JPS6329773B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an electron emitting substance (emitter) sealed in an arc tube, which is different from the conventional method.

Generally, in order to make metal halide lamps easier to start, thorium (Th) or thorium oxide (ThO ₂ ) is mixed or applied to the electrodes as an emitter and sealed inside the arc tube. These electrons are used as seeds to start the discharge. In other words, conventional metal halide lamps of the 400W type use approximately 20 mg of thorium oxide coated on the electrodes, and it is known that thorium has a half-life T of 1.4 x 10 ¹⁰ years. The number of thorium atoms in 20 mg of thorium oxide is approximately 4.54 × 10 ¹⁹ and the total decay constant of thorium is 1.6 × 10 ^-18 sec ^-1 , so thorium in 20 mg of thorium oxide decays on average about 72 atoms per second. If we assume that one electron is created for each α particle, the initial number Q of electrons per second is approximately 72. on the other hand,
The average starting time τ from when a voltage is applied to the lamp until it starts is the probabilistic average time when the initial electrons are emitted until the start of discharge, and is
This average starting time τ is a function of the initial number Q of electrons emitted from the electrode per second and the probability P that one emitted electron starts a discharge, as follows: τ=1/P・Q...(1) Given.

Therefore, Q in 20 mg of thorium oxide is 72
Since P is generally considered to be about 0.5, this type of lamp has τ=0.028 seconds, and discharge starts instantly after voltage is applied.

On the other hand, in the case of lamps that do not use thorium at all, the only source that supplies the initial number of electrons per second, Q, is natural radiation such as cosmic rays, and the number of initial electrons per second is Q0.1. The degree is
It becomes τ20 seconds. In other words, the average starting time for lamps that do not use thorium is about 20 seconds, which means that you have to wait about 20 seconds after voltage is applied before starting. Failure to start may occur approximately 5% of the time.

Furthermore, lamps with a particularly high discharge starting voltage require a pulse voltage at the time of starting, and the probability P of starting discharge exists only while the pulse voltage is applied to such lamps. Those that do not use P0.01 as an average
Therefore, it reaches around τ1000 seconds, and discharge does not start for an average of 20 minutes after voltage application, and in some cases nearly an hour.

In this way, the use of thorium makes it easier to start the discharge and shortens the starting time, but as mentioned above, thorium has a half-life of 1.4
10 It is relatively long, ¹⁰ years, and it is desirable to emit at least one electron during one cycle in order to ensure reliable starting even at the end of the life after 5 years, so even after 5 years. The number of collapses per second is
50 to 60 or more are required, and therefore, when encapsulating in the form of thorium oxide, an amount of at least about 20 mg is required. However, thorium reacts with the halogen of the metal halide sealed in the arc tube to form thorium halide, which emits light and suppresses the light emission of other highly efficient fillers, causing a decrease in luminous flux. Thorium vapor causes an increase in lamp voltage during the life of the lamp. In this way, thorium reacts with halogen and disappears during its life, so if you want this type of lamp to start reliably and smoothly even at the end of its life, say 10,000 hours, an even larger amount of thorium oxide is needed. However, increasing the amount of thorium oxide has the disadvantage of further decreasing the luminous flux.

Therefore, the present inventors focused on using a radioactive substance with a shorter half-life than thorium as an emitter instead of thorium, and found that the amount of emitter used could be reduced. However, radioactive substances with a short half-life tend to have an adverse effect on the human body when handled, and there are problems such as the difficulty of sealing them into a valve.

This invention was made based on the above circumstances, and its purpose is to provide a method for manufacturing a metal vapor discharge lamp in which a radioactive substance with a short half-life can be safely and reliably sealed into an arc tube. That is.

The details of this invention will be explained below with reference to the drawings.

Figure 1 shows the arc tube of a metal halide lamp, where 1 is the arc tube bulb made of quartz glass, 2,
2 is a sealing part formed on both ends, 3, 3 is a main electrode,
4 is an auxiliary electrode for starting; 5, 5 and 6 are metal foil conductors 7, 7 and 8 sealed in the sealing parts 2 and 2 are external lead wires. The bulb 1 is filled with starting rare gases such as scandium iodide (Sc1), sodium iodide (Na1), mercury, and argon, as well as a radioactive substance.

Radioactive substances have a half-life of about 0.5 years to about 10 years, and the amount of radioactivity per arc tube is small.
It is regulated to less than 100 microcuries. Such radioactive substances include sodium-22 ( ²² Na), calcium-45 ( ⁴⁵ Ca), and manganese.
54 ( ⁵⁴ Mn), iron 55 ( ⁵⁵ Fe), cobalt 60 ( ⁶⁰ Co), zinc 65 ( ⁶⁵ Zn), ruthenium 106 ( ¹⁰⁶ Ru), silver 110
( ¹¹⁰ Ag), Antimony 125 ( ¹²⁵ Sb), Barium 133
( ¹³³ Ba), Cesium-134 ( ¹³⁴ Cs), Cerium-144
( ¹⁴⁴ Ce), Promethium-147 ( ¹⁴⁷ Pm), Eurobium-155 ( ¹⁵⁵ Eu), Gold-195 ( ¹⁹⁵ Au), Thallium-204
( ²⁰⁴ Tl) and Qulium 242 ( ²⁴² Cm). At least one of these radioactive substances is sealed within the arc tube bulb 1.

However, the half-life of radioactive substances is approximately 0.5 years or more.
Describe the reason why it is 10 years or less.

Generally, the lifespan of metal vapor discharge lamps, including metal halide lamps, is about 10,000 hours, and assuming that they are turned on and used for 5 hours a day, they need to operate normally for about 5 years. At this point, the half-life is approximately
If it is a radioactive substance that has been around for more than 0.5 years, after 5 years (1/
2) Since it is ¹⁰ 1/1000, the starting function can be maintained because the radioactivity does not completely decay. Conversely, if it is a radioactive substance with a half-life of less than 0.5 years,
Because the decay is rapid, the decay is completed during the life of the lamp, resulting in a significant decline in starting performance at the end of the lamp's life.

On the other hand, if the half-life is too long, it takes time for the radiation to decay, resulting in poor startability, and it becomes necessary to encapsulate a large amount of radioactive material. It is desirable that radioactive materials decay to a level that does not adversely affect the living environment in about 100 years, and 1/100 in 100 years.
Assuming that it decays to around 0, its half-life is about 10 years.

Furthermore, even if radioactive materials are handled in the form of a sealed source, they are regulated by law to be less than 100 microkyries, so the amount of radioactivity per arc tube is less than 100 microkyries. It is necessary to keep it.

For these reasons, it is desirable that the half-life of the radioactive material sealed in the arc tube be within the range of approximately 0.5 years or more and approximately 10 years or less, and the amount of radioactivity per arc tube should be 100 microcuries or less. Something is required.

However, such radioactive substances are used for the purpose of minimizing the amount of radioactive substances enclosed.
Therefore, let's consider how much of the above-mentioned radioactive material is required.

As mentioned above, if at least one radiation is emitted during one cycle, the radiation rate is 50 to 60 per second.
10 ² collapses per second, allowing for a safety factor.
Assuming that the decay of 100 pieces is required, in the case of a radioactive element with a half-life of 0.5 years, after 5 years it will be approximately 2.3×
10 ⁹ elements are required, and at the beginning of inclusion
2.3×10 ¹² pieces will be required. In addition, in the case of radioactive elements with a half-life of 10 years, approximately
The number of elements is 4.5×10 ¹⁰ , and the same number of 4.5×10 ¹⁰ is required at the beginning of packaging. The number of these elements is 1/10 ⁷ to 1/10 ⁹ smaller than the 4.5×10 ¹⁹ elements of conventional thorium. Therefore, the radioactive material of the present invention can be It can be seen that the amount of encapsulation can be reduced by comparison.

In the case of a 400W metal halide lamp, about 30 mg of luminescent metals, Sc and Na, are enclosed in the form of iodides, and the number of Sc and Na elements in this weight is about ¹⁰²⁰ . According to the experiments of the present inventors, if the number of elements of the radioactive material is less than 1/1000 of the number of elements of the luminescent metal, the chemical influence of the radioactive element, that is, the formation of halogenated substances, can be ignored and black It has been found that it is possible to prevent luminescence to the extent that it causes oxidation and a decrease in luminous flux. Therefore, if it is a radioactive substance with a half-life of about 0.5 years or more but less than about 10 years, the amount of encapsulation is small, so it is possible to create a substance that reacts with halogen. Therefore, a decrease in luminous flux is less likely to occur during long-term use.

Therefore, a method for sealing the radioactive substance as described above in an arc tube will be explained. The above-mentioned radioactive substances are dangerous if their radioactivity scatters during handling, so they must be handled in the form of a sealed source. For this reason, in this embodiment, as shown in FIG. 2, a radioactive substance 9 is coated in advance on the auxiliary electrode 4 made of pure tungsten, and this radioactive substance 9 is further hermetically coated with a non-radioactive substance 10. Specifically, the tip portion of the auxiliary electrode 4 is plated with a radioactive substance 9, and the outer surface of the auxiliary electrode 4 is plated with a non-radioactive substance. In this case, the non-radioactive substance is preferably a luminescent metal or its oxide sealed in the arc tube, and may be a non-radioactive isotope of the radioactive substance, but it must not remain as an impurity in the arc tube, and The condition is that it can be easily peeled off in the removal process of the coating 10, which will be described later.

The starting auxiliary electrode 4 configured in this manner is incorporated into the bulb 1 to complete the arc tube. After that, a glow discharge is caused between the starting auxiliary electrode 4 and the main electrode 3 adjacent thereto, and then the main electrode 3,
Flushing is performed by generating a discharge during the 3-hour period. Then, the heat and the impact of charged particles generated along with this flashing discharge are applied to the starting auxiliary electrode 4, and the coating 10 is removed, and the radioactive substance 9
appears in the discharge space, the radioactive substance 9 will be diffused into the discharge space.

According to this method, since the radioactive substance 9 is held in the form of a sealed radiation source in the starting electrode 4, radiation is not emitted during handling of the auxiliary electrode 4, making it safe. Since the radioactive substance 9 is sealed in the bulb 1 by simply sealing the electrode 4 in the bulb 1, there is no need to change the conventional work process. Since the coating 10 is removed by flushing after the lamp is completed, no special means for peeling off the coating 10 is required, and the work of enclosing the radioactive substance 9 can be carried out very easily.

Note that embodiments of the present invention will be described.

[Example 1] Promethium 147 ( ¹⁴⁷ Pm) was applied 5 times to a starting auxiliary electrode made of pure tungsten with an outer diameter of 0.2 mm and a length of 15 mm over a 5 mm length from its tip.
It is plated with 10 ^-6 mg and then plated with scandium Sc to form a sealed radiation source. This starting auxiliary electrode is sealed in a quartz bulb with an inner diameter of 20 mm and a distance between main electrodes of 42 mm, and this bulb is filled with 30 mg of scandium sodium iodide, 50 mg of mercury, and 25 torr of argon gas for 400W. Make a metal halide lamp. After performing glow discharge for 3 minutes and removing the coating, apply 200V AC, 1500V height, 1.25μS width.
When I superimposed a pulse voltage on it, it started so instantaneously that it could not be measured with a stopwatch. and
The luminous flux after 1000 hours of lighting was 1.25 times that of conventional thorium-based products. Note that ¹⁴⁷ Pm has a half-life of β decay of 2.7 years, and releases 5 microcuries at 5×10 ⁻⁶ mg, or 18.5×10 ⁴ electrons per second. Even after eight years, it still emits 23,000 electrons every second.

[Example 2] A 100 Watt metal halide lamp arc tube with an inner diameter of 10 mm and a distance between main electrodes of 12 mm was charged with 5 mg of mercury and scandium.
Fill with 5 mg of sodium iodide and 80 torr of argon. In the case of this lamp, a radioactive element is sealed in the main electrode 3 shown in FIG. This is shown in FIG. 11 is the main axis of the electrode, 12 is the electrode coil, 9' is plated with 50 microcuries of Na ²² , and 10' is scandium metal coated on top of it to seal the Na ²² . It is about 0.1 mg. This electrode may be either one of the main electrodes, and the other main electrode may be a normal one.

In this example, 200V can be instantaneously generated without having to go through the scandium metal melting process using glow discharge in advance.
I was able to start it with power. However, a pulse voltage of 1.5 microseconds in width and 300V in height is applied to the power supply voltage. This is because the γ-rays and β ⁺ rays emitted by the decay of Na ²² in a sealed state pass through the scandium metal layer and are emitted into the discharge lamp arc tube, ionizing argon or mercury, etc.
Initial discharge electrons are generated by secondary electron emission at the wall of the arc tube. The half-life of Na ²² is 2.58 years, and the discharge lamp was lit for an average of 3 hours a day, and the discharge lamp started up 10 years later as well. In this case, the amount of radioactivity of Na ²² in the arc tube is approximately
It is estimated that the attenuation was 0.068 times, or about 3.4 microcuries, but no deterioration in startability was observed.

[Example 3] A 400 Watt metal halide lamp arc tube with an inner diameter of 20 mm and a distance between electrodes of 60 mm was filled with 17 mg of sulfur iodide, 50 mg of mercury, and 50 torr of xenon as a starting gas.

FIG. 4 shows the vicinity of the electrode. The main shaft 15 has an electrode coil 16 and a metal oxide and tungsten powder sintered emitter 17. The radioactive element Co ⁶⁰ (cobalt) 9" was plated with 45 microcuries. The top was plated with 10" of tin metal to seal the radioactive element 19.

Such main electrodes may be either or both main electrodes of the arc tube configured as shown in FIG.

When a pulse voltage with a pulse width of 5 microseconds and a height of 1500 V is superimposed on an AC commercial frequency voltage of 240 V and is applied to the lamp, it starts immediately. The lamp without the radioactive element encapsulation required pulsing for about 15 seconds. Further, the half-life of Co ⁶⁰ is 5.24 years, and after 10 years, about 1/4, or about 11 microcuries, remains, and it retains sufficient effectiveness. No significant influence of these radioactive elements was observed in terms of luminescence characteristics. Although the arc tube with the above configuration containing 10 mg of Th is started within a few cycles of the power supply waveform, luminescence of Th metal is observed after about 100 hours of life.
The color rendering properties deteriorated. In other words, the initial average color rendering index Ra = 92 did not change during the lifetime of the Co ⁶⁰ -sealed one, whereas the Th-sealed one did not change.
It decreased to Ra=85 in 1000 hours.

All types of luminescent metals sealed in the arc tube can be used except thorium, but scandium (Sc), yttrium (Y), rare earth metals, aluminum (Al), and sodium (Na), which have particularly high efficiency, can be used. , thallium (Tl), indium (In)
It is effective for metal vapor discharge lamps containing at least one of tin (Sn) and tin (Sn), which has good color rendering properties.

Furthermore, in the above embodiments, the starting auxiliary electrode was described as a carrier for the radioactive substance, but the carrier may of course be the main electrode, and especially in discharge lamps that do not use a starting auxiliary electrode, the main electrode is used. It is.

The invention described in detail above involves holding an electrode in advance with a radioactive substance having a half-life of about 0.5 years to about 10 years and an amount of radioactivity of 100 microcuries or less per arc tube. After the holding part is hermetically coated with a non-radioactive substance and such an electrode is sealed inside the arc tube, the coating is removed by heat or electron impact caused by the discharge between the electrodes, and the radioactive substance is released into the arc tube. It was designed to be enclosed in Therefore, according to this product, since the electrode is coated with radioactive material during handling, it is safe, and since it can be handled in the same way as conventional electrodes, it is easy to seal the electrode in the arc tube, and it is easy to seal the electrode. At the same time, radioactive materials are also introduced into the arc tube.
Moreover, since the coating is peeled off as a result of the discharge between the electrodes, the work of sealing the radioactive substance into the arc tube can be carried out very easily.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; FIG. 1 is a front view of the arc tube, FIG. 2 is a sectional view of the starting auxiliary electrode before sealing, and FIGS. 3 and 4 are views of other embodiments. It is a partial cross-sectional view of the main part. 1... Arc tube bulb, 3, 3... Main electrode, 4... Auxiliary electrode for starting, 9, 9', 9''... Radioactive material, 10,
10', 10''...Coating.

Claims (1)

[Claims] 1. A radioactive substance having a half-life of about 0.5 years or more and about 10 years or less and an amount of radioactivity per arc tube of 100 microcuries or less is held in an electrode in advance, and this radioactive substance is held in an electrode. After sealing the electrode with a non-radioactive substance and sealing it inside the arc tube, the coating is removed by heat or electron impact caused by the discharge between the electrodes, and the radioactive substance is exposed inside the arc tube. A method for manufacturing a metal vapor discharge lamp, characterized in that: 2 The above radioactive substances are ²² Na, ⁴⁵ Ca, ⁵⁴ Mn, ⁵⁵ Fe,
⁶⁰ Co, ⁶⁵ Zn, ¹⁰⁶ Ru, ¹¹⁰ Ag, ¹²⁵ Pb, ¹³³ Ba, ¹³⁴ Cs,
The method for manufacturing a metal vapor discharge lamp according to claim 1, characterized in that the material is at least one of ¹⁴⁴ Ce, ¹⁴⁷ Pm, ¹⁵⁵ Eu, ¹⁹⁵ Au, ²⁰⁴ Tl, and ²⁴² Cm. 3. The metal vapor discharge lamp according to claim 1, wherein the arc tube is provided with an auxiliary starting electrode, and the auxiliary starting electrode is used as a holder for the radioactive substance. manufacturing method.