Hartmann, J. J. Reidy, and W. Wilhelm. "Search for an Effect of the Ionic Charge on the Coulomb Capture of Muons in Cu, CuSCN and Cu(SCN)₂." Hyperfine Interactions  5.1 (1977): 215-18.  Springer . Web. 17 July 2014.