[Milsurplus] "Blue Glow" mystery.

[J. Forster]

> Yes, also the anode should be dense for productive generation of x-rays,
> also cobalt, iron or copper.

Actually, I think the target has to have a high atomic number...  a heavy
nucleus.

> I doubt a thin glass tube envelope would cut it.  Also 500 volts isn't
> much.

The link I posted earlier gives penetrating power of various energy
x-rays. 1 keV will only penetrate a couple of microns ( micro-meters) of
water.

> Also are the electrons actually accelerated or merely milling around?
> (so many questions...I quit)

No. they don't 'mill around' in an E field...  any more than a ball 'mills
around' if it rolls off a table. As soon as the ball is unconstrained by
the table, it starts to accelerate in the earth's gravitation field. In a
similar way, an eletron 'falling through' an E field will be accelerated.

The higher the table, the further the ball will fall and the faster it'll
go. Ditto, the electron. The bigger the potential difference (voltage) the
faster it'll go.

-John

================


>
> Richard
>
>
>> The x-rays are generated when the kinetic energy of a fast-moving
>> electron
>> is suddenly stopped. Some comes off as radiation, some as heat. The
>> reason
>> Tungsten is used is it's high melting point.
>>
>> -John
>>
>> =================
>>
>>
>>
>>> If the blue glow is within the tube, that's gas.  If the blue glow is
>>> on
>>> the
>>> surface inside the glass envelope that's electrons hitting the glass,
>>> and
>>> indicates a good vacuum.  When a tube is "cut-off" that does not mean
>>> there
>>> is absolutely NO electron flow.  As the tube approaches cut-off, it
>>> approaches it as a limit, and the current is reduced to a very small
>>> amount,
>>> maybe a few mils or microamperes.  Electrons may also find unintended
>>> paths
>>> around tube parts uncontrolled by the grid, etc.
>>>
>>> As an extreme example, early radar modulators used big triodes, passing
>>> amperes for a few microseconds with a tube voltage drop of maybe 1500
>>> volts.
>>> and a few milliamperes when cut off at 15 kv.  The result was the tubes
>>> dissipated almost as much power when cut-off as when conducting.
>>>
>>> X-Rays need much more voltage drop, 10 kv comes to mind for soft
>>> X-Rays.
>>> (of
>>> course I'm an expert.....) You also need the right kind of
>>> target/anode.
>>>
>>> Richard, AA1P
>>>
>>>
>>>>>    The dark blue glow that seems to be right at the glass
>>>>> is caused by x-rays from the tube.  Its commonly seen in
>>>>> tubes like audio output tubes with fairly high voltage on
>>>>> the plates. Some older tubes had a black coating on the
>>>>> inside of the glass to stop it.
>>>>
>>>> That's my big question and point.
>>>> You are of course correct about the blue glow,
>>>> but why is this one happening in a cut-off tube
>>>> with no current flow, then disappearing when
>>>> current is flowing?  That's opposite of what
>>>> I've seen before.