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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS - 1963
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ORNr. 2597
Conf-660920-12
HEALTH PHYSICS ASPECTS OF SUPERSONIC TRANSPORT*+
NOV 2 9 1966
Walter S. Snyder
Health Physics Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee, USA
jap.mygter
XQ
3.00
The supersonic transport aircraft, hereafter referred to as the SST, is being
Gesigned to cruise at altitudes of 60,000 to 80,000 feet. At these heights, passengers
and crew will be exposed to somewhat higher levels of cosmic radiation because the
overlying absorption thickness (g/cm2) of air is less than half what it is at 30,000 or
40,000 feet, the heights used by many present commercial aircraft. Undoubtedly,
the problem of solar flares, which produce radiation fields with intensity much above
the average levels, has served to call attention to the general problem of radiation
exposure entailed by the use of the SST. Consequently, there have been a number
of studies of the problem (for example, refs. 1-5), including one by an ICRP Task
Group, '°) and this paper is, in a sense, a summary of these reports and an updating
with what new information has been found during the last year.
The British and French governments are cooperating to produce an SST which
is termed the Concorde. Several U. S. firms are also actively at work on design, but
it appears the American planes may not be ready for commercial use as soon as the
Conco-de which is tentatively scheduled for service in 1971. The Concorde is designed
Research sponsored by the U. S. Atomic Energy Commission under contract
with Union Carbide Corporation.
*For presentarion at the First International Congress of the International Radiation
Protection Association, Rome, Italy, September 5-10, 1966.
LEGAL NOTICE

4
RELEASED FOR ANNOUNCEMENT
DE MUCILAR SCIENCE ABSIHACIS
This report was prepared as an account of Government sponsored work. Nellhor the Unilad
Blates, nor the Commission, nor any porson acting on behalf of the Commission:
.: A. Makes any warranty or representation, expressed or implied, with respect to the accu-
racy, completeness, or usefulness of the information contained in this report, or that the use
of any information, apparatus, method, or process disclosed in this report may not Infringe
privately owned rights; or
B. Assumes any liabilities with respoct to the use of, or for damages resulting from the
*Use of any information, apparatus, method, or process disclosed in this report.
As used in the above, "'person acting on behalf of the Commission" Includes any em-
ployee or contractor of the Commission, or employee of such contractor, to the extent that
such employee or contractor of the Commission, or employee of such contractor prepares,
disseminates, or provides access to, any information pursuant to his employment or contract
with the Commission, or his employment with such contractor,
to fly from New York to Paris, for example, in 3 hrs and 15 min, or from London
to Sydney in 13 hrs and 20 min, and will carry from 110 to 130 passengers. Nine
airlines have already placed orders for 45 of these planes, and the interest in the
American version is comparable. An artist's representation of the Concorde is shown
in Fig. 1.
The primary spectrum of cosmic radiation is fairly weil documented. There is
considerable absorption due to the 30 to 70 g/cm of air above these altitudes so that
this primary spectrum is considerably altered, and there have not been many direct
measurements of the radiation fields within this belt. Thus the radiation fields erra
countered be:ween 60,000 and 89,000 ft are not as well determined as those at lower
altitudes or those at higher altitudes. It is convenient to consider these radiation fields.
....
.--
under two separate categories -(1) galac. ic radiation, which originates outside the
solar system, and (2) solar radiation originating with the sun, the latter including solar
flares which are, in fact, only more intense and limited periods of solar radiation.
Galactic radiation consists primarily of energetic protons, alpha particles, and
to a lesser extent heavier nuclei, and it is relatively constant in intensity except for
effects due to magnetic fields associated with sun spot activity and solar flares. In Fig..
2, which is taken from ref. 1, the change of the composition of the cosmic ray beam with in
altitude is shown. The height of 60,000 ft is just beyond the region where the "transition
effect" occurs and the particle fluxes begin to decrease. At lower elevations the dose
will be primarily due to radiation of low LET, i.e., electrons and mesons, but at altitudes
of 50,000 to 80,000 ft, the flux of nucleons increases and makes a very significant con-
tribution to the dose and even more to the dose equivalent.
- 3-
In the upper atmosphere, the total ionization increases from the earth's
equator toward the poles owing to the magnetic field of the earth which deflects
low-energy particles. Because of this screening effect, the number of high-energy
primary particles reaching a given height above the earth increases with latitude,
being minimal at the equator. This screening effect is less at lower altitudes and is
hardly significant at sea level. Fowler and Perkins) have estimated this latitude
effect for a height of 70,000 ft, and the ir estimate is shown in Fig. 3. It is seen
that at 60° or more of north latitude the intensity of ionization is about three times
greater than at the equator. Many of the most travelled routes pass through these high
latitudes, and if it appears desirable to reduce dose to passengers or crew, one might
achieve a substantial reduction by following routes that lie in lower latitudes so far as
practicable. Crew members might be rotated so that the same individual did not fly
predominantly on the routes through high latitudes. However, while these are possibilities,
it is not at all clear that such practices will be required to meet current standards
limiting exposure of either passengers or crew.
In years of high solar activity such as 1958-1959, an interplanetary magnetic
field is superimposed on the earth's magnetic field. This effect is represe.ited in Fig.
4 which shows this effect for 1954, a year of low solar activity, and for 1937, a year
of high solar activity. In the region of 60,000 to 80,000 ft, this effect is only a difference
of 20-30%. The similar data for 1954 are, however, practically a factor of 3 higher than
for 1958 in northern latitudes and at an elevation of ~ 90,000 ft according to Neher and
Anderson.
Thus, this effect can account for a very substantial increase or decrease
in the total dose received from galactic radiation.
Fowler and Perkins y have summarized and evaluated the dose and dose equiv-
alent using the ICRP recommendations to obtain the quality factor (QF) from the linear
energy transfer (LET). A significant fraction of the total ionization is produced by protons
and heavier nuclei, but they have rather high energies so that the QF only averages 1.5
according to their estimate.
This estimate neglects the dose due to neutrons which
undoubtedly increases the value of QF. The ICRP Task Group, using data of Haymes, '')
evaluated the dose from neutrons separately. Using a QF of 8 for this dose, the QF for all dose
from galactic radiation averages about 2. However, it must be recognized that the measured
values on which this estimate is based only include neutrons of energy above 1 Mev, and,
while allowance has been made for the neutrons of lower energies, there is scine uncertainty
in the estimate, perhaps as much as a factor of 2. The ICRP Task Group estimates a dose
rate of 1.3 to 1.9 mrem/hr at heights of 60,000 to 80,000 ft, respectively, for polar
latitudes and for years of a quiet sun. Thus these dose rates are "conservative" so far as
latitude and solar effects are concerned.
Using the spectrum estimared by Perkins and Fowler, tº one finds that about
::
5-10% of the dose is due to nuclei with mass greater than that of an alpha particle,
and some of these have sufficient energy to produce a broad path, perhaps 10 u in
diameter, extending over many cell diameters. Schaefer has calculated the number
of these "thin-down" hits per day/cm," and they have been reasured by Yagoda."
egoda. (9)
- 5 -
The variations of these hits with altitude during years of a "quiet" sun and of an
"active" sun are shown in Fig. 5. The ICRP Task Group recognize the unique
problems posed by this type of radiation as have other investigators. Referring to
these "hin-downs," the Report notes that "Such tracks of affected cells have been
observed experimentally in the skin of mice exposed to cosmic radiation in the upper
atmosphere and, although of little functional importance in the skin, might be of much
greater importance in the embryo or in vital organs such as the brain. Attempts to
'
study this question with microbeam irradiation suggest that the observed changes per
exposed cell are smaller than for the same number of ions per cell delivered to a
larger volume of tissue; however, no RBE value can be cited for an effect that is
produced by high-LET radiation but not by low-LET radiation under the conditions
of interest. Some other means will have to be found, therefore, if such effects are
to be taken into account in calculation of the dose equivalent. Apart from this special
case, the risk-limiting somatic effects from high-energy radiations are not different
from those ordinarily considered in protection work. “
The dose rate from solar radiation averages somewhat less than that from galactic
radiation, as is indicated on Fig. 6 which is due to Fowler and Perkins. The solar
radiation is composed largely of fast protons, but as these penetrate to a depth of
60,000 to 80,000 feet in the atmosphere, a spectrum of secondaries is produced so
that the radiation field has much of the same complexity as does galactic radiation
at these depths. As will be noted from Fig. 6, the average intensity does not constitute
.6
.
.
a severe problem as compared with the galactic radiation field. However, solar radiation
varies greatly in intensity, the acrivity being closely correlated with sun-spot activity .
which follows a rather regular cycle of intense and depressed activity, one cycle .
representing about 10-11 years and the intensity of a particular burst or "Flare" may
vary over as much as 6 orders of magnitude. There have been seven giant flares that
have occurred during the last two solar cycles, that is, in the lasi 20 years, that have
carried substantial fluxes of photons of 1 GEV or higher energies. These flares have .
produced geophysical phenomena which could be used as a basis for detection soon .
enough for the SST to descend to a lower altitude and have the benefit of the shielding
of more of the atmosphere. The giant flare of February 23, 1956, is by far the largest
observed to date and is estimated to have produced doses ranging from 2-20 rads during
the first hour of the event at the 60,000 and 80,000-ft altitudes and over the polar
regions. The range of values, as estimated by Fowler and Perkins, is shown in Fig. 7.
The intensity at SST altitudes depends not only on the protons ejected by the sun but
also is markedly influenced by the state of the magnetic fields existing between the
sun and the earth which may serve to deflect much of the radiation or to facilitate its
passage to the earth. It must be recognized that there is considerable uncertainty in
.
.
this estimate, because there was no useiul balloon flight until 20 hours after the event,
and the dose est imates depend upon extrapolated data on the actual intensities and spectra
at SST altitudes.
.....
......
-7-
As Fowler and Perkins) state, "We must now ask the question as to whether
the sample over the last sunspot max imum is likely to have been representative. We
estimate that the outburst of 23rd February 1956 was responsible for approximately
one half of all the solar particles of energy > 100 MeV that have arrived since 1950,
and greater fractions of particles of higher energy. Are such outbursts to be expected
more or less often than once in 10 years - or could we expect even more severe outbursts
- say 10 or 100 times us great?
"We mentioned earlier that the 53 outbursts in the last solar cycle were spread
over an estimated range of 10° in intensity, and that this hugh range was due to propo-
gaiion conditions between the sunspot and Earth as well as to the intrinsic intensity of
the solar flare... So it seems likely that the probability of experiencing another solar
avent comparable to that of 23rd February 1956, or an even more intense one during
ine course of any 11 year sunspot period is rather high."
The question of taking evasive action, i.e., descending to lower altitudes
0r, in periods of intense activity, flying over routes which lie closer to the equator,
has been proposed and often arouses quite divergent opinions. It is estimated that an
SST in flight might have some 10-15 minutes warning before the arrival of the really
iniense build-up of the field which may reach peak intensity in a matter of minutes.
Crie rime course of neutron monitor readings, as observed at Deep River, Ontario, in
November 1960, are shown in Fig. 8.'
The sharp rise in intensity shown here, followed
by the gradual decline in intensity extending over hours is fairly typical. In the giant
io.ir
..
flare of February 23, 1956, Fowler and Perkins estimate that the total dose during
the entire day was only 50% higher than the dose during the first hour. Thus any
evasive action must be rather prompt.
It has been questioned whether a very prompt change in course might not
:
encil other hazards for the occupants of the SST'"
which would be more severe
ihan ihe hazard posed by the radiation fields. Certainly, those who propose that such
corion be taken are not envisioning actions which would involve any appreciable prob-
ability of wrecking the plane or causing, severe physical distress to the occupants. Those
designing the SST are well aware of the problem of radiation exposure and are investigating
the desirability and means of taking evasive action. Of course, this is not a definite
commitment to such a policy, but some of the working reports discuss in detail the type
ci monitoring instruments to be carried on the plane and, in one case, a "safe" range up to
5 mrem/hr, an "alerts or "warning" range up to 50 mrem/hr, and an "action" range above
50 mrem/hr have tentatively been selected. None of the working papers the author has
seen mention or discuss any hazard that might be involved in descending to lower altitudes,
Many airlines are distributing advance publicity concerning the SST in the material they
offer to passengers in the seat pockets on current flights. A survey of this literature reveals
..
,
inut several airlines are already educating the public as to the presence of these radiation
fields and reassuring them that adequate measures are being taken to meet the problem.
Several of these brochures mention the possibility of evasive action, and all indicate that
in the years before commercial flights begin, there will be considerable study of the
problem, and during the year or more of extensive testing of the craft, there will be
much more data on the problem than we now have.
In summary, the average levels of galactic and solar radiation do not pose.
cny great problems. The ICRP Task Group report estimates, conservatively, that the
average dose rate on a polar route and at 60,000 to 80,000 feet might be as much as
3 mrem/hr. For the great bulk of travelers who make only a few flights a year, this
is well within the limits on exposure of individuals of the population recommended by
the ICRP. For the crew, or the courrier who is continually making such trips, it is
Grother matter, and they may have to be classed as radiation workers. For example,
a schedule of 40 hrs/mo of time in actual flight over high latitudes might entail about
1.5 rem/yr as an average, although it must be remembered these are generally conservative
estimates. As mentioned above, some of the present plans provide for monitoring instruments
on board, and these will provide better estimates as flying experience accumulates. Also,
icking account of the fraction of the population likely to be involved and of time factors,
the contribution to the total genetic load is small as noted by the report of the ICRP Task
Group.
LLL
- 10 -
1. H. J. Schaefer, "Radiation and Man in Space, * p. 267 Auvances in Space
Science, Vol. 1, Frederick I. Ordway III, ed. (Academic Press, Inc., New
York, 1959).
2. T. Foelsche and E. H. Graul, "Radiation Exposure in Supersonic Transports, *
Atomprax is 8, 365 (1962).
3. P. H. Fowler and D. H. Perkins, "Cosmic Radiation and Solur Particles at Aircraft
Altitudes --Background Note," Air Registration Board, Supersonic Aeroplane Air-
worthiness Committee, SAAC/20 (1962). . .
4. E. J. Flamm and R. E. Lingenfelter, Science 144, 1566 (1964).
5. M. Leimdorfer, R. G. Alsmiller, Jr., and R. T. Boughner, "Calculations of the
Radiation Hazard Due to Exposure of Supersonic Aircraft to Solar Flare Protons, *
In press.
6. "Radiobiological Aspects of the Supersonic Transport" (A report of the ICR?
Task Group on the Biological Effects of High-Energy Radiations), Health Phys.
12(2), 209 (1966).
7. H. V. Neher and H. R. Anderson, J. Geophys. Res. 67, 1309 (1962).
8. R. C. Haymes, J. Geophys. Res. 69, 841 (1964).
9. H. Yagoda, "Cosmic-Ray Monitoring of the Manned Stratolab, Balloon Flights,"
Geophys. Research Directorate Notes, No. 43 (1960).
10. H. W. Patterson, "Hazards of Flight in the Supersonic Transport, " Health Phys.
12(9), 1151 (1966).

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INTENSITY OF IONIZATION AT MAXIMUM OF IONIZATION- -
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Variation of "in-dovn intcrsity with altitude for sensons of
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RADIATION INTENSITY IN REMS FOR GALACTIC AND
SOLAR COSMIC RAYS AS COMPUTED FOR THIS REPORT
HIGH RBE 9545
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- The radiation dose fos the 1 hour
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211 DEEP HIVER MEUTRON MONITOR ||
FIVE MINUTE READINGS
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END
DATE FILMED
2 / 14 / 167
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