Low Level Gamma Radiation...

[Mike Monett]

Mike Monett <spamme@not.com> wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

Why? It\'s super easy to protect against. There\'s no energy involved to
speak of.

Cheers

Phil Hobbs

Personal preference. I don\'t like the idea of feeding 800 volts into
electronics. Caps break down, pc traces arc from moisture or dirt,
things spark over as you mentioned earlier.

It doesn\'t matter which end gets the high voltage. Why take chances by
putting the high voltage on the anode. It works just as well by putting the
voltage on the cathode. I\'m not going to be using it long enough to worry
about ion migration.

Toyota Principle. Poka-Yoke: Catch mistakes before they occur.



--
MRM

 

[Mike Monett]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

> jlarkin@highlandsniptechnology.com wrote:

[...]

One could also hang an opamp on the anode to get some gain before AC
coupling down to ground. A clever circuit would subtract out the power
supply ripple up there, or couple into a grounded diffamp. There are
some cheap, low-capacitance dc/dc converters to power the opamp.

Well, the PMT has a gain of a million already.

BTW the gain of a PMT goes as some high power (like 8 or 11 or
something) of the bias voltage.

Cheers

Phil Hobbs

The high sensitivity means the HV supply has to be well regulated.

One site mentioned the HV has to be adjusted for each PMT to get the
spectrum lines to align with the corresponding MeV values, which makes
sense. I suppose the system would have to be recalibrated as the PMT ages.



--
MRM

 

[Mike Monett]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

[...]

BTW the gain of a PMT goes as some high power (like 8 or 11 or
something) of the bias voltage.

Cheers

Phil Hobbs

I wonder if that is because of the mechanism of operation, and the large
number of cascaded sections.

As I understand it, electrons hit a dynode and eject a number of electrons.
These electrons accelerated under the influence of the voltage between
electrodes, the same as in the old vacuum tubes. They hit the next
electrode and eject more electrons. The number of electrons depends on the
impact velocity, so the higher the voltage, the more electrons you get.

This process is repeated for each dynode, so the effect is multiplied each
time. This is why the PMT is so sensitive to the applied voltage.

And this is why it is so difficult to keep the spectrum aligned with the
known energy levels.




--
MRM

 

[Martin Brown]

On 22/07/2022 14:07, Phil Hobbs wrote:

Martin Brown wrote:

Life improved considerably when they moved onto turbo-molecular pumps
and for a while performance was improved even more by maglev ones.

Then one day an earthquake in Tokyo suddenly moved the Earth sideways
by an inch instantaneously and every damn one of them was destroyed. I
remember it well since in the quiet of the evening I heard the
earthquake coming (I have no idea how but I was wondering about the
strange train like sound outside when the jolt suddenly arrived).

We were busy doing turbo pump swaps for weeks and after that
conventional bearings were specified for earthquake zones.

The maglevs had been out in the field for a couple of years before
this rather nasty vulnerability became apparent.


Did any of the casings let go?

No. By then they had failure modes well under control.

The only time I have ever known it happen was with a much bigger high
power early model turbo pump (one of the largest available at the time).
Fortunately it failed at lunchtime and there was no-one in the lab. It
was pumping a big chamber about 1m^3 and something went horribly wrong.
The academic experimental setup was intrinsically not fail safe.

It shredded the blackout curtains, imploded the lab windows and doors.
The bang was heard all over the site and people went running to see what
had happened. Titanium rotor blades were stuck about 2\" into concrete,
and went through breezeblock walls in a worryingly large kill zone. Some
were also stuck in the casing walls. Miraculously no-one was harmed.

The replacement included external Kevlar armour and a host of other
safety measures to prevent a recurrence from harming experimenters.

--
Regards,
Martin Brown

 

[Phil Hobbs]

Mike Monett wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

[...]

BTW the gain of a PMT goes as some high power (like 8 or 11 or
something) of the bias voltage.

Cheers

Phil Hobbs

I wonder if that is because of the mechanism of operation, and the
large number of cascaded sections.


As I understand it, electrons hit a dynode and eject a number of
electrons. These electrons accelerated under the influence of the
voltage between electrodes, the same as in the old vacuum tubes. They
hit the next electrode and eject more electrons. The number of
electrons depends on the impact velocity, so the higher the voltage,
the more electrons you get.

This process is repeated for each dynode, so the effect is
multiplied each time. This is why the PMT is so sensitive to the
applied voltage.

Yes, that\'s right. The secondary yield generally isn\'t quite
proportional to the bias per stage, because at higher bias the incident
electrons penetrate deeper, so that their secondaries have to make their
way out through a thicker layer of material on average, and still have
enough energy to escape when they hit the surface.

There are negative electron affinity (NEA) photocathodes, where
essentially any free electron that reaches the surface will escape.
They have higher quantum yield, as you\'d expect, but are also slower
because it takes awhile for all those low-energy secondaries to bounce
around before reaching the surface. I\'d expect tubes with NEA dynodes
to follow the power law more closely.

And this is why it is so difficult to keep the spectrum aligned with
the known energy levels.

Well, and the fact that the energy resolution of CsI is the pits
compared with something like intrinsic germanium. On the plus side,
it\'s cheap and doesn\'t need liquid nitrogen.

Back in the days before really pure silicon and germanium crystals were
available, they used to be \"lithium drifted\", i.e. lithium interstitials
were introduced to bind to impurity trap states. Those ones had to be
kept at 77K continuously, or else they\'d be spoiled in a few days.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

i

 

[Phil Hobbs]

Mike Monett wrote:

Mike Monett <spamme@not.com> wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

Why? It\'s super easy to protect against. There\'s no energy involved to
speak of.

Cheers

Phil Hobbs

Personal preference. I don\'t like the idea of feeding 800 volts into
electronics. Caps break down, pc traces arc from moisture or dirt,
things spark over as you mentioned earlier.

It doesn\'t matter which end gets the high voltage. Why take chances by
putting the high voltage on the anode. It works just as well by putting the
voltage on the cathode. I\'m not going to be using it long enough to worry
about ion migration.

Toyota Principle. Poka-Yoke: Catch mistakes before they occur.



Provided you can insulate the can from the photocathode.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[server]

On Sat, 23 Jul 2022 08:14:52 -0000 (UTC), Mike Monett <spamme@not.com>
wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

[...]

BTW the gain of a PMT goes as some high power (like 8 or 11 or
something) of the bias voltage.

Cheers

Phil Hobbs

I wonder if that is because of the mechanism of operation, and the large
number of cascaded sections.

As I understand it, electrons hit a dynode and eject a number of electrons.
These electrons accelerated under the influence of the voltage between
electrodes, the same as in the old vacuum tubes. They hit the next
electrode and eject more electrons. The number of electrons depends on the
impact velocity, so the higher the voltage, the more electrons you get.

This process is repeated for each dynode, so the effect is multiplied each
time. This is why the PMT is so sensitive to the applied voltage.

And this is why it is so difficult to keep the spectrum aligned with the
known energy levels.

Add some source with a known narrow line, and servo on that.

 

[Phil Hobbs]

Martin Brown wrote:

On 22/07/2022 14:07, Phil Hobbs wrote:
Martin Brown wrote:

Life improved considerably when they moved onto turbo-molecular pumps
and for a while performance was improved even more by maglev ones.

Then one day an earthquake in Tokyo suddenly moved the Earth sideways
by an inch instantaneously and every damn one of them was destroyed.
I remember it well since in the quiet of the evening I heard the
earthquake coming (I have no idea how but I was wondering about the
strange train like sound outside when the jolt suddenly arrived).

We were busy doing turbo pump swaps for weeks and after that
conventional bearings were specified for earthquake zones.

The maglevs had been out in the field for a couple of years before
this rather nasty vulnerability became apparent.


Did any of the casings let go?

No. By then they had failure modes well under control.

The only time I have ever known it happen was with a much bigger high
power early model turbo pump (one of the largest available at the time).
Fortunately it failed at lunchtime and there was no-one in the lab. It
was pumping a big chamber about 1m^3 and something went horribly wrong.
The academic experimental setup was intrinsically not fail safe.

It shredded the blackout curtains, imploded the lab windows and doors.
The bang was heard all over the site and people went running to see what
had happened. Titanium rotor blades were stuck about 2\" into concrete,
and went through breezeblock walls in a worryingly large kill zone. Some
were also stuck in the casing walls. Miraculously no-one was harmed.

The replacement included external Kevlar armour and a host of other
safety measures to prevent a recurrence from harming experimenters.

Yikes.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Dimiter_Popoff]

On 7/23/2022 11:30, Martin Brown wrote:

On 22/07/2022 14:07, Phil Hobbs wrote:
Martin Brown wrote:

Life improved considerably when they moved onto turbo-molecular pumps
and for a while performance was improved even more by maglev ones.

Then one day an earthquake in Tokyo suddenly moved the Earth sideways
by an inch instantaneously and every damn one of them was destroyed.
I remember it well since in the quiet of the evening I heard the
earthquake coming (I have no idea how but I was wondering about the
strange train like sound outside when the jolt suddenly arrived).

We were busy doing turbo pump swaps for weeks and after that
conventional bearings were specified for earthquake zones.

The maglevs had been out in the field for a couple of years before
this rather nasty vulnerability became apparent.


Did any of the casings let go?

No. By then they had failure modes well under control.

The only time I have ever known it happen was with a much bigger high
power early model turbo pump (one of the largest available at the time).
Fortunately it failed at lunchtime and there was no-one in the lab. It
was pumping a big chamber about 1m^3 and something went horribly wrong.
The academic experimental setup was intrinsically not fail safe.

It shredded the blackout curtains, imploded the lab windows and doors.
The bang was heard all over the site and people went running to see what
had happened. Titanium rotor blades were stuck about 2\" into concrete,
and went through breezeblock walls in a worryingly large kill zone. Some
were also stuck in the casing walls. Miraculously no-one was harmed.

The replacement included external Kevlar armour and a host of other
safety measures to prevent a recurrence from harming experimenters.

Whoa! Having no people in the room makes that a fun story, the imploded
windows, shredded curtains etc. - hard to match. My closest electronics
related event compares to that like stumbling in the street to a plane
crash, I am somewhat envious .
[Once, almost 30 years ago, I reversed the power on a new board with
plenty of tantalum caps which exploded machine-gun like, pretty loud at
that. Lucy was in the next room and had frozen thinking she might have
lost me; unfroze with a huge sigh of relief some 10 seconds later when I
grasped what had happened and started to chain-swear].

 

[Mike Monett]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

[...]

Cheers

Phil Hobbs

Thanks very much for the lucid explanation.



--
MRM

 

[Mike Monett]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

Mike Monett wrote:
Mike Monett <spamme@not.com> wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

Why? It\'s super easy to protect against. There\'s no energy involved
to speak of.

Cheers

Phil Hobbs

Personal preference. I don\'t like the idea of feeding 800 volts into
electronics. Caps break down, pc traces arc from moisture or dirt,
things spark over as you mentioned earlier.

It doesn\'t matter which end gets the high voltage. Why take chances by
putting the high voltage on the anode. It works just as well by putting
the voltage on the cathode. I\'m not going to be using it long enough to
worry about ion migration.

Toyota Principle. Poka-Yoke: Catch mistakes before they occur.



Provided you can insulate the can from the photocathode.

Cheers

Phil Hobbs

I\'ll find out soon. Thanks



--
MRM

 

[server]

On Fri, 22 Jul 2022 23:39:20 -0000 (UTC), Mike Monett <spamme@not.com>
wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

Mike Monett wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

[...]

Looks like it\'s for short circuit protection. A spark across the
output terminals could be quite unpleasant for T3 otherwise.

Cheers

Phil Hobbs

That is precisely why I do not want to run mine with 800 Volts on the
anode.



Why? It\'s super easy to protect against. There\'s no energy involved to
speak of.

Cheers

Phil Hobbs

Personal preference. I don\'t like the idea of feeding 800 volts into
electronics. Caps break down, pc traces arc from moisture or dirt, things
spark over as you mentioned earlier.

I\'ll run my cathode at -800 volts where nothing can be damaged.

Incidentally, a 10nF cap discharges from 800V to zero in about 50ms.

People say modern leds are crazy brilliant. I wonder if one will glow at
90uA to make a safety warning light that high voltage is present.

People often complain about leds staying lit on leakage currents in wiring,
but nobody measures the current.

90 uA should be pretty visible into a decent LED. Some are visible in
room light at 1 uA.

Here is my high-voltage blinker:

https://www.dropbox.com/s/53vtce00svlwur4/Blink_1.jpg?raw=1

It makes bright flashes.

 

[Thory Monsen]

On Sunday, June 26, 2022 at 6:53:17 PM UTC-4, John Miles, KE5FX wrote:

On Saturday, June 25, 2022 at 11:16:45 AM UTC-7, Mike Monett wrote:
I tried to order one. Does not ship to Canada. Can you order one and mail it
to me? I can pay you via Paypal. Thanks.
Maybe. I\'ll have to surf through the Commerce and ITAR lists to see if there\'s
a reason why the seller doesn\'t ship to Canada. Shifty folk, Canadians.

(It\'ll be a few days before I have time to deal with it, for various reasons.)

-- john, KE5FX

There are a few reasons we do not ship internationally. Main one is ITAR and having to figure out what is and isn\'t can be a pain and it\'s not worth it for us. Second would be shipping issues. We have no control over the shipping and a lot of items would get lost in the past and then it\'s on us to refund. I know there are some new ebay programs which reduce this risk and it is something we are considering for the future. I am really happy we were able to save this tube from the scrap heap and that so many are finding it useful.

 

[Thory Monsen]

On Sunday, June 26, 2022 at 6:53:17 PM UTC-4, John Miles, KE5FX wrote:

On Saturday, June 25, 2022 at 11:16:45 AM UTC-7, Mike Monett wrote:
I tried to order one. Does not ship to Canada. Can you order one and mail it
to me? I can pay you via Paypal. Thanks.
Maybe. I\'ll have to surf through the Commerce and ITAR lists to see if there\'s
a reason why the seller doesn\'t ship to Canada. Shifty folk, Canadians.

(It\'ll be a few days before I have time to deal with it, for various reasons.)

-- john, KE5FX

There are a few reasons we do not ship internationally. Main one is ITAR and having to figure out what is and isn\'t can be a pain and it\'s not worth it for us. Second would be shipping issues. We have no control over the shipping and a lot of items would get lost in the past and then it\'s on us to refund. I know there are some new ebay programs which reduce this risk and it is something we are considering for the future. I am really happy we were able to save this tube from the scrap heap and that so many are finding it useful.

 

[Thory Monsen]

On Sunday, June 26, 2022 at 6:53:17 PM UTC-4, John Miles, KE5FX wrote:

On Saturday, June 25, 2022 at 11:16:45 AM UTC-7, Mike Monett wrote:
I tried to order one. Does not ship to Canada. Can you order one and mail it
to me? I can pay you via Paypal. Thanks.
Maybe. I\'ll have to surf through the Commerce and ITAR lists to see if there\'s
a reason why the seller doesn\'t ship to Canada. Shifty folk, Canadians.

(It\'ll be a few days before I have time to deal with it, for various reasons.)

-- john, KE5FX

There are a few reasons we do not ship internationally. Main one is ITAR and having to figure out what is and isn\'t can be a pain and it\'s not worth it for us. Second would be shipping issues. We have no control over the shipping and a lot of items would get lost in the past and then it\'s on us to refund. I know there are some new ebay programs which reduce this risk and it is something we are considering for the future. I am really happy we were able to save this tube from the scrap heap and that so many are finding it useful.

 

[John Miles, KE5FX]

On Tuesday, January 10, 2023 at 1:50:05 PM UTC-8, Thory Monsen wrote:

There are a few reasons we do not ship internationally. Main one is
ITAR and having to figure out what is and isn\'t can be a pain and
it\'s not worth it for us. Second would be shipping issues. We have
no control over the shipping and a lot of items would get lost in
the past and then it\'s on us to refund. I know there are some new
ebay programs which reduce this risk and it is something we are
considering for the future. I am really happy we were able to save
this tube from the scrap heap and that so many are finding it useful.

True, better safe than sorry when it comes to that sort of thing. It\'s probably
safe enough to ship them to Canada. But I wouldn\'t want to risk it with
China or Russia, given that I don\'t even know the ECCN #.

Very cool little gadget, in any case!

-- john, KE5FX

 

[John Miles, KE5FX]

On Tuesday, January 10, 2023 at 1:50:05 PM UTC-8, Thory Monsen wrote:

There are a few reasons we do not ship internationally. Main one is
ITAR and having to figure out what is and isn\'t can be a pain and
it\'s not worth it for us. Second would be shipping issues. We have
no control over the shipping and a lot of items would get lost in
the past and then it\'s on us to refund. I know there are some new
ebay programs which reduce this risk and it is something we are
considering for the future. I am really happy we were able to save
this tube from the scrap heap and that so many are finding it useful.

True, better safe than sorry when it comes to that sort of thing. It\'s probably
safe enough to ship them to Canada. But I wouldn\'t want to risk it with
China or Russia, given that I don\'t even know the ECCN #.

Very cool little gadget, in any case!

-- john, KE5FX

 

[John Miles, KE5FX]

On Tuesday, January 10, 2023 at 1:50:05 PM UTC-8, Thory Monsen wrote:

There are a few reasons we do not ship internationally. Main one is
ITAR and having to figure out what is and isn\'t can be a pain and
it\'s not worth it for us. Second would be shipping issues. We have
no control over the shipping and a lot of items would get lost in
the past and then it\'s on us to refund. I know there are some new
ebay programs which reduce this risk and it is something we are
considering for the future. I am really happy we were able to save
this tube from the scrap heap and that so many are finding it useful.

True, better safe than sorry when it comes to that sort of thing. It\'s probably
safe enough to ship them to Canada. But I wouldn\'t want to risk it with
China or Russia, given that I don\'t even know the ECCN #.

Very cool little gadget, in any case!

-- john, KE5FX