Daily and annual variations of the ambient gamma ray exposure rates on the Korean Peninsula from 2003 to 2006

A study of the ambient gamma ray exposure rate is essential as a background for underground particle physics experiments such as the neutrino and the non-bayonic dark matter experiments. Here, we report patterns for the daily and the annual variations of the ambient gamma ray exposure rate measured at the Cheongju Regional Radiation Monitoring Post from January 2003 to December 2006 by using a pressurized ionization chamber. The daily ambient gamma ray exposure rate appears to have a sinusoidal pattern with an annual average daily variation of 0.17 μR/h. The maximum ambient gamma exposure rate appears from 7 : 30 am to 9 : 30 am and the minimum from 7 : 30 pm to 10 : 30 pm. The annual average of the ambient gamma ray rate was 12.78 μR with an annual variation of 1 μR/h for the years from 2003 to 2006. The fluctuation in the seasonal variation was 7.8 percent while the fluctuation the daily varition was 1.3 percent during the years from 2003 to 2006.