Chuichiro Nakano

Multi-nuclide AMS with a middle-sized tandem accelerator of MALT

With a middle-sized tandem accelerator of the multipurpose facility of the University of Tokyo we have developed an AMS system to perform multi-nuclide AMS. Starting with 10Be- and 26Al-AMS development, 14C-AMS has been also developed modifying the gas stripper, the injection system, the ion source and so on. The newly designed gas ionization chamber lowered the background level for the detection of 10Be and 26Al by more than one order of magnitude. 14C-AMS is now precise enough for practical use, though the repeatability is not better than ±0.7%. However, more time is still necessary until our 14C-AMS will run stable with good precision of better than ±0.5%. A gas filled magnet (GFM) and a TOF system have been developed successfully for the detection of 36Cl and 129I, respectively. Researches on 59Ni-AMS system by using the inverse PIXE technique are now underway and 41Ca will be the next target for MALT-AMS.

Current status of the AMS system at the University of Tokyo

Abstract AMS has been applied to many application researches at the new tandem accelerator facility of the University of Tokyo since April of 1995. The reproducibility of the measurements has not been good enough especially for 14 C-AMS, although, the larger acceptance of the stripper canal is found useful for it to be better. The minimum detection sensitivity is on the level of practical use.

Dual detector system for PIXE measurement covering a wide element range

Abstract Two different type of X-ray detectors were used for simultaneous PIXE measurement over a wide element range. One is a pure-Si detector with a thin Be-window, which is to keep high sensitivity for the detection of low Z element. The other is a CZT detector with a thick Be window of 250 μm. It has almost 100% detection efficiency for the X-rays with high energy of up to about 80 keV. By using the CZT detector that was arranged to have a large solid angle, the detection sensitivity of the high energy X-rays of around 30 keV was enhanced by about two orders of magnitude than that by the pure-Si detector. A pair of small permanent magnet was used to sweep away the back-scattered protons from the detector. With this magnet system, the background level in the spectrum of the pure-Si detector was significantly reduced.

New interpretation of the 10Be and 26Al content in cosmic spherules

Abstract The observed concentrations of cosmogenic nuclides in extraterrestrial matter are usually interpreted in terms of the exposure history of the irradiated specimen or in terms of the history of the cosmic radiation itself. For small meteorites in the microgram mass range we present a theoretical approach which allows a new interpretation of the measured concentrations. In particular, we show how to determine the size distribution of the interplanetary dust and how to investigate the related phenomena (radiation pressure, mutual collisions, atmospheric entry). For this, the concentrations of the radioisotopes 10Be and 26Al contained in spherules from deep sea sediments were measured by means of the AMS technique. Due to the small sample size, the carrier amount was successfully kept very low: around 50 μg for Be and between 100 and 200 μg for Al.

Tandem accelerator laboratory of the University of Tokyo

We started construction of the new tandem facility at Research Center for Nuclear Science and Technology, The University of Tokyo in 1992 and completed the facility in spring of 1994. Now, using the machine, we are performing experiments mainly for the elements and isotopes analyses. Also we have some plans to introduce new items for the extension of the researches.