Category Archives: timeline

position of PEARL in OYSTER reconfirmed by MT

Today, in a meeting of the management team (MT) of the RID/RST department, the importance of PEARL was (re-)confirmed by that MT. The MT has put the PEARL diffractometer on the top of the beam line instruments that are in the OYSTER program. Super!

Especially in the ambitious program of OYSTER, this guarantees that we get the required resources to have PEARL installed in the summer of 2013.

NICE results detector tests!!

We have done some more testing on the scintillator detectors developed by ISIS, UK these last few days. The aim was a “stress-test for the scintillator bank”, something quite popular these days. The previous tests (April) showed that the efficiency of the detector was some 80% of a standard 3-He detector (used to be approx 20% before these developments). We then also tried to determine the gamma sensitivity of the scintillator detector, which is/was ‘the other concern’ compared to 3-He detectors. We never seemed to manage to produce enough gammas to actually quantify that number.

This time we had the help of our radio protection service to provide us with some gamma sources that we would use to illuminate the detector while it was counting neutrons. Due to some technical and regulatory restrictions we have only determined the gamma sensitivity to be well below 1e-5 and probably below 1e-6. The reason for that is that you need so many gammas to get the damn detector out of balance. Eventually, taking the detector out of the neutron beam and putting the gamma source right in front of the detection surface, we got a hint of some ‘double counting’. The gamma sensitivity (in the no-neutron case) is approx 1e-8.

There’s still some analysis going on, but with these results so far, we can already conclude that this ISIS detector is very good alternative to an expensive 3-He detector! We now aim to have (a part of) the final detector ready for testing on our beam line within a year.


Thanks to Jeroen for the initiative! Thanks to the ISIS team for the collaboration!


The PEARL will be present(ed) at the Synew 2011 workshop tomorrow in De Rode Hoed, Amsterdam!

new tests in June of the scintillator detector

The scintillator detector as designed by the detector group of ISIS, UK has proven to be a valuable alternative to the ‘classical’ 3He detector. This was shown by the tests we did (2 May 2011) at our TOF reflectometer. As mentioned in that post, the gamma discrimination abilities need to be tested more thoroughly. We foresee those tests in June, where we will try to disturb the registration of TOF neutrons by the detector, by simultaneously overloading it with gammas from an external source.


Okay, the colloquium went fine this afternoon, but WHY DID NO-1 ask what the name “PEARL” stand for? I had a quiz in mind for the audience, but never mind. Apparently the connection of ‘PEARL’ with the near-future OYSTER project of our reactor is enough justification.

There was plenty of audience and some good questions. “PEARL”-awareness of the RID people was the aim. Mission accomplished.

Institute colloquium on 12/May/2011 15h

This Thursday (12th May 2011) the first presentation of our diffractometer (plans) for our colleagues of the institute RRR/RID. The ‘New Neutron Dutch Diffractometer’!

testing detectors…

The ISIS detector group has visited our facility to perform some tests with us on their new scintillator detectors. Scintillator detectors are usually more gamma sensitive and less neutron sensitive than the standard 3-He detectors. But since the enormous increase in the price of 3-He, more efforts have been put into the development of scintillator based detectors. The ISIS team came to the RID for tests and demonstration of clear-fibre and wavelength-shifting fibre detectors and a whole set of electronics to evaluate the output of these detectors.

During a three-day test on our reflectometer, we have compared these detectors with the standard 3-He detector of the reflectometer. The preliminary results of these tests show that the neutron detection efficiency is some 70-80% of this 3-He detector and the gamma sensitivity (without optimization of the pulse analysis of the scintillator electronics) is between 20 and 50% higher than the 3-He tube. More involved tests and optimizations need to be done for the gamma-sensitivity. A more severe testing would be counting neutrons in a strong(er) gamma background.


detector tests setup

The photo above shows the installation of one of the detectors (the aluminium box) inside the sample-chamber of our neutron-reflectometer at RID. The neutron beam impinges from the left on the scintillators inside the box (not visible) and the light generated by these scintillator crystals is amplified by the photon-multiplier-tubes (PMTs) which are read out by the electronics (not visible). The pulse-shape- and coincidence analysis of these electronics determine whether a neutron or a gamma is detected. The detectors were tested on the reflectometer, so that we could use the time-of-flight option and diafragms of this instrument. 

website announcement

The neutron powder diffractometer (in spe) is now properly announced on the web page of our group Neutron and Positron Methods in Materials (NPM2) under "Facilities" (although we’re of course in development still….).

The NPM2 group is part of the research teams "Radiation, Radionuclides & Reactors" (RRR) housed at the reactor facility Reactor Institute Delft (RID). The RRR is a section of the Faculty of Applied Sciences of the Delft University of Technology.

Now you have the complete overview….

Shopping components

With the detailed planning of the development project of the neutron diffractometer, we also need to know more precisely what the components will cost.
The two most demanding items on the list of instrument components are the neutron detector that needs a high spatial resolution and a monochromator with the right crystalite mosaic.

In a short visit to the ILL we have discussed the possibilities to develop a detector and a monochromator for our needs. On our side, we now need to see what part of that development can be done in-house at the university. This should then clarify how much budget we have to reserve for these components. The collaboration on the development has to be formally signed by both institutes.

Institute wide co-operation for the development project

The director of the institute prof. Bert Wolterbeek has formally initiated the ‘task force Diffractometer’ on Monday. Now that the main specs of the instrument are known (those that define the performance of the instrument), we foresee that we could for instance trade off some neutron beam intensity for a lower radiation background. Or the monochromator take-off angle could be reduced for easier accessibility:

Time for team work!

We need to iterate over several designs of the instrument as well as radiation shielding and technical solutions to choose the –over-all– best layout. This means the design engineers need to be involved in detail, together with shielding and radio-protection experts. The management board of the institute keeps an eye on progress.The first meeting of the task force will be coming Monday. A first rough Gantt chart of the planning is done and people need to have their say about it.