SPATIAL LOCALIZATION OF MEASUREMENTS FOR THE GAMMA-RADIATION PROBING OF COALS

1. The part of the rock volume under analysis which forms the maximum contribution to the flux at the detector is situated at a depth of about one half the relaxation length and is found beneath the detector where the measurement unit is pressed to the surface of the sample; as the measurement unit ascends above the sample, this region shifts toward the source of photons. 2. The maximum depth at the level of 5% of the maximum flux does not exceed 1.3-1.5 the relaxation length of the quanta in the sample. The depth at a level of 50% of the flux is00.5-0.7 the relaxation length. 3. The area of the surface layer which forms the flux at the detector increases significantly with increasing distance between the measurement in it and the surface of the sample. 4. The maximum depth at the level of 5% of the maximum flux increases very slightly with increasing measurement base. On changing the measurement base from 10 cm to 20 cm, the depth increases by 35%, while a further increase in the base does not lead to an increase indepth. In estimating the depth of the region forming the signal with a level of more than 50% of the maximum value, its decrease from 3.5 cm on a base of 10 cm to 3.0 cm on a base of 30 cm is noted. This leads us to conclude that the increase in depth on bases of the order of (1-3)·l is explained by the effect of the contribution of repeatedly scattered quanta. The reduction in depth on large bases is explained by the reduction in the fraction of the contribution made by repeatedly scattered radiation. In this case, a flux of scattered quanta is formed in the layer adjacent to the surface at depths not exceeding the relaxation length of the quanta in the absence of collimation. © 1992 Plenum Publishing Corporation.