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Many suggestions were forthcoming as to the best site for the burial of Time Capsule Expo '70. Among the most interesting were the bedrock of the Japan Alps, somewhere in Hokkaido (the northernmost of Japan's main islands and the least populated) or, looking further afield, the moon, the Antarctic and beneath the sea. The common thought behind all these suggestions was their remoteness. Ideally the two capsules should be buried in a place where they will not be disturbed.
The Senri hills, in the conurbation of Osaka, the site of Expo '70, was the first serious candidate. This area is suitable from the standpoint of geology and seismic activity Its main disadvantage is its potential for development; it was felt that when the exhibition closed the area might be attractive to developers who could take advantage of the transport and other services laid on for Expo '70. In Japan, foundations are driven deep into the earth as a precaution against earthquake damage. It would not be appropriate for the capsules to become enmeshed in the subterranean structures of a high-rise development.
Osaka Castle Park was the next site to be considered. Geologically, this area is somewhat newer than the Senri hills area but for the past several thousand years at least there is no record of it having been a sea or river bed. The area in which the park stands is one of the most stable in the Osaka Plain. Moreover, the land is Government property administered by the City of Osaka and, from 1970, it would be designated a protected site of historical importance by the Cultural Affairs Agency.
The park extends across the inner and outer walls of one of Japan's most illustrious fortresses, Osaka-jo. The original castle was built between 1583 and 1587 by one of the most remarkable men in Japanese history, Toyotomi Hideyoshi, the de facto ruler of Japan between 1585 and 1598. It was a sumptuous castle with a five-storied donjon at the centre and a complex of graceful wooden pavilions which, according to surviving records, were decorated with gold both inside and out. The tiles of the donjon's upturned, gabled roofs were also gilded. The castle was surrounded by bulwarks built of massive stones and there were three wide moats. In 1614, the castle was besieged by the 200,000 strong army of Hideyoshi's former ally, Tokugawa Ieyasu, and the following year the castle was burned to the ground. During the siege the outer moat was filled in and it was never restored.
In 1628, a new castle was built by the Tokugawa military government. The residential quarters were in a reserved style similar to that of a surviving Tokugawa palace, the Nijo-jo in Kyoto. A new donjon was also built but this was destroyed by lightning in 1665. During the following 200 years the castle was the headquarters of the Tokugawa government in the Osaka area and it was entrusted to the care of a resident keeper of high rank, but the long era of Tokugawa power came to an end in 1868 and during the turmoil of the time the castle buildings were once again destroyed. The only structure that remains from the 17th century is a section of wall roofed with tiles which stands on the inner bulwarks.
A donjon resembling that of Hideyoshi's time was built within the inner bulwarks of the castle in 1931. It is the centre of Osaka Castle Park and a museum devoted largely to the life and times of Hideyoshi. When bores were put down in front of the donjon, the levels of previous castle buildings were apparent and rubble at the upper levels suggested that the proposed time capsule burial site would be within the area of the Tokugawa palace. A ground plan of the castle as it looked in 1630 confirms that this is so.
Since the bores were satisfactory, the technical and selection committees reached an informal decision to bury the capsules in Osaka Castle Park. Formal application was made to the Cultural Affairs Agency and final agreement was received on March 24th, 1969.
In order to provide constant temperature it was determined that the capsules would have to be buried 8 to 15 metres below ground level. At that depth the ambient temperature is 17±1ºC regardless of the temperature above ground. The biggest problem for those concerned with the burial was the design of a substructure which could contain and protect the capsules at the required depth.
Initial studies centred on the prospect of building a deep circular vault. However, on closer investigation, it was found that any such rigid structure would have little chance of survival for 5,000 years. Moreover, in the event of total collapse, the capsules would be subjected to severe shock. A safer alternative was to design a protective enclosure around each capsule and bury these enclosures directly in the earth. Drawings of the enclosures, the earthworks and the final underground plan are given in Section II (pages 37-53).
First, each capsule was placed in a tubular outer container made of SUS-32 stainless steel. The space around the capsule was packed with silica sand before the containers were hermetically sealed by welding. In the case of Capsule No. 1, the steel container was then placed in an enclosure made up of three concentric layers of reinforced concrete. The enclosure of Capsule No. 2 consisted of one layer of reinforced concrete so as to simplify its removal for examination purposes. In both cases, the space between the tubular steel container and the concrete enclosure was filled with bentonite, partly with a view to waterproofing.
Excavation work at the Osaka Castle site began on October 1st, 1970. It involved the sinking of 20 auger piles and 20 double soil piles at equal intervals to a depth of 15.4 metres. On January 20th, 1971, Capsule No. 1, contained in its concrete enclosure, was lowered onto a concrete raft 14.4 metres below ground level; the hole was then filled in up to 10 metre level with coarse sand. Capsule No. 2 was buried above Capsule No. 1 on January 28th, 1971, and the hole backfilled to just below ground level.
The ring of soil piles used for soil retention during excavation is not expected to provide any long-term protection for the capsules. Ultimately, these piles will crumble and collapse. It is, in fact, desirable that the capsule enclosures and the rafts on which they stand should move independently within their different levels of clay sub-soil.
Inside and outside the capsules are stored the devices which measure the passage of time and temperature underground, and provide guidance to those who will unearth the capsules in the future.
In compartment No. 24 of each capsule is a plutonium timekeeper (N-23-1-2) a record of the passing of time and an example of the level of nuclear technology in the year 1970. The timekeeper was developed specially for the Time Capsule Expo '70 project. The movement of the clock, which is graduated in steps of 100 years from zero to 5,000, is inspired by the atomic disintegration of plutonium Pu239. In the preparation of each clock, plutonium oxide equivalent to 1 gram of Pu239 was wrapped in ten layers of gold foil, 1 micron in thickness, and placed in six small containers made of oxygen-free copper. These containers were placed within a set of bellows and the bellows were filled with helium gas at an atomospheric pressure of 1.
It is a fundamental property of radioactive elements such as plutonium that energy is emitted spontaneously. The emission of the radiated particles is progressive and constant throughout the half-life of the element. In the case of the plutonium timekeeper, alpha particles radiated by the Pu239 are transformed into atomic helium on passing through the gold foil. These particles expand and create pressure in the bellows, causing the hand to move on the face of the clock. Thus the emission of radiation is expressed as a measurement of time.
Both capsules also contain a sample of Pu239 in the form of plutonium oxide which will disintegrate progressively into uranium. In this case, the lapse of time will be measurable by reference to the amount of uranium produced. In connection with this phenomenon, it was decided to store a sample of radiocarbon C14, an element often used at this time for the dating of archaeological remains. The half-life of C14 has been given as either 5,568 or 5,400 years. Those who open the capsule in 5,000 years time will have the opportunity to determine precisely which figure is correct.
Resting above the enclosure of each capsule is a maximum-minimum thermometer (N-23-1-4) encased in an airtight tube of fused quartz and an outer cylinder of stainless steel. The anticipated temperature at the depth of either capsule is 17±1ºC. Should there be any major rise or fall in ambient temperature caused by unusual circumstances, a record of this occurance will be useful in relation to the condition of the capsules and their contents. Both of the maximum-minimum thermometers were remotely reset in April, 1972, after the temperature of the ground had stabilised. This was done through electric cables in conduits beneath the monument.
The instructions for unearthing and opening the capsules were buried immediately beneath the monument in a stainless steel cylinder. These lead the finder to a complete list of contents and a guide to examination procedures contained in the uppermost compartment, No. 29, of each capsule. The English transcription of these instructions is given in Section II of this book.
The burial site is 133 metres south of the centre of the restored donjon of Osaka Castle; it is surrounded on all sides by the gardens and pathways of the park. A short distance away to the east is the Osaka City Museum, a brick building in Western style. The design of the monument was required to harmonize with these surroundings while making a bold statement as to the existence and nature of Time Capsule Expo '70.
After consultation with various authorities concerned with the park as to size, height, material and so on, the project designers prepared a suitable design: a lowlying monument of SUS-27 stainless steel standing on a pavement of polished granite. The overall height from ground level is a little under one metre; the total area, 36 square metres. This graceful, yet strong, monument protects the capsules from above while being a clear signpost to their existence underneath.
On March 15th, 1971, the first anniversary of the opening of the Japan World Exposition, 1970, the monument was unveiled in the sight of all those who had worked so long and so hard on the project. On the same day the capsules and site were officially placed in the care of the Japanese Government at a ceremony attended by the sponsors, the Under-Secretary of the Japanese Ministry of Education, the Governor of Osaka Prefecture and the Mayor of Osaka. The Custodial agreement is reproduced in Appendix 9.
The two capsules that remained above ground, together with duplicate sets of contents, were duly located in places where they could be cared for and seen by the public. The capsule that had been on display in the Matsushita Pavilion at Expo '70 was presented to the Osaka City Museum in Osaka Castle Park in November, 1971. Another capsule was housed in the Matsushita House of History at the Head Office of Matsushita Electric Industrial Company in Kadoma, Osaka.
The capsule in the Osaka City Museum is displayed in a room specially set aside for the purpose. From the windows of the room, the resting place of the buried capsules can be seen clearly. It seems eminently fitting that the capsules should lie within the stout and enduring walls of Hideyoshi's castle; as a man of vision, he would have understood the meaning of their long journey and approved of their being here.
The contents of this site are excerpted from THE OFFICIAL RECORD OF TIME CAPSULE EXPO'70(March 1975). Please note that company and organization names may differ from those of the current ones.
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