Tag Archives: Gran Sasso

Distillation campaign for XENONnT finished

The up-coming XENONnT experiment utilizes a total of 8.3 tonnes of xenon to search for the ever elusive dark matter particles. In addition to the existing 3.3 tonnes of ultra-pure xenon from XENON1T, another 5 tonnes of xenon were purchased by the XENON collaboration. 

Before the new gas can be used for XENONnT, it needs to be purified. Besides oxygen, nitrogen and water that potentially absorb the light and charge signals in the detector, the radioactive noble gas Kr-85 within the xenon needs to be removed. Kr-85 is a man-made isotope created in nuclear bomb testing and nuclear fuel reprocessing. It makes up a fraction of 10-11 of the natural krypton (Kr-nat) abundance.

The commercially available xenon arrives with a Kr-nat in xenon concentration on the order of 10-6 (ppm, parts per million) to 10-9  (ppb, parts per billion) and needs to be purified down to a concentration of 0.1 x 10-12 (ppt, parts per trillion). To put this in relation: When purchased, an Olympic swimming pool filled with liquid xenon contains a 10 liter bucket of krypton. After purification, 200 Olympic swimming pools filled with liquid xenon contain together just one single droplet of krypton.

The purest xenon on Earth can be produced with the help of our Krypton Distillation Column located underground in the service building of XENON1T/nT as seen in the picture below. The purification method is based on the separation due to the different boiling points of xenon and krypton. While xenon is in its liquid form at -100°C, krypton, as the lighter atom, prefers to stay in its gaseous form. Like that, krypton is enriched at the top of our distillation tower from where it is removed and stored in a bottle as so-called “offgas”. The purified xenon can exit the distillation system at the bottom.

The picture shows the service building of XENON1T/nT. Bottles with new xenon, containing tiny trace amounts of the radioactive noble gas Kr-85, were connected to the “Bottle rack” (Blue-red-dashed line). The xenon is guided into the “Distillation column” to separate krypton from xenon. At the top, krypton-enriched xenon is extracted as “offgas” (red line), while at the bottom, the purified xenon is taken out (Blue line). Purified xenon is either stored inside “ReStoX-I” (Left side, blue line), the storage system of XENON1T, or in “ReStoX-II” (Right side, blue line), a newly installed storage system for XENONnT.

In total, over 100 bottles of freshly delivered xenon were installed in two bottle batches at the “Bottle rack”. Here, xenon samples from each batch were measured with a connected residual gas analyzer (RGA) system. Xenon from one of the bottle batches was continuously filled to the distillation system. Purified xenon was stored  either to the Recovery and Storage for XENON1T (ReStoX-I) (left side of the picture) or to the ReStoX-II system (right side of picture), a newly installed subsystem for XENONnT. ReStoX-II is a system designed to rapidly recover and safely store up to 10 tonnes of xenon, that will serve as an fast recovery system during operation of the XENONnT experiment as well as xenon storage previous to the start of the experiment.

The full distillation campaign was split into three phases starting from April 2019 and was finished in July 2019. Xenon samples were extracted to measure the purified xenon purity at MPIK Heidelberg with a rare gas mass spectrometer

As always in our collaboration, this operation too was an interplay between different groups: The bottle rack was installed by MPIK Heidelberg, the Distillation Column was operated by WWU Münster, and the ReStoX-I and -II systems were built and monitored by Columbia University in New York and Subatech-CNRS. The existing slowcontrol system was updated for the distillation campaigns by the Weizmann Institute of Science. Furthermore, local support was given by the group of INFN. Finally, to exchange bottles and to monitor the system 24/7, shifters from all over the collaboration supported the core distillation team.

On Tuesday, May 30, we presented the first XENON1T results in a seminar at LNGS, the laboratory where our experiment is hosted. The seminar was presented by Marco Selvi (INFN Bologna) in the Fermi room, the main auditorium at LNGS, and introduced by the LNGS director prof. Stefano Ragazzi in front of about 40 scientists.

After a short introduction on Dark Matter (you may guess that at LNGS they are well aware of the details of this physics puzzle! ), we described the construction and commissioning phase of the various systems crucial to run our detector.

We then focused mainly on the performances of XENON1T in the first science run,
where we reached the lowest ER background ever achieved in a dark matter experiment.

Also our sensitivity is very good, being it also the best out of the various direct search dark matter experiment, even with just 34 days of data acquisition.

With our result, XENON1T (and LNGS with) is back at the frontline of the race to finally detect dark matter particles … we look forward to analyse the already acquired >70 days of data !

 

Farewell to ICARUS

The ICARUS experiment just left Hall B at the Gran Sasso underground laboratory in Italy for its journey to CERN in Switzerland. We had designed the XENON1T water tank a bit smaller than originally planned to allow ICARUS to move past. Everything went smoothly, but it was a tight fit…

ICARUS moving

Part of the ICARUS experiment is hanging from the large crane in Hall B of the Gran Sasso underground lab, tightly squeezing past the XENON1T water tank on its way to CERN.

We wish our colleagues all the best with the future of their experiment. Read the full story of this move at interactions.org.

Like Mushrooms

The XENON1T is shielded from ambient radioactivity by a large water tank that is equipped as a muon veto. The tank has a diameter of 10 meters and is 10 meters high. It is constructed from top to bottom and went up in the Gran Sasso underground laboratory within less than a month:

 

Construction Started

The XENON1T experiment has been approved by the INFN executive committee to be built in Hall B of the underground laboratory Laboratori Nazionali del Gran Sasso (LNGS) near Assergi, Italy. The experiment is designed to perform a search for Dark Matter with a sensitivity that is more than two orders of magnitude better than the current best sensitivities in the field.

XENON at Gran Sasso

Drawing of the XENON experiment at the Gran Sasso underground laboratory. Left the water shielding with the cryostat, on the right the service building with the electronics and xenon handling systems.

XENON1T will contain more than 3000kg of liquid xenon that are instrumented as a two-phase (liquid/gas) time projection chamber. The cryostat is housed in a water tank ten meters high and ten meters in diameter, shown on the left in the picture. This water tank shields the experiment from ambient radioactivity. A three-story service building, shown on the right in the picture, houses the systems required for handling, cooling and purification of the xenon as well as electronics and computing required for data taking. First filling with liquid xenon is expected in 2014.