Patent Number: 041467965
Section: summary

BACKROUND OF THE INVENTION The present invention relates to a novel apparatus to determine the depth of radiation sources within a body of material such as soil, for the purpose of determining density, moisture content, and the like of the material. The measurement of soil density and soil moisture content is an important determination in the construction and agricultural industries. In the past, the method of obtaining such measurements has included the removal of the soil to a laboratory for testing. This technique is time consuming and not consistantly accurate since the sample removed may change its particular characteristics during transportation and handling. Relatively recent developments have included the use of a radiation source such as radioactive materials available in the industry. Such radiation sources emit gamma radiation and neutrons which may be subsequently detected by backscatter and transmission techniques. Reference is made to U.S. Pat. No. 3,655,977, issued Apr. 11, 1972, which fully describes an apparatus which may be employed, without excessive handling, for either backscatter or transmission measurement techniques. Focusing on the transmission technique, a pre-drilling of a small hole in the material is initially required. A source support, which may take the form of an elongated rod, is inserted within the hole a predetermined distance. A detector on the material surface would then gage the radiation signal, the intensity of which is proportional to the density of the soil. The transmission technique eliminates the problem of surface roughness which has a marked effect on the backscatter technique performed on the surface of the body of material being measured. However, the depth of the radiation source in the material must be exactly determined in order to produce accurate results. The advent of microprocessors requires that the depth determination be in the form of an electrical signal understandable by a computer. The work of the computer eliminates time consuming and costly human computations. No prior devices are known which produce a depth determination of a radiation source within a body for use with a transmission technique for determining soil density. SUMMARY OF THE INVENTION In accordance with the present invention a novel apparatus for determining automatically the depth of a radiation source within a body material is provided. The apparatus includes a radiation source holder to direct and to transport the radiation source within the body. In the case of the heretofore described transmission technique, the radiation source holder may be a rod which travels into a pre-drilled hole in the body. The rod may be enclosed in a guide tube having external visual indication of the rod's position within the body. The radiation source holder may mount on the detection means for convenient usage. A plurality of switches are positioned such that the switch contacts are fixed in relation to the movement of the radiation source holder, and the radiation source thereon, within the hole in the body. Trigger means activates any of the switches at a preselected depth of the radiation source within the body of material. The trigger means may be attached to the rod holder, but in any case, the trigger means moves with the radiation source. Means for indicating the activation of any of the plurality of switches would produce a signal corresponding to the depth of the radiation source. Such indicating means may take the form of a series of resistors electrically connected or linked to a source of power. The plurality of switches connect to an electrical ground; each of the switches being connected to the series of resistors. Means for detecting a signal produced by activation of any of the switches may take the form of an ammeter, galvanometer and like devices. Thus, a circuit forms by the electrical connection of the ground any of the plurality of switches, a certain number of the series of resistors and the power source. The current signal of the created circuit would serve as a representation of the depth of the radiation source. The apparatus may employ magnetically activated switches while the trigger means would be embodied in a magnetic field source, such as, but not limited to, a permanent magnet. In this instance, the guide tube may interpose the plurality of switches without hindrance to the workability of the apparatus. As may be surmized, a new and useful invention has been described and it is therefore an object of the present invention to provide an apparatus for determining the depth of a radiation source in a body of material which may be used with a portable moisture and density measuring device employing a radiation source in such determinations. It is another object of the present invention to provide an apparatus for determining the depth of a radiation source in soils pertaining to construction and agricultural uses. It is yet another object of the present invention to provide an apparatus for determining the depth of a radiation source in a body of material in terms of an electrical signal useable by a computer for automatically plotting parameters of the body of material, employing a radiation transmission attenuation technique. It is still another object of the present invention to provide an apparatus for determining depth of a radiation source in a body of material to a high degree of accuracy for the purpose of obtaining highly accurate parameters of the body of material. The invention possesses other objects and advantages especially as concerns particular features and characteristics thereof which will become apparent as the specification continues. Various aspects of the present invention will evolve from the following detailed description of the preferred embodiments thereof which should be taken in conjunction with the accompanying drawings.