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Due to the high sensitivity for hydrogen, the detection and quantification of moisture and moisture transport processes are some of the key topics in neutron imaging. Especially when dealing with hygroscopic material, such as wood and other porous media, it is crucial for quantitative analyses to know and control the ambient conditions of the sample precisely. In this work, a neutron transparent climatic chamber is presented, which was designed and built for the imaging facilities at the Paul Scherrer Institut (PSI), Villigen (CH). The air-conditioned measuring system consists of the actual sample chamber and a moisture generator providing air with adjustable temperature and relative humidity (%RH) (up to a dew point temperature of 70°C). The two components are connected with a flexible tube, which features insulation, a heating system and temperature sensors to prevent condensation within the tube. The sample chamber itself is equipped with neutron transparent windows, insulating double walls with three feed-through openings for the rotation stage, sensors for humidity and temperature. Thermoelectric modules allow to control the chamber temperature in the range of -20°C to 100°C. The chamber allows to control the climatic conditions either in a static mode (stable temperature and %RH) or in dynamic mode (humidity or temperature cycles). The envisaged areas of application are neutron radiography and tomography investigations of dynamic processes in building materials (e.g. wood, concrete), food science and any other application necessitating the control of the climatic conditions.
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Physics Procedia 88 ( 2017 ) 200 207
Available online at www.sciencedirect.com
1875-3892 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of ITMNR-8
doi: 10.1016/j.phpro.2017.06.028
ScienceDirect
8th International Topical Meeting on Neutron Radiography, Beijing, China, 4-8 September 2016
Design and applications of a climatic chamber for in-situ neutron
imaging experiments
David Mannes
*
, Florian Schmid, Timon Wehmann, Eberhard Lehmann
Laboratory for Neutron Scattering and Imaging, Paul ScherrerInstitut, CH-5232 Villigen PSI, Switzerland
Abstract
Due to the high sensitivity for hydrogen, the detection and quantification of moisture and moisture transport
processes are some of the key topics in neutron imaging. Especially when dealing with hygroscopic material, such
as wood and other porous media, it is crucial for quantitative analyses to know and control the ambient conditions of the sample
precisely. In this work, a neutron transparent climatic chamber is presented, which was designed and built for the imaging
facilities at the Paul Scherrer Institut (PSI), Villigen (CH). The air-conditioned measuring system consists of the actual sample
chamber and a moisture generator providing air with adjustable temperature and relative humidity (%RH) (up to a dew point
temperature of 70°C). The two components are connected with a flexible tube, which features insulation, a heating system and
temperature sensors to prevent condensation within the tube. The sample chamber itself is equipped with neutron transparent
windows, insulating double walls with three feed-through openings for the rotation stage, sensors for humidity and temperature.
Thermoelectric modules allow to control the chamber temperature in the range of -20°C to 100°C. The chamber allows to control
the climatic conditions either in a static mode (stable temperature and %RH) or in dynamic mode (humidity or temperature
cycles). The envisaged areas of application are neutron radiography and tomography investigations of dynamic
processes in building materials (e.g. wood, concrete), food science and any other application necessitating the
control of the climatic conditions.
© 2017 The Authors. Published by Elsevier B.V.
Peer-review under responsibility of the organizing committee of ITMNR-8.
Keywords: Neutron imaging; in-situ experiments; climate controlled sample chamber
* Corresponding author. Tel.: +41 56 310 4610; fax: +41 56 310 3131.
E-mail address: david.mannes@psi.ch
© 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of ITMNR-8
David Mannes et al. / Physics Procedia 88 ( 2017 ) 200 – 207 201
1. Introduction
Qualitative and quantitative investigations on the moisture content and its changes over time are one of the
important topics which are studied using neutron imaging methods. The examined materials and questions are
manifold and range amongst others from porous building materials such as concrete, asphalt, stone or timber
(Poulikakos et al. 2013, Zhang et al. 2011, Dewanckele et al. 2014, Sedighi-Gilani et al. 2012) over the water
content of fruits (Defraeye et al. 2016) to the behaviour of canvas used for paintings (Boon et al. 2015). As most of
the studied materials are hygroscopic, the ambient climatic conditions are crucial for the interpretation. So far, for
many experiments carried out at PSI only the temperature and relative humidity could be documented but in many
cases not controlled in a proper way. For several experiments, first attempts to control the climate were successfully
carried out using provisional solutions (Mannes et al. 2009, Hendrickx et al. 2016), nevertheless these were no
permanent reliably reproducible solution unlike the permanent installation, which is available at the NIST imaging
facility (Hussey et al. 2010). To overcome this issue, a dedicated climate controlled in-situ measurement system was
constructed and built for the neutron imaging facilities at PSI.
Nomenclature
PTFE Polytetrafluoroethylene
PSI Paul Scherrer Institut
RH relative humidity in %rh
ROI region of interest
'T temperature difference achievable compared to ambient temperature in K
2. Methods
The system for the control and regulation of climatic condition, i.e. temperature and relative humidity (RH), consists
of three components: a neutron transparent sample chamber, a vapour/moisture generator and a connecting tube. The
experimental chamber as well as the moisture generator can also be used separately for experiments or
preconditioning and storage of samples. The experimental chamber features automatic temperature control, the
moisture generator produces an air flow with a defined temperature and moisture content; the connecting tube
transports the moist air from the moisture generator to the experimental chamber assuring that any condensation
within the transporting tube is minimised. In normal (i.e. combined) operation all three components are
electronically connected and controlled by a computer using a LabView based interface.
In the following the three components will be described in detail.
2.1. Sample chamber
The sample chamber is designed to fit the medium-sized detector system (Midi-Box) used at the neutron
imaging facilities at PSI featuring a maximum field-of-view of 150 mm x 150 mm (Kaestner et al. 2011). The
design of the experimental chamber follows the dimensions of the indicated setup as the neutron transparent
windows in the front and back side of the chamber fit these dimensions. The inner dimensions of the actual
measuring chamber are 160 x 160 x 160 mm3. Figure 1 shows a detailed drawing of the sample chamber.
The walls of the chamber are built as a multi-layered sandwich construction. The innermost layer consists of 1
mm thick borated aluminium fixed at a distance of 20 mm on copper plates, which differ in thickness from 10 mm
on the lateral sides to 5 mm on top and bottom. The borated aluminium, which can also be found on the front panel
around framing the neutron transparent window, reduces the irradiation and thus activation of the copper chamber as
well as capture of neutrons scattered by the sample. The copper cuboid is covered by a 30 mm thick aerogel
insulation layer wrapped in neoprene. This insulation layer is finally enclosed by a 1.5 mm aluminium cladding
serving as protection against mechanical damage and fixation point for external components. The front and back
panel of the experimental chamber show similar composition with exception of the neutron transparent windows,
202 David Mannes et al. / Physics Procedia 88 ( 2017 ) 200 – 207
Figure 1: Drawing of the temperature controlled sample chamber; A) outside view: a neutron transparent window, b cooling system, c- inlet for conditioned air; B) cutaway view: d
borated aluminium, e heat exchanger, f copper wall, g aerogel insulation, h aluminium cladding, i stone wool, j thermo-electric module, k circulating fan, l PTFE-shaft
to rotation stage, m aluminium sample holder / rotation table, n humidty / tempereature sensor
David Mannes et al. / Physics Procedia 88 ( 2017 ) 200 – 207 203
which consists of 1 mm of aluminium on the inside, 20 mm of stone wool in the back panel respectively 30 mm of
stone wool in the front panel and 0.5 mm aluminium on the outside. The front panel can be removed to access the
inside of the chamber and to insert or retrieve a sample; the back panel, towards the detector is fixed.
The temperature in the chamber can be regulated with two thermo-electric modules mounted in the lateral copper
walls. The heat is removed by two CPU water cooled systems which are mounted onto the modules and connected
to a ventilator system on the top side of the chamber. The thermo-electric modules have each a power of 200 W and
allow to regulate the wall temperature and hence the air temperature within the experimental chamber compared to
the ambient temperature within a range of 'Tmin=-40K to Tmax=100°C. The temperature within the chamber can thus
be adjusted with a given ambient temperature of 20°C in a range between -20°C and 100°C. The maximum heating /
cooling rate is limited to approx. 2 Kmin-1. The temperature and relative humidity are controlled by sensors
embedded in the wall of the chamber and giving feedback to the control electronics.
The air inside the closed chamber is circulated by two fans positioned in the lateral sides; they transport the air
from the centre through circular openings in the lateral sides of the borated aluminium onto the position of the
thermoelectric modules fixed on the outside of the copper layer. From here, the air flows up and downwards the gap
between the lateral borated aluminium layer and the copper layer, which is also the location of the inlet for the
conditioned air arriving from the moisture generator. In the gap a heat-exchange system is placed, whose cooling
fins additionally help to define the air flow direction. After the air flow reaches the gap at the top and bottom side it
is redirected to the front and back side of the chamber and flows back into the main chamber along the neutron
transparent windows. This system allows to regulate the temperature quickly and mix the air within the chamber
with the moist air from the moisture generator without adding too much of a directed air flow in the vicinity of the
tested sample.
The bottom plate shows three circular openings ( = 20 mm) through which a shaft connecting the rotation stage
with one of the disc shaped sample holder can be fitted. These inlets are at 17 mm, 42 mm and 82 mm from the back
neutron windows inner wall, allowing to minimise the distance to the detector according to the dimension of the
investigated sample. The connecting shaft is made of Polytetrafluoroethylene (PTFE), while the sample holders
consist of Aluminium disks with a respective diameter of 25 mm, 75 mm and 150 mm. An additional circular
opening with a diameter of 30 mm is positioned in the centre of the top side. The opening allows for the feed-
through of additional cables or tubes and limited in-operandi manipulation of a sample without having to open the
whole box and thus disturb the conditions inside the chamber.
The chamber can either be used in combination with the moisture generator and the connecting tube or stand-
alone; then only the temperature can be regulated via the integrated electronic control.
2.2. Connecting tube
The connecting tube transports conditioned air from the moisture generator to the experimental chamber
minimising the risk of condensation on the way. The tube itself is 2 m long and consists of a polyamide tube ( = 4
mm), which is wrapped with heating winding and insulated with a 5 mm thick aerogel layer and covered with a 13
mm neoprene layer and a fabric tube as outermost layer. The tube features temperature sensors at both ends of the
tube, which give feedback to the control electronics regulating the heating winding.
2.3. Moisture generator
The moisture generator is a customised aGEPRO-V4 (by ADROP, Fürth, Germany). The generator works along
the principle of mixing dry and humid air. The dry air is provided by a pressurised air supply system, while the
humid air is produced in an internal humidifier chamber. The two gas flows are adjusted with a mass flow controller,
the actual moisture regulation is effected by a reference moisture sensor and a microcontroller. The conditioned air
can be adjusted in a RH-range from 5%rh to 90%rh and a temperature range from 10°C to 70°C with an air flow up
to 1 lmin-1.
Besides the normal operation with the presented climate chamber, the moisture generator is also available as
stand-alone system or to provide a conditioned air flow to any potential in-situ measuring chamber custom-designed
for a specific experiment.
204 David Mannes et al. / Physics Procedia 88 ( 2017 ) 200 – 207
Table 1 gives an overview on the specifications of the full climate controlled system.
Table 1: Overview on the specification of the climate controlled system
Specifications
Inner dimensions of the sample chamber
160 x 160 x 160 mm3
Maximum field of view
150 x 150 mm2
Temperature range
'Tmin=-40K to Tmax=100°C
Heating / cooling rate
2 Kmin-1
Relative humidity range
5%rh to 90%rh
Air flow
1 lmin-1
3. First experiments Results and Discussion
First experiments were carried out at the NEUTRA (Lehmann et al. 2001) and ICON (Kaestner et al. 2011) beam
line at PSI using a thermal and cold neutron spectrum respectively. Figure 2A shows the experimental setup at
ICON. The climatic chamber is directly mounted on the detector and connected to the moisture generator with the
insulated and heated connecting tube. The experiment with the empty sample chamber shows a relatively high
homogeneity over the whole field of view. The experimentally determined mean transmission in the area of the
neutron transparent window is 90% for ICON and 94% for NEUTRA (cf. Figure 2B). Another transmission test
series at ICON with the empty chamber at 20°C and 5%rh, 60%rh and 95%rh showed no effect of the relative
Figure 2: A) First experimental setup at the ICON beamline at PSI: a) detector; b) experimental chamber; c) insulated, heated connecting tube;
d) moisture generator; B) flat-field corrected transmission image trough the neutron transparent window of the climatic chamber with false
colour coding.
David Mannes et al. / Physics Procedia 88 ( 2017 ) 200 – 207 205
humidity on the transmission. Figure 3 shows an estimate to which extent the transmission will be affected by water
vapour saturated atmosphere within the sample chamber at higher temperatures for the beamlines NEUTRA and
ICON. The transmission is barely affected by the water content within a temperature range from -20°C up to 50°C,
as the decrease is here always clearly below 1%; at 50°C the transmission is diminished by 0.48% at NEUTRA and
by 0.65% at ICON. With increasing temperatures up to 100°C and water saturated atmosphere the transmission will
decrease by 3.3% at NEUTRA and 4.5% at ICON.
As a first performance test measurement, D2O was frozen in-situ at the cold neutron beam-line ICON. As
detector system a scintillator-digital camera was used, including an Andor neo sCMOS-camera with 2560 x 2160
pixels and a field-of view of 117 mm x 99 mm, resulting in a pixels size of 46 µm. The scintillator was a 100 µm
thick 6LiF:ZnS screen while the exposure time was set to 8 s. For the experiment the temperature was first set to 0°C
for several hours to check how fast the temperature can be reached starting from ambient temperature, how fast the
regulation would take effect, when reaching the desired value (overshoot) and if and how good the temperature
could be held constant over time. Control of the relative humidity was neglected for this experiment. After 300
minutes at 0°C the temperature was set to -15°C which was the minimum possible with the ambient temperature of
25°C. Figure 4 A shows the D2O-filled cylinder during the experiment; Figure 4 B shows the recorded values for the
air temperature and relative humidity inside the experimental chamber during the experiment. The set minimum
temperature was reached relatively fast as the cooling of the chamber was already started before the chamber was
closed and the actual experiment started. The overshoot was moderate (-1.3°C) and corrected within few minutes.
The temperature was then held constant at the set 0°C within a very narrow temperature band of r 0.05°C. Freezing
of the D2O started only after the temperature was reduced after 300 minutes to values beneath 0°C. The images
shown in Figure 4 A have all been recorded in the short time between the minute 300 and 350 with exception of the
first one in the upper left corner. The freezing itself starts as thin layer from the bottom and then spreads to the outer
wall. After the start, the freezing process only takes a couple of minutes until the full sample is frozen.
Figure 3: Theoretical transmission change (
Transmission) for water vapour saturated atmosphere at different temperatures and within the
sample chamber at the neutron imaging facilities NEUTRA (thermal spectrum) and ICON (cold spectrum) induced by increasing water content.
206 David Mannes et al. / Physics Procedia 88 ( 2017 ) 200 – 207
4. Summary
A system to perform neutron imaging experiments under controlled climatic conditions was designed,
constructed and implemented at the neutron imaging facilities at PSI. The system consists of three components: a
temperature controlled sample chamber, a moisture generator and a temperature controlled connecting tube. Sample
chamber and moisture generator can be used as stand-alone devices.
First functional tests have been carried out successfully at the two neutron imaging beamlines at PSI, showing the
performance of the system which allows to control temperature (ca. -20°C to 100°C) and relative humidity (ca.
5%rh to 90%rh). The system showed quick responsivity and good stability. The transmission for neutrons is with 90%
for a cold neutron spectrum and 94% for a thermal neutron spectrum adequate to perform even time dependent
processes with relatively short exposure time. The system is fully electronically controlled and can be either be
accessed via user interfaces on the sample chamber and the moisture generator or directly via LabView based user
interface on a computer. This allows to control and to document the climatic conditions over the experiment
duration. The system can either be run in a static mode with stable temperature and relative humidity or in dynamic
mode with changing climatic conditions (e.g. cycles or ramps).
The setup is available as infrastructure at the neutron imaging facilities at PSI and is accessible through the user
office.
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Figure 4: A) Freezing of D2O in a thin-walled aluminium cylinder mesured at the ICON-beamline at PSI. The less dense and hence less
attenuating ice front starts growing from the bottom and the wall. B) Diagram showing the relative humidity and the air temperature inside the
experimental chamber during the first performance test.
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... The drying experiment was realized in a climate chamber of size 160 × 160 × 160 mm 3 [27], which was cooled by two Peltier elements. It was equipped with an individually designed depressurized cylindrical aluminum drying chamber with an inner diameter of 25.5 mm, outer diameter of 28.75 mm, and height of 30 mm, mounted on a rotating plate in the center of the climate chamber ( Figure 2). ...
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