Update: 4 February 2013

Answers to frequently asked questions relating to the accident at the Fukushima
Daiichi nuclear power plant

1. Questions about radiation and radioactivity

Q
Q11
A
A11

What types of radiation are there?
There are two main types of radiation:
 Radiation with same properties as those of light: X-rays and gamma rays
 Radiation in particles: Alpha, beta, and neutrons
 X-rays are electromagnetic waves (same properties as those of light) thatare generated using high-voltage X-ray generators. The penetrating
power of such rays is relatively strong.
 Gamma rays are electromagnetic waves produced in a process of“radioactive decay” of radioactive isotopes (radioactive materials). They
are electromagnetic waves like X-rays, and their penetrating power isstrong.
 Alpha particles are emitted by radioactive nuclei such as uranium or
plutonium in a process known as “atomic decay.” An alpha particle iscomposed of two neutrons and two protons (a helium nucleus). The
penetrating power of alpha rays is so weak that they can be stopped with
one sheet of paper. Concern regarding external exposure to alphaparticles is unnecessary.
 Beta particles are electrons emitted in the process of “atomic decay” ofradioactive isotopes. In general, most beta particles cannot reach a depth
exceeding 1 cm.
 Neutrons are emitted in a process of “nuclear fission” of uranium andplutonium. The uncharged nature of the neutron contributes to their highpenetrating power, but water can stop neutron penetration. (A neutron is
the same weight as a proton in the hydrogen nucleus, and hence it canbe stopped by the principle of billiard-ball motion.)(Note)
Atomic decay: An isotope is defined as an atom with the same number ofprotons but a different number of neutrons. (For example, there are three
types of hydrogen atoms: the most common form of hydrogen with one
neutron, deuterium with two neutrons, and tritium with three neutrons. Only
tritium is radioactive.) Some isotopes will release extra energy in the form ofradiation and decay into stable atoms (frequently accompanied by anincrease or decrease in atomic number). This is what is called “atomic decay.”
Nuclear fission: The splitting of the nucleus of an atom such as uranium andplutonium resulting from collision with neutrons.

Q
Q22
A
A22

What does 1,000 μSv/h mean?

Q
Q33

What is meant by internal exposure?

“1,000 μSv/h” indicates that one is exposed to 1,000 microsieverts ofradiation per hour. Total annual natural radiation dose for people living inJapan is estimated to be about 1,000 microsieverts (i.e., 1 millisievert,
excluding radiation from radon), and hence the figure indicates that you
would be exposed to the typical total annual radiation dose in one hour.

1

A
A33

Ingestion or inhalation into the body of radioactive substances leads tointernal exposure. The speed of excretion of the radioactive substance fromthe body depends on the type of radioactive element involved.

Q
Q44
A
A44

What is half-life?

Q
Q55

I hear that radioactive cesium emitted in the accident turns into barium-137
through beta decay. Does this reaction occur even when radioactive cesium turns
into compounds such as oxides or chlorides?

A
A55

Decay (disintegration) of an atomic nucleus is not affected whatsoever by themolecular form of the compound. Therefore, the speed and the products of decay
are the same regardless of whether the compound is cesium chloride or cesiumhydroxide. However, cesium-137 emits strong gamma rays after beta decay andis therefore a gamma emitter as well as a beta emitter.

Q
Q66

Is it radiation or radioactivity that is leaking from the power plant? And, into whereis it leaking?

A
A66

Both radiation and radioactivity (radioactive substances, i.e., radioisotopes)
leaked from the plant. Due to the hydrogen explosions at that time, radioactive
substances were released into the surrounding environment all at once, andthese substances are now emitting radiation. Please refer to theeasy-to-understand explanation on the difference between radiation andradioactivity on the RERF website at http://www.rerf.jp/general/whatis/index.html.
Radioactive substances (radioisotopes) released into the environment due to thehydrogen explosions were derived from nuclear fission products when nuclear
energy was produced at the power plant. Various radioisotopes were generated,
and there have been particular concerns about effects of radiation emitted fromiodine and cesium radioisotopes. Such radioisotopes did leak from the destroyed
nuclear reactors, but as far as we know, leaks of the sort that could cause
problems have already stopped. Unless there is another serious accident, there
is no need to worry about such leaks. The present issues are the levels ofradiation doses emitted by the radioactive substances (radioactivity) released
into the environment at the time of the hydrogen explosions and the degree of
their effects on human health.

Q
Q77

Is it radiation or radioactivity that leaked into the soil and water? If it is radiation,
how long will restoration to the original condition take?

A
A77

What remain in soil are radioisotopes. These radioisotopes emit radiation during
the process of decay of atomic nuclei. To determine how long restoration of theenvironment will take, the physical half-lives of such radioisotopes must be taken
into account. Further, it is necessary to consider how these elements behave(how they spread) in the environment.

Half-life is a term used to express the amount of time required for a
substance’s radioactivity to decay by half. When two times this half-life period
elapses, the radioactive intensity does not equal zero—rather it becomes
one-quarter of the original quantity, due to the formula 1/2  1/2 = 1/4.

2. Questions about radioactive contamination

Q
Q88

What is meant by radioactive contamination?

2

A
A88

Radioactive contamination means a state in which radioactive substances are
not safely managed and therefore may cause radiation exposure on thehuman body, including when radioactive substances are attached to clothes
and skin.

Q
Q99

What should we do if we are contaminated? What is decontamination? Where
can we be decontaminated?

A
A99

Decontamination needs to be performed if we become contaminated.
Decontamination means elimination of radioactive materials from clothes andskin. Washing any exposed clothes and skin with soap would be best.
However, when washing skin, don’t rub too hard. If you scratch your skin,radioactive materials could infiltrate the body through such openings.
It is impossible to accurately determine the need for decontamination without
measurements using a radiation measurement device. For more information
about measurement of radiation doses, please refer to Q
Q2244.

Q
Q1100
A
A1100

What should one do in the case of rain?

Q
Q1111
A
A1111

Are Hiroshima and Nagasaki still radioactive?

The radioactive substances suspended in the atmosphere can be absorbed
by rain and fall to earth in that form. Therefore, it would be prudent for people
in the vicinity of the nuclear power plants and areas with high radiation levels
to avoid being rained on, although getting wet in the rain would notnecessarily pose a threat to health.

The practical answer is, “No.”
There are two ways residual radioactivity is produced from an atomic blast.
The first is due to fallout of the fission products or the nuclear material
itself—uranium or plutonium (uranium was used for the Hiroshima bombwhereas plutonium was used for the Nagasaki bomb)—that contaminate theground. Similar ground contamination occurred as a consequence of theChernobyl accident, but on a much larger scale.
The second way for residual radioactivity to be produced is by neutron
irradiation of soil or buildings (neutron activation), causing non-radioactive
materials to become radioactive.
Fallout
The Hiroshima and Nagasaki bombs exploded at altitudes of 600 meters and503 meters, respectively, then formed huge fireballs that rose with theascending air currents. About 10% of the nuclear material in the bombs
underwent fission; the remaining 90% rose to 10-50 km in the sky with thefireball.
Subsequently, the material cooled down and some of it started to fall with rain
(black rain) in the Hiroshima and Nagasaki areas, but probably most of theremaining uranium or plutonium was dispersed widely in the atmosphere.
Because of the wind, the rain did not fall directly on the hypocenters but
rather in the northwest region (Koi, Takasu areas) of Hiroshima and theeastern region (Nishiyama area) of Nagasaki.
The maximum estimates of dose due to fallout are 10–30 mSv in Hiroshima
and 200–400 mSv in Nagasaki. The corresponding doses at the hypocenters
are believed to be 1 mSv or lower in Hiroshima and 50 mSv in Nagasaki.
Nowadays, the radioactivity is so miniscule that it is difficult to distinguishfrom trace amounts (including plutonium) of radioactivity caused by worldwide
3

fallout from atmospheric (as opposed to underground) atomic-bomb tests thatwere conducted around the world in past decades, particularly in the 1950s
and 1960s.
Neutron activation
Neutrons comprised 10% or less of the A-bomb radiation, whereas gamma
rays comprised the majority of A-bomb radiation. Neutrons cause ordinary,
non-radioactive materials to become radioactive, but gamma rays do not. The
bombs were detonated far above ground, so neutron induction of radioactivity
on the ground did not produce the degree of contamination people associatewith nuclear test sites (Nevada test site in southwestern U.S., Maralinga testsite in South Australia, Bikini and Mururoa Atolls, etc.).
Past investigations suggested that the maximum cumulative dose at the
hypocenter from immediately after the bombing until today is 800 mSv in
Hiroshima and 300–400 mSv in Nagasaki. When the distance is 0.5 km or 1.0
km from the hypocenter, the estimates are about 1/10 and 1/100 of the value
at the hypocenter, respectively. The induced radioactivity decayed very
quickly with time. In fact, nearly 80% of the above-mentioned doses werereleased within a day, about 10% between days 2 and 5, and the remaining
10% from day 6 afterward. Considering the extensive fires near the
hypocenters that prevented people from entering until the following day, it
seems unlikely that any person received over 20% of the above-mentioned
doses, i.e., 160 mSv in Hiroshima and 60–80 mSv in Nagasaki.

Q
Q1122

Aren’t volatile radioactive substances gases? If they are, do these gases
contaminate soil? Please tell me about the mechanisms by which gases
contaminate soil. Do non-volatile substances spread in the form of fine particles?

A
A1122

Volatile radioisotopes, such as radioactive iodine, turn into gases and float in the
air. There also is the possibility that such gases adhere to soil or dissolve inwater, contaminating the environment. Non-volatile metallic radioisotopes also
spread, and some of them are thought to dissolve in water and turn into ions.

Q
Q1133

This is a question about the series of nuclear power plant accidents. Using
numbers that have been published as examples in order to compare
contamination levels by atomic bombs and the accidents in Chernobyl and
Fukushima, what would be the contamination levels for the Fukushima andChernobyl accidents if the level for Hiroshima is assumed to be 1?

A
A1133

Contamination levels can be calculated by multiplying the radiation per unit areaby the total area of the contaminated zone. Typically, however, adequate
information is lacking on low-level contamination, even though information isoften available on measurements of areas that are contaminated so heavily as tomake it impossible for people to live there. Moreover, in Hiroshima and Nagasaki,
because the temperatures when the bombs exploded were as high as 10,000 ℃,
all the nuclear substances and nuclear fission products were vaporized andspread widely due to the updrafts that produced the mushroom clouds.
Therefore, the ground surfaces nearby were not substantially contaminated(radioactive substances were contained in the rain that fell in some parts of thesuburbs, however). Thus, there are no definitive answers to this question.

Q
Q1144

I have heard that, according to some calculations, the level of radiation emitted in
Chernobyl was reported to be 8,000 times higher than that in Fukushima. Is that
true?

A
A1144

Both nuclear power plants and atomic bombs use energy from nuclear fission,
but nuclear power plants have a much larger amount of nuclear substances4

(fuel). The longer the period during which fuel is burned, the more radioactive
products accumulate. One site on the internet indicates that a 1,000,000-kilowatt
nuclear power plant produces as much death ash (radioactive products) a day as
6 Hiroshima-type atomic bombs (according to the Wikipedia page on atomic
bombs). However, it is unknown how much radioactive material was released
from the accident of the Fukushima nuclear power plant.

Q
Q1155

I hear that there should be no concerns any longer about soil contamination in
Hiroshima and Nagasaki. If radioactive contamination in Fukushima were to stop
now, how long would it take for the effects on human health to disappear?

A
A1155

It is difficult to answer the question because the minimum radiation level that cancause effects is unclear. Because the half-life of cesium-137 is 30 years, theeffects may persist unless those radioisotopes are washed away (theradioactivity will only decrease to one-half in 30 years and to one-quarter of thetotal amount in 60 years). However, research aiming at reducing contamination
will apparently be initiated, so some measures definitely will be taken. If a houseis contaminated, there are two options: having it decontaminated or moving out.
One would have to decide which option to choose, taking necessary costs into
consideration. Even if decontamination is carried out, however, dose levels would
probably not fall to zero, so some compromise would be necessary. In that case,
one cannot avoid the issue of how much contamination one can put up with. It
would be difficult to solve this problem by simply drawing a line someplace,because people have different opinions on this matter.

Q
Q1166

I plan to purchase secondhand a piece of heavy machinery that had been used in
Fukushima. If I were to use such equipment over the long term, would my healthbe affected?

A
A1166

It cannot be denied that heavy machinery used close to the nuclear power plantmight have been contaminated with radioactivity. It is advisable to have thecontamination level of the equipment tested before purchase. Generally
speaking, however, because contamination levels were very low, most of thecontamination could probably be washed away with water. Except for equipmentused on site at the nuclear power plant, there have been no reports of high-levelcontamination that may cause health effects.

Q
Q1177

After I bought seedlings (roots) of “myoga” (Japanese ginger) the other day, I
noticed that they were harvested in November or thereafter in an area designatedas “contaminated” according to maps showing radioactive contamination
distributions. Because I was concerned, I inquired by telephone and got a
response indicating that although the farm had not been decontaminated,
contamination levels of its products had been measured, and that products had
been shipped only after it was confirmed that no contamination was detected.
This response makes me wonder, though; aren’t all the products shipped fromareas designated as contaminated according to the radioactivity maps affectedby radioactivity?

A
A1177

Because contamination released into the air due to the hydrogen explosions of
the nuclear reactors was carried away by the wind and fell to the ground, they
have been detected at distant locations. Fallout was scattered over long
distances, and that is why so few contaminated farms have been found. There
should be no problem with the farm products that you bought.

3. Questions about radiation measurements and radiation doses

5

Q
Q1188
A
A1188

How would one find out his or her level of radiation exposure?

Q
Q1199

We often see on TV people using plastic-wrapped measurement devices, butdoes such protection do anything? Those who are measuring look like they
are wearing normal clothes. Do such devices wrapped in plastic measureaccurately?

A
A1199

Measurement equipment is usually wrapped in plastic because it does notgive accurate results when contaminated with radioactive materials. The
plastic is replaced when it is dirty. It measures high levels of radiation, which
may have adverse effects on human health, and therefore it does not pose
any problem in measurements since radiation of such levels will penetrate
plastic.

Q
Q2200

I recently read an article that indicated cesium and plutonium were detected on
the air-conditioner filters of cars. Can we consider that such materials were
stopped by the filters and did not enter the cars by passing through the filters?
Also, I measured radiation doses in my car using a dosimeter for X-rays andgamma-rays and obtained a value of 0.06. I do not consider the number to bevery high, but is there any way to determine, based on this value, whether any
plutonium is present?

A
A2200

In the case of Fukushima, cesium was probably released in the form of gas, so
there is a possibility that cesium gas was not stopped by the filters. However,even if cesium atoms had been released in the form of gas, they might
subsequently have become compounds through chemical reactions. In that case,they may have been large enough to have been stopped by the filters.
It is not clear in what kind of compound plutonium was released, but it is said that,in the case of radioactive fallout from nuclear tests, plutonium was released in theform of small particles (‘hot’ particles). If that was the case with Fukushima, it ishighly likely that plutonium was captured by filters.
The value 0.06 microsievert measured inside the car (per hour) is considered to
be normal in terms of natural radiation levels (that figure can be converted to anannual level of 0.53 millisievert). However, it cannot be determined based on thisvalue alone whether a minute amount of plutonium was included.

The estimate from the perspective of the physics field would be: “The hourly
radiation dose rate at the location of exposure”  “the number of hours
present at that site.”
Biological estimates are arrived at in the following two ways, with theestimation methods requiring significant time and money and lacking a large
number of experts to carry them out. For those reasons, the measurementsthat can be carried out are limited in number and unavailable even in the caseof requests from individuals.
 One method involves investigation of chromosomes in blood
lymphocytes after two-day cultures (this method requires at least 2 cc ofblood).
 The other method of deriving such estimates involves investigation of
tooth enamel through the use of the electron spin resonance technique.
The method is problematic as it can result in inaccurate assessment if theteeth used are not molars. Such measurement typically requires a pulled
tooth, and therefore the method is not useful at times of emergency whentime is short.
Such measurement methods are applicable for cases in which radiation
exposure is at a level of at least 300 millisieverts (or 300,000 microsieverts).

6

Q
Q2211

If radiation doses at point X from radiation sources A and B (which is not on line
X-A) are a and b (sievert/h), respectively, can we consider that the total radiationdose at point X is a + b?

A
A2211

Yes, a + b is correct because there is no interaction between different forms ofradiation.

Q
Q2222

I measured radiation by placing a scintillation counter directly on the ground. The
value fluctuated between 0.09–0.10 microsievert/h. Is this radiation-dose
fluctuation due to sine waves produced when cesium and other atoms in the
ground radiate electromagnetic waves?

A
A2222

There may not be a clear answer to this question, but this fluctuation is a very
common phenomenon. The range of 0.09–0.10 represents a normal
measurement fluctuation. It can be caused by detection sensitivity of the counter(in other words, signal pulse resolving time); it can also be measurement
fluctuation due to radiation randomly entering the detector. At these low radiation
doses, which are within the range of environmental background levels,
measurements can fluctuate to some extent.

Q
Q2233

Concentration and accumulation of radioactive fallout in soil must have begun along time ago. There are data (Meteorological Research Institute) showing thatseveral thousand times more radioactive substances (such as Cs-137 and Sr-90)
than usual continued to fall for about 20 years between 1955 and 1975, whenatomic and hydrogen bombs were tested frequently. There was a large amount of
fallout from the accident of the Fukushima nuclear power plant, but at the sametime, there must have been a large amount of radioactive substances that fell andaccumulated during that 20-year period, with such substances emitting
substantial levels of radiation. Is it possible to take measurements, conduct
analysis, and make categorizations to determine when radioactive substances
emitting the radiation measured currently in hot spots were produced (whether
they originated from the past accumulations or from the Fukushima accident)?

A
A2233

Some of the radioactive substances falling on the ground are washed away withrain, and so on, with time, and the remaining substances seep into the ground.
An inexpensive mobile radiation counter only counts the total level, but an
expensive counter (not mobile) can measure the energy of gamma rays as well
as beta rays. Types of released energy differ by nuclide of radioactive
substances, so there is a possibility that recent contamination (mainly
cesium-137) and past contamination can be distinguished. An easier way tohandle this issue is to assume that contamination due to past nuclear tests is
spread almost uniformly throughout the country and then subtract those doses
from the calculation of the doses from the accident.

Q
Q2244
A
A2244

What should one do if potentially exposed to radiation?
Radiation dose will be estimated based on behavior records. Please refer to
Q
Q1188 for estimation methods.
You would be advised to go to a location where radiation measurement
devices are being used for detection of radiation contamination, and undergo
measurement for detection of any radiation.
Radiation can be measured at the following sites: Hiroshima University Radiation Emergency Medicine Promotion Center Institutes related to health care for the radiation-exposed (eastern Japan)(primary and secondary)7

Institutes related to health care for the radiation-exposed (westernJapan) (primary and secondary)Those at locations distant from the nuclear power plant need not be overly
concerned.



4. Questions about radiation risk and radiation protection

Q
Q2255
A
A2255

How do you protect yourself from radiation leaks?

Q
Q2266

How far should I stay away from the power plant? Is there any association
with length of stay in the affected area?

A
A2266

Radiation has the same properties as light, and radiation dose therefore is ininverse proportion to the square of distance from the source of radiation(amount of radiation decreases to one-fourth when distance is doubled), as
long as radiation is released from one source.
Radiation dose rate (in units of microsievert per hour), which has been
touched on in the news, indicates the amount of radiation that someone will
receive based on the assumption that s/he remains at the same location foran hour. The total amount of radiation dose is calculated by multiplying theradiation dose rate by the length of stay in the affected area.
Radioactive materials released from the nuclear power plant will be spread by
the wind. The wind blowing to the east will likely spread most radioactive
materials over the Pacific Ocean.

Q
Q2277
A
A2277

Is it possible to prevent disease after one has been exposed to radiation?

Q
Q2288
A
A2288

When is iodine used? Where can it be obtained?

The best way to protect yourself from radiation is to keep away from radiation
sources or minimize the time spent around them. It is recommended thateveryone stay clear of nuclear power plants releasing radioactive substances
and any other areas with high radiation levels, and that you minimize the timeof your stay around such areas. If you have passed by the power plant,measurement of radiation levels with a survey meter would help you feelreassured. For more information on such measurement, please refer to Q
Q2244.

Once you are exposed to radiation, the effects cannot be reversed. The
development of sickness due to radiation exposure (in this case, “acuteradiation sickness”) happens when the level of exposure exceeds 1 sievert (1sievert = 1,000 millisieverts = 1 million microsieverts). For ordinary citizens toreach this level of exposure is very unlikely.
When radiation enters the body through food and the like (internal exposure),
there are very few methods established for the prevention of sickness (except
for cases of prevention of thyroid exposure by taking iodine prior
to/immediately after exposure). Medical procedures would be undertaken fortreatment of any specific symptoms that arise.

Radioactive iodine is an element created in great quantities through theprocess of nuclear fission of uranium. This radioactive iodine is characterized
by its propensity to accumulate in the thyroid gland once it is ingested in the
body. Therefore, by taking non-radioactive iodine in tablet form ahead of time,in the case of potential contamination by nuclear fission products, the iodine
would compete with the uptake of the radioactive form of iodine from entering
8the thyroid gland on the off chance that it entered the body, and thereby
reduce exposures.
In the case of a radiation accident, iodine is administered on the basis of adetermination made by the office in charge of responding to the accident.
Besides such cases, a physician’s prescription is necessary, and therefore
nonprofessionals should not be taking iodine on their own.

Q
Q2299

What differences are observed in health effects between short-term andlong-term exposures to radiation, when total exposure doses are the same?

A
A2299

Generally, when doses of radiation exposure (in terms of total exposure dose
resulting from multiplication of radiation dose per hour by exposure time) are
the same, health effects decrease as exposure time is prolonged. However, it
is highly likely that the degree of decrease in such effects differs dependingon the radiation dose (the degree of decrease is more significant for highlevels of radiation exposure). Therefore, at low doses (e.g., 100 millisievertsor less), there may be only slight differences in health effects between
long-term and short-term exposures. Expert opinions differ with regard to thismatter.

Q
Q3300

Would there be any effects on fetuses (pregnant women), and babies to be
born?

A
A3300

It is believed that radiation exposure of a fetus during the period oforganogenesis (2-8 weeks after fertilization) poses risk of congenital anomaly(deformation), although there is no such data for A-bomb survivors. A fetus isvery vulnerable to radiation during the fetal period of 8-15 weeks after
fertilization when brain cells are actively dividing. The data of A-bomb
survivors indicates that the rate of microcephaly (involving intellectual
impairment) increased. However, such effects are unlikely to emerge at alevel of less than 100 millisieverts.

Q
Q3311
A
A3311

Are there any health effects from radioactive cesium?

Q
Q3322

Please tell me about the effects of radioactivity on surfers in the ocean off thecoast of that part of Japan.
Please refer to radiation doses published on the website of the Ministry of
Education, Culture, Sports, Science and Technology. Please ask the departmentof health and welfare of the coastline prefectures if radiation doses listed on thewebsite are safe both on the shore and in the ocean. It is also recommended tocall the Health Consultation Hotline (0120-755-199) of the said ministry.

A
A3322

Q
Q3333
A
A3333

Radioactive cesium (cesium-137 or 134) is a strong emitter of gamma (andbeta) radiation, and hence it is easy to measure. It is a type of atom produced
as a result of nuclear fission of uranium and plutonium, and the half-life ofcesium-137 and cesium-134 are 30 years and 2 years, respectively. Greater
health effects are expected with increases in radiation dose.

Would 0.12 Bq of urinary cesium compared with ordinary levels increase the riskof cancer?
It is difficult to answer the question directly because there is no description of thevolume of urine measured. However, if the measured volume were 100 cc, itmeans that the level was 1.2 Bq per liter, and if that is the case, there should be
9

no problem at all.
Even if the measured volume were 50 cc, it means that the level was 2.4 Bq perliter, which was the average among Japanese during the time when atmosphericnuclear tests were being conducted frequently.
Reference-information websites:
Atomic encyclopedia ATOMICA
http://www.rist.or.jp/atomica/data/pict/09/09010411/03.gif
http://www.rist.or.jp/atomica/data/dat_detail.php?Title_Key=09-01-04-11

Q
Q3344

A
A3344

Isn’t it virtually unnecessary to worry about effects of low-dose exposure? Peopleof the generation who were born and brought up in the days when nuclear
weapons were tested frequently (people around 40 now; several thousand times
more radioactive substances than usual continued to fall and accumulate forabout 20 years, starting in around 1955, according to the data of the
Meteorological Research Institute) must have been exposed repeatedly to
low-dose radiation (both internally and externally) for a long time since they were
infants. However, rates of abnormalities and health issues in this generation are
not considered to be high. Doesn’t this mean that people of this generation andtheir parents prove, through their own experience, that there shouldn’t be any
serious concerns about low-dose exposure?
Because contamination spread nationwide during the days when nuclear
weapons were tested frequently, no control group for comparison exists in the
country. Therefore, all we can say is that no effects could be detected, eventhough there might actually have been some effects. There is the possibility thatthe economic growth and the increase in average lifespan experienced during
this period might have offset any detrimental effects.

Q
Q3355

I am looking for data and materials concerning results of thyroid examinations
conducted as part of the “Fukushima Residents Health Management Study” todetermine the effects of the accident at the Fukushima nuclear power plant.
From a layperson’s perspective, the percentage of people who were diagnosed
with health issues according to the website
http://www.pref.fukushima.jp/imu/kenkoukanri/240426shiryou.pdf
seems high, but I am having difficulty in interpreting the information because
there are no numbers that can be used for comparison purposes. If a similar
examination were to be conducted on the general population of people notaffected by the Fukushima accident, what would be the percentage of those withhealth effects? It would be appreciated if you could inform me of any past
information, including research data, showing such percentages.

A
A3355

Unfortunately, there have been no reports on results of the frequency of nodules
based on thyroid examinations of a large number of children among the general
population.
Several reports were published on the frequency of nodules detected byultrasonography among adults, and a comprehensive report summarizing thesefindings was published in English in 1996.1) “Guidelines Concerning Thyroid
Tumor Therapy, 2010,”2) published in Japanese, introduces the content of thesaid report, and states that thyroid nodules were found in 17–64% of the subjects
in four prospective studies using ultrasonography. These studies, which show
frequencies that vary substantially, were conducted before 1996, and theperformance of ultrasonography machines used in these studies was quite
different from that of machines used today. With improved performance, current
machines can detect very small nodules of 1–2 mm. Therefore, if examinations
were to be conducted with modern equipment, the frequency should be evenhigher. Usually, secondary examinations are conducted when a nodule of 10 mmor larger is found in an adult. In Fukushima, stricter criteria are used, with10

secondary examinations being conducted when a nodule of 5.1 mm or larger isfound.
1) Tan G, Gharib H. Thyroid incidentalomas: management approaches to non
palpable nodules discovered incidentally on thyroid imaging. Ann Int Med 1997;
126: 226-231
2) Guidelines Concerning Thyroid Tumor Therapy, 2010, edited by the Japan
Association of Endocrine Surgeons and the Japan Thyroid Association,
published by Kanehara & Co., Ltd.

5. Other questions
Q
Q3366 Are experiments using animals, such as mice, being conducted to study the
degree of effects of radiation exposure?

A
A3366

Various experimental animals, plants, and cultured cells are being used.

Q
Q3377

Culling of livestock(1) Are animals destroyed because they were exposed to radiation or becauseradioactivity was taken up into their bodies internally?
(2) If one were to eat such culled livestock, what detrimental effects would there
be on one’s health?
(3) Does radiation continue to remain in the bodies of animals exposed toradiation?

A
A3377

(1) It is virtually impossible to measure how much radiation farm animals were
exposed to, i.e., their radiation doses. Radiation does not remain in the body after
exposure (only neutrons activate substances, but no neutrons were emitted fromthe accident). The issue is, therefore, what quantities of radioactive substanceswere taken up internally into the bodies of animals.
(2) As to mechanisms of possible detrimental effects of eating such culled
livestock, there is a concern that radioisotopes with long half-lives, such as
cesium-137, may be taken up into the human body and cause internal exposure.
Even in such cases, however, careful consideration should be given to internal
exposure doses. Serious questions should be raised about the argument thatsuch animals are dangerous simply because they were contaminated, if theargument is not based on any discussion of radiation doses.
(3) Needless to say, radioactive substances entering the bodies of animals andhumans decay in accordance with their half-lives. In the case of radioactive
iodine, which has a half-life of 8 days, for example, radioactivity will decrease to
one-half after 8 days and to one-quarter of the original amount after 16 days. In
addition, radioactive substances in the body are excreted from the body throughnatural biological processes. Thus, together with the substantial contribution of
biological half-life, such processes aid in the reduction in amount of radioactive
substances in the body. However, some radioisotopes are absorbed into boneand organs, and thereby remain in the body for long periods of time. To
understand this idea, it would be helpful to look at the periodic table that we allstudied in chemistry class, and imagine that atoms similar to the molecules andatoms that make up bone and muscle become radioactive (for example, please
compare the molecular structures of calcium, an element that constitutes bone,and strontium).

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