A Trial to Natural Neutron Radiography

Neutron radiography system without the use of artificial neutron source has been developed. It uses only natural neutrons which exist continuously in any place. The system consists of a high sensitivity neutron imaging device and neutron moderator. The imaging device used was a 2-dimensional photon counter system which has been developing so far for high sensitivity neutron imaging. However, further improvement of neutron sensitivity and reduction ofγ-ray response is no doubt indispensable, whileγ-rays originated by cosmic rays and environmental radio isotopes also exist with the flux in several orders of magnitude large compared with that of the neutrons.The environmental neutrons are originated by cosmic ray. The intensity of natural neutrons is changed with the environmental conditions. Interestingly, the neutrons were observed to increase considerably with the condition near the massive iron blocks. The phenomenon is useful for our purpose, while the main object of the natural neutron imaging system is the field inspection of large iron structures.