1.
ACTIVITY REPORT – Operation of Ge-diodes in liquid nitrogen
TASK LEADER: Stefan Schönert
Activity progress per contractor and task
 Contractor which participated to the activity:
Max-Planck-Institut for Nuclear Physics Heidelberg (MPIK), Germany;
Universitad de Zaragoza (UNIZAR), Spain

The main focus of the first phase of this project is the selection of adsorber materials for the purification of liquid nitrogen
from trace amounts of radioactive noble gases. In particular the purpose is to remove 222Rn, 85Kr and 39Ar from liquid
nitrogen. An adequate adsorber must have 1) an intrinsic low contamination of 226Ra (progenitor of 222Rn) in order to avoid a
recontamination of the liquid nitrogen, and 2) a high retention ability for argon, krypton and radon in order to achieve a high
separation efficiency.
Theoretical studies: The retention ability of adsorbers depends strongly on the distribution of its pores. First we investigated
the binding energy of different gas particles in pores of different sizes. A simple model based on van-der-Waals forces was
applied to determine the optimized pore size for each of the gases of interest. The results for carbon-based adsorbers are
shown in Table 1.
Best pore
size (carbon
based
adsorbers)
Ar
6.8 Å
Kr
7.0 Å
Rn
~8Å
Table1: The optimized pore size for the adsorption of Ar, Kr and Rn in carbon-based adsorbers.
Trace
component
The knowledge of the pore size distribution alone is not sufficient to determine the separation efficiency. In a realistic model
the interaction of the carrier gas (nitrogen) with the trace components (Ar, Kr, Rn) also has to be addressed. Our studies
suggested that non-polar adsorbers are more favourable for our purposes.
Result: From our investigations we can conclude that an optimized adsorber for nitrogen purification from noble gases has to
have a negligible internal polarity and a dedicated pore size distribution. Consequently standard molecular sieves with their
large internal polarities are no good candidates for adsorbers. However so-called hydrophobic zeolites have small internal
polarities and are promising materials. Further there are many kinds of (non-polar) carbon based adsorbers on the market.
Their disadvantage is that during their production it is not possible to control the creation of pores in a well-defined way.
Therefore they usually have a very wide pore size distribution and only a small fraction of pores has the right size.
Materials selection: Using the results of our theoretical studies we started to search for appropriate materials on the market.
Two types of hydrophobic zeolites and several types of carbon-based adsorbers were identified as possible candidates. They
are listed in Table 2:
Adsorber
Manufacturer
Hydrophobic
zeolite MFItype
Zeochem
Hydrophobic
zeolite BEAtype
Südchemie
Synthetic
carbon F3/F4
Carbon
Cloth FM 1250
CarboAct
Charcoal
Cloth
Main
characteristics
Very low
internal
polarity, pores
~5.3 Å
Slightly larger
internal
polarity, pores
~6.6 Å
Low 222Rn
emanation rate
Fabric (no
grains)
Optimized
pores for
CarboTech
solvent
recovery
Table 2: Overview of several adsorber materials selected as candidates for the purification of nitrogen from noble gases.
Activated
carbon C
38/2
Radio contaminations: it is planned to measure the relevant adsorber candidates with Rn emanation techniques.




For this report, no milestones and deliverables are due, however, the work is progressing as scheduled and we are confident
to meet our goals as outlined in the first 18 months implementation plan.
We developed the criteria on which basis to select adsorber materials based on our theoretical understanding of the
purification process by adsorbtion. Various materials have been procured. Experimental tests are ongoing in order to
compare their performance with respect to the theoretical predictions. It is expected that this work is completed according
the original time schedule including radon emanation measurements.
There is no deviation from the planned activity for the moment. However, we intend to widen the scope of the research. We
will 1) include measurements of krypton, argon and radon concentration depending on the supply chain and 2) will
investigate liquid argon as an alternative to liquid nitrogen as a cooling and shielding medium. The motivation for the latter is
motivated by the higher density of liquid argon (1.4 g/l) with respect to liquid nitrogen (0.8 g/l) which would reduce the
dimensions of the cryogenic tank. Moreover, the scintillation light of liquid argon can be used for background suppression
techniques. Therefore, we intend to study in the future with the similar priorities both cryogenic liquid nitrogen and argon.
First measurements will address the radon contamination in industrial produced liquid argon and the radon removal by
activated charcoal in the liquid phase.
Several informal meetings at MPIK have taken place to discuss progress of this project. After allocation of EU IDEA funds,
we intend to organize a formal meeting at the end of the first 6 months period to discuss the results and take decision how to
proceed.
TASK
LEADER
TASK TITLE: Operation of Ge-diodes in liquid N2
Stefan Schönert
AMOUNT SPENT
AMOUNT FORESEEN Year 1
Remaining Budget
(EUR)
SHORT DESCRIPTION
OF THE WORK IF
REQUIRED
COST CATEGORY
Euro
Personnel
0
Travel
0
Durable Equipment
0
Consumables
0
Subcontracting
0
Other Costs
0
Total
0
Description
NOTE: EU funds were not
available. Research
carried out and reported
here are financed by
institutional funding
Euro
Description
30,000 €
Postdoc financed
from autumn 2004
by idea
Postdoc at MPIK to study
adsorber materials
5000 €
Liquid
nitrogen/argon;
adsorber materials
for test
measurements
Experimental test and comparison
theoretical expectiation of
adsorber materials (cf. text)
35,000 €
Euro