3B SCIENTIFIC PHYSICS U19152 Mode D'emploi page 6

3. Technical data
Filament voltage:
Filament current:
Anode voltage:
Anode current:
Screen current:
Luminescence screen:
5.1: fluorescent red, approx. 625 nm, medium
short decay time
5.2: fluorescent blue, approx. 450 nm, medium
decay time
5.3 fluorescent green, approx. 510 nm fluores-
cent, approx. 515 nm phosphorescent, long de-
cay time
Glass bulb: approx. 130 mm diam.
Total length: approx. 260 mm
4. Operation
To perform experiments using the luminescence
tube, the following equipment is also required:
1 Tube holder D
1 High voltage power supply 5 kV
or
1 High voltage power supply 5 kV
1 Ultra-violet light source
1 Infrared light source
4.1 Setting up the tube in the tube holder
The tube should not be mounted or removed
unless all power supplies are disconnected.
•
Push the jaw clamp sliders on the stanchion of
the tube holder right back so that the jaws
open.
•
Push the bosses of the tube into the jaws.
•
Push the jaw clamps forward on the stanchions
to secure the tube within the jaws.
4.2 Removing the tube from the tube holder
•
To remove the tube, push the jaw clamps right
back again and take the tube out of the jaws.
5. Example experiments
5.1 Excitation by cathode ray bombardment
•
To better observe the afterglow effects (phos-
phorescence), carry out the the last step of the
experiment in a darkened room.
•
Set up the luminescence tube as shown in fig.1.
6.3 V AC/DC (8.0 V max.)
1.8 A typical at U = 6.3 V
F
2000 - 5000 V DC
180 µA typical at
U = 4000 V
A
100 µA typical at
U = 4000 V
S
U19100
U33010-115
U33010-230
•
Connect both the screens and the anode to
earth for maximum safety.
•
Set the voltage U
•
Observe the luminescence.
The three phosphors fluoresce at different wave-
lengths (colours).
•
Vary the voltage between 2000 V and 4000 V.
•
Observe the change of the luminous phe-
nomenon.
While the intensity of the fluorescence varies with
the voltage, wavelength does not.
•
With U at 4000 V use a hand held spectroscope
A
to view the emissions from each phosphor.
Note that the emission from the red phosphor
comprises a number of discrete emission lines.
•
Switch off the power supply and observe the
afterglow (phosphorescence).
The removal of the source of thermionic bom-
bardment causes luminescence to cease. The decay
of emission from the phosphors is particularly
apparent on the green phosphor.
5.2 Excitation by ultra-violet light
•
Carry out the experiment in a darkened room.
•
Set up the luminescence tube as shown in fig.2.
•
Do not switch on the power supply.
Note that there is no visible photoluminescence
due to the ambient light levels.
•
Illuminate the gun side of the screen with
ultra-violet light and note the initial time de-
pendency of emission intensity.
The three phosphors fluoresce at the same wave-
length as when excited by cathode ray bombard-
ment.
•
Vary the intensity of the ulta-violet light, either
by changing the distance between the light
source and the phosphor, or by interposing
suitable filters.
While the intensity of the fluorescence varies with
the intensity and energy of the exciting radiation,
wavelength does not.
•
Remove the ultraviolet light and observe the
afterglow (phosphorescence).
The decay characteristic of the green phosphor
appears longer than was observed after removal of
cathode ray bombardment. The reason for this is
that the phosphorescence of this material is
quenched by infra-red radiation. When the fila-
ment supply is switched off there remains sufficient
infra-red emission from the cooling filament to
partially quench phosphorescence.
•
Set the voltage to about 4500 V and note the
current flowing (typically 0.02 μA due to leak-
age on or through the glass bulb).
2
to about 3500 V.
A