JAEA-Conf 2011-002 - 日本原子力研究開発機構

JAEA-Conf 2011-002
changer. The target changer mounts blank, ZnS
viewer and 241 Table 1 List of targets
Am checking source as well as
Thickness Physical Form
five targets. Table 1 shows the list of target Graphite 208 g/cm2 Self support
foils for the experiments. Al2O3 and AlN on Ta Al 0.8m Self support
foils were for oxygen and nitrogen cross Al2O3 1.05m Sputtering on Ta
section measurement with subtracting Al and AlN 0.91m Sputtering on Ta
Ta contribution by separate runs. Fragments Ta 10m Self support
from the target were measured by the BCCs Ti 1m Self support
mounted on the 30, 60, 90 and 120 port of the
scattering chamber.
Cu 1m Self support
Figure 2 shows schematic view of the
BCC. The BCC has been developed as a
detector satisfying requirement for fragment
measurement in intermediate energies, large
solid angle, small energy loss, low threshold
energy, and, insensitivity to protons [8,9].
The BCC is a parallel plate ionization
chamber with a grid. The structure is contained
in a stainless steel cylindrical chamber. The
distances between cathode and grid, and, grid
and anode are 300 mm and 5 mm, respectively.
The field shaping rings maintain uniformity of
the electric field. High voltage is applied to the
Fig. 2 Schematic view of the BCC
cathode, field shaping rings and grid electrodes to form electric field for electron drift. The cylindrical
chamber is sealed using O-rings to keep low-pressure counting gas, 267 kPa (200 Torr) Ar+10% CH4 gas,
inside. The cathode side of the chamber has a hole of 20 mm in diameter covered with a thin entrance
window, 0.5 m thick SiN supported by window frame, to introduce fragments from the target.
Fragments which entered the BCC stops and produces electrons through ionization process. The
number of electrons along its trajectory is proportional to the energy loss of the fragment, i.e, Bragg curve.
The electrons drift toward to the grid with keeping their distribution along the electric field between the
cathode and grid. The grid potential is chosen to allow that all electrons reach to the anode with passing
through the grid. Under this condition, time distribution of the anode signal has inverse shape of the
original distribution of electrons that equal to Bragg curve. Thus, the energy and atomic number of the
fragment can be deduced from integral and peak height of the anode signal.
Two dimensional plots of events at 30 from 80 MeV proton induced reaction on carbon are
shown in Fig 3. The vertical and horizontal axes correspond to fragment Z and energy. The events within
the dotted circle (i) in Fig.3 have too low energy to identify using the Bragg curve vs energy plot. These