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Symposium "Entwicklungen im Strahleschutz" , Munich, 29 November, 2001
IONIZING RADIATION IN THE 20TH CENTURY AND BEYOND
Zbigniew Jaworowski
Central Laboratory for Radiological Protection
Ul. Konwaliowa 7, 03-194 Poland; jaworo@cloor.waw.pl
Radiation protection is not only a matter of science. It is a problem
of philosophy, morality and the utmost wisdom.
Lauriston S. Taylor, 1957
After ionizing radiation and radioactivity were discovered at the end of the 19th century, their
social perception has alternated between enthusiastic acceptance and rejection. This stemmed
from recognition of their three basic aspects: 1) usefulness for medical applications and for
technical and scientific aims; 2) beneficial effects of their low levels; and 3) harmful effects of
high levels. In the first part of the 20th century acceptance prevailed, in the second - rejection.
The change of the public mood which had occurred rather abruptly after the World War II
was not due to discovery of some new danger of radiation, but was caused by political and
social reasons, unrelated to the actual effects of radiation (Jaworowski, 1999).
The possibilities that ionizing radiation offered for medical diagnostics were first
demonstrated by W. K. Roentgen, one month after his discovery, by publishing in Nature in
January 1896 an x-ray photograph of the hand of his wife. In 1902 Pierre Curie, together with
two physicians: C. Balthazard and V. Bonchard, discovered that radium rays are useful in
cancer therapy. The theoretical basis for this therapy was first provided in 1906 by Bergonie
and Tribondeau (Bergonie and Tribondeau, 1906) as the result of their experiments with rats.
They coined the following law: " X-rays are more effective on cells which have a greater
reproductive activity". "From this law, they deduced, perhaps over-optimistically, that it is
"easy to understand that roentgen radiation destroys tumours without destroying healthy
tissues".
The beneficial or hormetic effects of low doses of ionizing radiation were found two years
after Roentgen, and independently A.H. Beckerel, announced the discovery of ionizing
radiation. First such effects in algae were reported by Atkinson (Atkinson, 1898). He noticed
an increased growth rate of blue green algae exposed to x-rays. This particular observation
was followed by thousands of publications on hormetic effects, and it was repeated and
confirmed 82 years later (Conter et al., 1980).
That ionizing radiation can be hazardous for man was first announced in 1896 in the German
Medical Weekly (Marcuse, 1896). The early students and users of radiation voluntarily or
unknowingly exposed themselves to high radiation doses. Among the pioneers of radiation
and radioactivity from 23 countries, scientists, physicists, medical doctors, nurses, and x-ray
technicians, about 100 persons died by 1922, and 406 died until 1992, with afflictions that
could be related to radiation. The first fatal victim of ionizing radiation was, in 1900, a
German engineer, F. Clausen. The names of all these victims are recorded in the "Book of
Honour of Roentgenologists of All Nations", published in Berlin in 1992 (Molineus et al.,
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1992). This experience sounded an alarm, and the need for protection against high doses of
radiation was realised quite early.
In the 1920s the concept of "tolerance dose" was introduced, defined as a fraction of the dose
that caused skin reddening. This fraction corresponded originally to an annual dose (in
modern units) of 700 mSv. In 1936 it was reduced to 350 mSv, and in 1941 to 70 mSv. The
concept of tolerance dose, which was effectively a statement of threshold, served as the basis
for radiation protection standards for three decades (Kathren, 1996) until 1959, when the
International Commission on Radiological Protection based its recommendations on the linear
no-threshold principle (LNT) (ICRP, 1959). Introducing the LNT principle to radiological
protection was stimulated by undue concern in the 1950s with the disastrous genetic effects
on the human population of ionizing radiation produced by man. In the literature on ionising
radiation at that time, one could often see the following statements of geneticists: "...we have
reached a stage where human mistakes can have a more disastrous effect than ever before in
our history - because such mistakes may drastically change the course of man's biological
evolution" (Westergaard, 1955). This was menacingly echoed in the texts of some humanists,
e.g.: "Negative eugenics has become increasingly urgent with the increase of mutations due to
atomic fallout, and with the increased survival of genetically defective human beings..."
(Huxley, 1964). In the years that followed, especially from the observations of the progeny of
survivors of nuclear attacks on Hiroshima and Nagasaki, it became clear that this concern was
an overreaction, in tune with strong emotions, evoked by the menace of nuclear war.
However, emotions are not a good basis for regulations. Professor W.V. Mayneord, the late
chairman of the ICRP Committee IV, made the following comment on using LNT as a
regulatory basis: " I have always felt that the argument that because at higher values of dose
an observed effect is proportional to dose, then at very low doses there is necessarily some
'effect' of dose, however small, is nonsense" (Mayneord, 1964). Mayneord's concern about the
values applied in ICRP recommendations was in "the weakness of the biological and medical
foundations coupled with a most impressive numerical façade".
During the past several decades there was a tendency to decrease the levels of dose applied in
standards of radiation protection to lower and lower values. In the 1980s and the 1990s these
became 20 mSv per year for occupationally exposed people, and 1 mSv per year for the
general population. For an individual who receives no direct benefit from a source of
radiation, a maximum dose of 0.3 mSv in a year has been recently proposed (Clarke, 1999),
and for some instances - an exemption level of 0.01 mSv per year (Becker, 1998).
Justification for such low levels is difficult to conceive, as no one has ever been identifiably
injured by radiation while standards set by the ICRP in the 1920s and the 1930s were in force,
involving dose levels hundreds or thousands of times higher (Taylor, 1980) (Coursaget and
Pellerin, 1999). The life expectancy of the survivors of nuclear attacks on Hiroshima and
Nagasaki was found to be higher than that in the control groups (Kondo, 1993), no adverse
genetic effects were found in the progeny of survivors (Schull, 1998). There is also ample
evidence of beneficial effects of low doses of radiation in people occupationally, medically or
naturally exposed to doses much higher than the current radiation protection standards (see
e.g.: (Tubiana, 1998), and Table 1).
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Table 1. Mortality in large populations exposed to low radiation doses (1 - 500 mSv)
A = all causes; C = cancers; L = leukemia; NC = non-cancers; LC = lung cancers
High background area, USA
15% lower
C*
(Frigerio and Stowe, 1976)
High background area, China
15% lower
C
(Wei, 1990)
Nuclear industry workers, Canada
68% lower L
(Gribbin et al., 1992)
Nuclear shipyard workers, USA
24% lower
A
(Matanoski, 1991)
58% lower
L
Nuclear workers, combined Hanford,
9% lower
C
(Gilbert et al., 1993)
ORNL, Rocky Flats, USA
78% lower
L
British medical radiologists after 1955- 32% lower
A
(Berrington et al., 2001)
1979
29% lower
C
36% lower
NC
Plutonium workers, Mayak
29% lower
L
(Tokarskaya et al., 1997)
Eastern Ural, Russia
High residential radon, USA
35% lower
LC
(Cohen, 1995)
Accident in Eastern Ural, Russia
39% lower
C
(Kostyuchenko and
Kresitinina, 1994)
Chernobyl accident, recovery workers 13% lower
C
(Ivanov et al., 2001)
15% lower
A
Swedish patients diagnosed with
38% lower
C
(Hall et al., 1996)
iodine-131 **
 incidence; ** thyroid doses 0 - 257,000 mGy
To adhere to regulations based on standards involving such low dose limits, the society is
paying hundreds of billions of dollars, with no detectable benefit. Each human life
hypothetically saved by implementing the present regulations costs about $2.5 billion (Cohen,
1992). Such spending is morally questionable, as: (1) the limited resources of the society are
spent on prevention of an imaginary harm, instead of achieving real progress in health care,
and (2) because low radiation doses are beneficial for the individual. For these two reasons,
such expenditures may have actually an adverse effect on the population.
In this presentation I wish to compare the levels of radioactivity and radiation in various
environmental situations, influenced by natural processes and human practices. Such a
comparison may help to view radiation standards in a realistic perspective.
RADIOACTIVITY
When life began some three and half billion years ago, the natural level of ionizing radiation
at the planet's surface was about three to five times higher than presently (Karam and Leslie,
1996). At that time, the long-lived potassium-40, uranium-238, and thorium-232 had not yet
decayed to their current levels. Their content in the contemporary Earth's crust is still quite
high, and it is responsible for the highest radiation exposure of every living being. One ton of
average soil contains about 1.3 x 106 Bq of potassium-40, thorium-232 and uranium-238 and
their daughters. This corresponds to 2.6 x 1015 Bq per cubic kilometer (Table 2). Decay of
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these natural radionuclides present in 1 kilometer thick soil layer produces 8000 calories per
square meter annually (Draganic et al., 1993).
TABLE 2. Average activity (Bq) of complete chains of natural radionuclides in the
continental crust and soil, and total activity of wastes from nuclear power. After (Jaworowski,
1990) and (UNSCEAR, 2000b).
K-40
Th-232
U-238
Total
Concentr. of parents in 1 g of soil
0.420
0.045
0.033
0.498
Number of radionuclides in chain
1
9
14
24
7.3 x 1024
7.8 x 1023
5.7 x 1023
8.6 x 1024
Soil (in 1 ton)
4.2 x 105
4.1 x 105
4.6 x 105
1.3 x 106
Soil (in 1 km3)
8.4 x 1014
8.1 x 1014
9.2 x 1014
2.6 x 1015
Content in crust
(17.3 x 1024 g)
Wastes from nuclear power
reactors in 1997
Wastes accumulated until 2000
from the whole civilian nuclear
fuel cycle, after 500 years cooling
2.2 x 1015*
7.4 x 1015*
* This paper
We can compare the natural, extremely long-lived activity of potassium-40 (T1/2 = 1.28 x 109
years), thorium-232 ( T1/2 = 1.4 x 1010 years) and uranium-238 (T1/2 = 4.47 x 109 years) in
soil, with the activity of much shorter-lived radioactive wastes from the nuclear power cycle.
In 1997 the total annual production of electricity in nuclear reactors was 254.5 GW
(UNSCEAR, 2000a). Assuming that annual production of wastes in nuclear power reactors is
8.8 x 109 Bq per MWe (Saas, 1997), the global production of radioactive wastes from this
source amounts to 2.2 x 1015 Bq per year, with the longest lived plutonium-244 (T1/2 = 8.26 x
107 years). Such amount of average natural activity is contained in a relatively small block of
soil 0.9 by 0.9 km wide and 1 km deep. None of the man-made component of these wastes has
appreciably higher radiotoxicity (expressed as Sv/Bq) than the natural thorium-232 (IAEA,
1996).
No special barriers prevent the natural radionuclides from migration from, say, a depth of 1
km to the surface of the ground. They can be transported by mechanical action, or move in
solution. Thorium is not susceptible to leaching under most geological conditions and its
principal mode of occurrence is in refractory minerals. Uranium is highly mobile, and may
migrate with ground water to distances of several tens of kilometres or more. Radium is
mobile in sulphate-free neutral or acidic solutions. The average volcanic injections of alpha
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emitting 210Po into the global atmosphere during non-eruptive activity amount to about 5 x
1015 Bq per year, i.e., almost twice as much as the 1997 production of radioactive wastes from
nuclear power reactors (Table 3). Geochemical differences between uranium, thorium and
radium may lead to drastic changes in their radioactive equilibrium (Jaworowski, 1990).
In contrast, for man-made radioactive wastes many effective, sophisticated barriers are
provided in deep underground depositories. At a first glance, one can see in Table 2 that it
would take about 3 billion years of such a global production of wastes from nuclear power
reactors as in 1997, to double the total activity of natural radionuclides in the Earth's
continental crust.
The activity of wastes accumulated until the end of 2000 from the whole global civilian
nuclear fuel cycle is much greater. It amounts to 200 000 tones of "heavy metals", which after
10 years cooling corresponds to an activity of about 7 x 1021 Bq (Semionov and Bell, 1993).
Disposal of high level wastes and spent fuel in geologic repositories may result in doses to
population that do not begin to accumulate until well after 500 years (OECD, 2000). After
500 years activity of all high level wastes will decrease to about 7.4 x 1015 Bq
(Chwaszczewski, 1999), corresponding to natural activity contained in a block of soil about
1.7 by 1.7 km wide and 1 km deep.
It is interesting to compare the annual flows into the global atmosphere of radionuclides from
natural sources with flows from nuclear weapon explosions and production, nuclear power
cycle, coal burning, and the Chernobyl catastrophe. Except for the Chernobyl catastrophe, the
flows of nine radionuclides, with the greatest potential impact on public health, were
compared by (Jaworowski, 1982). Here I present only the highest flows of activity from
particular sources (Table 3). To account for various energy emissions by different nuclides,
the flows of radiation energy are also given.
Table 3 demonstrates that the flow of activity from the natural sources into the global
atmosphere is 2 to 5 orders of magnitude higher than from particular man-made sources, and
the flow of radiant energy is 3 to 5 orders of magnitude higher. It appears that at the global
scale, the anthropogenic emissions of radionuclides and their impact are dwarfed by the
natural ones. In the case of nuclear power the highest flow of activity is that of 3H (5.6 x 1016
Bq per year), but the highest flow of radiation energy is that of 222Rn, because of its decay
energy (5.5905 MeV) higher by a factor of 300 than the decay energy of 3H; 222Rn activity
flow is only 1.5 x 1016 Bq per year.
This might not necessarily be the case at the local scale, especially in military practices. The
widest civilian contamination of the ground surface occurred after the Chernobyl accident.
According to data in (UNSCEAR, 2000c), on the first day after this, probably greatest
possible, civilian nuclear catastrophe, a high ground contamination consisting of two patches
with a lethal dose rate of 1 Gy per hour, covered in an uninhabited location an area of about
0.5 km2, and reached a distance of 1.8 km from the burning nuclear reactor. Several hundred
meters outside the 1 Gy isolines the dose rate dropped by 2 orders of magnitude (Figure 1).
Fortunately, this situation did not pose immediate danger to the general population. This can
be compared with an isoline of 1 Gy per hour after a 10 MT surface nuclear explosion,
reaching (at calm weather) to a distance of 440 km (Miller, 1968), and covering tens of
thousands square kilometres with lethal fallout. In the localities remote from the Chernobyl
power station deposition of radionuclides was much lower, and did not reach levels which
could led to acute radiation health effects, or to chronic effects, such as genetic disturbances,
leukaemia or solid cancers (UNSCEAR, 2000c). The only exception might be the increase of
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registration of thyroid cancers in children and adults, which, however, may be a result of
causes other than Chernobyl radiation (UNSCEAR, 2000c), most probable among them being
the screening effect.
TABLE 3. Most important annual flows of activity of radionuclides and of their radiation
energy into the global atmosphere.
SOURCE
Natural
Nuclear weapons: explosions & production a
Chernobyl b
Nuclear power c
Natural: Volcanic activity (non-eruptive)
Coal burning d
ENERGY (J) e
ACTIVITY (Bq)
222
Rn
3.3 x 1019
3
Rn
3.0 x 107
7.0 x 1018
3
H
2.1 x 104
Cs
7.0 x 1016
137
Cs
6.1 x 103
3
H
5.6 x 1016
222
Po
5.1 x 1015
Rn
8.5 x 1014
H
137
210
222
222
Rn
210
222
1.3 x 104
Po
4.4 x 103
Rn
7.6 x 102
a
Annual average for 1945-1980; b emission during ten days in 1986; c average for 1981; d average for
1980; e decay energies after (Magill, 1999), f calculated from data of (Berresheim and Jaeschke, 1983)
and (Lambert et al., 1988).
RADIATION DOSES
The global distribution of radionuclides in the biosphere, and the use of radiation are reflected
in the radiation doses received by the population from various sources. During the past several
decades UNSCEAR was collecting data on doses from radionuclides in the environment and
from their medical and other uses. Although far from being complete, the UNSCEAR
compilation of data is probably the most comprehensive one, and enables estimation of the
temporal changes in average annual radiation doses received by the global population from
particular sources. In its reports to the General Assembly of the United Nations UNSCEAR
refrained from presenting in graphic form the results of such estimations expressed in units of
rems or sieverts. I present them in Figure 2, based mainly on internal documents of
UNSCEAR (for a part of medical and natural exposure), and on the UNSCEAR data
published or approved for publication (UNSCEAR, 1988; UNSCEAR, 2000a; UNSCEAR,
2000b; UNSCEAR, 2000c).
The highest annual radiation dose is received from natural sources. The average value for the
external and internal exposure of the global population currently estimated by UNSCEAR is
2.4 mSv per year. The natural dose ranges widely in particular regions of the world.
UNSCEAR’s estimates for a part of East Asia and part of Europe suggest that a 39% fraction
of the population receives annual doses from terrestrial gamma radiation lower than 1.5 mSv,
30% doses of 1.5 - 1.99 mSv, 18% doses of 2.0 - 2.99 mSv, 6.3% doses of 3.0 - 3.99 mSv,
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and only 0.4% doses higher than 10 mSv. However, this estimate does not cover the areas of
high natural radiation background, such as those in Iran, India or Brazil. For example, in the
State of Kerala, India, the annual radiation dose reaches up to 76.4 mGy (lifetime dose of >5
Gy), and it is not associated with an increased cancer incidence or cytogenetic aberrations
(Nair et al., 1999). In the area of Araxa, Brazil, (74 000 inhabitants) the average annual
radiation dose is 2800 mGy. In the city of Ramsar, Iran the absorbed dose rate in air reaches
up to 17 500 mGy per year (UNSCEAR, 2000b). In some parts of Ramsar people live in
houses where the annual radiation dose is about 700 mGy (Mortazavi, 2000), which
approaches the value of the tolerance dose from the 1920s, and corresponds to a lifetime dose
of about 50 Gy. In the area of Ramsar people have been exposed to such a high radiation level
over several generations. Cytogenetic studies have shown differences between these people
and control populations, but increases in cancers and leukaemia incidence were not observed.
Compared with the apparently non-harmful annual doses in the high natural radiation areas,
the average doses received by the global population from man-made sources seem to be of no
importance. This statement if valid also for about 4.8 million people leaving in areas
contaminated by the local fallout from the Chernobyl accident (UNSCEAR, 2000c), where
the average annual radiation dose is about 6 mSv. The highest average dose to the global
population from Chernobyl fallout, of 0.045 mSv, occurred in 1986. The global exposure
from medical diagnostics is growing rapidly growing since the 1950s, probably due to
steadily increasing access to x-ray technology in the developing countries. Since the 1980s
this exposure seem to have stabilised. Even at its heyday at the beginning of the 1960s, the
average global exposure from nuclear weapons tests (0.113 mSv in 1963) was much smaller
than the medical exposure. The exposure from the civilian nuclear power cycle grew steadily
since 1955, reaching a trifle value of 0.002 mSv in 2000.
CONCLUSIONS
Man's contribution to the contents and flows of radionuclides and of radiation energy in the
particular compartments of the environment consist but a tiny fraction of the natural
contribution. In some areas in the world the natural radiation doses to man and to other biota
are many hundreds times higher than the currently accepted dose limits for the general
population. No adverse health effects were found in humans, animals and plants in these
areas. In the future reconstruction of the edifice of radiation protection which now stands on
the abstract LNT foundations, a down-to-earth approach will be necessary, taking into
account the apparently safe chronic doses in high natural radiation areas. It seems, therefore,
that studies of these areas deserve special attention and support in the coming years.
The twentieth century witnessed the dawn of man-made ionizing radiation and radioactivity,
the use of the best human knowledge to kill people in Hiroshima and Nagasaki, and the
greatest nuclear catastrophe in Chernobyl. This catastrophe claimed only about 30 fatal
occupational victims and probably none among the public, ultimately proving that nuclear
energy is a comparatively save means of power production. It was also found that high semiacute doses of radiation can cure cancers, and that small chronic doses of radiation are
beneficial for health. It seems that the discovery of "new" radiation and of radioactivity
which opened the gate to an unlimited energy resource, has a significance to man similar to
that of the discovery of fire some 500 000 years ago. Fire made man the most ubiquitous
species and enabled expansion of life outside the Earth's biosphere. Our ancestors had to
8
mentally adapt to fire for many thousands of years, sometimes even deifying it. It seems that
one century has not been long enough for man to adapt in the same manner to ionizing
radiation and radioactivity. But there is hope yet – everything now seems to go faster than
before.
ACKNOWLEDGEMENTS
Thanks are due to Prof. S. Chwaszczewski, Prof. L. Dobrzyński, Dr. A. Strupczewski and Dr.
M. Waligórski for helpful discussions.
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Westergaard M. (1955) Man's responsibility to his genetic heritage. Impact of Science on
Society 4(2), 63-88.
11
FIGURE 1. Measured exposure rates in air on 26 April 1986 in the local area of the
Chernobyl reactor. Units of isolines are R h-1. After (UNSCEAR, 2000c)
12
FIGURE 2. Annual trends in average individual global radiation doses.
a
v
e
r
a
g
e
:
2
.
4
m
S
p
e
r
y
e
a
r
N
A
T
U
R
A
L
1
7
0
0
0
.
3
6
.
0
N
E
A
R
C
H
E
R
N
O
B
Y
L
0
.
4
M
E
D
I
C
A
L
WHOLEBDYRADITONDSE(mv)
0
.
2
0
.
1
N
U
C
L
E
A
R
E
X
P
L
O
S
I
O
N
S
C
H
E
R
N
O
B
Y
L
0
.
0
N
U
C
L
E
A
R
P
O
W
E
R
1
9
4
0
1
9
5
0
1
9
6
0
1
9
7
0
1
9
8
0
1
9
9
0
2
0
0
0
Y
E
A
R
13