Division Particle & Astroparticle Physics
 
 

Research: History

Earlier Neutrino Physics Projects at MPIK



1) The GALLEX / GNO Experiments


A main target in 20th century astrophysical research was the Sun. Understanding of the structure and the processes inside the Sun is mandatory for any kind of star formation, galaxy formation or cosmological models. As the sun is the closest star, it offers a unique approach for observation. Hans Bethe and some others developed in 1938 a model, explaining the energy production in stars and especially inside the Sun by nuclear fusion process of protons. Together with a model of the structure of the Sun and the conditions in its center (temperature, pressure, particle density etc.) this reaction chain predicts an enormous flux of neutrinos, roughly 100 billion per second through a thumbnail, spread over a wide range of energy (0.1 - 15 MeV).


Calculated energy spectrum of the solar neutrinos (with 1 standard deviation uncertainty) according to the Standard Solar Model [1].

Ray Davis and coworkers were the first who tried to observe solar neutrinos with a radiochemical detector. They used a chlorine solution as a target for inverse β-interactions:

νe + 37Cl → 37Ar + e.

The radioactive 37Ar could be extracted from the target and the decay could be detected with proportional counters. The experiment of Davis had to face fundamental problems: It was only sensitive to neutrinos with a energy higher than ∼0.8 MeV; thus it could only detect neutrinos from the 7Be and 8B branch. And, even more crucial, the observed neutrino flux was to low compared with the modell prediction. This discrepancy lead to the so-called solar neutrino problem.

GALLEX: a radiochemical GALLium EXperiment to detect solar pp neutrinos

Until the year 1990 there was no observation of the initial reaction in the nuclear fusion chain. This changed with the installation of the Gallium Experiments. Gallium as target allows neutrino interaction via

νe + 71Ga → 71Ge + e.

The threshold of this reaction is 233 keV, low enough to detect neutrinos from the initial proton fusion chain. Low energy threshold is of great importance here since more than 98 % of the neutrinos produced in the Sun are sub-MeV (pp: ∼91 %, 7Be: ∼7 %). Moreover the pp-neutrino flux is coupled to the solar luminosity and therefore should be measured as precise as possible. Stringent limitations of departures from the Standard Solar Model can be obtained if the flux of pp-neutrinos is deduced.
    The target tank and the counting system was located in Hall A of the LNGS. The rock overburden shields the detector against interfering cosmic radiation. This unique site is to find in central Italy in the Abruzzo region, close to L'Aquila at the highway A 24. The highway tunnel through the highest mountain south of the Alps, the Gran Sasso (2912 m), gives easy access to the worlds largest underground laboratory, with 3 large halls, where several experiments were built in the last years.
     The GALLEX was performed by the international collaboration with scientists from France, Germany, Italy, Israel, Poland and the US, headed by MPIK Heidelberg. Spokesman of the collaboration was the former head of the MPIK Neutrino Group, Prof. Till Kirsten.

Outline of the experiment
In the time period of 1986 - 1990 the detector was constructed. The data taking started in May 1991. The first campaign (GALLEX I) was finished in May 1992. The average result of the GALLEX I 15 solar runs was (83.4 ± 19) SNU [2]. It was announced for the first time at the "Neutrino 1992" conference in Granada on June 8th.


A transparency by T. Kirsten announcing the first observations of the pp neutrinos by GALLEX. Neutrino 1992 conference, Granada, June 8th.

Until February 1997 (end of solar data taking) there were three more campaigns: GALLEX II, III and IV. During that period the detector was calibrated twice using an artificial neutrino source (51Cr): in 1994 [3] and in 1995/1996 [4]. This was a very important demonstration of the reliability of the GALLEX detector and of the radiochemical method in general. At the end of the experiment, in 1997, an arsenic test was also performed (using 71As). The goal was to check the influence of the so called "hot chemistry" on the observed neutrino rates [5].
     Recently the data form GALLEX (including the calibration tests) were re-evaluated using a full pulse shape analysis instead of originnaly applied rise-time techniques [6].

The GALLEX detector and 71Ge extraction procedure
As already mentioned the GALLEX target consists of 30.3 t gallium in the form of a concentrated GaCl3-HCl solution (total weight 101 t). For safety and redundancy reasons, GALLEX had two nearly identical target tanks (A and B). Until April 1992 the solar neutrino measurements have been performed in the B tank (GALLEX-I). On April 30, 1992, the GaCl3 solution was transferred to the A tank which is equipped with a central reentrant tube designed to hold a 51Cr neutrino source (for future calibration experiments). After various tests were performed, measurements of the solar neutrino flux were resumed in August 1992.

Scheme of the GALLEX detector tank with the absorber system and the Chromium source inserted inside the thimble.

3 solution. For this the non-radioactive isotopes 72Ge,74 Ge and 76Ge, later also 70Ge, are sequentially used in order to monitor carryover from one run to the next one. After three or up to weeks of exposure time, desorption starts by purging the target solution with 1900 m3 of nitrogen in 20 hours. Because tank A is equipped with a more efficient sparger system, the desorption time there was reduced to 12 hours. Germanium is removed from the solution as volatile germanium chloride (GeCl4). The gas stream was passed through a system of water scrubbers where the GeCl4 was absorbed. At the end of desorption all the germanium was contained in a volume of about 30 liters in the first scrubber. A series of smaller columns serves to further concentrate the germanium in a volume of about 1 liter of water. The final concentration step is an extraction into CCl4 and a back-extraction in to 50 ml of tritium-free water. This step also serves to separate the germanium from any tritium in the tank or the absorber system, since tritium would contribute to the background in 71Ge counting. The last part of the chemical procedure is the conversion of GeCl4 to the gas GeH4 by means of the reducing reagent sodium borohydride (NaBH4). The GeH4 is dried and purified by gas chromatography . Its volume is then measured in order to determine the overall yield of the chemical procedures. Finally, it is placed together with Xenon into a miniaturized proportional counter. The volume ratio Xe:GeH4 is 70:30, the total counting gas pressure is about 800 Torr. The total chemical yield (i.e. the ratio of the Ge amount extracted to the amount of Ge carrier added to the target solution at the beginning of the run) was about 99 %.

Counting with miniaturized proportional counters.
The 71Ge decay rates expected in GALLEX even if the SSM signal would be observed are below 1 per day . The measurement of such low decay rates is an extreme low-level task and could only be achieved with miniaturized proportional counters. 71Ge decays by K (87.7 %), L (10.3 %), and M (2.0 %) electron capture. Neglecting the M events, the energy deposition from Auger electrons and X-rays emitted in the decay results in a energy spectrum with two peaks: an L peak at 1.2 keV and a K peak at 10.4 keV. All provisions typical for low-level counting have to be applied in order to reach the extremely low background rates required: for the proportional counters itself this implies miniaturization and the use of ultrapure (with respect to radioactive contamination) materials. The counter body is made from Suprasil quartz. A special quartz blowing technique allows to standardize the counter dimensions. The cathode is either made from zone-refined iron (Fe counters) or machined from a single Si crystal (Si counters). The anode is a 13 μm tungsten wire. The active volume (volume inside the cathode) is typically 87 % of the total gas volume (which is about 1 cm3).

Miniaturized ultra-low background proportional counter HD-II type.

Scheme of the proportional counter shielding tank installed at the counting building inside a faraday cage.

214Pb and 214Bi. In order to keep this background contribution as low as possible, the shielding tank is air sealed by a glove box system installed around it. Counters were transferred in to the shield or removed from it by means of an air lock. The radon content inside and outside the shield is continuously monitored by two Lucas chambers with 5 hours integration time. While the radon content of the air outside the shield (depending on the venting situation in hall A) fluctuates between ∼50 and 100 Bq/m3 (in extreme cases 1000 Bq/m3 were reached) the level inside the shield is usually below 1 Bq/m3 (detection limit for the used Lucas cell). From a calibration measurement we know that such a level amounts to (0.0015 ± 0.0005) counts per day in the counting windows on the active side. On the passive side the effect is 20 times lower. The counter shield together with the electronics was installed inside a Faraday cage.
     In order to calibrate the energy and rise-time scale of the GALLEX counters, a 153Gd-Ce X-ray source was used. The europium X-rays following the electron capture decay of 153Gd (T1/2 = 242 days) excite the characteristic K alpha and K beta X-rays from a Cerium target. These are used to illuminate the entire proportional counter volume rather homogeneously leading (in addition to the photopeak from the 35 and 40 keV X-rays) to three peaks at energies of 1.03, 5.09 and 9.75 keV which result from the escape of Xe X-rays. Typical energy resolutions (FWHM) of the GALLEX counters were 43 % for the L peak and 26 % for the K peak. Average absolute counting efficiencies were 28.6 % in the L window and 33.9 % in the K window for the nine counters with Fe cathode used in the GALLEX I runs. The corresponding average value for the six counters with Si cathode are 29.7 % (L) and 31.7 % (K).

Outcome of the experiment.
After four campaigns: GALLEX I - GALLEX IV, 65 solar runs and 1594 days of data taking the final GALLEX result was (77.5 ± 7.7) SNU which should be compared with the expected 126 SNU according to the Standard Solar Model and no-oscillation scenario. From the calibration tests with the 51Cr source the obtained ratios of measured to expected rates were (1.00 ± 0.11) and (0.83 ± 0.10), respectively confirming the proper performance of the detector. Any Ge-yield errors above 1 % was excluded according to the 71As test.
     GALLEX provided the very first observation of the solar pp neutrinos and thus an important confirmation of the nuclear fusion process inside the Sun. The measured neutrino signal was smaller than predicted by the Standard Solar Model (c.a. 60% of the total expected flux has been measured), however the reduction factor was different then in the chlorine experiment. At that time two explanations were possible: either the model is not correct, or the neutrino has some features which were not yet taken into account in the Standard Model of elementary particles.

     In 2007 the GALLEX data were re-evaluated using a full pulse shape analysis (instead of applied originally rise-time technique). In addition all individual counters were calibrated what resulted in the calibration error reduction. Also radon cut efficiency has been improved. After corrections the overall GALLEX result has slightly decreased down to (73.1 ± 7.2) SNU. As can be seen in the Figure below among the four GALLEX data taking periods, by far the largest change is for GALLEX IV. This period had created some concern because of a ±2 σ deviation from the mean, which is now reduced ±1 σ. Re-analysis of the 51Cr experiments has been performed with new efficiencies and an improved solar subtraction (including also GNO data). This update has changed the average result (ratio of the measured to expected neutrino flux) from (93 ± 8) % down to (88 ± 8)%. Taking also into account the Cr-source results obtained by the SAGE collaboration one should consider re-evaluation of the 71Ge production rate on Ga, which should be reduced by ∼2 SNU for 7Be neutrinos from 34.8 SNU down to 32.7 SNU (there is no change for pp neutrinos).

GALLEX single run result overview. The left hand scale is the measured 71Ge production rate; the right hand scale, the net solar neutrino production rate (SNU) after subtraction of side reaction contributions. Error bars are ± sigma statistical only. The label 'combined' applies to the mean global value for the total of all 65 runs. Horizontal bars represent run duration; their asymmetry reflects the 'mean age' of the 71Ge produced.

Re-evaluated GALLEX data (in red). The biggest change appeared for the GALLEX IV period. The overall result is by 4.4 SNU lower than reported earlier.



GNO: the Gallium Neutrino Observatory.

GNO was the successor project of GALLEX, with scientists from Italy and Germany, now headed by the Milano group of the INFN. Spokesman of the Collaboration was Prof. Enrico Bellotti (Milano, Italy).
     GNO aimed to measure the flux of solar electron neutrinos from the proton-proton fusion during a full solar cycle. A special goal of the collaboration was the reduction of systematic uncertainties in the result of the observation (with respect to GALLEX), and, simply due to the prolonged time of observation, a smaller statistical error. During 1997/98 big effort was set on an upgrade of the DAQ electronics and some modifications in the synthesis process. It has been proposed to the scientific community and to the funding agencies to increase the mass of gallium up to 100 tons (from 30.3 tons). The first solar runs started in April 1998 and the last one was performed in 2002. The experiment was officially finished in 2004.

    Main changes in the GNO experimental procedures as compared to GALLEX are the following [7]:

  • Desorption time and desorption gas volumes for GNO have been reduced from 12 to 9 hours and from 2500 to 1700 m3 (at 20 C and 0.9 bar). This simplified the operating schedule at the expense of a slightly less efficient Ge desorption. The un-desorbed Ge-isotope carrier fraction remaining in the tank was expected to increase from about 0.2 % to values between 1 % and 2 %. The fact that a homogeneously distributed Ge hold-back carrier level never drops below ∼10−13 mol per liter helps to exclude hypothetical 71Ge loss scenarios that would involve the carrying of non-measurable ultra-low trace impurities below that level.
  • The major contribution to the systematic errors of the GALLEX results (∼4 %) came from the insufficient knowledge of counter efficiencies (3.5 %). This is due to the fact that efficiencies for counters used in solar runs have not been measured directly because of contamination risk. Instead, they have indirectly been evaluated from measurements on other counters combined with a scaling procedure based on Monte Carlo simulations. However, some of the inputs needed in these MC simulations (counter volume, gas amplification curve) are not known with the accuracy that one can ambitiously desire. In order to decrease this systematic error substantially, the GNO Collaboration has developed a method that allows direct counter efficiency calibrations without introducing a major contamination risk. The resulting total errors came out between 0.8 % and 1.4 % (average 1.1 %) what constitutes a substantial reduction, as anticipated.
  • An elaborate radon test was performed with a modified counter containing a 226Ra source. The aim was to improve the characterization of radon events in the GNO proportional counters. The recordings lasted from May 1999 through March 2001 (1.8 years of counting time). After this long-lasting measurement, the emanation valve was closed and the intrinsic background of the counter was measured for 2.0 years. Using these data, we re-evaluated the inefficiency of the radon cut. The result is consistent with zero and the (2 σ) upper value is 7.3 %. This replaces the formerly determined value used in GALLEX: (9 ± 5)%.
  • Analog and digital electronics, power supplies and data acquisition system have been completely renewed and reorganized after the accomplishment of GALLEX data taking. The analog bandwidth of the system has been increased to 300 MHz, the typical RMS noise is 2.8 mV. Due to these improvements and to a thorough screening of counters used in solar runs, the background in GNO is 0.06 counts per day in the relevant windows, corresponding to a 40% background reduction compared to GALLEX.
  • In addition to solar runs, one-day-exposure blank runs were also performed regularly in order to verify the absence of any artifact or systematics related to the target. During the period of operation of GNO, 12 blank runs were successfully performed. The absence of spurious effects or unknown background is confirmed by the fact that the small excess of 71Ge counts in the blanks is consistent with the neutrino-induced production rate during the short exposure and the carry-over of the previous solar run.
  • For the selection of the 71Ge events a new neural network pulse shape analysis (NNPSA) and a subsequent maximum likelihood analysis has been used instead of rise-time technique (GALLEX).

Outcome of the experiment.
The total GNO neutrino exposure time was 1687 days (58 runs). During this time, the maximum likelihood analysis identified a total of 258 decaying 71Ge atoms (131 L, 127 K), 239 of them (or 4.1 per run) due to solar neutrinos. The mean 71Ge count rate per run and counter at the start of counting is ∼0.27 counts per day. This may be compared with the time independent counter background as low as ∼0.06 counts per day (average). The individual run results for the net solar production rates of 71Ge (based on the counts in the K and L energy- and neural network acceptance region, after subtraction of 4.55 SNU for side reactions and after corrections for annual modulations) are plotted in Figure below. The combined net result for all GNO runs is 62.9+6.0-5.9 SNU (1 σ, including systematics).

GNO single run results. Plotted is the net solar neutrino production rate in SNU after subtraction of side reaction contributions. Error bars are ±1 σ, statistical only.

Combined analysis of the GALLEX and GNO data.
The Figure below shows single run results for GNO and GALLEX (before re-analysis) during a full solar cycle. Plotted is the net solar neutrino production rate in SNU after subtraction of side reaction contributions. Error bars are ±1 σ, statistical only.
     The joined GNO + GALLEX result after 123 solar runs is 67.5 ± 5.1 SNU (1 σ, after GALLEX data reanalysis). The joint result confirms the earlier GALLEX outcome which made the case to claim strong evidence for non-standard neutrino properties because the production rate predictions from the various standard solar models have always been much higher (120 - 140 SNU) than the measured rates. The updated result of the SAGE experiment, 66.9+5.3-5.0 SNU (1 σ), agrees well with the GALLEX+GNO analysis.
     The GALLEX and GNO data have been also analyzed relative to a correlation with the seasonal Earth-Sun distance variation. The 123 solar runs have been divided into 6 about equally populated bins of similar heliocentric distance d. The fit assuming a solar neutrino rate constant in time and affected only by the 1/d2 geometrical modulation yields a confidence level of 69 % (χ2 = 3.0 with 5 d.o.f.). The difference between rates of the solar runs performed in winter time W (defined as perihelion ±3 months) and in summer time S is δ(W −S)=−7.6 ± 8.4 SNU (the value expected from the 1/d2 modulation only is +2.3 SNU). The finding that the solar data are consistent with a production rate constant in time does not invalidate however other hypotheses that might give similar or even better (short) time dependent fits.

GALLEX and GNO data with marks indicating the calibration and arsenic tests.

GNO/GALLEX signal vs. heliocentric distance of the Earth. The straight line indicates the expected flux variation due to purely geometrical (1/d2) effects.


If the LMA (MSW) solution is the correct explanation of the SNO/SK data, then vacuum oscillations must dominate below 1 MeV and the mixing angle is estimated as (32 ± 1.6) degrees. From the GALLEX (and GNO) data one can extract the survival probability Pee for pp-neutrinos after subtraction of the 8B and 7Be contributions based on the experimentally determined 8B- (SNO/SK) and 7Be- (Borexino) neutrino fluxes as Pee (pp only) = 0.52 ± 0.12. The results imply the experimental verification of the solar model and of the neutrino oscillation mechanisms at sub-MeV energies that are otherwise inaccessible.


Summary

Radiochemical experiments gave cumulative measurement of the integral solar neutrino interaction rate (as opposed to real-time event detection, also there was no spectral or directional information). For the first time the low-energy pp-neutrinos have been registered confirming the nuclear fusion process inside the Sun. After a long time of operation of these first generation detectors (Cl, Ga), the statistical errors equaled the intrinsic systematic errors. The success of these experiments implied their end.
     However, there were still reasons to continue observations of the low energy neutrinos (GNO):

  • Continuous pp-neutrino monitoring is an astrophysical necessity
  • pp-observations simultaneously with Borexino real-time beryllium neutrino observations
  • Further neutrino source experiments to improve the knowledge of relevant cross sections


References

[1] Bahcall, Serenelli and Basu, ApJ, 621, L85 (2005)
[2] GALLEX Collaboration PL B285 (1992) 376 and PL B285 (1992) 390
[3] GALLEX Collaboration PL B342 (1995) 440
[4] GALLEX Collaboration PL B420 (1998) 114
[5] GALLEX Collaboration PL B436 (1998) 158
[6] F.Keather, PhD Thesis, Heidelberg University, 2007
[7] GNO Collaboration PL B616 (2005) 174


Sources

[1] W. Hampel: Talk at the Royal Society, London, 1994. Published in "Phil. Trans. R. Soc. Lond. A (1994) 343, 3-13"
[2] T. Kirsten: Talk at the TAUP 2007 Conference, 11-15.09.2007 Sendai, Japan


People involved


2) Heidelberg Moscow

The Heidelberg-Moscow-Experiment was a German-Russian Collaboration between the Max-Planck-Institut für Kernphysik and the Kurchatov Institute in Moscow, Russia. The experiment searched for neutrinoless Double Beta decay of 76Ge. The experiment was operated in the Gran Sasso Underground Laboratory in Italy with five detectors with a total mass of 10.9kg of Germanium which was enricht to 86% with the double beta emmitter 76Ge. The Gran Sasso underground laboratory reduces the cosmogenic muon flux by six orders of magnitude and further shielding was provided by lead around the detectors. Finally, further background reduction was achieved by Puls Shape Analysis (PSA) which allows to discriminate background from signal events. A sub group of the original collaboration claims as a final result for the half life of neutrinoless double beta decay of 76Ge: T = (2.23 +0.44 -0.31) x 1025 years (99.97% C.L.) This positive result has been heavily debated amongst experts. This result is even very interesting if a sigal can not be established, since it is still the strongest limit on neutrinoless double beta decay unti now. This has profound implications on physics beyond the Standard Model, like supersymmetry, Left-Right Symmetry, Compositeness... which will be tested at LHC.

People involved

  • Prof. H.V. Klapdor-Klingrothaus

3) M-Cavern


M-Cavern: Micro-Chemistry Analysis of Various Extra-terrestrial and environmentally found RadioNuclides.

Scientists from MPIK have gathered wide expertise in the field of low-background physics, working in meteorite and mineral research, GALLEX/GNO, BOREXINO and LENS. Measurement devices like Ge or NaI gamma spectrometers, proportional counters, scintillation cells, mass spectrometer etc. are routinely used at LNGS and at the MPIK. Furthermore, the MPIK is equipped with an on-site Low-Level-Laboratory, providing a shelter against the hadronic constituents of cosmic rays.
     In 2002 MPIK in Heidelberg, Germany and the Space Science Division, E. O. Hulbert Center for Space Science of the US. Naval Research Laboratory (a laboratory involved in many aspects of solar satellite research and space exploration) created a cooperative research project according to a proposal of F. Hartmann located at Gran Sasso: MCavern [1]. The MCavern project combines mutual expertise to create a new low background counting facility for the development of detectors and techniques. It was expected not only to be of use to the field of Particle Astrophysics, but to Fundamental Chemistry and applications in Space, Atmospheric and Ocean Science, as well.
     The project comprises, in the first stage, the construction of new ultra-low background germanium detectors as well as proportional counters, a shielded counting setup, a gas and vacuum system, counter filling lines and some already existing chemistry equipment. A sample handling area and small (sub-gram) chemistry units were proposed thereafter.

Ge-spectrometers: GeMPI II and III
In the frame of the project a new GeMPI-type [2] germanium spectrometer has been constructed at the LNGS (the next - GeMPI III is under construction). The cutaway view of the detector shows (see below) the sample entry air-lock system, glove box access holes, shield (copper and lead), specially designed cryostat and liquid nitrogen dewar holding special charcoal absorbers. Samples pass through the air-lock, past a heavy sliding lead copper door and into position just above the germanium crystal whose special housing of ultra-low background parts is all fabricated by MPIK engineers and scientists. A specially constructed lead block made by INFN shields from the internal electronic components within the crystal can.
Recorded background spectra show background level which is slightly lower than that observed for GeMPI I [2].


A schematic view of the GeMPI II detector with the shield and the Rn-box. The design was based on the GeMPI detector operated by MPIK since 1998 and used for material screening in the frame of several projects like BOREXINO or LENS.

The gas counting project
The gas counting project was based on the development of a new instrumental capability:

1) to count multiple gases at the few event level, not tuned to just one specific gas
2) to separate and collect a number of different gas components from the same gas sample
3) to be able to analyze the gas content of liquids (e.g. scintillators)
4) to be able to synthesize counting gases from low level source materials

     This system evolved from prior systems [3,4,5]. The basic design is that inherent in the approach of Ray Davis. The first gas line used for few atom counting of Ar was an essential feature of the Homestake Chlorine Experiment. This type of line was later modified and extended to handle the specific needs of the Gallex Experiment by Brookhaven and MPIK. The actual GALLEX lines transferred to the GNO Project (also upon which the Brookhaven group exited). A goal since then was to extend the capability to other gases. During GALLEX it was found using a dedicated "Rn counter" that few atoms of 222Rn could be processed in the GALLEX lines and counted. But the GALLEX lines as constructed were not suited to be dedicated to this purpose. In addition to these synthesis lines, there was in GALLEX a counter filling line. This line was later transported to Hall C at LNGS to support 222Rn measurements in the BOREXINO Project. This line is primitive in construction and essentially comprised of discarded parts and systems. In addition to the gases of 222Rn [6], the lines at Gran Sasso have seen limited scope handling of 133Xe, 135Xe counting as part of GALLEX tests [7]; and most significantly GALLEX studied the removal of 71As also produced as a gas. The counting of 133Xe, 135Xe later became a sub-project in the LENS arena. Some ideas to count gases from the BOREXINO scintillator (at first CO2 and 85Kr) ran into difficulties because of the lack of a separate gas facility. Since then a counter filling line at Heidelberg was modified to incorporate 85Kr counting and tests of this were quite good [8]. Even with the clearly limited capability of use of the two modified counter filling lines (the one at Gran Sasso lacking gas chromatography) Heidelberg has achieved remarkable success in contributing to low background measurement for the projects at Gran Sasso.
     A diagram showing the proposed line structure and support system is shown in figure below. As mentioned the design was based on the existing devices located in Heidelberg and at Gran Sasso.


Diagram of the Gas Handling, Chromatography and Counter Filling System. The system is built up around the Chromosorb 102 column designed for efficient separation of gases with low 222Rn emanation as developed for Ar (Homestake), Ge, Xe, Rn (GALLEX, BOREXINO) and tested for Kr by H. Simgen in the BOREXINO Project. Essential features evolve since the original Brookhaven lines and the GALLEX/GNO system used in germane synthesis.


The engineering picture portrays the appearance of the counting system for the gas proportional counter set-up. The system is encased in a Radon Box cover (not shown) which is used to provide a controlled atmosphere environment along with an air lock for the insertion of counters. Shown here is one gas counter copper box inserted into a counting hole. The counter box is in a copper block made from specially shipped NOSV copper from Nord Deutsche Affinerie, currently stored underground at MPIK. The lead housing is selected from low background lead. The NRL group's engineers and scientists handle this piece of the project with MPIK engineering design assistance.

Achievements of the project
The project was officially ended in 2006. The following has been achieved:
 - Construction of the ultra-low background Ge spectrometer (GeMPI II) operated now at the Gran Sasso laboratory
 - Construction of 6 low-background miniaturized proportional counters
 - Construction of the counting system for the gas proportional counters  - Design study of a new counter filling line


References

[1] Underground Ultra-Low Background Micro-Chemistry and Counting at Gran Sasso: The M-Cavern Project, LNGS-LOI 31/03
[2] H. Neder, G. Heusser, M. Laubenstein, "Low level gamma-ray germanium-spectrometer to measure very low primordial radionuclide concentrations", Appl. Radiation and Isotopes 53 (2000) 191-195.
[3] C. Schlosser, "Germanium-Ausbeutekkontrolle und Charakterisierung von Untergrund beit ragen in Gallex Sonnenneutrino Experiment", Universitaet Heidelberg and MPIK, Heidelberg (1992).
[4] R. Wink et. al. incl. G. Heusser, T. Kirsten, Nucl. Inst. and Methods in Phys. Res. Ser. A 329 (1993) 541.
[5] W. Hampel et. al., (GALLEX Collaboration), "Gallex Solar Neutrino Observations: Results for Gallex III)", Phys. Lett. B388 (1996) 384-396.
[6] H. Simgen, Diploma Thesis, MPIK and University Heidelberg (2000).
[7] S. Pezzoni, "Non solar-neutrino production of 71Ge in Gallex", PH.D. Thesis, Max Planck Instutut fur Kernphysik, Heidelberg MPIH-V2-1995 (1995).
[8] H. Simgen, Ph. D. Thesis, MPIK and University Heidelberg (2003).



People involved:

 
 


Last modified: Mon 10. April 2017 at 16:37:59