Ikuo Kanno

A Current-Mode Detector for Unfolding X-ray Energy Distribution

To turn the advantage of energy measurement in x-ray transmission diagnosis into practice, we propose a novel detector for the estimation of x-ray energy distribution. This detector consists of several segment detectors arrayed in the direction of x-ray incidence. Each segment detector measures x-rays as current. With unfolding measured currents, the x-ray energy distribution is obtained. The practical application of this detector was verified by estimating the iodine thickness in an acryl phantom.

Measurement of Fragment Mass Dependent Kinetic Energy and Neutron Multiplicity for Thermal Neutron Induced Fission of Plutonium-239

Kinetic energy and neutron multiplicity as a function of fragment mass were measured for the thermal neutron induced fission of 239Pu. By measuring the velocities and energies of two fission fragments simultaneously, both of the pre-neutron emission fragment mass m* and the post-neutron mass m were obtained. The fragment mass dependent neutron multiplicity ν(m*) was deduced by subtracting m from m*. The fragment mass dependent total kinetic energy TKE(m*) was also obtained from this data. The fragment velocity was measured by time-of-flight (TOF) method, for which the start signal was triggered by a very thin plastic scintillation film detector (TFD) and the stop signal was obtained by a silicon surface barrier detector (SSBD) which was also used for the measurement of [he fragment kinetic energy. The present result of ν(m*) is in good agreement with that of Apalin et al. and that in the light fragment region of Fraser et al. The obtained TKE(m*) agrees well with the data of Wagemans et al. A calculation ...

Cryogenic InSb detector for radiation measurements

The energy spectra of 241Am alpha particles were measured by a detector employing the compound semiconductor InSb at an operating temperature below 4.2 K. The fabrication method and current–voltage curves are shown. Though the energy resolution of the detector is not discussed in this article, this is the first report on an InSb radiation detector.

Simultaneous measurement of prompt neutrons and fission fragments for 239Pu(nth, f)

The multiplicity and energy of the prompt neutrons emitted from the fission fragments for 239Pu(nth, f) were measured as functions of the fragment mass and total kinetic energy. The results were compared with those for 233U(nth, f) and with the predicted values by the multi-channel fission theory with the random neck rupture model. The measured and predicted values of the neutron multiplicity, ⟨V⟩(m*), show the saw-tooth trend and agree with each other. The total neutron multiplicity decreases linearly with increasing total kinetic energy resulting in —d⟨TKE⟩/d⟨Vtot⟩=16.5±0.4MeV/neutron. The slope of the neutron multiplicity vs. the total kinetic energy, —d⟨V⟩/d⟨TKE⟩, was plotted against the fragment mass. Its shape agrees with that for 233U(nth, f). The average neutron emission energy, ⟨η⟩(m*), follows a bell shape about the symmetric fission accompanying higher values for very asymmetric fissions and agrees with that for 233U (nth, f). The total excitation energy (TXE)(m*) was determined by two manners: (1) neutron data and (2) Qmax—⟨TKE⟩. Both results satisfactorily agree with each other as the case of 233U( nth, f), and thereby the present derivation of ⟨TKE⟩ from the neutron data is confirned.

Models of formation and erosion of a plasma column in a silicon surface‐barrier detector

Quantitative models of the formation and erosion of the plasma column are presented. With the model of formation, the radius, volume, and surface area of the plasma column and the number and the density of the electron‐hole pairs are calculated. In the model of the erosion, the change of the dielectric quality of the plasma column due to the enlargement of its volume is considered to be the cause of the erosion. The internal electric field strength of the plasma column is determined as a function of time. With this model, plasma delays are estimated for alpha particle, 40Ar and 129Xe ions and are compared with other author’s experiments. Ideally the recombination effect should be calculated as a product of the recombination rate and the time interval of the plasma delay. However, it is estimated here using two parameters for the fission fragments from thermal‐neutron‐induced fission of 235U because of the lack of adequate experimental data.

Energy Measurement of X-rays in Computed Tomography for Detecting Contrast Media

The advantages of energy measurement of x-rays over current measurement in transmission radiography and computed tomography (CT) for detecting iodine contrast media are discussed. Simulation studies on both methods of measurement are carried out, followed by experiments. As data for energy measurement of x-rays, the event ratio of two energy regions with a K-edge of iodine between them is employed. The energy measurement method is immune to beam hardening, while current measurement suffers greatly with changes in x-ray tube voltage and thickness of the body under measurement. This method is useful in interventional radiology and in CT. It will also be useful for detecting other types of contrast medium.

Radiation measurements by a cryogenic pn junction InSb detector with operating temperatures up to 115 K

Pn junction-type radiation detectors were fabricated with an InSb substrate. The detectors had 1000 times higher resistances than those of previously reported Schottky-type detectors. The output pulses of the preamplifier were analyzed from the point of view of the contribution of electrons and holes. The energy spectra of 241Am alpha particles were measured at operating temperatures of up to 115 K. The inherent voltage of the detector was estimated.

Low Exposure X-ray Transmission Measurements for Contrast Media Detection with Filtered X-rays

A feasibility study of X-ray transmission measurements for contrast media with less exposure using filtered X-rays and their energy information is described. Based on measurements of the energy spectra of La-filtered X-rays, sensitivity to the contrast media and the relative quantity of dose exposure of filtered X-rays as the ratio to white X-rays are shown. The dose exposure for the measurement of iodine contrast media is reduced by more than 50% with a 400/xm thick La filter. By using a filter with atomic number close to that of iodine such as Cs and Ba, a greater reduction in dose exposure with a smaller increase in the current of the X-ray tube is expected.

A model of charge collection in a silicon surface barrier detector

Charge collection process in a silicon surface barrier detector (SSB) was investigated as a following phenomenon of the formation and erosion of a plasma column the author reported elsewhere [Rev. Sci. Instrum. 5 8, 1926 (1986)]. As an application of Ramo’s theory, a model of charge collection process was presented. With this model, the top and bottom position and disappearance time of a plasma column were determined analytically. The induced currents and charges were calculated for alpha particle and 4 0Ar ion whose plasma delays were determined as a function of field strength by other authors’ experiments. The contributions of electrons and holes to the induced currents and charges were determined separately. The times of the plasma column disappearance and the last hole arrival to the negative electrode, and the maximum induced currents were tabulated. The peak time of the induced currents became slightly longer as the bias voltage of the SSB increased from 50 to 200 V.

Unfolding Method with X-ray Path Length-Dependant Response Functions for Computed Tomography Using X-ray Energy Information

The computed tomography (CT) values obtained by the energy subtraction method with a transXend detector, which measured X-rays as current and gave the corresponding X-ray energy information, show the disadvantage that the CT values are dependent on the thickness of a homogeneous phantom. In order to obtain constant CT values for a uniform material, a new unfolding method is proposed using variable response functions of the transXend detector according to the X-ray path length in the phantom. The CT values measured using the new unfolding method are discussed with respect to the energy range used in the unfolding process, the number of segment detectors, and the substrate of the segment detectors.