Kunihide Nishizawa

Detection of extremely low level radioactivity with imaging plate

Imaging plate (IP) is useful for in-situ detection and distribution measurements of extremely low-level radioactivity. Exposure of IP for several hours makes it possible to detect down to about 10−4 Bq in a spot with an area of around 1 mm2 or less. Methods to determine radionuclide species by only a single exposure are proposed; the several sheets lamination method and the several times successive read-out method. Although the latent image degraded with time after exposure, simultaneous exposure of α-, low-energy β- and high-energy β-calibration sources together with the specimen led to a quantitative analysis.

Nuclear Fusion in Solid

Spontaneous neutron emissions were intermittently detected from activated palladium rods well soaked with deuterium gas in a closed glass bulb. By the stimulation of the palladium rods with a high voltage discharge between the rods, a burst of neutron flux 2×104 times larger than background was detected. Atoms or molecules of mass number 1, 2, 3, 4, 5 and 6 were found in the residual gas. Nuclear fusion in solid is interpreted in terms of the supersaturation of the solid solution of deuterium.

Measurement of the radioactivity distribution of material surfaces with an imaging plate

Abstract An imaging plate has a very high sensitivity, and it is useful for in situ measurements of the distribution of extremely low levels of radioactivity, down to about 10 −3 Bq/mm 2 , of material surfaces such as stones, vegetables etc. A method to determine the radioactivity is proposed in such applications.

In-vivo thyroid 125I monitoring method using imaging plate.

A new in vivo thyroid monitoring system was devised with radioluminography using an imaging plate. The counting features of the system were investigated by using a neck-thyroid phantom. A clear thyroid image was obtained at thin prethyroid tissue thicknesses and short distances between IP and neck surface. The characteristic 125I thyroid image made it possible to visually confirm that the thyroid definitely accumulated 125I. The counting efficiency in 100xcps Bq(-1) of the imaging plate system was determined by setting a region of interest on the thyroid image resulting in a maximum efficiency of 0.5%. The higher efficiency was obtained for thinner tissue thickness overlaying the thyroid, smaller thyroids, and shorter distances between the imaging plate and neck surface. The imaging plate thyroid monitoring system was sensitive to thyroid 125I. Its minimum detection limit of 23 Bq for a 10-min measurement was considerably lower than the annual thyroid burden limit of 300 kBq.

Radioactivity distribution measurement of various natural material surfaces with Imaging Plate

Distribution images of natural radioactivity in natural materials such as vegetables were obtained by using Imaging Plate. In such cases, it is necessary to reduce background radiation intensity by one order or more. Graded shielding is very important. Especially, the innermost surface of a shielding box should be covered with acrylic resin plate. We obtained natural radioactivity distribution images of vegetables, sea food, meat etc. Mostly β-rays emitted from40K print the radioactivity distribution image. Comparison between γ-ray intensity of KCl solution measured with HPGe detector and that of natural material specimen gave the radioactivity around 0.06∼0.4 Bq/g depending on the kind and the part of specimens.

Feasibility of in vivo thyroid 131I monitoring with an imaging plate

A new in vivo thyroid 131I monitoring method was devised by using an imaging plate (IP). A thyroid image obtained with a realistic neck-thyroid phantom showed a unique shape characteristic of the thyroid gland. A 131I thyroid imaging allows visual confirmation of thyroid accumulation of 131I. The detection limit of the IP system of 290 Bq was about 1/100 of the screening level of 30 kBq in cases of public emergencies. The IP system is applicable for thyroid 131I monitoring.

Automatic activity measurement and data processing system using image analyzer

Abstract An automated counting and data processing system for determining the radioactivity of 32 P was devised by using an image analyzer, an imaging plate, and a personal computer. This system can measure 18 samples containing 32 P concurrently and print out the results as a report.

Correction of a nonuniform imaging plate response

Abstract A method for measuring the relative Imaging Plate (IP) sensitivity at any location was developed by using 32P radioactive point sources. IP sensitivity distribution demonstrated a definite gradient which depended upon the direction of insertion of the IP into the inherent image reader in an imaging analyzer system. Nonuniformity was effectively corrected by a simple calculation with the reciprocal numbers of the average relative sensitivity.

Alignment of x‐ray tube focal spots for spectral measurement

A general method to align a diagnostic x-ray machine for x-ray spectrum measurement purpose was theoretically and experimentally investigated by means of the optical alignment of focal pinhole images. Focal pinhole images were obtained by using a multi-pinholed lead plate. the vertical plane, including the central axis and tube axis, was decided upon by observing the symmetry of focal images. the central axis was designated as a line through the center of focus parallel to the target surface lying in the vertical plane. A method to determine the manipulation of the central axis in any direction is presented.

Feasibility of in vivo measurement of 239Pu distribution in lungs using an imaging plate

An in vivo measurement system using an imaging plate (IP) system was developed, which displayed images reflecting (239)Pu distribution in the lung of a phantom. The detection limits of the IP system for 1-12h exposures were between 1670 and 245 Bq at a 1.6 cm chest wall thickness. The detection limit of the IP system for a 2.5h exposure was equal to that of a germanium detector for a 0.5h measurement. The IP system could be used as a new device for in vivo measurement of (239)Pu in the lung.