SAMADHA - CHACALTAYA LABORATORY

The Chacaltaya Laboratory

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ENVIRONMENTAL DOSIMETRY Cosmic rays interact with the atmosphere nuclei producing cascades of secondary particles: gamma-rays, electrons, muons, neutrons, mesons. The particles that reach the ground contribute to the total dose of ionizing radiation received by the population. Even if the neutron flux is much lower than that of other secondary particles, neutrons contribute significantly to the effective dose, because of the higher damage they can cause to human tissues. The secondary particle flux increases with altitude, because of the lower absorpion of the atmosphere. At Chacaltaya, the neutron flux is about 25 times higher than at sea level.

Spectroscopic and dosimetric instruments installed at Chacaltaya

NEUTRON DOSIMETRY At Chacaltaya, the neutron dose rate is continuously monitored by a Thermo WENDI-2 neutron detector (rem counter), sensitive to neutrons of energy up to 5 GeV. WENDI-2 provides the dose in terms of Ambient dose equivalent, denoted as H*(10), measured in Sievert (Sv). The neutron dose rate is locally modulated by the atmospheric pressure. When the pressure is high, cosmic ray particles are more absorbed by the atmosphere, then less neutrons reach the ground. A pressure increase of one hPa causes the neutron dose to decrease by about 0.7%, and vice versa.

REAL TIME neutron dose rate - Last 10 days (each point = 2 hour average) REAL TIME neutron dose rate percent variation - Last 30 days (each point = 12 hour average)

LINEAR ENERGY TRANSFER (LET) SPECTROMETRY

The LABDOS spectrometer measures the energy deposited in a Silicon diode by ionizing radiation. The figure below shows the distribution of the deposited energy up to about 10 MeV. The absorbed dose in Silicon (i.e. the absorbed energy per mass unit, measured in Gray) is calculated by integrating the deposited energy spectrum.

REAL TIME LABDOS absorbed dose rate in Silicon - Last 10 days (each point = 2 hour average) REAL TIME absorbed dose rate in Silicon percent variation - Last 30 days (each point = 12 hour average)