- Email: [email protected]
The search for an ultra-thin tritium source for the neutrino mass measurement
Nuclear Instruments and Methods in Physics Research B10/11(1985) 382-386
382
North-Holland, Amsterdam
THE SEARCH FOR AN ULTRA-THIN MEASUREMENT J.L. GALLANT
TRITIUM SOURCE FOR THE NEUTRINO MASS
and P. DMYTRENKO
Atomic Energy of Canada Limited Chalk River Nuclear Laboratories, Chalk River, Ontario, Canada KW IJO
The mass of the electron anti-neutrino can be determined from a precise measurement of the shape of the tritium spectrum near its end point. Several methods of producing appropriate tritium sources have been investigated including the tritiating of ultra-thin titanium films on quartz substrates.
1. Intruduction The Chalk River rrfi iron-free beta spectrometer has been recommissioned and is being upgraded for a precise measurement of the shape of the tritium spectrum near the end-point [I], from which the mass of the electron anti-neutrino can be determined. The experiment now being planned at Chalk River is the result of’ the interest stirred by the report of a non-zero mass by Lubimov et al. [2]. This paper is concerned only with the search for an appropriate tritium source for ‘the neutrino-mass experiment. The constancy of source quality during the experiment is essential as one must know the energy-loss contribution to the energy response function when analysing the experimental data in order to interpret it quantitatively. Also of concern are energy shifts in the beta spectrum due to the final state excitation of the ‘He atom whose contribution depends on the nature of the sour&uce matrix. For these reasons several experimental methods have been investigated. They are: (1) The preparation of deuterium-rich carbon films prepared by the glow discharge cracking of hydrocarbons. (2) The fabrication of polyethylene films by dilution. (3) The evaporation of polyethylene in vacuum. (4) The preparation of ultra-thin titanium deuteride films. For obvious reasons, deuterium was used in all the tests, and its content measured by the 2H(3He, P)~H~ reaction.
mining large quantities of hydrogen is produced. Investigations of the hydrogen wntent by several laboratories [3-51 have found concentrations of 30 to 50 at. %. The carbon-hydrogen structure appears to be stable at room temperature. Deuterated acetylene was prepared by heating a barium-carbonate magnesium-metal mixture to 800°C and reacting the magnesium carbide with 99.8% deuterium oxide to form the deuterad hydrocarbon. The acetylene was cracked by high-voltage glow discharge and the carbon collected on an aluminum substrate. 2.2. Fabrication of thin polyethylene films by dilution For experimental purposes, 200 mg. of deuterated polyethylene CD,. CD, was dissolved in 200 ml of xylene and heated to just below the boiling point (= 100°C). Aluminum substrates were dipped in the solution and cooled. The substrates were heated to 100°C to repolymerize the polyethylene. 2.3. The evaporation of polyethylene in vacuum Deuterated polyethylene in a molybdenum boat was sublimed in vacuum starting at a pressure of 10T4 Pa (1O-6 Torr) and collected on an aluminum substrate. 2.4. The preparation of ultra-thin titanium deuteride films Titanium was evaporated from a titanium filament onto a quartz substrate heated to 400°C. The titanium films were then exposed to a 13 kPa (100 Torr) pressure of deuterium.
2. General procedures 2.5. Deuterium content 2.1. The preparation of deuterium rich curbon films When a hydrocarbon such as acetylene CH CH is cracked in a high voltage glow discharge, carbon wn0168-583X/85/$03.30 @ Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
The deuterium content was measured by the 2H(3He, p)4He reaction at 700 keV in a precalibrated experimental setup. Deuterium-rich carbon films and
J. L Gallant, P. Dmytrenko / Search for an ultra-thin tritium source
383
the deuterated polyethylene layers did not appear uniform nor did they show reproducible deuterium concentration. However the titanium deuteride films were uniform and did show better deuterium occlusion as discussed later. Therefore this paper will be concerned primarily with the investigation of the titanium deuteride films.
3. The preparation aud characterization of ultra-thin titanium deuterfde films Titanium is an excellent getter@ material. To assure the highest purity possible in a sublimited titanium film, one must use clean and very low pressure techniques. For this reason a bakeable vacuum system has been constructed (fig. 1). It consists of a stainless steel chamber with several feedthroughs required to evaporate titanium, heat a substrate, measure fihn conductance and carry thickness monitoring signals (fig. 2). It is equipped with a moveable mask, which is operated externally through a stainless steel bellows. It also contains a crystal thickness-monitor sensor head. The chamber is evacuated by an ion and titanium pump combination, the initial vacuum being achieved by turbo-molecular pumping. The reaction chamber is isolated by a high vacuum valve. 3. I. Detailed procedure Quartz substrates were chemically cleaned and placed onto a substrate heater. A titanium filament (1 mm thick) was placed between two large titanium metal cylinders 2.5 cm diameter fixed to two copper feedthroughs. The evaporation-source configuration restricted high temperatures to the filament and avoided excessive degassing of the copper electrical feedthroughs. The system was evacuated and baked, and the substrate
Fig. 2. The top section of the apparatus in fig. 1, which will contain the rectangular quartz plate holder with substrate heater. The baffle plate at the right can be actuated externally. The crystal thickness-sensor head is shown at the left.
heated to 400°C. When a pressure of lo-’ Pa (10v9 Torr) had been achieved, the filament was heated slowly and = 100 A of titanium sublimed into the chamber while the mask was in position. The mask was then removed and the required thickness of titanium evaporated onto the quartz substrate. Next, the high vacuum valve was closed and deuterium introduced to a pressure of 13 kPa (100 Torr) for several hours. The substrate was cooled and the titanium deuteride fihn assemblies were removed and kept under argon. 3.2. Results The titanium thickness was determined by Rutherford Scattering of a ‘He beam from a 2 MeV accelerator. The deuterium content was measured, as already
Table 1 Titanium thickness measurements
Fig. 1. Photograph of apparatus constructed to produce titanium Wide sources.
Sample #
Measurement of titanium thickness of quartz crystal frequency monitoring
Measurement of titanium by the Rutherford Scattering of a H beam
1 2 3 4 5 6 7 8 9 10 11 12
1.0 1.04 1.5 1.5 1.5 2.0 2.0 2.27 3.0 5.0 5.2 10.0
1.37 0.98 1.53 1.73 1.80 1.77 2.34 2.12 2.43 4.31 6.0 9.50
III. NUCLEAR
PHYSICS/ASTROPHYSICS
J. L. Gallant, P. Dmytrenko / Search for an ultra -thin tritium source
384
I I I I I /
I I I
Ij/// /
I I I I I I
I I
.?
I
/
I
Fig. 4. Auger survey spectrum from the surface of a “thick” titanium deuteride fii on gold substrate. The titanium layer had a nominal thickness of 66 A (i.e. about 3 rg/cm2).
I
I
I
/ 1
Fig. 3. Graph of deutekm
2
3
4
5
concentration versus titanium
thickness.
described by the reaction ‘H(‘He, p)4He. The measured thickness of the titanium was in good agreement with the “m-situ” crystal thickness monitor measurement (table 1). The uptake of deuterium was found to be dependent upon the absence of oxygen nitrogen and hydrocarbons from the titanium enviromnent during the evaporation and the occlusion. Fig. 3 shows the deuterium uptake in ng/ctr? as a function of the titanium thickness determined by Rutherford Scattering. These results imply oxidation of the first 1.3 pg/c& of titanium and a D to Ti ratio of about 1.5 : 1 in the non-oxidized region of the thick film.
4. characterization
of titanium &uteri&
the fihu is composed of titanium oxygen and carbon. Auger analysis of a second, thinner sample (nominally 22 A) of Ti on a fold substrate, which had been prepared under much better vacuum and clean conditions, showed carbon and oxygen in lesser quantity. In this sample (figs. 6 and 7) Auger peaks from the gold substrate are detectable at the surface probably because of clustering or alloying due to the 400°C substrate temperature.
“9-r
90
.
DEPIW SPullER
90
.
70
-
PROFILE FloM
5AMPLE
1
Au
RATE 4NMmN
1
films by Auger
adysis
Samples of thin titanium films prepared on gold substrate (instead of quartz) were examined in an Auger scanning microscope. Profiling was carried out by rasteringanAr+ionbeamoveralxlmn?areatogivea = 35 PA/& ion-current density. A sample of titanium, 66 A thick on a gold backing, which had been prepared at higher pressures (i.e. under less than ideal conditions), showed silicon, carbon and oxygen surface contamination (fig. 4). Subsequent depth profiling (fig. 5) showed that the silicon is only present in the first 20 A and that
SPUTTER TIME
MIN
Fig. 5. Depth profile of the sample described in fig. 4.
J. L. Gallant, P. Dmytrenko / Search for an ultra-thin tritium source
Fig. 6. Auger survey spectrum from the surface of a thinner titanium deuteride on gold substrate. The nominal thickness of titanium in this case was = 22 A ( = 1 pg/d).
4. I. Electrical conductance of evaporated and deuterated titanium films
In order to study the effects of deuteration and oxidation of thin titanium films, an experiment was done in which the film resistance was monitored during and after deposition. A 1.7 mm wide by 60 mm long strip of titanium was evaporated on a quartz substrate heated to 300°C between previously evaporated gold contacts. Electrical conductivity between the gold contacts was first observed after about 3 A of titanium had
lob
MPTH GUTTER
90 .
PROFILE FROM SAMPLE 2 RATE 1.e NM&IN
NOTECLEVELISTOO
HK3I
DUET0
INTERFERENCE
FROM A
MINOR
Au PEAK tC IS NOl
00
I
Fig. 8. EIeetricaI conductance of an evaporated titanium deuteride layer of nominal thickness 22 i\ (1 rg/cm*). Oxidation of the surface of the titanium as a function of time is deduced from the decrease in electrical conductance.
been evaporated. At the final thickness of 22 A the resistance was 23.4 kB, corresponding to a bulk resistance of about 151 pba. This is comparable to published values for fihns evaporated under similar vacuum conditions of 10m5 Pa (10F7 Torr). The deuterium was begun by filling the chamber with D, from a heated uranium trap, and the uptake was completed in 3.4 min, as monitored by the resistance which increased from 23.4 kS1 to about 33.4 kO. When the fihn was exposed to air the resistance rose rapidly at first and then more slowly. Taking the initial titanium thickness from the thickness monitor and making the simple assumption that the electrical conductivity is proportional to the thickness of the conducting titanium layer, we deduce the curve in fig. 8, a plot of the “oxide thickness” versus the logarithm of the time. The near linearity of the plot is striking and it represents a rate of growth of the oxide layer that varies inversely with time. The deuterated film was much more resistant to oxidation than a similar non-deuterated titanium film tested earlier. In that case the fii resistance doubled in less than 3 min as compared to about 24 h for the deuterated film.
5. doaelllsion
MTECTARLE
n 1
385
2
3
SPUTTER TIME MIN
Fig. 7. Depth profile of the sample described in fig. 6.
To measure precisely the shape of the tritium spectrum near the endpoint, up to two hundred conducting source-strips, 100 mm long X 1 mm wide on a 1 m radius, will be required (fig. 9). Each source will have a tritium content of 10 ng/c& or 2: 0.9 mCi 3H. The results of the Auger analysis and the conductance experiment provide an explanation of why the intake of deuterium was so low in earlier thin films, i.e. for fii of 1 &cm*, the thickness required Necessary steps III. NUCLEAR PHYSICS/ASTROPHYSICS
386
J.L.. Gallant, P. Dmytrenko / Search for an ultra-thin tritium source 200 CONDUCTINGSOURCE STRIPS EACH .9mm WIDE x 100mm HIGH
The authors wish to thank Drs R.L. Graham, H.R. Andrews and J.S. Geiger for their invaluable assistance and council. We also wish to thank H. Plattner of the Solid State Science Branch for the titanium and deuterium measurements and R.D. Davidson of Systems Materials Branch for the Auger analysis.
References
Ul R.L. Graham, M.A. Lone, H.R. Andrews, J.S. Geiger, J.L.
I2 to 6kVl
Fig. 9. Schematic of multi-element titanium tritide source.
such as improving the vacuum and keeping prepared source under argon can now be taken to improve the procedure of preparing very thin titanium tritide films of acceptable source strength. We now have high hopes of achieving the tritium concentrations needed, and of producing acceptable sources for the neutrino-mass experiment.
Gallant, J.W. Knowles, H.C. Lee and G.E. Lee-Whiting, AECL-7094 (1982). PI V.A. Lubimov, E.G. Novikov, V.Z. Nozik, E.F. Tretyakov, V.S. Kozik and N.F. Myasoedov, Phys. L&t. 94B (1980) 266. [31 N.R.S. Tait, D.W.L. Toefree, P. John, I.M. Odeh, M.J.K. Thomas, M.J. Tricker, J.J. Wilson, J.B.A. England and D. Newton, Nucl. Instr. and Meth. 176 (9180) 433. 141 B. Huck, E. Jaeschke, W. Kratschmer, R. Repnow and H. Wirth, Nucl . Instr. and Meth. 184 (1981) 215. 151 G.C. Ball, J.S. Forster and J.L. Gallant, AECL Progress Report RP-P-128; AECG7234 (2.25), 1980. 161 S.L. Lehoczky, R.J. Lederich and J.J. Bellina Jr, Thin Solid Films 55 (1978) 125.
382
North-Holland, Amsterdam
THE SEARCH FOR AN ULTRA-THIN MEASUREMENT J.L. GALLANT
TRITIUM SOURCE FOR THE NEUTRINO MASS
and P. DMYTRENKO
Atomic Energy of Canada Limited Chalk River Nuclear Laboratories, Chalk River, Ontario, Canada KW IJO
The mass of the electron anti-neutrino can be determined from a precise measurement of the shape of the tritium spectrum near its end point. Several methods of producing appropriate tritium sources have been investigated including the tritiating of ultra-thin titanium films on quartz substrates.
1. Intruduction The Chalk River rrfi iron-free beta spectrometer has been recommissioned and is being upgraded for a precise measurement of the shape of the tritium spectrum near the end-point [I], from which the mass of the electron anti-neutrino can be determined. The experiment now being planned at Chalk River is the result of’ the interest stirred by the report of a non-zero mass by Lubimov et al. [2]. This paper is concerned only with the search for an appropriate tritium source for ‘the neutrino-mass experiment. The constancy of source quality during the experiment is essential as one must know the energy-loss contribution to the energy response function when analysing the experimental data in order to interpret it quantitatively. Also of concern are energy shifts in the beta spectrum due to the final state excitation of the ‘He atom whose contribution depends on the nature of the sour&uce matrix. For these reasons several experimental methods have been investigated. They are: (1) The preparation of deuterium-rich carbon films prepared by the glow discharge cracking of hydrocarbons. (2) The fabrication of polyethylene films by dilution. (3) The evaporation of polyethylene in vacuum. (4) The preparation of ultra-thin titanium deuteride films. For obvious reasons, deuterium was used in all the tests, and its content measured by the 2H(3He, P)~H~ reaction.
mining large quantities of hydrogen is produced. Investigations of the hydrogen wntent by several laboratories [3-51 have found concentrations of 30 to 50 at. %. The carbon-hydrogen structure appears to be stable at room temperature. Deuterated acetylene was prepared by heating a barium-carbonate magnesium-metal mixture to 800°C and reacting the magnesium carbide with 99.8% deuterium oxide to form the deuterad hydrocarbon. The acetylene was cracked by high-voltage glow discharge and the carbon collected on an aluminum substrate. 2.2. Fabrication of thin polyethylene films by dilution For experimental purposes, 200 mg. of deuterated polyethylene CD,. CD, was dissolved in 200 ml of xylene and heated to just below the boiling point (= 100°C). Aluminum substrates were dipped in the solution and cooled. The substrates were heated to 100°C to repolymerize the polyethylene. 2.3. The evaporation of polyethylene in vacuum Deuterated polyethylene in a molybdenum boat was sublimed in vacuum starting at a pressure of 10T4 Pa (1O-6 Torr) and collected on an aluminum substrate. 2.4. The preparation of ultra-thin titanium deuteride films Titanium was evaporated from a titanium filament onto a quartz substrate heated to 400°C. The titanium films were then exposed to a 13 kPa (100 Torr) pressure of deuterium.
2. General procedures 2.5. Deuterium content 2.1. The preparation of deuterium rich curbon films When a hydrocarbon such as acetylene CH CH is cracked in a high voltage glow discharge, carbon wn0168-583X/85/$03.30 @ Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
The deuterium content was measured by the 2H(3He, p)4He reaction at 700 keV in a precalibrated experimental setup. Deuterium-rich carbon films and
J. L Gallant, P. Dmytrenko / Search for an ultra-thin tritium source
383
the deuterated polyethylene layers did not appear uniform nor did they show reproducible deuterium concentration. However the titanium deuteride films were uniform and did show better deuterium occlusion as discussed later. Therefore this paper will be concerned primarily with the investigation of the titanium deuteride films.
3. The preparation aud characterization of ultra-thin titanium deuterfde films Titanium is an excellent getter@ material. To assure the highest purity possible in a sublimited titanium film, one must use clean and very low pressure techniques. For this reason a bakeable vacuum system has been constructed (fig. 1). It consists of a stainless steel chamber with several feedthroughs required to evaporate titanium, heat a substrate, measure fihn conductance and carry thickness monitoring signals (fig. 2). It is equipped with a moveable mask, which is operated externally through a stainless steel bellows. It also contains a crystal thickness-monitor sensor head. The chamber is evacuated by an ion and titanium pump combination, the initial vacuum being achieved by turbo-molecular pumping. The reaction chamber is isolated by a high vacuum valve. 3. I. Detailed procedure Quartz substrates were chemically cleaned and placed onto a substrate heater. A titanium filament (1 mm thick) was placed between two large titanium metal cylinders 2.5 cm diameter fixed to two copper feedthroughs. The evaporation-source configuration restricted high temperatures to the filament and avoided excessive degassing of the copper electrical feedthroughs. The system was evacuated and baked, and the substrate
Fig. 2. The top section of the apparatus in fig. 1, which will contain the rectangular quartz plate holder with substrate heater. The baffle plate at the right can be actuated externally. The crystal thickness-sensor head is shown at the left.
heated to 400°C. When a pressure of lo-’ Pa (10v9 Torr) had been achieved, the filament was heated slowly and = 100 A of titanium sublimed into the chamber while the mask was in position. The mask was then removed and the required thickness of titanium evaporated onto the quartz substrate. Next, the high vacuum valve was closed and deuterium introduced to a pressure of 13 kPa (100 Torr) for several hours. The substrate was cooled and the titanium deuteride fihn assemblies were removed and kept under argon. 3.2. Results The titanium thickness was determined by Rutherford Scattering of a ‘He beam from a 2 MeV accelerator. The deuterium content was measured, as already
Table 1 Titanium thickness measurements
Fig. 1. Photograph of apparatus constructed to produce titanium Wide sources.
Sample #
Measurement of titanium thickness of quartz crystal frequency monitoring
Measurement of titanium by the Rutherford Scattering of a H beam
1 2 3 4 5 6 7 8 9 10 11 12
1.0 1.04 1.5 1.5 1.5 2.0 2.0 2.27 3.0 5.0 5.2 10.0
1.37 0.98 1.53 1.73 1.80 1.77 2.34 2.12 2.43 4.31 6.0 9.50
III. NUCLEAR
PHYSICS/ASTROPHYSICS
J. L. Gallant, P. Dmytrenko / Search for an ultra -thin tritium source
384
I I I I I /
I I I
Ij/// /
I I I I I I
I I
.?
I
/
I
Fig. 4. Auger survey spectrum from the surface of a “thick” titanium deuteride fii on gold substrate. The titanium layer had a nominal thickness of 66 A (i.e. about 3 rg/cm2).
I
I
I
/ 1
Fig. 3. Graph of deutekm
2
3
4
5
concentration versus titanium
thickness.
described by the reaction ‘H(‘He, p)4He. The measured thickness of the titanium was in good agreement with the “m-situ” crystal thickness monitor measurement (table 1). The uptake of deuterium was found to be dependent upon the absence of oxygen nitrogen and hydrocarbons from the titanium enviromnent during the evaporation and the occlusion. Fig. 3 shows the deuterium uptake in ng/ctr? as a function of the titanium thickness determined by Rutherford Scattering. These results imply oxidation of the first 1.3 pg/c& of titanium and a D to Ti ratio of about 1.5 : 1 in the non-oxidized region of the thick film.
4. characterization
of titanium &uteri&
the fihu is composed of titanium oxygen and carbon. Auger analysis of a second, thinner sample (nominally 22 A) of Ti on a fold substrate, which had been prepared under much better vacuum and clean conditions, showed carbon and oxygen in lesser quantity. In this sample (figs. 6 and 7) Auger peaks from the gold substrate are detectable at the surface probably because of clustering or alloying due to the 400°C substrate temperature.
“9-r
90
.
DEPIW SPullER
90
.
70
-
PROFILE FloM
5AMPLE
1
Au
RATE 4NMmN
1
films by Auger
adysis
Samples of thin titanium films prepared on gold substrate (instead of quartz) were examined in an Auger scanning microscope. Profiling was carried out by rasteringanAr+ionbeamoveralxlmn?areatogivea = 35 PA/& ion-current density. A sample of titanium, 66 A thick on a gold backing, which had been prepared at higher pressures (i.e. under less than ideal conditions), showed silicon, carbon and oxygen surface contamination (fig. 4). Subsequent depth profiling (fig. 5) showed that the silicon is only present in the first 20 A and that
SPUTTER TIME
MIN
Fig. 5. Depth profile of the sample described in fig. 4.
J. L. Gallant, P. Dmytrenko / Search for an ultra-thin tritium source
Fig. 6. Auger survey spectrum from the surface of a thinner titanium deuteride on gold substrate. The nominal thickness of titanium in this case was = 22 A ( = 1 pg/d).
4. I. Electrical conductance of evaporated and deuterated titanium films
In order to study the effects of deuteration and oxidation of thin titanium films, an experiment was done in which the film resistance was monitored during and after deposition. A 1.7 mm wide by 60 mm long strip of titanium was evaporated on a quartz substrate heated to 300°C between previously evaporated gold contacts. Electrical conductivity between the gold contacts was first observed after about 3 A of titanium had
lob
MPTH GUTTER
90 .
PROFILE FROM SAMPLE 2 RATE 1.e NM&IN
NOTECLEVELISTOO
HK3I
DUET0
INTERFERENCE
FROM A
MINOR
Au PEAK tC IS NOl
00
I
Fig. 8. EIeetricaI conductance of an evaporated titanium deuteride layer of nominal thickness 22 i\ (1 rg/cm*). Oxidation of the surface of the titanium as a function of time is deduced from the decrease in electrical conductance.
been evaporated. At the final thickness of 22 A the resistance was 23.4 kB, corresponding to a bulk resistance of about 151 pba. This is comparable to published values for fihns evaporated under similar vacuum conditions of 10m5 Pa (10F7 Torr). The deuterium was begun by filling the chamber with D, from a heated uranium trap, and the uptake was completed in 3.4 min, as monitored by the resistance which increased from 23.4 kS1 to about 33.4 kO. When the fihn was exposed to air the resistance rose rapidly at first and then more slowly. Taking the initial titanium thickness from the thickness monitor and making the simple assumption that the electrical conductivity is proportional to the thickness of the conducting titanium layer, we deduce the curve in fig. 8, a plot of the “oxide thickness” versus the logarithm of the time. The near linearity of the plot is striking and it represents a rate of growth of the oxide layer that varies inversely with time. The deuterated film was much more resistant to oxidation than a similar non-deuterated titanium film tested earlier. In that case the fii resistance doubled in less than 3 min as compared to about 24 h for the deuterated film.
5. doaelllsion
MTECTARLE
n 1
385
2
3
SPUTTER TIME MIN
Fig. 7. Depth profile of the sample described in fig. 6.
To measure precisely the shape of the tritium spectrum near the endpoint, up to two hundred conducting source-strips, 100 mm long X 1 mm wide on a 1 m radius, will be required (fig. 9). Each source will have a tritium content of 10 ng/c& or 2: 0.9 mCi 3H. The results of the Auger analysis and the conductance experiment provide an explanation of why the intake of deuterium was so low in earlier thin films, i.e. for fii of 1 &cm*, the thickness required Necessary steps III. NUCLEAR PHYSICS/ASTROPHYSICS
386
J.L.. Gallant, P. Dmytrenko / Search for an ultra-thin tritium source 200 CONDUCTINGSOURCE STRIPS EACH .9mm WIDE x 100mm HIGH
The authors wish to thank Drs R.L. Graham, H.R. Andrews and J.S. Geiger for their invaluable assistance and council. We also wish to thank H. Plattner of the Solid State Science Branch for the titanium and deuterium measurements and R.D. Davidson of Systems Materials Branch for the Auger analysis.
References
Ul R.L. Graham, M.A. Lone, H.R. Andrews, J.S. Geiger, J.L.
I2 to 6kVl
Fig. 9. Schematic of multi-element titanium tritide source.
such as improving the vacuum and keeping prepared source under argon can now be taken to improve the procedure of preparing very thin titanium tritide films of acceptable source strength. We now have high hopes of achieving the tritium concentrations needed, and of producing acceptable sources for the neutrino-mass experiment.
Gallant, J.W. Knowles, H.C. Lee and G.E. Lee-Whiting, AECL-7094 (1982). PI V.A. Lubimov, E.G. Novikov, V.Z. Nozik, E.F. Tretyakov, V.S. Kozik and N.F. Myasoedov, Phys. L&t. 94B (1980) 266. [31 N.R.S. Tait, D.W.L. Toefree, P. John, I.M. Odeh, M.J.K. Thomas, M.J. Tricker, J.J. Wilson, J.B.A. England and D. Newton, Nucl. Instr. and Meth. 176 (9180) 433. 141 B. Huck, E. Jaeschke, W. Kratschmer, R. Repnow and H. Wirth, Nucl . Instr. and Meth. 184 (1981) 215. 151 G.C. Ball, J.S. Forster and J.L. Gallant, AECL Progress Report RP-P-128; AECG7234 (2.25), 1980. 161 S.L. Lehoczky, R.J. Lederich and J.J. Bellina Jr, Thin Solid Films 55 (1978) 125.