Radiation Inverse Problmes are briefly introduced. In particular, the problems in the spectrum unfolding of radiations, and image reconstruction problems in CTs are discussed. Generic algorithm for the estimation of plasma current profile as well as other recent techniques is also introduced as a new paradighm for the inverse problem solving. It is pointed out that the reduction methods of the ill-conditions and uniqueness confirmation of the solutions are important in the applied purpose.

  The needs of neutron spectrometer observing recoil-proton pulse-height distribution is claimed, and the difficulties in relation to unfolding procedure are pointed out in preface. Minimum bases for understanding “neutron spectra unfolding problem” are given in chapter 2 for the people in other fields than nuclear radiation detection. In chapter 3, some of unfolding codes properly chosen out of existing ones are briefly reviewed with short comments. In chapter 4, “Maximun entropy principle” is outlined as a preparation for chater 5, where the principle fully plays important role in establishing an unfolding theory which completely rejects artificial requirements and assumptions but brings physically acceptable solutions.

  Response functions of a neutron counter which is applicable to neutron spectroscopy, dosimetry and an estimation of mean direction of neutron source are calculated by a Monte Carlo Method. The responses are slightly directional, which means that the measured energy spectra vary as the response functions calculated for different geometries. The influence of the directional feature of the response functions on the measured energy spectra is evaluated by experiments using ²⁵²Cf and ²⁴¹Am-⁹Be neutron sources.

  A reconstruction problem using the region-of-interest (ROI) imaging method in X-ray computed tomography has been studied. The measured data by using this method become the incomplete data set, then the reconstruction from these set is usually incomplete. Under the point of view to reconstruct the inside shape of the ROI area, it was mathematically indicated that its shape could be reconstruct perfectly from the incomplete data set, and the algorithm for the shape reconstruction using the ROI method was lead. Here the shape means the locus of the discontinuous points.

  Solving method for radiation inverse problems is discussed specifically on the image reconstruction problems in CTs. A new technique based on the Bayes' theory alone is demonstrated for the image reconstruction problems in both two types of CTs, emission type CT (ECT) and transmission type CT(TCT). Finally the emphasis is placed on the capability of the new method in the case of so called ill-conditioned CT, i.e., cases of the limited observing angle, and ROI setting. Concerning the ROI method, a new concept of CT: structure adaptive CT is introduced.

  A new method to reconstruct plasma shape and plasma current distribution from magnetic measurements using a combinatorial optimization technique are proposed. The reconstruction of plasma current profile from magnetic measurements is regarded as an optimum allocation problem of currents into cross section of the vacuum vessel of the Tokamak. In order to solve this optimization problem, we use a genetic algorithm. The effectiveness of this method is shown by the application of this technique to JT-60U plasmas.