Sievert (English spelling)

Japanese: シーベルト(英語表記)sievert
Sievert (English spelling)
The unit of radiation absorption (dose equivalent) in the International System of Units (SI). The symbol is Sv. It is recommended by the International Commission on Radiation Units and Measurements (ICRU) as a replacement for rem, which had long been used as a unit of radiation absorption in living organisms. Since the effects of ionizing radiation such as X-rays, gamma rays, and neutron rays on living organisms differ slightly depending on the type, the sievert is calculated by taking into account the relative biological effectiveness (RBE) of ionizing radiation, just like rem. Generally, 1 Sv is defined as a dose that has approximately the same biological effect as 1 Gy (gray, = 100 rad) of gamma rays. Since the dose expressed in sieverts is very large and inconvenient for various applications, millisieverts (mSv), which is 1/1000 of 1 Sv, are often used. 1 mSv is equivalent to the energy absorption of 10 ergs of gamma rays per gram of living organism. The amount of natural radiation from cosmic rays and other sources that a person living a normal life is exposed to in a year is about 2.4 mSv worldwide on average, and about 1.5 mSv for Japanese people. (→ Radiation damage)

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:
国際単位系 SIにおける放射線吸収量(線量当量)の単位。記号は Sv。放射線の生体吸収量の単位として長らく用いられていたレムに代わるものとして,国際放射線単位測定委員会 ICRUが推奨している。X線,γ線,中性子線などの電離放射線は種類によって生体組織への影響がわずかに異なるため,シーベルトもレムと同様に,電離放射線の相対的生物学的効果比 RBEを加味して算出する。一般に 1Svは,1Gy(グレイ。=100rad〈ラド〉)のγ線と生物学的効果がほぼ同等の線量と定義される。シーベルトで表される線量は非常に大きく,各種の応用に不都合なため,1Svの 1000分の1を表すミリシーベルト(mSv)が用いられることが多い。1mSvは,生体組織 1gあたり 10erg(エルグ)のγ線のエネルギー吸収に相当する。通常の生活をしている人が 1年間に受ける,宇宙線などによる自然放射線の量は,世界平均約 2.4mSv,日本人の平均は約 1.5mSv。(→放射線障害)

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