M. Noma

A new type of proportional counter using a capillary plate

Abstract We have developed a new type of proportional counter with the capability of fine position resolution and high gas gain. It consists of a bundle of fine glass capillaries with electrodes on both the inlet and the outlet. The capillaries are 100 μm in diameter and 800 μm in length and gas multiplication was found to occur in each capillary with an applied voltage between the inlet and the outlet. The resulting proportional counter was found to operate up to a gain of 104 without the onset of breakdown and had an energy resolution of 26% for 5.9 keV X-rays at a gas gain of 7000. Its detection efficiency was identical to a conventional single wire device.

The form of X-ray photoelectron tracks in a capillary gas proportional counter

We have successfully detected images of tracks of photoelectrons from the 22 keV and 30 keV X-rays of /sup 109/Cd and /sup 241/Am, utilizing an optical imaging gas detector with a CCD camera. Most of the 30 keV photoelectrons have track lengths greater than 1 mm in xenon gas. The images of the tracks contain clusters of pixels, and the brightest of these clusters, for each track, were investigated in detail. It was found that the average shape of these clusters was oval-like and that the geometrical center differs from the point of maximum energy loss. These data have important implications for X-ray polarimetry.

Hard x-ray polarimeter utilizing Compton scattering

A prototype polarimeter with a 50 mm diameter has been constructed. With polarized x-rays from a simple polarizer, the detection efficiency and modulation factor of the polarimeter with a 40 mm thick scatterer were 3.2% and 0.57%, respectively, at 60 keV. The fabrication and performance of the polarimeter and polarizer are presented.

The development of a new type of imaging X-ray detector with a capillary plate

A new type of optical imaging X-ray detector with a capillary plate was constructed. The instrument consists of a CGPC (Capillary Gas Proportional Counter), a focusing mirror system, and an image intensified CCD camera. Both the charge signal and the light signal from the CGPC were proportional to energy up to hard X-rays of 60 keV. The light output of the CGPC was approximately 250 times larger than that of a NaI(Tl) scintillator. The light yield of the CGPC at gas gain of 300 was 1.2 photons per electron for a gas mixture of xenon +5% methane at 1 atm. Using the optical imaging detector, an image of a track due to an /spl alpha/-particle was detected. Also the first evidence was obtained that the light emission was due to gas multiplication occurring in a thin capillary. Our goal is to use this new type of optical imaging detector as an X-ray polarimeter.

A novel proportional counter made of a capillary plate

A new type of proportional counter utilizing a capillary plate with the capability of fine position resolution and high gas gain has been developed. It consists of a bundle of fine glass capillaries with electrodes on both the inlet and the outlet. The capillaries are 100 /spl mu/m in diameter and 800 /spl mu/m in length, and gas multiplication was found to occur in each capillary with an applied voltage between the inlet and the outlet. The proportional counter was found to operate up to a gain of 10/sup 4/ at gas pressures of 1, 0.75 and 0.5 atm. The energy resolution for 1 atm was 20.8% for 5.9 keV X-rays at a gas gain of 4000. The detection efficiency was comparable to a conventional single wire proportional counter. The dependences of energy resolution on the drift and applied voltage to the capillary plate are investigated and discussed, using calculated electric fields for the drift and capillary regions.

Characteristics of capillary gas proportional counter

A new type of gas proportional counter employing a capillary plate has been developed. The capillary plate consists of a bundle of fine glass capillaries with electrodes on both the inlet and the outlet. The capillaries are 100 micrometer in diameter and 800 micrometer in length and gas multiplication occurs in each capillary. The operational conditions of the electric fields in the drift region were investigated by applying the drift potential. The better electric fields were around 0.28 volts/cm(DOT)Torr for argon+10%methane at the pressure of 760 Torr. The energy resolution was 21% for 5.9 keV x rays at the gas gain of 3,000. The gas gain, the energy resolution and the detection efficiency were uniform at the radial positions in diameter of 16 mm for the capillary plate of 20 mm in diameter. The non-uniformity was within 2% of the average for the gas gain. We can expect imaging detectors with the capability of fine position resolution as an application.

Development of an imaging plate as a heavy-nuclide detector

It is very important for the study of nucleosynthesis in supernova explosion to be able to measure the abundance of heavy nuclides in cosmic rays. There are not, however, efficient large-area detectors with which to make such measurements. To address this need, we are developing a new type of heavy nuclide detector using an Imaging Plate which is manufactured by Fuji Film Co. Ltd. This film has a position resolution of 25 /spl mu/m and a sensitivity 1000 times higher than X-ray film. Moreover it is easy to enlarge since the area of one plate can be 20/spl times/25 cm/sup 2/ and the accumulated cosmic-ray-interaction information can be read out in about 10 minutes. To measure the characteristics of the Imaging Plate for heavy nuclides, we irradiated it with several kinds of nuclides using an accelerator in the National Institute of Radiological Sciences. These tests demonstrated that the imaging plate was able to separate carbon, silicon, and argon nuclides.

Pulse height distributions of /spl beta/ rays in /sup 14/C measurement with liquid scintillation counting system Quantulus

To investigate the variations of the solar activity over a long time scale, we have started the measurements of /sup 14/C in an ancient tree, synthesizing 10 g benzene from the tree rings and using the liquid scintillation counting system Quantulus with ultra low background level. The background rate of the Quantulus was 1.2 cpm while the counting rate of /sup 14/C was 91.0 cpm for the ancient tree. The pulse height distribution of /spl beta/ rays from /sup 14/C was well fitted with theoretical /spl beta/ rays spectrum. The Quantulus detected /spl beta/ rays down to 7.5 keV with good detection efficiency. It was confirmed that the total counts from the /sup 14/C in the sample benzene can be measured within 0.2% accuracy on the basis of the pulse height distribution of a standard benzene sample, using the least squares fitting method.

New type of imaging x-ray detector using a capillary plate

We constructed an optical imaging x-ray detector with a capillary gas proportional counter (CGPC), a focusing mirror system, and an image intensified CCD camera. The CGPC consists of an absorption region for x-rays, which also operates as a drift region of electron clouds, and a gas proportional scintillation region in a capillary plate. With a gas mixture of Xe plus 2% CH4 at 1 atm and a gas gain 8000, the light output from the CGPC is several tens thousand times larger than that of a typical NaI(Tl) scintillator and it is enough to image electron clouds due to a few tens keV x rays. To investigate the imaging ability, images for tracks due to (alpha) particles (241Am) of 5.5 MeV were taken in the gas mixture of Xe plus CH4, for the several reduced fields in the drift region. We confirmed that the images were most clearly observed at around the reduced fields of 40 V/cm(DOT)atm.

Development of a new hard x-ray polarimeter

We designed a new type of polarimeter for polarized hard x rays from stellar objects, utilizing the principle that the direction of the Compton scattered x rays depends on the electric vector of the polarized incident x rays. The characteristics of the new designed polarimeter were investigated by measurements of basic data and computer simulations. From them, it is shown that the polarimeter is capable of observing the interesting astrophysical objects by using a balloon or a satellite. In this paper, we report the characteristics and the expected performance of the new designed hard x-ray polarimeter.