CA1142215A - Mercury arc discharge lamp with altered isotopic distribution of mercury - Google Patents
Mercury arc discharge lamp with altered isotopic distribution of mercuryInfo
- Publication number
- CA1142215A CA1142215A CA000396601A CA396601A CA1142215A CA 1142215 A CA1142215 A CA 1142215A CA 000396601 A CA000396601 A CA 000396601A CA 396601 A CA396601 A CA 396601A CA 1142215 A CA1142215 A CA 1142215A
- Authority
- CA
- Canada
- Prior art keywords
- mercury
- radiation
- arc discharge
- resonance radiation
- isotopic distribution
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Vessels And Coating Films For Discharge Lamps (AREA)
- Luminescent Compositions (AREA)
Abstract
ARC DISCHARGE DEVICE HAVING IMPROVED EFFICIENCY
ABSTRACT
In a mercury-containing arc discharge device for converting electrical energy into resonance radiation, the isotopic distribution of the mercury in the device is altered from that of natural mercury so as to reduce imprisonment time of resonance radiation and thereby increase the efficiency of conversion of electrical energy into resonance radiation.
ABSTRACT
In a mercury-containing arc discharge device for converting electrical energy into resonance radiation, the isotopic distribution of the mercury in the device is altered from that of natural mercury so as to reduce imprisonment time of resonance radiation and thereby increase the efficiency of conversion of electrical energy into resonance radiation.
Description
This application is a division o ~anadian Application 333,599 filed August lO, 1979.
TEE INVENTION
This invention concerns a mercury-containing arc discharge device for converting electrical energy into resona~ce radiation. It is particularly concerned with improving the efficiency of such conversion.
An example o~ such a device is a fluorescent lamp. Such a lamp comprises a tubular glass envelope having electrodes at its ends, containing a fill of mercury and an inert gas, and having a phosphor coating on the inner envelope wall. In fluorescent lamps, electrical energy is converte into the kinetic energy of free electrons which in turn is converted into the internal energy of atoms and molecules, which in turn is converted into radiant energy, and chiefly into the resonance radiation at the 254 nanometer (nm) region of the electromagnetic spectrum, which in turn is converted into luminous energy by the phosphor. A great deal of effort has gone into improving the luminous efficacy of such lamps by improving the phosphor blent, the fill gas pressure~ and tube geom~try~
Such effort has, fund~mentally, been direc~ed toward optimizing the number density of mercury atoms in the aggregate and opt~mizing the photon conversion efficiencies of the fluorescent materials.
Defining a quantum of resonance radiation energy as the energy of a single mercury atom excited to its Pl state, in its esca?e from the discharge tube such a quantum may exist either as an e~cited atom or as a photon emitted by an excited atom. Because of the presence of mercury atoms in their lowest energy state (ground state) in tbe plasma which can absorb such photons, thereby becoming excited atoms, which may ~ .~
. - ~P
z215 ' I
D-21,56~ ¦ subsequently re-emit a photon of substantially the same energy as they I absorbed, a quantum of resonance radiation energy (created by electron impact excitation of a mercury atom) escapes the discharge tube by a series of stepwise emissions and absorptions, alternately changing its form from excited atom to photon and vice versa before it finally escapesi the discharge tube as a photon.
Each time the quantum is absorbed and becomes an excited atom, a ~ I
period equal to the natural life time of the excited atom (about 1.17 x ¦
10 7 second) must elapse on the average before it can be re-emitted.
Thus, the multiple emission, absorption and re-emission process, known ac imprisonment of radiance radiation, greatly prolongs the length of time the quantum spends as an excited atom before it can escape the tube eo many times the single natural lifetime it would reside as an excited àto~ if the photon escaped without re-absorption.
Whilo the quantum resides as an excited atom, there is a finite probability that some non-radiative process may OCCUl' to dissipate its energy. T~e longer the imprisonment time, that is, the time required for , `~
the quantum to escape, the greatsr is the total probability of such non-radiative loss and the lower the efficiency. The proble~ of imprisonment time and quantum escape has been considered theoretically; see, for example, "Imprisonment of Resonance Radiation in ~ases. Il" by T. Holstein (Physical Review, Volume 83, Number ~, September 15, 1951) and "Electric Discharge Lamps" by John F. Uaymouth, The ~.I.T. Press (1971), Cambridge, Massachusetts, and London, England, pages 122-126. Lamp optimization relating, for example, to envelope diameter, fill pressure or operating temperature, has been based on prior art treatments of the proble~ of radiation transfer. A common feature of all of these treatments Xnown to the prior art is that imprisonment time increases on the average as the concentration of total mercury atoms in the vapor phase increases, and this act is responsible for the declining efficiency of such lamps for mercury pressures higher than 6xlO 3 torr, corresponding to the pressu~e ¦
of saturated vapor above liquid mercury at 40 C, which is about the pressure in fluorescent lamps.
-, - 2 -.~ Il 1142;~15 D-21,564 ll As previously stated, the fluorescent lamp operates by using resonance radiation from a plasma to excite a phosphor which emits visible light.
Previous improvements ;.n the performance of the discharge have been l attained by changing lamp structure, fill gas composition and pressure, I
¦ and mercury pressure. We have discovered that the efficiency of fluo-- ¦
rescent;lamps, and of any mercury-containing arc discharge device for converting electrical energy into resonance radiation, can be improved byl altering the content of the mercury in tbe device. This i~vention is bas!d on the recognition that the imprisonment time of mercury resonance radiat~on depends not only on the number density of mercury atoms in the aggregate, but dso on the number den~ity of the var~ou~ mercury isotopes. If, for example, the 254 nm emissions of the indivitual isotopes have the same spectral shape but lie in distinct, non-overlapping, wavelength regions, and if each of the isotopes ha~ the same probability of being excited and subsequently emitting 254 nm radiation, then each isotope could only absorb radiation emitted by an isotope of identical mass nu~ber, and one ~-would expect minimum imprisonment and maximwm 254 nm radiation if ali is~topes were equally abundant. Such an isotopic distribution stands in ¦
marked contrast to that in naturally-occurring mercury, which is as follo 20Isotope ~Mass Number)Natural Abundance 196 0.1467.
198 10.0 %
199 16.8 %
25 . 201 13 21 7 202 29.8 %
204 6.8S %
In fact, the 254 nm spectral emissions of some of the isotopes do overlap, but the emission of the Hgl96 isotope is not one of them. We 3~ have discovered that the entrapment time of 254 nm mercury resonance radiation can be reduced and the output of 254 nm resonance radiation can be increased in a device which incorporates relatively more of ehe Hg lsoeope than is found in naturally-occurring mercury.
,.
.. .
~1~2215 According to the present invention there is provided a mercury-containing arc discharge device for converting electrical energy into resonance radiation, the Hgl96 content of the mercury within the device being greater than that in natural mercury in order to increase the efficiency of converting said electrical energy into said resonance radiation.
` ~
~ 20 :
:
- 3a -11 114~215 D-21,564 l The drawing shows a mercury-containing arc discharga device fabricat~d so as to permit measurement of the 254 nm resonance radiation. The device comprises a sealed 4 foot envelope 1 having electrodes 2 at each !l end thereof. Envelope 1 contains mercury and an ir.ert gas such as argon.
I An lntermediate short length 3 of envelope 1 is made of fused silica instead of the usual soft glass which ccmprises the rest of envelope 1 in order to transmit 254 nm radiation, soft gLass being opaque to such radiation.
Three such devices were made and about 5 mg of mercury were added to each device. In the first device, used as a control, ~he mercury was naturally-occurring mercury, having the isotopic distriroution prevlously mentioned. In the secont and thirt devices the zmou~t of Hg isotope in the 5 mg of mercury was increased as follows. Enriched Hg 6 was obtained from Oak Ridge National Labs, Oak Ridge, Tennessee, in the form of mercuric oxide the mercury content o~ which was 33~97Z
Rg 96. The isotopic distribution of said mercury content was as follows:
Hgl96 _~33 ~977O; Hgl98 ~ 17.597o; Hgl99 ~ 16.02%; Hg200 _ 14-7270; Hg ~ ~ i 5~93%; Hg2 _ lO~lg7o; Hg 4 - 1.5~to. The mercuric oxide was thermally decomposed to yield elemental mercury, 2.25 mg of which was added to the second device and 0.55 mg of whi~ was added to the third device. In each device, sufficient naturally-occurring mercury was added to bring thl a total mercury charge to about 5 mg. Thé individual mercury compositions were as follows:
Isotope Control #2 #3 196 0.146%15 ~3% 3 ~75%
198 .10~0 13~4 10~8 199 16.8 16.5 16.75 200 23.1 19 ~35 22 ~2 201 13.2 9. 95 12.4 202 29.8 21.0 27.7 ' 204 6.85 4.5 6.3 The devices were operated at 430 milliampere constane current and the relative outputs of 254 nm radiation were measured using a monochromator ant photomultiplier tube by techniques well known in the art. The output :
of devices 2 and 3 were 4.2% and 4.~/O greater, respectively, than that of " ' .
ll ~142ZlS
-21,564 ~ the controL. This is a significant gain. In a 4 foot fluorescent lamp, it represents an improvement of better than 100 lumens. At a constant !
wattage of 40 watts, devi-e ~3 yielded a 3.6Z increase in output over thel l control. ¦
¦ It is apparent that substantial enhancement of the efficiency of I generation of the 254 nm resonance radiation emission has been achieved, ¦ and surprisingly, that such increase in efficiency has occurred for Hg isotope enrichments which are well below the equal proportion value.
Since the c~-~ercial practicality of this invention will ultimately depend on the cost of enriching natural mercury in the ~g 9 isotope, ant that cost will strongly depend on the level of enrichnent required, it is clear that this is a highly significant finding. On the basi~ of the results of devices 2 and 3, it is expected that an enric~ment of Hgl96 isotope as little as l~/o would yield a significantly economic increa :e in efficiency. ~ i The only prior art teachings of which we are aware regardin8 isotope effects on the imprisonmene time of 254 nm resonance radiation in mercury vapor are those in "Isotope Effect in the Imprisonment of Resonance Radiation" by T. HolsteinJ D. Alpert, & A.O. McCoubrey (Physical Review, Volume 8S, Number 4, March 15, 1952). The authors investigatedthe impris~ ~n- , ment time of a mercury vapor mixture consisting predcminantly of the single isotope Hg , with small impurities of Hg and Hg . ~hey tetermined that about a six fold longer imprisonment time occurred at vapor pressures in the vicinity of 6xlO torr than in natural mercury.
In no case did they observe an imprisonment time shorter than that of natural mercury Although the improvement in efficiency of converaion of electrical energy to mercury resonance radiation has been demonstrated primarily for 254 nm radiation, it is equally applicable to mercury resonance radiation at other frequencies, for example, 185 nm~ The 254 nm ratia-tion is of primary importance in fluorescent lamps ~hile 1~5 nm radiation is of importance in ozone producing devices as well as in some types of ¦
fluorescent lamps. -- 1 ~ .
TEE INVENTION
This invention concerns a mercury-containing arc discharge device for converting electrical energy into resona~ce radiation. It is particularly concerned with improving the efficiency of such conversion.
An example o~ such a device is a fluorescent lamp. Such a lamp comprises a tubular glass envelope having electrodes at its ends, containing a fill of mercury and an inert gas, and having a phosphor coating on the inner envelope wall. In fluorescent lamps, electrical energy is converte into the kinetic energy of free electrons which in turn is converted into the internal energy of atoms and molecules, which in turn is converted into radiant energy, and chiefly into the resonance radiation at the 254 nanometer (nm) region of the electromagnetic spectrum, which in turn is converted into luminous energy by the phosphor. A great deal of effort has gone into improving the luminous efficacy of such lamps by improving the phosphor blent, the fill gas pressure~ and tube geom~try~
Such effort has, fund~mentally, been direc~ed toward optimizing the number density of mercury atoms in the aggregate and opt~mizing the photon conversion efficiencies of the fluorescent materials.
Defining a quantum of resonance radiation energy as the energy of a single mercury atom excited to its Pl state, in its esca?e from the discharge tube such a quantum may exist either as an e~cited atom or as a photon emitted by an excited atom. Because of the presence of mercury atoms in their lowest energy state (ground state) in tbe plasma which can absorb such photons, thereby becoming excited atoms, which may ~ .~
. - ~P
z215 ' I
D-21,56~ ¦ subsequently re-emit a photon of substantially the same energy as they I absorbed, a quantum of resonance radiation energy (created by electron impact excitation of a mercury atom) escapes the discharge tube by a series of stepwise emissions and absorptions, alternately changing its form from excited atom to photon and vice versa before it finally escapesi the discharge tube as a photon.
Each time the quantum is absorbed and becomes an excited atom, a ~ I
period equal to the natural life time of the excited atom (about 1.17 x ¦
10 7 second) must elapse on the average before it can be re-emitted.
Thus, the multiple emission, absorption and re-emission process, known ac imprisonment of radiance radiation, greatly prolongs the length of time the quantum spends as an excited atom before it can escape the tube eo many times the single natural lifetime it would reside as an excited àto~ if the photon escaped without re-absorption.
Whilo the quantum resides as an excited atom, there is a finite probability that some non-radiative process may OCCUl' to dissipate its energy. T~e longer the imprisonment time, that is, the time required for , `~
the quantum to escape, the greatsr is the total probability of such non-radiative loss and the lower the efficiency. The proble~ of imprisonment time and quantum escape has been considered theoretically; see, for example, "Imprisonment of Resonance Radiation in ~ases. Il" by T. Holstein (Physical Review, Volume 83, Number ~, September 15, 1951) and "Electric Discharge Lamps" by John F. Uaymouth, The ~.I.T. Press (1971), Cambridge, Massachusetts, and London, England, pages 122-126. Lamp optimization relating, for example, to envelope diameter, fill pressure or operating temperature, has been based on prior art treatments of the proble~ of radiation transfer. A common feature of all of these treatments Xnown to the prior art is that imprisonment time increases on the average as the concentration of total mercury atoms in the vapor phase increases, and this act is responsible for the declining efficiency of such lamps for mercury pressures higher than 6xlO 3 torr, corresponding to the pressu~e ¦
of saturated vapor above liquid mercury at 40 C, which is about the pressure in fluorescent lamps.
-, - 2 -.~ Il 1142;~15 D-21,564 ll As previously stated, the fluorescent lamp operates by using resonance radiation from a plasma to excite a phosphor which emits visible light.
Previous improvements ;.n the performance of the discharge have been l attained by changing lamp structure, fill gas composition and pressure, I
¦ and mercury pressure. We have discovered that the efficiency of fluo-- ¦
rescent;lamps, and of any mercury-containing arc discharge device for converting electrical energy into resonance radiation, can be improved byl altering the content of the mercury in tbe device. This i~vention is bas!d on the recognition that the imprisonment time of mercury resonance radiat~on depends not only on the number density of mercury atoms in the aggregate, but dso on the number den~ity of the var~ou~ mercury isotopes. If, for example, the 254 nm emissions of the indivitual isotopes have the same spectral shape but lie in distinct, non-overlapping, wavelength regions, and if each of the isotopes ha~ the same probability of being excited and subsequently emitting 254 nm radiation, then each isotope could only absorb radiation emitted by an isotope of identical mass nu~ber, and one ~-would expect minimum imprisonment and maximwm 254 nm radiation if ali is~topes were equally abundant. Such an isotopic distribution stands in ¦
marked contrast to that in naturally-occurring mercury, which is as follo 20Isotope ~Mass Number)Natural Abundance 196 0.1467.
198 10.0 %
199 16.8 %
25 . 201 13 21 7 202 29.8 %
204 6.8S %
In fact, the 254 nm spectral emissions of some of the isotopes do overlap, but the emission of the Hgl96 isotope is not one of them. We 3~ have discovered that the entrapment time of 254 nm mercury resonance radiation can be reduced and the output of 254 nm resonance radiation can be increased in a device which incorporates relatively more of ehe Hg lsoeope than is found in naturally-occurring mercury.
,.
.. .
~1~2215 According to the present invention there is provided a mercury-containing arc discharge device for converting electrical energy into resonance radiation, the Hgl96 content of the mercury within the device being greater than that in natural mercury in order to increase the efficiency of converting said electrical energy into said resonance radiation.
` ~
~ 20 :
:
- 3a -11 114~215 D-21,564 l The drawing shows a mercury-containing arc discharga device fabricat~d so as to permit measurement of the 254 nm resonance radiation. The device comprises a sealed 4 foot envelope 1 having electrodes 2 at each !l end thereof. Envelope 1 contains mercury and an ir.ert gas such as argon.
I An lntermediate short length 3 of envelope 1 is made of fused silica instead of the usual soft glass which ccmprises the rest of envelope 1 in order to transmit 254 nm radiation, soft gLass being opaque to such radiation.
Three such devices were made and about 5 mg of mercury were added to each device. In the first device, used as a control, ~he mercury was naturally-occurring mercury, having the isotopic distriroution prevlously mentioned. In the secont and thirt devices the zmou~t of Hg isotope in the 5 mg of mercury was increased as follows. Enriched Hg 6 was obtained from Oak Ridge National Labs, Oak Ridge, Tennessee, in the form of mercuric oxide the mercury content o~ which was 33~97Z
Rg 96. The isotopic distribution of said mercury content was as follows:
Hgl96 _~33 ~977O; Hgl98 ~ 17.597o; Hgl99 ~ 16.02%; Hg200 _ 14-7270; Hg ~ ~ i 5~93%; Hg2 _ lO~lg7o; Hg 4 - 1.5~to. The mercuric oxide was thermally decomposed to yield elemental mercury, 2.25 mg of which was added to the second device and 0.55 mg of whi~ was added to the third device. In each device, sufficient naturally-occurring mercury was added to bring thl a total mercury charge to about 5 mg. Thé individual mercury compositions were as follows:
Isotope Control #2 #3 196 0.146%15 ~3% 3 ~75%
198 .10~0 13~4 10~8 199 16.8 16.5 16.75 200 23.1 19 ~35 22 ~2 201 13.2 9. 95 12.4 202 29.8 21.0 27.7 ' 204 6.85 4.5 6.3 The devices were operated at 430 milliampere constane current and the relative outputs of 254 nm radiation were measured using a monochromator ant photomultiplier tube by techniques well known in the art. The output :
of devices 2 and 3 were 4.2% and 4.~/O greater, respectively, than that of " ' .
ll ~142ZlS
-21,564 ~ the controL. This is a significant gain. In a 4 foot fluorescent lamp, it represents an improvement of better than 100 lumens. At a constant !
wattage of 40 watts, devi-e ~3 yielded a 3.6Z increase in output over thel l control. ¦
¦ It is apparent that substantial enhancement of the efficiency of I generation of the 254 nm resonance radiation emission has been achieved, ¦ and surprisingly, that such increase in efficiency has occurred for Hg isotope enrichments which are well below the equal proportion value.
Since the c~-~ercial practicality of this invention will ultimately depend on the cost of enriching natural mercury in the ~g 9 isotope, ant that cost will strongly depend on the level of enrichnent required, it is clear that this is a highly significant finding. On the basi~ of the results of devices 2 and 3, it is expected that an enric~ment of Hgl96 isotope as little as l~/o would yield a significantly economic increa :e in efficiency. ~ i The only prior art teachings of which we are aware regardin8 isotope effects on the imprisonmene time of 254 nm resonance radiation in mercury vapor are those in "Isotope Effect in the Imprisonment of Resonance Radiation" by T. HolsteinJ D. Alpert, & A.O. McCoubrey (Physical Review, Volume 8S, Number 4, March 15, 1952). The authors investigatedthe impris~ ~n- , ment time of a mercury vapor mixture consisting predcminantly of the single isotope Hg , with small impurities of Hg and Hg . ~hey tetermined that about a six fold longer imprisonment time occurred at vapor pressures in the vicinity of 6xlO torr than in natural mercury.
In no case did they observe an imprisonment time shorter than that of natural mercury Although the improvement in efficiency of converaion of electrical energy to mercury resonance radiation has been demonstrated primarily for 254 nm radiation, it is equally applicable to mercury resonance radiation at other frequencies, for example, 185 nm~ The 254 nm ratia-tion is of primary importance in fluorescent lamps ~hile 1~5 nm radiation is of importance in ozone producing devices as well as in some types of ¦
fluorescent lamps. -- 1 ~ .
Claims
1. A mercury-containing arc discharge device for converting electrical energy into resonance radiation, the isotopic distribution of the mercury being altered from that of natural mercury so as to reduce imprisonment time of resonance radiation, a thereby increasing the efficiency of converting electrical energy into resonance radiation.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000396601A CA1142215A (en) | 1978-09-05 | 1982-02-18 | Mercury arc discharge lamp with altered isotopic distribution of mercury |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US939,558 | 1978-09-05 | ||
| US05/939,558 US4379252A (en) | 1978-09-05 | 1978-09-05 | Arc discharge device containing HG196 |
| CA000333599A CA1136688A (en) | 1978-09-05 | 1979-08-10 | Mercury arc discharge lamp with altered isotopic distribution of the mercury |
| CA000396601A CA1142215A (en) | 1978-09-05 | 1982-02-18 | Mercury arc discharge lamp with altered isotopic distribution of mercury |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1142215A true CA1142215A (en) | 1983-03-01 |
Family
ID=27166361
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000396601A Expired CA1142215A (en) | 1978-09-05 | 1982-02-18 | Mercury arc discharge lamp with altered isotopic distribution of mercury |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1142215A (en) |
-
1982
- 1982-02-18 CA CA000396601A patent/CA1142215A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |