1 prototyping megaton-scale detectors jason trevor doe review july 25, 2007 developing a new...
Post on 20-Dec-2015
222 views
TRANSCRIPT
1
Prototyping Megaton-Scale
Detectors
Jason TrevorDOE ReviewJuly 25, 2007
Developing a New Lower-Cost Scintillator Design
2
The Problem Neutrino and cosmic ray physics continue to require ever larger detectors for measurements of interest.
All existing technologies have limitations Water Cerenkov – Cheap, but limited by
low energy cut-off Liquid Scintillator – High light yield, but
difficult to work with and environmentally hazardous Solid Scintillator – Many desirable characteristics, but
too expensive for use in very large detectors Water Soluble Scintillator – Highly desirable, but no
practical scintillators of this type are currently known
Conclusion: Construction of future large-scale detectors will require the development of new technologies which will lower unit detector cost.
3
An idea inspired by MACRO and MINOS Scintillator
In a MINOS scintillator strip, only 5-10% of the light produced actually makes it into the WLS fiber.
There are three main cause of light absorption before the WLS fiber:
Self absorption by the fluors and polystyrene in the scintillator.
Imperfect surface reflectivity. Absorption through either of the
preceding processes after the light has reflected off the fiber/glue/polystyrene interface.
MINOS Scintillator Strip
WLS Fiber
TiO2 Cladding Polystyrene
4
Plastic Scintillator Granules in Water?
What would happen if granules of plastic scintillator are mixed into water at a 5% concentration with a grid of WLS fibers? The effective attenuation length of
the bulk material is increased by about a factor of 20
Absorption in the reflector is reduced
A better optical coupling is achieved for light at the WLS fiber boundary
Water is free - Cost per unit mass is reduced by 80-90% (est.)
PMT
~Water
Scintillator Granules
WLS Fibers
5
Proof of Principle
19cm x 19cm x 13cm Constructed using left-over
MINOS scintillator and WLS Fiber Water and scintillator granules
were circulated by small pumps Light output in this prototype
was lower than the nominal goal for a practical large detector, butThe scintillator was of poor qualityThe prototype was too small…
losses were still dominated by absorption in the walls
Solution: Scale up volume by a factor of 200
6
One Cubic Meter Tank Detector
Our ADR grant proposal was funded (1yr $48k)
Scintillator strands replaced granulesEasier to extrude high quality
scintillatorNo circulation system requiredMore realistic configuration for
larger tank detectorsBut, more difficult to construct
Construction is complete(with the help of Caltech Undergrads)
WLS Fibers
(A 1 m cube) Scintillator Strands
PMT
10
Readout Topology
Tank is divided into eight regions
All WLS fibers from a given region are routed to one of eight phototube boxes
Muon triggers are centered over the inner four regions
Inner regions are 30cm x 30cm
Muon Triggers are 18cm x 18cm
6
52
0 7
43
1 Meter
1
11
A Few EventsTwo typical events
Event 897 – Single trigger event – These are mostly muon events
Event 4 – Multiple trigger event – Other stuff (Electrons, hadrons, etc)
Numbers shown are estimated light output in P.E.s – exact calibration still needs to be completed
Preliminary numbers suggest the light output is ~2 – 5 times that of MINOS – A more detailed analysis is necessary to confirm this
13
Summary Construction of the one cubic meter prototype
is complete – undergrad student labor was an essential part of the construction effort
Initial results suggest the light output is 2 – 5 times that of MINOS, but more detailed analysis is necessary
Recent addition of Leon Mualem and Alex Himmel has accelerated progress.
This is a promising new technology More R&D is necessary – The design is far from
optimal
We plan to apply for further ADR funding
A paper is in the works