Permissible Dose - Permissible Dose

The concept and evaluation of the permissible dose have undergone several changes to date, but the 1954 recommendation of the International Commission on Radiological Protection (ICRP) defined it as "the amount of ionizing radiation which, in the light of present knowledge, is unlikely to cause any appreciable physical damage at any time during a person's lifetime." In this context, "appreciable physical damage" means "physical damage or effects that the average individual would find unpleasant, or that the appropriate medical authorities would consider harmful to the health and well-being of an individual." A concept similar to the tolerance dose was first proposed in 1925 by A. Mutscheller of the United States. However, unlike today, at that time it was believed that the human body could tolerate a certain dose of radiation, even if it was continuously exposed over a long period of time, i.e., even if the total dose received over a lifetime was large, so the concept of the tolerance dose was born (the translation for this is tolerable dose, not permissible dose). However, it is not possible to clearly answer the amount of radiation that a person can tolerate even if exposed for a lifetime. Therefore, in 1950, the ICRP replaced this inappropriate term with the term we now call the permissible dose. This is a limit dose set based on the idea that while the use of ionizing radiation is unavoidable for human beings, there is no such thing as a radiation dose that is completely harmless to an individual or his/her descendants. The specific value is set under the name of the maximum permissible dose, which is different from the permissible dose. In 1957, the recommended limit was 100 mrem per week (5 rem per year), and this has remained to this day. The above is the occupational exposure limit for short-term exposure within controlled areas, but the exposure limit for the general public outside controlled areas is one order of magnitude stricter. As knowledge of the effects of radiation on the body deepens, the permissible dose is expected to be further reduced in the future. The concept of limiting the total radiation dose received up to a certain age, i.e., the accumulated radiation dose, has also been introduced by the ICRP since 1956, and maximum permissible accumulated radiation doses have been set for exposure to the gonads, blood-forming organs, and other parts of the body.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

許容線量に関する概念と評価は，いくたびかの変遷を経て今日に至っているが，1954年の国際放射線防護委員会(International Commission on Rediological Protection：ICRP)の勧告は，これを「現在の知識に照らして，生涯のいずれの時期にも感知されうる程度の身体的障害を起こさないと思われる電離放射線の量」と定義した．ここに，「感知されうる程度の身体的障害」とは，「平均的な個人が不愉快と思う身体的障害または影響，あるいは適当な医学の権威者が個人の健康と幸福に有害とみなす障害または影響」を意味する．許容量に近い概念は，1925年にアメリカのA. Mutschellerによってはじめて提案された．ただし，当時は今日とは異なって，ある線量以下の照射であれば，長期にわたり連続的に被ばくしても，すなわち，一生の間に受ける総線量はたとえ大きくても，人体はこれに耐えうると考えられ，tolerance doseという概念が生まれた(この訳語は耐容線量であって，許容線量といってはあたらない)．しかし，人が一生ばく射されていても耐えうる放射線量がどのくらいかを明確に答えることはできない．そこで，1950年にICRPは，この不適当な表現のかわりに，今日のいわゆる許容線量(permissible dose)という用語を用いるようになった．これは，人類にとって電離放射線の使用が不可避と認める一方，個人またはその子孫に対し，まったく無害な放射線量というものはありえない，との考え方に立って設定する制限線量のことである．具体的な数値は，最大許容線量の名称で定められており，許容線量と区別されるが，週に100 mrem(年間5 rem)というのが1957年に勧告され，今日に至っている．以上は管理区域内における職業上の短期間内の被ばく限度であるが，管理区域外の一般人の被ばく限度は，さらに1けた厳しい数値となっている．放射線の身体に及ぼす影響についての知見が深まるにつれ，許容線量は今後さらに下げられることが予想される．また，一定の年齢に達するまでの総線量，すなわち，蓄積線量を制限するという考え方も，1956年以来ICRPが導入し，生殖腺と造血器官，そのほかの身体の部分の被ばくに対して，最大許容蓄積線量が定められている．

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