What kind of unit is "millisievertte" or "microsievert" and how dangerous is it from? Summary of radiation dose measurement unit

Many people are increasingly concerned about listening to the words "radiation dose has exceeded the reference value" and "people exposed to radiation" have been heard. I hear it in the press before I actMirisue belt"Micro Sv BeltLet's see what kind of unit is actually, how dangerous it is from.

Details are as below.
Lethal dose of short term exposure

Humans are constantly exposed to radiation regardless of where they live on the earth. On average in the world, the human body is about 2.4 mmSievert(2.4 mSv: one thousandth of 1 sievert. × 2.4) of natural radiation at all times. The lethal dose when radiation is exposed to the whole body in a short period is 2 sievert (2000 mSv), 5% lethal dose (dose to 1 in 20 people of the exposed person), 50% lethal dose 4 Sievert, a 100% lethal dose is said to be 7 sievert,With exposure below 200 mSv, acute clinical symptoms (Acute radiation disease) Is not allowedIt has been with.

Please think that "short-term" here is about one hour. It is the danger that one person in 20 people will die when absorbing 1000 times the amount of radiation absorbed in one year by one hour when living normally. It is said that 50% of people will die within 30 days when 3 sievert is exceeded, feeling nausea with 2 sievert, 2 to 5 sievert hair loss of hair.

◆ "Sievert" and "Sievertle hourly"

"Sometimes" is sometimes omitted in the coverage, but Sievert is a unit that expresses "the sum of the amounts exposed to a certain period of time", and the person who spends 1 hour in that place is 1 sievert "exposure" The condition that you will be "1 sievert per hour (Sv / h)". Of course, you can express "every second" or "every year", but unless you explain otherwise it is like "every hour" because it is omitted in the reporting of television and so on, for example in a certain area "1 micro sievert is observed If there is a report saying "If you spend 1 hour there, think that you will" exposed "one microsievert. "2.4 millisieverts per hour" is the level that you take a normal dose and take a yearly radiation dose in an hour.

There are many expressions such as "Expression of usual ○ × multiples was measured", but since one year is 8760 hours (24 × 365), roughly "The amount that is spent normally and it takes 1000 years to 1 hour If you think that the lethality rate is 5% when bathed in "8.76 million timesPlease think about the extent that one person in 20 people dies if you spend an hour without protection with protection where you are.

◆ How much is "400 mSv / h"?

It was announced at 11:00 on March 15, 2011"400 mSv / h in the vicinity of Fukushima Daiichi nuclear power plant 3Although the number is here, the amount of exposure when you spend an hour without any protection here is one fifth of the 5% lethal dose (2 sievert = 2000 mSv). In other words, if you are exposed to this 5 times dose for about 1 hour, there is a possibility that 1 in 20 people will die. Also note that this number is observed very close to the nuclear reactor to the last.

◆ Let's start with the difference between "milli" and "micro"

If you hear "8217 microsievert (μSv)" "1941 microsiever" etc. in the news, it may seem like an enormously large number,"Micro" is an additional 1 / 1000th of microsiever of "milli" is one millionth of one sievert.Because it is 5% lethal dose at 2 million microSv Belgium, 2000 microSv Belgium is also 1 / 1,000 of the 5% lethal dose.

In other words, it will be as follows if you express it clearly.

1 Sievert (Sv) = 1,000 mSv (mSv) = 1 million microsievert (μSv)

Large amounts of radiation are harmful to the human body,There is no effect on the human body if it is a trace amount.Although it is important to take measures as much as possible in the unlikely event, those who live in the Kanto and elsewhere should keep in mind that 'microseib belt' is a very small unit, It is something that I want to be aware of not going into a panic state by acting impatiently.

Relationship between radiation exposure and health impact. Unit is micro sievert (the unit of the value "8217" "1557" on the left is "microsieverted hourly"), but as the number of people who become cancer increases if it exceeds 100,000 microsievert (100 mSv) It is being done.


It may be drunk when asking, "People who become cancerous" increases, but this means that not all people will become cancer with a high probability but cancer risk increases. Even if we say "increased risk of carcinogenesis", for example, even if we take habitual ingestion of so-called "carcinogen", not everyone is carcinogenic, not all smokers will be lung cancer, but lung cancer Remember that not all of the people who became died will not die, please do not worry beyond necessity.

◆ What is "Sievert" in the first place?

There are also a lot of people who are muy doing how to express the influence of invisible radiation on the human body "SIVEL"? I would like to explain it so that it can be grasped as intuitively as possible although it will be a little longer.

"Sievert"(Sievert, Sv) is a Swedish physicist with great credentials in radiation protection studiesRolf · Maximilian · SievertIn order to understand this in units named after "GrayIt might be easier to know who knew about the unit called (Gy).

"GrayIs absorbed by the substance irradiated with radiationEnergy per mass (kg) (J:Joule),1 Joules per kgofAbsorbed doseIs defined as 1 gray.

Joule is obtained by "mass x acceleration x distance"amount of workIt is a unit of the same dimension as "kilowatt-hours (kWh)" which we listen frequently in the topic of electricity. One joule is one watt (Ws), which is the amount divided by 1000 (kilometers) per kilowatt-hour divided by 3600 (since it is 3600 seconds per hour). Since it is said to be 1 kWh when the washing machine is operated three times, 1 Ws is quite a trace amount of electric energy. Is it easy to image when asking that 1 joule is equivalent to the workload when lifting a small apples (about 102 g) against the gravity and 1 meter?

"Exposure"Worked by radiationThat. If a human body tissue exposed to radiation receives 1 Joules per kg of work, it will be exposed to 1 Gray radiation. A person who is not familiar with the expression "to be worked", for example, when a finger strikes against a stove, the temperature rise (Internal EnergyChange ")," When I was done ", when my mother lifts the baby against gravity against her, the mother told the baby about the height (Potential energyChange ")" You did the work "Please think.

"Sievert" is also a unit of dimension of "J / kg" just like "Gray", but there are various kinds of radiation, and when radiation is exposed to "people" rather than "objects" The influence received by the type of radiation (alpha ray, gamma ray, etc.) varies.

Even with the same 1 gray absorbed dose, if human tissue is absorbed, for example, if it is 1 gray absorbed dose on alpha radiation, it is said that the influence is greater by 20 times than in case of 1 gray with beta ray, according to thisRadiation load coefficientIf you are exposed to 1 gray radiation on alpha radiation, the impact on the human body will be 20 Sv. (Sv). Based on the "influence on the human body" instead of the physical quantityEquivalent doseIt is a unit based on the concept.

In addition, it is true that "masses absorb more energy", but it is not true if 80 kg people are more dangerous than people weighing 40 kg if they are in the same place. So "gray" and "sievert" that you think about "per kg" have meaning.