I placed a photo of a cosmic ray muon pulse in the Images du Jour section. I've been counting and measuring cosmic rays, (I'm afraid neutron counting is still far off into the future for me), just trying to get familiar with my newly constructed scintillator. As always, I was really excited when it worked as advertised!
Thanks to everyone here for sharing their knowledge. It makes my projects go much smoother!
Any and all comments welcome.
Jon Rosenstiel
Muon scope pic, Images du Jour
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Jon Rosenstiel
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Richard Hull
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Re: Muon scope pic, Images du Jour
Very wise, Jon!
Study the realities.........!
A good hour spent pouring over captured cosmic pulses and logging the data will be well spent.
While little info is contained regarding precise energy of what hit, a qualitative "feel" for what is cosmic and what is terrestrial is important.
I cut out my discriminator at first with the BC-720 and tried a gang of radio sources I had on hand to see the results. Gammas were the big boys on the scope and although the hottest gamma I had was from Co60, I got a "feel" for the average amplitude of these puppies. It is unlikely that any terrestrial source of photons will exceed this level. I discriminated about 2X the largest gamma associated pulse seen and now settled in for a week long, hour at a time combination backgorund count and digital storage scope observathon. Scott Little and I did this almost co-jointly and agreed that some muons were so potent that they almost blew the neutron detector off the bench or at least came close to splitting the scintillator crystal. Some rare events were in the 3 volt range! Without having a consistent neutron source, we gathered that an SCA or windowed discriminator could be used to atleast mask out the hottest cosmics as well as the terrestrial crap.
It was only with the BF3 counters that the cosmics sort of became a non-issue and is the reason I sort of temporarily abandoned the BC-720 in favor of the BF3.
A look around at what the big boys preferred, (discussions with the chief radiation phyicists at NRL and others), proved that in spite of its age and low efficiency, the venerable ole' BF3 or He3 detectors are the only game in town.
I spent a lot of time and money on the BF3 route and now have it well established in my repetoire. I will soon embark on the large BC-720 project which has languished since 2000.
The key point, is you will definitely need to see what the neutrons do!!!!! This means either a known neutron source or a working fusor. Fast neutrons in the BC-720 are almost a full order of magnitude above the highest gammas. (good terestrial noise immunity figure). With the homemade scintillator, you just don't have a significant picture of the neutron response pulse level. Joe Zambelli had to go to a local college to use their neutron source to calibrate his simple scintillator discriminator level.
It is true that you could run the detector counting every thing including terestrial stuff too, but the need for close pre and post count runs is stringent. I found over a 10% differential could exist over an hour! I would hate to include the entire 10% as being real neutrons in a fusor run through subtraction of background. It would make the fusor look better that it was. Wahtsmore, if the error went the other way, it would make it look like a fusor PROBLEM.
Anyway, I am sure you will ultimately resolve all issues regarding your scintillator and become the Guru of the homemade fast neutron sensor. This will be a welcome change to buying expensive items from the big boys.
Richard Hull
Study the realities.........!
A good hour spent pouring over captured cosmic pulses and logging the data will be well spent.
While little info is contained regarding precise energy of what hit, a qualitative "feel" for what is cosmic and what is terrestrial is important.
I cut out my discriminator at first with the BC-720 and tried a gang of radio sources I had on hand to see the results. Gammas were the big boys on the scope and although the hottest gamma I had was from Co60, I got a "feel" for the average amplitude of these puppies. It is unlikely that any terrestrial source of photons will exceed this level. I discriminated about 2X the largest gamma associated pulse seen and now settled in for a week long, hour at a time combination backgorund count and digital storage scope observathon. Scott Little and I did this almost co-jointly and agreed that some muons were so potent that they almost blew the neutron detector off the bench or at least came close to splitting the scintillator crystal. Some rare events were in the 3 volt range! Without having a consistent neutron source, we gathered that an SCA or windowed discriminator could be used to atleast mask out the hottest cosmics as well as the terrestrial crap.
It was only with the BF3 counters that the cosmics sort of became a non-issue and is the reason I sort of temporarily abandoned the BC-720 in favor of the BF3.
A look around at what the big boys preferred, (discussions with the chief radiation phyicists at NRL and others), proved that in spite of its age and low efficiency, the venerable ole' BF3 or He3 detectors are the only game in town.
I spent a lot of time and money on the BF3 route and now have it well established in my repetoire. I will soon embark on the large BC-720 project which has languished since 2000.
The key point, is you will definitely need to see what the neutrons do!!!!! This means either a known neutron source or a working fusor. Fast neutrons in the BC-720 are almost a full order of magnitude above the highest gammas. (good terestrial noise immunity figure). With the homemade scintillator, you just don't have a significant picture of the neutron response pulse level. Joe Zambelli had to go to a local college to use their neutron source to calibrate his simple scintillator discriminator level.
It is true that you could run the detector counting every thing including terestrial stuff too, but the need for close pre and post count runs is stringent. I found over a 10% differential could exist over an hour! I would hate to include the entire 10% as being real neutrons in a fusor run through subtraction of background. It would make the fusor look better that it was. Wahtsmore, if the error went the other way, it would make it look like a fusor PROBLEM.
Anyway, I am sure you will ultimately resolve all issues regarding your scintillator and become the Guru of the homemade fast neutron sensor. This will be a welcome change to buying expensive items from the big boys.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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guest
Re: Muon scope pic, Images du Jour
It is amazing that your good results come from small gear. At Ole Miss our antique muon telescope fills a good sized room.
Larry Leins
Physics Teacher
Larry Leins
Physics Teacher
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Jon Rosenstiel
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Re: Muon scope pic, Images du Jour
I believe those rare super-sized pulses may be electromagnetic showers. I've seen a couple of them. I don't know how high, (or how wide) they were because they ran off of the scope!
Jon Rosenstiel
Jon Rosenstiel
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Jon Rosenstiel
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Re: Muon scope pic, Images du Jour
After building Richard Hester's pulser, (I built the second of the two and it worked great!), I was able to run down the cause of the "ringy" pulse, (see Muon scope pic in the Images du Jour forum). The ringing was due to improper grounding of the pmt's electrostatic shield. I had grounded the electrostatic shield to the pmt housing which in turn was grounded to the low and high voltage supply shields, but not the pmt's ground. Once I connected the pmt ground, (using a short wire from the shield to the pmt base), to the electrostatic shield all was good, no more ringing. I noticed that the ground lead length is quite critical. The longer the ground lead the more "ringy" the pulse becomes.
Jon Rosenstiel
Jon Rosenstiel
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Re: Muon scope pic, Images du Jour
Your findings are interesting - I'll have to think about what was going on. It's certainly a caution I will remember, as I'll be putting my own scintillator assembly together soon. All the tomes say the electrostatic shield should be at photocathode potential. I take it you first grounded the shield at the power supply return rather than directly at the tube base.
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Jon Rosenstiel
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Re: Muon scope pic, Images du Jour
Yes, and the power supply return was back in the power supply, which meant the ground "signal" had to travel through 10 feet of cable shield to reach it.
When I assembeled my second detector I noticed a clipped ground lead coming off of the pmt base and my immeadiate thought was, "Hey, that looks like it was connected to a pmt shield at one time, I should probably do the same!" So I did, and the second detector worked fine. I should also note that I left the copper strap coming off of the electrostatic shield as it was originally, (contacting the pmt housing and connected to the back cover).
Another thing I did that I'm not sure about was to wrap the electrostatic shield directly on top of the magnetic shield. (They're contacting each other). Do you think that's ok? I didn't think one would want the magnetic shield "floating".
Jon Rosenstiel
When I assembeled my second detector I noticed a clipped ground lead coming off of the pmt base and my immeadiate thought was, "Hey, that looks like it was connected to a pmt shield at one time, I should probably do the same!" So I did, and the second detector worked fine. I should also note that I left the copper strap coming off of the electrostatic shield as it was originally, (contacting the pmt housing and connected to the back cover).
Another thing I did that I'm not sure about was to wrap the electrostatic shield directly on top of the magnetic shield. (They're contacting each other). Do you think that's ok? I didn't think one would want the magnetic shield "floating".
Jon Rosenstiel
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guest
Re: Muon scope pic, Images du Jour
Connecting the electrostatic shield to the magnetic shield sounds ok. It's much better than leaving it floating. I was thinking of using my magnetic shields as electrostatic shields, as they snug up to the tubes anyway... If not, it's always easy to cut one out of copper foil.
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Tom Dressel
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Re: Muon scope pic, Images du Jour
I have a salvaged "Products for Research" refrigerated PMT enclosure. The tech support guy "Products For Research" told me that the enclosure is designed to have the electromagnetic shield tied to the high voltage supply through a 100 meg.ohm resister built into the enclosure. I am not exactly sure why this is the case, does anyone know why?
Tom Dressel
Tom Dressel
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Re: Muon scope pic, Images du Jour
The shield is probably tied to high voltage because the anode of the PMT is grounded and the cathode is at negative HV. This is common for applications needing a DC signal out of the PMT, but is not necessary for applications where the PMT is used in pulse counter mode. Having the PMT cathode as the high voltage electrode is a pain in the bottom precisely because of the necessity of biasing the shield at -HV, and having the scintillator close to high voltage. This is not so much of a problem when using a plastic scintillator, but is a royal pain if you're using something like an NaI scintillator in an aluminum can.
Life is much easier when the photocathode is tied to ground and the anode is at high voltage, with a coupling capacitor for the output signal. I have gotten some PMTs with the sockets wired for minus HV. I will be rewiring all of them for +HV.
Life is much easier when the photocathode is tied to ground and the anode is at high voltage, with a coupling capacitor for the output signal. I have gotten some PMTs with the sockets wired for minus HV. I will be rewiring all of them for +HV.
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Richard Hull
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Re: Muon scope pic, Images du Jour
Richard Hester's reply is correct. For pulse mode work, the positive HV on the anode and grounded photocathode is best.
To answer another portion of the question.....Why the 100meg resistor?.......... the shield is electrostatic in nature and you want the potential there but no current delivery for safety's sake. Possible shorts or accidental human contact would not blow out the HV supply or injure anyone. Ultra high ohm resistors are often used to relay dangerous potentials without the possibility of lethal shock in addition to setting up precision leaks for measurement purposes. Such resistors are often found in charge sensitive preamps. They are most often supplied in a sealed glass envelope to avoid contamination and retain stability.
Richard Hull
To answer another portion of the question.....Why the 100meg resistor?.......... the shield is electrostatic in nature and you want the potential there but no current delivery for safety's sake. Possible shorts or accidental human contact would not blow out the HV supply or injure anyone. Ultra high ohm resistors are often used to relay dangerous potentials without the possibility of lethal shock in addition to setting up precision leaks for measurement purposes. Such resistors are often found in charge sensitive preamps. They are most often supplied in a sealed glass envelope to avoid contamination and retain stability.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
-
guest
Re: Muon scope pic, Images du Jour
If you (Thomas) rewire the PMT for grounded photocathode (+HV) operation, the resistor will not be needed for the shield, since it will be at ground potential. If you continue with the original -HV configuration, the resistor is a very good idea, as R. Hull pointed out. A layer or two of mylar over the shield is also a good idea, since you will need to insulate the shield from the outer case.