An Example of Estimation of Archeomagnetic Field lntensity by Old Roof Tiles

An Example of Estimation of Archeomagnetic Field lntensity by Old Roof Tiles

Creators Domen Haruo

Usual Thellier's method has been modified by the present author and this modified method was employed for the estimation of the ancient geomagnetic field intensity using old roof tiles. A half of the procedure in usual Thellier's method (Thellier and Thellier, 1959) should be carried out under the magnetic field free condition and this is not so easy to be done because of the difficulty of obtaining the complete non-magnetic space in the laboratory. In the present method, the test specimen was partially demagnetized and remagnetized successively in the present geomagnetic field at the laboratory. After the successive stepwise thermal treatment and measurement of any change which might be occurred in the remanent magnetization of test specimen, the ratio of the ancient geomagnetic field to the present one was estimated. Several couples of rod-like specimens cut out of the roof tiles from Japanese style houses had been prepared as same as possible in dimensions. The test specimen should be placed in the non-inductively wound electric oven in such a way that a couple of the test specimens were placed as each remanent magnetic vector in parallel and anti-parallel to the ambient magnetic field respectively. Then the specimen thus oriented was once heated up to a certain temperature and then cooled down to the normal temperature. In the present geomagnetic field, both of these procedures were successively performed. Consequently a part of natural remanent magnetization (NRM) initially having was taken its place by partial thermo-remanent magnetization (PTRM) newly given. When the roof tile was baked originally in the kiln, the tile was heated up once at least over 800℃ and cooled down in the geomagnetic field at that time, then the original remanent magnetization, that is NRM, of the tile thus baked may fossilize the ambient geomagnetic field as so-called thermo-remanent magnetization (TRM). At first, the test specimen was cut out in the rod-like shape

[ISSN]0513-1693

[NCID]AN00243950