Hi All,
Here's the QE measurement of the most recent chicklet produced within the
USB evaporator on 6/29/06 (please see attached). Judging by these nice
results, it seems the optimistic scenario is the correct one. BTW, is it
possible in the QE calc at Stony Brook, that the 80% of full QE result is
due to the fact that the GEM transparency was not corrected for, which of
course is on the order of 80%? In any case, hopefully this last measurement
right before the long weekend will allow us to enjoy it a little more...
Best Regards,
Bob
----- Original Message -----
From: "Thomas K Hemmick" <hemmick@skipper.physics.sunysb.edu>
To: "Itzhak Tserruya" <itzhak.tserruya@weizmann.ac.il>
Cc: "PHENIX HBD" <phenix-electron-l@bnl.gov>
Sent: Thursday, June 29, 2006 2:45 AM
Subject: Re: QE mystery for most recent cathode production.
> Hi Itzhak
>
> We never saw in the quantitative BNL tests 33% QE at 160 nm (20%
> high). These were always the same as the measurements that Ilia
> made...27% at 160nm. We could not explain why the QE measurement at
> Stony Brook was high, but we also never claimed that this measurement
> was well controlled in the same manner as the measurements from Bob
> and Ilia. We only knew that it was consistently high by 20% over the
> past months. Now it seems instead to measure the "correct answer",
>
> I also hope for the optimistic scenario and we should know whether
> this is true very soon.
>
> Tom
>
> On 6/29/06, Itzhak Tserruya <itzhak.tserruya@weizmann.ac.il> wrote:
>> Dear Tom,
>> A small question: the 20% higher QE at 160 nm, that you measured
>> many times in the past, was it confirmed by the QE measurements over the
>> entire wavelength made on chicklets at BNL? From the graph that you
>> included in your e-mail I would say no. This would then support
>> your "optimist" scenario.
>>
>> I agree with you that the QE measurement of the chicklets from the
>> last shot will be a crucial diagnostic.
>>
>> Best,
>> Itzhak
>>
>>
>> |====================================================================|
>> |Itzhak Tserruya ITZHAK.TSERRUYA@WEIZMANN.AC.IL |
>> |Department of Particle Physics |
>> |The Weizmann Institute of Science tel: 972 - 8 - 934 4052 |
>> |REHOVOT 76100 ISRAEL fax: 972 - 8 - 934 6021 |
>> |
>> |====================================================================|
>>
>> On Thu, 29 Jun 2006, Thomas K Hemmick wrote:
>>
>> > Date: Thu, 29 Jun 2006 01:58:11 -0400
>> > From: Thomas K Hemmick <hemmick@skipper.physics.sunysb.edu>
>> > To: PHENIX HBD <phenix-electron-l@bnl.gov>
>> > Subject: QE mystery for most recent cathode production.
>> >
>> > Hi all
>> >
>> > The most recent dry run of the QE apparatus at Stony Brook produced a
>> > QE result that was only 80% of the result we have been achieving to
>> > date.We have been pouring over the issue since this result came out
>> > and have the following information to share (but no true solution):
>> >
>> > 1)Two known changes exist in the system since the previous run:
>> > a-- We have used up the first of our two (presumed identical) blocks
>> > of CsI and started to use the second one.
>> > b-- The PMT wires in the QE system were accidentally knocked off and
>> > Bill repaired this part of the system.
>> >
>> > 2)The current measured by the photocathode when exposed to light is
>> > exactly the same as we have always seen.
>> >
>> > 3)The PMT "light on" current is higher than we have seen in the past.
>> >
>> > 4)The PMT "light off" (or dark) current is higher than we have seen
>> > in the past.
>> >
>> > 5)The PMT net current is higher than we have seen in the past.
>> >
>> > The low QE seems to come from the PMT registering more current from
>> > the lamp than it had in previous tests.The present result (repeated
>> > multiple times this afternoon, with varied conditions NONE of which
>> > made ANY difference at all) is a QE of 27% at 160 nm.Interestingly
>> > enough, the WIS measurements and the BNL measurements at 160 nm both
>> > showed that excellent cathodes have a QE of 27% at 160 nm.A
>> > long-standing anomaly in the QE system built into the evaporator
>> > system has been that we were routinely getting 33% QE at this
>> > wavelength, 20% higher than the known true value.
>> >
>> > An optimist would say that Bill repaired the reference PMT system and
>> > that the anomalously high QE it measures has now become a correct
>> > reading for the first time.A pessimist would say that some other
>> > change (like going over to the second CsI block) has reduced the QE by
>> > 20% and that we need to understand why immediately.
>> >
>> > The latest shot includes a pair of chicklets.These will be delivered
>> > to Bob tomorrow after we have finished an upgrade the internal
>> > railroad system of the glovebox (presently disassembled).
>> > Additionally, we have received 3 more blocks of CsI from Craig (each
>> > from different manufacturer and each known to be high purity and an
>> > excellent scintillator).We will keep you informed as this story
>> > plays out.
>> >
>> > Tom
>> >
>> > PS--The block ofCsI we are presently, Craig assures me, was at the
>> > time of its manufacture among the purest CsI crystals ever produced.
>> >
>>
>>
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