Due to the electricity saving campaign going on in Japan, my company decided to trade some of our Saturdays and national holiday for a full week of holidays in July. In order to escape the heat and the crowd of Tokyo, I aimed for cooler altitude in Yamanashi prefecture. To be precise, I was aiming with full camping gear to Kita-dake, the second highest peak in Japan, culminating at 3193 metres above sea level in the city of Minami-alps.
Even though this prefecture west of Tokyo, host to Mount Fuji, was not likely to be contaminated by radioactive particle from Fukushima, it was a perfect occasion to measure the effect of cosmic rays occurring naturally at such altitude. So I strapped my Geiger counter (CRM100) to my backpack and started my trip.
Waiting for the bus in Koufu, Yamanashi prefecture, I took my first measurement finding a fair 0.124uS/h. Two hours bus then brought me to the starting point of my hike, Hirogawara, Minami-alps city. After hiking about one hour I took my first measurement at about 1800 meters above sea level to find an only slightly more elevated 0.145uS/h. Finally, I reached my first camp at the Shironeoike lodge at 2200 meters above sea level where I found already about 0.218uS/h.
After a good night sleep, I attacked the 1000 meters climb to Kita-dake. On the way, around 2800 meters above ground level I measured 0.342uS/h. And at the top I measured a surprisingly low 0.197uS/h while the ground at that place was 0.282uS/h, consistently about the same as air, indicating that no contamination is present. Next, I measured 0.301uS/h at the next summit, ainotake, 3185 meters above sea level. To finish the day, I measured 0.342uS/h at the campsite of Noutori lodge.
I was lucky enough to start the last day of my trip with the sunrise on Mt. Fuji at 4.30am the next morning.