Mariko Segawa

New Production Routes for Medical Isotopes 64Cu and 67Cu Using Accelerator Neutrons

We have measured the activation cross sections producing 64Cu and 67Cu, promising medical radioisotopes for molecular imaging and radioimmunotherapy, by bombarding a natural zinc sample with 14 MeV...

Counting-type neutron imaging detectors of the energy-resolved neutron imaging system RADEN at the J-PARC/MLF

The recently commissioned Energy-Resolved Neutron Imaging System, RADEN, located at the J-PARC Materials and Life Science Experimental Facility (MLF), is the worlds first dedicated high-intensity, pulsed neutron imaging instrument. In addition to conventional radiography and tomography, the wide bandwidth and accurate measurement of neutron energy by time-of-flight is utilized to perform energy-resolved neutron imaging. Such techniques allow direct imaging of the macroscopic distribution of microscopic properties of materials in situ, including crystallographic structure and internal strain, nuclide-specific density and temperature distributions, and internal/external magnetic fields. To carry out such measurements in the high-rate, high-background environment at RADEN, we use cutting-edge detector systems, recently developed in Japan, employing micro-pattern detectors or fast Li-glass scintillators with high-speed, Field Programmable Gate Array-based data acquisition. These counting-type detectors offer sub-μs time resolution, high neutron count rates, and event-by-event gamma rejection. The available detectors offer a range of spatial resolutions from 0.3 to 3 mm and counting rates from 0.6 to 8 Mcps. In the present paper, we show the performance of these detectors as measured at RADEN. We also consider planned improvements to the detector systems that will allow us to achieve finer spatial resolutions by several factors and order-of-magnitude higher count rates.

Production of an Isomeric State of 90Y by Fast Neutrons for Nuclear Diagnostics

90g Y radiopharmaceuticals for cancer therapy have been used together with 111 In radiopharmaceuticals for diagnostics, since a daughter nucleus of 90 Sr, the ground state of 90 Y, 90g Y, is a pure β-ray emitting nucleus with no γ-ray emissions, providing no practical way for imaging. We have noted that the 682 keV isomeric state of 90 Y, 90m Y, with a half-life of 3.2 h as well as 90g Y can be populated significantly by 90 Zr( n , p ) 90 Y and 93 Nb( n ,α) 90 Y at a neutron energy of 14 MeV. On the basis of the result, we have proposed a new method to use 90 Y radiopharmaceuticals containing 90m Y for diagnostics and 90g Y for therapy, since the isomeric state decays to the ground state of 90 Y by emitting 480 and 203 keV γ-rays, appropriate energies for imaging. 90 Y radiopharmaceuticals containing 90m Y could solve long-standing problems associated with the use of 90g Y together with 111 In for imaging.

Development of the next-generation micro pixel chamber-based neutron imaging detector (μNID) for energy-resolved neutron imaging at the J-PARC/MLF

The Energy-Resolved Neutron Imaging System RADEN, located at the J-PARC Materials and Life Science Experimental Facility in Japan, is the worlds first dedicated high-intensity, short-pulsed neutron imaging beam line. To carry out energy-resolved neutron imging at RADEN, we use cutting-edge detector systems employing micropattern detectors and data acquisition systems based on Field Programmable Gate Arrays to provide the necessary sub-μs time resolution, high counting rates, and event-by-event background rejection. One such detector, the Micro Pixel Chamber-based Neutron Imaging Detector (μNID), provides a spatial resolution of 120 μm (s), time resolution of 0.6 μs, 18% detection efficiency for thermal neutrons, and effective gamma sensitivity of less than 10−12. We have recently increased the rate capacity of the μNID from 600 kcps to more than 8 Mcps via an upgrade of the readout electronics and the introduction of a new gas mixture optimized for higher count rate, better spatial resolution, and higher detection efficiency. We are also developing new detection elements with strip pitches of 280 μm and 215 μm, down from 400 μm, with a corresponding improvement in the spatial resolution expected. Here, we present the progress of the ongoing development of the μNID, including the results of recent on-beam tests performed at RADEN.

New Approach for Measuring the (n,γ) Cross Section of a Nucleus by a Few keV Neutron

We have for the first time determined with high precision the energy spectrum of low-energy neutrons ( E n <10 keV) which are produced in the 7 Li( p , n ) 7 Be reaction, by detecting γ-rays of the 197 Au( n ,γ) 198 Au reaction whose cross section is known. An anti-Compton NaI(Tl) spectrometer played an essential role in detecting the γ-rays with a good signal to noise ratio by discriminating large background due to thermalized neutrons in the measurement room. The low energy neutrons thus derived were successfully used to measure the 62 Ni( n ,γ) 63 Ni reaction cross section. The present low energy neutrons could be extensively used for cross section measurements for neutron capture reactions and elastic scatterings from nuclei of nuclear astrophysical interests.

Development of a Three-dimensional Computed Tomography System using High-speed Camera at a Pulsed Neutron Source

The neutron energy resolved three-dimensional imaging system using a high-speed video camera has been newly developed at Japan Proton Accelerator Research Complex (J-PARC). The aim for this research is to investigate more rapidly a spatial distribution of several elements and crystals in various kinds of materials or substances. A high-speed video camera (CMOS, 1300 k frame/sec) of the present system allows us to obtain TOF images consecutively resolved into narrow energy ranges in the pulsed neutron energy region from 0.01 eV to a few keV. We confirmed that the neutron transmission ratio obtained by the present system was consistent with that of theoretical expectation when a step-wedge sample made of Fe, from 5 mm to 10 mm in thickness, was used as a sample. And three-dimensional images reconstructed by the Filtered Back Projection method could be successfully enhanced the image contrast of specific materials by selecting neutron energy. The results show that there is the possibility to apply the present system for practical use in near future.

Super-Resolution Processing for Pulsed Neutron Imaging System Using a High-Speed Camera

Super-resolution and center-of-gravity processing improve the resolution of neutron-transmitted images. These processing methods calculate the center-of-gravity pixel or sub-pixel of the neutron point converted into light by a scintillator. The conventional neutron-transmitted image is acquired using a high-speed camera by integrating many frames when a transmitted image with one frame is not provided. It succeeds in acquiring the transmitted image and calculating a spectrum by integrating frames of the same energy [3]. However, because a high frame rate is required for neutron resonance absorption imaging, the number of pixels of the transmitted image decreases, and the resolution decreases to the limit of the camera performance. Therefore, we attempt to improve the resolution by integrating the frames after applying super-resolution or center-of-gravity processing. The processed results indicate that center-of-gravity processing can be effective in pulsed-neutron imaging with a high-speed camera. In addition, the results show that super-resolution processing is effective indirectly. A project to develop a real-time image data processing system has begun, and this system will be used at J-PARC in JAEA.

Feasibility study on visualization of transient phenomena using high resolution on-line neutron imaging system at J-PARC

A neutron energy resolved imaging system with a time-of-flight technique has been newly installed at Japan Proton Accelerator Research Complex (J-PARC) with the aim to investigate more preciously spatial distribution of several elements and crystals including various kinds of materials or substances on transient phenomena. A camera (CMOS, 48 frame/sec) equipped the system allows to obtain one TOF image resolved into narrow energy ranges with an each single pulsed neutron consecutively in the energy region from 0.01 to a few keV. Qualities of the images obtained with the system, such as spatial resolution (defined by modulation transfer function, 1.8 at En∼ 0.01 eV), neutron energy selectivity of the system, and capability for visualization of transient phenomena, were examined experimentally. The results obtained in the experiments show that the system can visualize the real-time neutron energy resolved images with a good spatial resolution even at transient phenomena.

Measurement of E1 and E2 cross sections of 12C(α,γ)16O using pulsed α beams

We have measured the γ‐ray angular distribution of the 12C(α,γ)16O reaction at a center‐of‐mass energy of Ecm = 1.6 MeV and Ecm = 1.4 MeV. In this experiment, we used high efficiency anti‐Compton NaI(Tl) spectrometers to detect a γ‐ray from the reaction with a large S/N ratio, intense pulsed α beams to discriminate true events from neutron induced background by using a time‐of‐flight (TOF) method, and the monitoring system of target thickness. We could pick up true events from the reaction free from intense neutron background with high statistics.

E1 and E2 cross sections of the 12C(α,γ)16O reaction at Ecm∼1.4 Mev using pulsed α beams

We have installed a new system to measure the γ‐ray angular distribution of the 12 C (α,γ) 16 O reaction at the 3.2 MV Pelletron accelerator laboratory at Tokyo Institute of Technology to accurately determine the E1 and E2 cross sections. In this experiment, we used high efficiency anti‐Compton NaI(T1) spectrometers to detect a γ‐ray from the reaction with a large S/N ratio, intense pulsed α beams to discriminate true events from neutron induced background with a time‐of‐flight (TOF) method, and the monitoring system of target thickness. We succeeded in removing a background due to neutrons and could clearly detect the γ‐ray from the 12 C (α,γ) l6 O reaction with high statistics.We have measured the {gamma}-ray angular distribution of the {sup 12}C({alpha}, {gamma}){sup 16}O reaction at the 3.2 MV Pelletron accelerator laboratory at Tokyo Institute of Technology to accurately determine the E1 and E2 cross sections. In this experiment, we used high efficiency anti-Compton NaI(Tl) spectrometers to detect a {gamma}-ray from the reaction with a large S/N ratio, intense pulsed {alpha}-beams to discriminate true events from background events due to neutrons from {sup 13}C({alpha}, n){sup 16}O reaction with a time-of-flight method, and the monitoring system of target thickness. We succeeded in removing a background events due to neutrons and clearly detected the {gamma}-ray from the {sup 12}C({alpha}, {gamma}){sup 16}O reaction with high statistics.