Transcript A novel large-volume Spherical Detector with Proportional

A novel large-volume Spherical Detector with
Proportional Amplification read-out
--low energy threshold (sub-keV)
--good energy resolution
--large drift volumn with one single
channel
--cheap, simple, robust, seal mode
What is the sphere good for?
• Searching for WIMP(Weakly Interacting Massive Particles)
• detecting low energy neutrinos (via coherent nuclear scattering)
• Precise measurement of the neutron background
• Copper hull: 1.3 meter in
diameter and 6 mm thick
• A ball in the center as the
anode, with high voltage
applied. Supported with
rod.
Radial electric field:
Drifting ions:
• Pulse observed by a 55Fe x-ray (black line) well reproduced by the calculation (red
line)
Symmetry broken by the rod
The inhomogeneity in gain is
magnified by the usual
exponential dependence of the
avalanche gain with the
electric field
Results in the simplest electric field
configuration
• using only the ‘good’ hemisphere
• 55Fe source in sphere with adjustable distance
• The volume was pumped by a primary pump followed by a turbo
molecular pump, reaching a level of vacuum below 10^-6 mbar.
• outgassing rate measured below 10^-9 mbar/s
• Ar + 10% CO2, Ar + 2% Isobutane(异丁烷), at different pressure
Run using calibration source of 109Cd,
high voltage at 22 keV in Ar + 10% CO2 gas
Time dispersion of the signal as function of
the depth of interaction
drift velocity ~ E,
Longitudinal diffusion
coefficient (D) ~ E^-2,
the time dispersion ~ r^3
Precision: about 10 cm
Field corrector
1) approaches more an ideal
spherical symmetry (hard to
achieve);
2) makes all (or most) of the
field lines end up in the
spherical electrode, and not in
the rod;
3) the amplification associated
with each of those field lines is
sufficiently similar
Annular, conical, cylindrical…
222Rn radioactive source,
Injected into the sphere
so that it’s
homogeneously active
over the full detector
volume
“a good energy resolution of .5% has been achieved”
More complicated improvements
• More concentrical cylinders:
improving the sphericity of the drift and reducing the voltage between
electrodes (allowing for higher working voltages/gains)
• Micromegas structure:
amplification and drift fields are decoupled, and the geometrical
requirements are therefore less stringent; the amplification in a
Micromegas is well known and has well-proven nice features in terms
of energy and time resolution.