Solar neutrinos: The Beginning at MPIK · 2017. 6. 19. · Ge extraction from GaCl 3 solution...

Solar neutrinos: The Beginning at MPIK

W. Hampel

W. Hampel - Solar neutrinos:The beginning at MPIK Workshop: From Cosmochemistry to Solar Neutrinos

Heidelberg, June 7, 2017

1976-1978: Geochemical Bromine-Krypton Experiment

1979-1982: Gallium Pilot experiment with1.26 tons of Gallium

1983-1986: Transition phase from the pilot experiment to GALLEX



Geochemical Bromine – Krypton Solar Neutrino Experiment

Basic idea:Extract 81Kr from about 10 tons of Bromine which has been produced over about 106 years in10 tons of natural Bromine by solar7Be neutrinos

Isotopic composition of Bromine: 79Br 50.7%

81Br 49.3%

log ft = ? (4-6)

threshold 490 keV



Kali- und Salz AGMine at Bad Salzdetfurth(between Hannover and Kassel)Mining down to a depth of 900 m

Daily output: ~ 5000 tons of potassium salt

Bromine content 0,2%(corresponds to 10 tons of Br)

Expected: about 10-13 cc STP 81Kr(for an assumed log ft value of 5)

can in principle be measuredby mass spectrometry)

Kassel

Hannover

Salzdetfurth

Sylvite (KCl)Carnallite (KMgCl3*6 H2O)Kainite (KMg[Cl|SO4]*2.75 H2O)Langbeinite (K2Mg2(SO4)3)

Potassium salt deposits in Northern Germany



Kassel

Hannover

Salzdetfurth

Results (mainly from the PhD thesis K. Büchler 1980):

Retention age for Krypton > 1 million years: ok

We tried to measure the log ft value for the

relevant transition: result >3.3 (expected 4-6)

Muon-induced production at 900 m depth:

about 10-13 cc STP 81Kr

(same as solar-neutrino-produced 81Kr)

Mining not deep enough

Dissolved stable Krypton in salt: 2x10-10 cc STP/g

This leads to a ratio 81Kr/82Kr of 10-12

not possible to be measured without

isotopic separation

Background by (α,p)(p,n) reactions through

uranium and thorium:

For a 10% bkg: 0.5 ppb U

Measured 9 ppb in one case, mostly > 200 ppb

much too high



Talk of T.Kirsten at the Informal Conference on Status and Future of Solar Neutrino Research (organized by Ray Davis and his collaborators inJanuary 1978):

Further consideration of the 81Br- 81Kr system

At this time: it was clear that theBr-Kr experiment was not feasable with the potassium salt target of Salzdetfurth

However: after the conference we were invited by R. Davis and his collaborators to discuss a possible participation in a Gallium solar neutrino experiment: this led to the Gallium

Pilot experiment Collaboration



Visit of Ray Davis jr. at Heidelberg in 1978

Donald D. Clayton (Humboldt Research Awardee MPG)Oliver A. Schaeffer (External Scientific Member MPIK)



Thanks to an agreement between Raymond Davis and Till Kirsten:

1978/1979: Stay at the Chemistry Department,Brookhaven National Laboratory, Upton, New York, USA.Group of Raymond Davis

Raymond Davis jr.Physics Nobel Prize 2002

Bruce T. Cleveland

Ge extraction from GaCl3 solutionTritium-free GeCl4 conversion to GeH4Counter construction and filling

Data evaluation for the Chlorine experiment: Maximum Likelihood MethodMonte Carlo Calculations



Meeting at BNL which led to the contract between BNL andMPIK to perform a pilot experiment with 1.26 tons of gallium

March 1979



Pilot experiment with 1.26 tons of Gallium

Collaboration

Brookhaven National Laboratory, Upton, NY (Ga 2/3)

Max-Planck-Institut für Kernphysik Heidelberg (Ga 1/3)

Weizmann Institute Rehovot

Institute for Advanced Studies Princeton

University of Pennsylvania at Philadelphia



Ray Davis jr. Israel Dostrovsky Keith Rowley John Bahcall

1914 – 2006 1918 – 2010 1929 – 2006 1934 – 2005

Four members of the pilot experiment collaboration

(also GALLEX member) (also GALLEX member)



Pilot experiment installationin the basement of the Chemistry Department atBrookhaven National Laboratory

2.8 m3 tank with Kynar and teflon lining1.26 tons Gallium4.65 tons of GaCl3 solution



Very first Ge extraction from the pilot tank

99.6% of the germanium initially present in the GaCl3 solution of the pilot tank (~200 mg) have been extracted in a 32-hour sweep

April 1980:

Pilot tank is filled with 4.65 tons of GaCl3 solution



Low Level Proportional Counter Davis-type

Davis type

Counter type used for counting GeH4 samples from the pilot tank.

Gerd Heusser has used this type of counter already a few years before the pilot experiment for the measurement of 37Ar and 39Ar in meteorite samples.

.

Similar to the counters used by Ray Davis in the Chlorine experiment



Measurement of the 71Ge production rate by cosmic rays in the pilot tank

110 ± 30 71Ge atoms /day

(Shielding: a few meters of water equivalent)

Run 7 of the pilot experiment

Here we used about 3 mg of Ge carrierthis results in about 1 cm3 of GeH4

Counting gas is pure GeH4Non-linear energy scale



Outcome of the Pilot experiment:

A full scale solar neutrino experiment with 30 tons of gallium is feasible!



Plans to perform a full scale experiment (share of gallium costs: ¾ BNL, ¼ MPIK)

First step: perform a 51Cr source experiment with 12.8 tons of gallium in theAsarco zinc mine in Tennessee (500m underground)

Second step: full scale experiment with 50 tons of gallium in the Homestake mine

BNL requested in several proposals to the Department of Energy and to the National Science Foundation to finance the US share of Gallium:

they all failed

BNL director: decided to stop working on the gallium experiment (January 1984)

After the end of the pilot experiment:

End of the pilot experiment collaboration



Reduction factor for 2ν vacuum maximal mixing as a function of ∆m2 for the chlorine and gallium solar neutrino detectors

Vacuum neutrino oscillations:

have in principle long been on the list of possible explanations for the low solar neutrino capture rate in the Cl experiment

However: substantial reduction forthe Cl signal needs very specificand rather low ∆m2 values (close to10-10 eV2)



10th International Workshop on Weak Interactions (WIN 1985)16-22 June, 1985, Savonlinna, Finland

Talk given by Alexei Smirnov (authors Stanislav Mikheyev and Alexei Smirnov) on a new effect concerning neutrino mixing in matter based on earlier work of Lincoln Wolfenstein (later called the Mikeyev-Smirnov-Wolfenstein effect)

Bogdan Povh (former director of the MPIK) visited this conference. He recognized the importance of this work for the gallium experiment and reported this to us.

This triggered extensive numerical calculations by the Saclay group and our group on the MSW effect, especially for the Gallium solar neutrino detector:

J. Bouchez, M. Cribier, W. Hampel, J. Rich, M. Spiro and D. Vignaud:Matter effects for solar neutrino oscillationsZ. Phys. C32, 499-511 (1986).

M. Cribier, W. Hampel, J. Rich and D. Vignaud:MSW Regeneration of Solar νe in the Earth,Phys. Lett. B182, 89-94 (1986).

The Mikheyev-Smirnov-Wolfenstein Effect



Current Large mixing angle solution for 2ν mixing:

∆m2 = 4.7 x 10-5 eV2

sin22Θ = 0.85

Final result:GALLEX/GNO: 69.3 ± 5.5 SNU

WH 1986

{

Contour lines for possible gallium detector results asa function of the mixing angle Θ and the squared mass difference ∆m2



After the end of the Pilot Experiment Collaboration:

Till Kirsten investigated the possibilities to perform the Gallium solar neutrino experiment in Europe. His efforts were successful in all aspects:

The European GALLEX Collaboration was formed (1984)

Funding for 30 tons of Gallium through the combined efforts of MPIK Heidelberg, Max Planck Society, Krupp Foundation and the German Federal Ministry of Research and Technology was assured (December 1985)

The italian INFN assigned the required underground space in the newly constructed Laboratori Nazionali del Gran Sasso (1985)



Heidelberg Low Level Proportional Counter Development

HD-1

HD-2

Aluminum cathode evaporated onto the inside of the quartz body in order to minimize the dead volume. Stop cock close to the counting volume

First stage of the preamplifier close to the counting volume

Final type: HD-2

(which was usedin GALLEX)

1985: after the GALLEX collaboration was formed: tried to improve our low-level counters

Intermediate step: HD-1



1986: The Heidelberg GALLEX group with the counting shield still sitting in Heidelberg



First visit of the GALLEX Collaboration at theLaboratori Nazionali del Gran Sasso, April 1985

At this visit: (1) Hall B was already complete(2) excavation of hall A just had started(3) there was no hall C yet



Many thanks to Till Kirsten:

Through his long-lasting efforts the GALLEX solar neutrino experiment became reality!

this enabled many of us to take part in this fundamental and successful experiment of astrophysics!

Solar neutrinos: The Beginning at MPIK · 2017. 6. 19. · Ge extraction from GaCl 3 solution...

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