急求一篇关于宇宙的英文简介最好是符合高中生的水平的.谢拉!感激不尽.最好尽快

急求一篇关于宇宙的英文简介最好是符合高中生的水平的.谢拉!感激不尽.最好尽快
急求一篇关于宇宙的英文简介
最好是符合高中生的水平的.谢拉!感激不尽.最好尽快

急求一篇关于宇宙的英文简介最好是符合高中生的水平的.谢拉!感激不尽.最好尽快
Cosmic Radiation
Cosmic radiation and air travel
Cosmic radiation is part of our natural environment,and we are constantly exposed to a certain amount of ionizing radiation.Radiation originating from outer space and the sun is called cosmic radiation and contributes about 13% of the background radiation level on Earth (a greater part is due to radon).
Special features of cosmic radiation
Cosmic radiation is a complex mixture of charged and neutral particles,some of them generated when primary particles from space interact with the earth's atmosphere.This complexity also leads to difficulties in measuring radiation doses from cosmic radiation,but physicists have developed sophisticated approaches to deal with this situation.For the human exposure situation one feature of cosmic radiation is of particular importance:a large percentage of the effective radiation dose from cosmic radiation is due to neutrons of different energy levels.Neutrons are subatomic particles which - when compared to X-rays or Gamma rays - cause more biological damage per dose unit.
Exposure during flying
As a rule,cosmic radiation levels rise with increasing altitude (up to about 20 km above ground).The actual radiation level is influenced by a number of factors,most importantly through the shielding provided by the earth's atmosphere.The overall effect for flight crew and travellers is an increased radiation exposure during flights as compared to staying on the ground.Flight crew passes up to 1000 hours per year on board of flying planes,which leads to annual effective radiation doses in the range of 2 to 5 milliSievert (mSv) for most crew.Occasional travellers obtain a fraction of this value through less frequent leisure or occupational flights.In comparison,the natural background radiation amounts to 2 to 3 mSv per year at most geographical locations worldwide.
Cosmic radiation and health
A series of studies concerning health issues associated with cosmic radiation has been conducted in the past few years.The WHO Information Sheet summarizes the current knowledge and ongoing research activities,and gives target-group specific recommendations on actions concerning cosmic radiation.