Hollow cathode lamps - FAQ

Frequently Asked Questions

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Question
What is the difference between standard lamps and coded lamps???
Answer
The only difference is that a coded lamp allows the newer Atomic Absorption Spectrometer instruments to recognise the lamp. ie Instrument knows lamp is a Copper lamp with a wavelength set to 324.8nm etc, while a std lamp will not be recognised. This is not totally necessary. Mainly used for automation i.e. Overnight runs.

Question
What is the difference between the Standard 37mm HC lamps and the Standard 51mm Perkin Elmer lamps ? Just the length and the glass window, or also a difference in brightness?
Answer
The Main Difference is the Diameter of the lamp envelope. Which also means more gas is contained in the std PE type hence a longer lamp life. However the P903 is an exception because it has some intensity problems and we recommend the smaller 37mm type or a super lamp. Quartz or pyrex windows depend on wavelength recommended for each element. Each different element lamp varies in intensity. ie An Arsenic lamp is not as intense as a copper lamp. Historically the two types come from two different companies Varian = std 37mm lamp and Perkin Elmer = 51mm Lamp

Question
Why are SUPER Lamps super ?
Answer
Well for say 15 elements the intensity is up to 15 times greater than a std hollow cathode lamp. Arsenic and selenium Super lamps are the most popular. The reason for the greater intesity is that of a secondary discharge. Sulivan and Walsh of CSIRO developed this idea and called it a Boosted discharge lamp. This concept was further improved by R.M. Lowe of the same group. Photron used his concept and improved the design and cathode material which resulted in the Super Lamp.

Question
Which sort of fill gas do the Standard Hollow Cathode Lamps use ? Neon ?? (if yes, are other fill gasses available as well, e.g. Argon ??)
Answer
Filling Gas is mostly neon and some argon all other noble gases are avialable. Deuteruim gas is available as well for a few elements(D2 is a reactive gas).

Question
Do you have lamp mounts/holders and power supply for these lamps too ?
Answer
We do make a Power Supply for HCL lamps, However as this is not sold very often we need a months lead time. Power supply's will be built with your purposes in mind. As for lamp mounts or holders we can get them custom built, we will quote you.

Question
Can we use Photron lamps as substitutes for IL Visimax lamps?
Answer
Yes, these are the same lamps.

Question
Do Super Lamps For a PE 3110 need a special power supply?
Answer
Yes, they require the Photron Power Supply (Part Number P8200A). At the moment all PE instrument require our power supply only some GBC instruments have our Power Supply in built. The new Unicam instrument also has a power supply able to run Super lamps.

Question
Can you supply HCL lamps for a pe3300?
Answer
Yes, please refer to photron's P900 series of hollow cathode lamps.

Question
Why is the light output modulated?
Answer
Modulation is more to do with the instrumentation, i.e. Atomic Absorption Spectrometers, than our lamps. However, using modulation on our lamps will generally increase lamp life, because the lamp is only at the recommended current at the peak of the cycle. If modualation is not used then a flat DC signal applies.

Question
Last Super Lamp Power supply we received there was inaccuracies in installation instructions. Instrument is Varian Spectra 300/400 8-place lamp turret. A Customer asked following questions. Instruction says connect yellow wire. THERE IS NO YELLOW WIRE at all. There is RED wire Not in the instructions. Also asked do you have to connect in the position 1 Please E-mail or fax me correct installation instructions so that I can help our customer
Answer
MODIFICATION OF VARIAN TURRET IN SPECTRA SERIES
ATOMIC ABSORPTION SPECTROMETERS
1. Disassemble one turret on wheel suggest turret No 4 or No 1.
2. Desolder and isolate connecting wires to pin5 and 7 on octal socket. This is for coded lamp signal and must disconnected for super lamp position.
3. Drill hole through the release button (lamp clamp).
4. Desolder pin 1 and 3.
5. Insert lead of adaptor kit through wheel and lamp clamp.
6. Insert spring over lead.
7. Cut wire end to suitable length and fit appropriate heat shrink over red and black wires.
8. Solder red wire to wire that was connected to pin 3 and black wire to wire from pin 1 and insulate with the heat shrink.
9. Solder Blue wire to pin 1.
Solder Violet wire to pin 7.
Solder White wire to pin 3.
Solder Orange wire to pin 5.
10. Reassemble turret assy to wheel
11. Connect octal plug P1 to octal socket on flying lead from Super Lamp Power Supply.
12. Connect octal socket S1 to male octal plug mounted on rear of Power Supply.

Question
Would like to understand the mechanism of operation of hollow cathode lamps in AA Spectroscopy?
Answer
Hollow cathode lamps, produce a spectral line source of the element or elements contained within the lamps cathode. One type of AA spectroscopy(Double beam AA), splits the hollow cathode lamps beam into two, one as a reference beam, the other to pass through a flame or furnace of free atoms. The beam that passes through the flame or furnace is then partially absorbed by the free atoms of the same element that is within the cathode of the lamp. Hence, the difference between the two beams is proportional to the concentration of the element within the sample solution.

Question
Please explain how a dual lamp like a Ca/Mg lamp can detect both metals in a sample? What wavelength to you recommend?
Answer
The hollow cathode lamp cathode material is made up of Calcium and Magnesium alloy. When running this lamp in an Atomic Absorption spectometer, you must tune the instrument to the apropriate wavelength of the element you wish to analysis. Therefore for a Ca/Mg lamp, tune your instrument to 422.7nm for Calcium and 285.2nm for Magnesium.

Question
By changing the pressure in hollow cathode lamp what will this do to the absorption specturm? Will this increase the spectral line width?
Answer
Changing the pressure in a hollow cathode lamp will do very little to the spectral line, ie by maybe 0.3 of an angstrom. If the pressure is increased sufficiently the lamp will no longer operate as a glow discharge.

Question
Can you explain how a hollow cathode lamp works?
Answer
A hollow cathode lamp is a "glow discharge lamp".
It works by having a potential difference between to points(anode +ve and a cathode -ve) and an inert gas between them at a particular pressure. The inner lining of the cathode is made out of the desired element, this material is struck by ions. The ions cause atoms of the material to be removed from the surface, this is called sputtering. These sputtered atoms are then ionised by being struck by more ions. The atom is then at an excited state ( higher energy level). To return to the normal energy level (ground state) the atom loses this energy by releasing units of energy known as photons or light. The wavelength of the element is specific to its atomic electron structure. Most elements give off many different spectra but there is always a single strong line that is unique to a given element (resonance line).
An Atomic absorption spectrometer then uses the light from the hollow cathode lamp to help it determine concentrations of elements in samples.

Question
What is the black/silver spot in Photron hollow cathode lamps?
Answer
This is black/silver spot is what we call the getter. If you look closely at the lamp at the centre of the black spot on the internal lamp structure, there is a ring. This ring is a barium getter, which has been activated by an RF generator, hence the black/silver spot. What does it do? The material on the inside wall acts as a trap, to catch impurites within the gas of the lamp, if a di-atomic particle hits this material, it becomes stuck to the wall. Therefore, the getter keeps the gas clean throughout the life of the lamp.

These pages have been produced by Jeff Green.

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