  A thin coating of thorium on aluminium substrates with the areal density of
110 to 130 $\mu g/cm^2$ is developed over a circular area of 22 mm diameter by
using the electrodeposition method. An electrodeposition system is fabricated
to consist of three components; an anode made of a platinum mesh, a
cylindrical-shape vessel to contain the thorium solution, and a cathode in the
form of a circular aluminium plate. The aluminium plate is mounted
horizontally, and the platinum mesh is connected to an axial rod of an electric
motor, mounted vertically and normal to the plane of the aluminium. The
electrolyte solution is prepared by dissolving a known-weight thorium nitrate
powder in 0.8 M HNO3 and isopropanol. The system is operated either in constant
voltage (CV) or constant current (CC) mode. Under the electric field between
the anode and cathode, thorium ions were deposited on the aluminium substrate
mounted on the cathode. In the CV mode at 320, 360, and 400 V and in the CC
mode at 15 mA, thorium films were formed over a circular area of the aluminium
substrate. The areal density of thorium coating was measured by detecting
emitted alpha particles. The areal density of thorium varied from 80 to 130
$\mu g/cm^2$ by changing the deposition time from 10 to 60 min. The results
from the CV mode and CC mode are compared, and the radial dependence in the
measured areal density is discussed for different modes of the electric field.
The developed thorium coatings are to be used in the in-house development of
particle detectors, fast neutron converters, targets for thorium fission
experiments, and other purposes.
