Photomultiplier: Oops!!!!

[guest]

Subject:
[nuclear-physics] Accident at Super-Kamiokande neutrino lab
Date:
Fri, 16 Nov 2001 11:29:50 +0530
From:
"P. V. Madhusudhana Rao"
Reply-To:
nuclear-physics@yahoogroups.com
Organization:
Nuclear Science Centre, New Delhi, India
To:
Nuclear Physics Forum




Accident at Super-Kamiokande neutrino lab
=========================================
15 November 2001

Neutrino physics has suffered a serious blow following an accident at one of the field?s leading facilities. The Super-Kamiokande detector in Japan which in 1998 announced evidence for the existence of neutrino mass - will be out of action for at least a year after most of its 11 000 photomultiplier tubes imploded. Officials at super-Kamiokande have not confirmed the cause of the accident but it is thought that the pressure of the water inside the detector was too high.
The Super-Kamiokande experiment located a kilometre underground in central Japan -consists of a tank filled with 50 000 tons of water surrounded by photomultiplier tubes. These tubes detect the faint flashes of light known as Cerenkov radiation given off by electron- and
muon-neutrinos when they interact with electrons in the water molecules.

One of these tubes - each of which contains a vacuum - is thought to have imploded as the detector was being refilled with water following maintenance work. It is believed that the energy released from this implosion caused a shock wave in the water, leading to a chain reaction of implosions in the remaining tubes. According to the New York Times, about 7000 of the tubes imploded, which puts the cost of the accident at about $20 - $30m since each tube costs about $3000.

The director of the Kamioka Observatory, the organization that owns Super-Kamiokande, is putting on a brave face. ?We will rebuild the detector,? says Yoji Totsuka. ?There is no question?. Totsuka proposes to restore the number of photomultiplier tubes to about half of the
original number in order to resume the K2K experiment as soon as possible, perhaps within a year. This experiment - in which a beam of muon neutrinos travels from the KEK particle physics lab on the east coast of Japan to Super-Kamiokande - needs to run for about another two years in order to confirm its initial results on neutrino mass.

Once this experiment is complete, Totsuka says that Super-Kamiokande will be upgraded in time to receive neutrinos from the Japanese Hadron Facility (JHF), which is due to be commissioned in 2007. The JHF will provide a beam of neutrinos much more intense than that from K2K, allowing more precise measurements of neutrino oscillations and other
properties of neutrinos. The upgraded facility should also be able to detect the thousands of neutrinos produced by rare supernovae explosions in the Milky Way.

"It would be a great loss to the field not to get these results", says Dave Wark, a particle physicist at the Rutherford Appleton laboratory in the UK. ?In light of that I hope that Super-Kamiokande gets the support it needs to recover completely from this disaster. One should always
remember that building state-of-the-art experiments like
Super-Kamiokande always involves pushing the edge of what is
technologically possible, so setbacks are inevitable?.

*******
Author: Edwin Cartlidge is News Editor of Physics World

[guest]

I think this a good waste of money as neutrinos in my mind don't exsist ( See autodynamics ). And if the did exsist
what useful information does it give? To me it looks like random noise.

[guest]

Waste of money it may be but just think of those huge PMT's hitting the ebay auctions!!!!!

[Richard Hull]

I can't remember, but I believe those PMTs were 30 inch jobs. I am also quiet sure that the $3000.00 price on those Hamamatsu tubes was not our price, but a contract price for the lot! If they appeared on e-bay I would grab one for a door stop. Can any one fathom what a 30" diameter, 2" thick BC-720 would cost to go with the tube?

I am with Ben on the Neutrino issue. The detection of flashes in th' "SUPER" is, in fact, literally millions of flashes (real and noise) a minute. A simple 2" PMT has enough noise at the low end to drive me nuts at times.

I can only imagine the incredible flood of data streaming into their little computers which are doing the analysis based on some all too cleverly arrived at bit cruncher.

I realize that they spent a lot of time probably figuring out the exact energy to within a few tenth thousanths of an electron volt of the electron or meson neutrinos imagined interaction with an electron. I am also sure that with billions of collected and culled through noise pulses, statistics will supply several of those energies perfectly. I am also sure that they have mathematicians who can declare they are not noise but the real Mc Coy.

The detection of neutrinos is strictly by artful statistics. 99.9999999% of the data are real clean events leaving the .0000001% of remainder as plain old noise to be culled through for what someone had the temerity to label neutrinos.

Remember, They see nothing! There are no tracks! There are definitely billions if not trillions of events analyized over time from which they make their pronouncements. Rest assured also, that the computers do the selection and from a small resultant sampling, someone has to pass judgment!

How dey do dat?

Richard Hull

[guest]

Does this chain reaction constitute Fission?

[DaveC]

Does anyone know what the predicted rate of Neutron generation is expected to be? Don't these experiments do a beam on beam off analysis? I guess you would have to then decide if the difference is statistically significant... but I would be surprised if people would risk their scientific credibility and reps on a poorly done analysis.

But having said that... it seems to me, nearly incredible that there was no anticipation of this type fo failure and/or no protective shells around each tube.

Dave Cooper

[Richard Hull]

I doesn't surprise me at all that this scenario was not thought of. I am sure they designed the tubes to withstand water pressure in the deep pit which is back filled with water. I have seen images of folks in life rafts in this area as the cave is filled with water. They were cleaning the tubes at water level as it was flooded. Peak pressure waves can reflect and focus themselves to create gigantic pressure in localized areas. This is how they blast kidney stones sonically in lithotripsy (hope I spelled that right)

Once the pressure wave breaks one tube, it is like a floor covered with set mouse traps with a ping pong ball thrown into the middle....all hell breaks loose.

Richard Hull

[Jon Rosenstiel]

Here is a link to the 25 page accident report.

http://superk.physics.sunysb.edu/uno/un ... cident.pdf

Jon Rosenstiel

[Richard Hull]

Thanks Jon. Good stuff. I knew it was really bad. Anyone want to guess the cost of 6,779 new 20" hamamatsu PMTs? I am sure the 1,017 blown up 8" PMTs are just mere chump change by comparison. Then there are those new custom cast/extruded 11,146 20" lucite PMT housings needed to avoid future implosion events.

All to try and detect what is effectively, the undetectable.

Richard Hull

[Jon Rosenstiel]

I'm guessing those 20" pmt's would be around $4500.00 each. Multiply 6,779 by $4500.00 and you get $30,505,500.00 At the current exchange rate of ¥112 that would be ¥3,416,616,000. That's a lotta' yen!

Do you suppose the chain reaction implosion scenario was considered during the design stage?

Jon Rosenstiel

[JohnCuthbert]

It's a lot of yen, but the population of Japan is about 125 million; I guess they can afford 25 cents each. I have a feeling that nobody thought of the chain reaction during the early plans. If they thought of it once they had started I guess they just hoped.

[ningauble]

I wonder if the tech who dropped the shifter or screwdriver onto
the first PMT that started it off ever owned up to it.

[Richard Hull]

To Jon's Question: I don't think implosion shock wave propogation was a design issue originally. They obviously looked at pressure failures of the PMTs, but I don't think they thought forward to a pressure wave launching that would affect other tubes.

A thorough look at the whole paper has the author asking the question near the end.... "Was the first Super Kamiokande just too lucky?" (jenglish or Japanese English) Remember, this baby seemed to do fine for a few years. It was when they drained it to upgrade and retrofit that stuff went south.

Oh well, a Billion here, a Billion there, and pretty soon you are talking real money.

Richard Hull