Pittsford Mendon High School, Physics Regents Honors period 1 THE EFFECT OF BAROMETRIC PRESSURE AND TIME OF DAY ON COSMIC RAY MUON RATE Pittsford Mendon High School, Physics Regents Honors period 1 RESULTS ABSTRACT METHODS DISCUSSION Students in the Period 1 Regent Physics Honors class at Pittsford Mendon High School analyzed data in order to find relationships between barometric pressure and Muon rate and between muon rate and time of day. Data was taken at the U of R during the month of October 2006. The class found an anticorrelation between muon rate and barometric pressure. A daily cycle was established which appeared to be sinusoidal. The relationship between muon rate and pressure was an anticorrelation. More muons are able to reach the earth’s surface when there is lower pressure because the air is less dense. When there is high pressure, the air is very dense and there are more interactions which makes it harder for the muon to reach the earth’s surface. The relationship between muon rate and time of day was sinusoidal. During the hours without sun, the rates were lower. Just after the sun reached its highest point in the sky, around 2 p.m. EST, muon rates were their highest. Since only about one percent of the cosmic rays that hit the earth are from the sun, this could explain the daily variation in muon rate. In this lab data from the U of R website was used to make graphs. The first graph shows the relationship between average muon rate (Hz) and barometric pressure (hPa). The second graph shows the relationship between muon rate (Hz) and the time of day (in five minute intervals). INTRODUCTION Cosmic rays are particles formed from protons or nuclei traveling at high speeds outside the earth’s atmosphere that bombard the earth’s surface. There are two types of cosmic rays: primary and secondary. Primary rays normally decompose into secondary rays before reaching the earth’s surface. A type of secondary ray is the muon which is very similar to the electron. Both have a charge of negative one, but muons are two hundred times larger than electrons. Both are also very unstable with a half life of only 2.2 micro seconds. They travel great distances due to their extremely high velocity (almost the speed of light) and reach earth’s surface where they are recorded. CONCLUSION This experiment supports prior Mendon research which established an anticorrelation between muon rate and barometric pressure as well as a sinusoidal daily muon rate cycle.