Nuclear electronics for NCC measurements and training

1. Nuclear electronics for NCC measurements and training J. Bagi, J. Huszti, K. Szirmai Department of Radiation Safety huszti@iki.kfki.hu

2. Contents • IKI list mode equipment • Neutron coincidence counting • IKI instruments and software • Comparison with JSR-14 • Virtual source • Concept • Applications • Educational use

3. Neutron coincidence counting Basic assumption: Spontaneous fission rate is proportional to plutonium mass • Spontaneous fission produces multiple neutrons per event • (α,n) processes are more frequent • Fission neutrons are not detected coincidently but they are time correlated • Rossi-alpha distribution • Event probability after a trigger • Time correlated events are in the near field • Far field events are not correlated with trigger

4. Multiplicity counting • Multiplicity distribution • Probability of event numbers in a time interval • Building event number distribution in a near and far gate • Difference of near and far gate describes coincident neutrons • Point model • Uses first three multiplicity moments • Solution for effective plutonium mass, neutron multiplication factor and (α,n) contribution

5. IKI list mode equipment • Virtual instrument • Hardware box connected to a PC • All controls and display are on the PC monitor • List mode • Saving follow-up times • Evaluating with different parameters • Instrument family • Based on the same hardware platform: uniform look • Control and data transfer is made via USB line • Hardware identifies itself • Handles impulse rates up to 3∙106 cps

6. IKI instruments • Single channel list mode hardware • High voltageoption • Multichannel list mode hardware • Simple model • Model with channel number handling Virtual source

7. Multichannel device • Multichannel device • Detectors contain several amplifiers • Amplifier outputs are merged for data acquisition • Deadtime loss due to merging is growing with count rate • Correction may be greater than measured value • Multichannel operation reduces deadtime correction considerably at high count rates

8. Channel information handling • Saves channel number with each follow-up value • Channel information handling extends PTR by several new features • Increased reliability by checking individual channels • Coincidence rates and Rossi-alpha distribution for individual channels • Data of defect channel can be subtracted after acquisition • By groupingof channels ring ratios can be calculated

9. Data acquisition software • Handles single channel and multichannel units • Displays channel and ring rates • Repeated measurements • Graph expandable and collapsible even while data acquisition • Displaying previously recorded data files • Channel operations on list mode files

10. Coincidence rate calculation • Very fast processing • Predelay, gate width and long delay can be set • The same data set can be evaluated with different parameters • Program performed well at ESARDA NDA Benchmark test

11. Rossi-α distribution • Detection probability after a trigger event in function of time • Random events have a uniform distribution whereas fission neutrons are time correlated • Dieaway calculation by fitting

12. JCC-31 Comparison with JSR-14 • For multichannel measurements preamplifier outputs of detector were used • JCC-31 has only six preamplifiers JSR-14 Copy PTR-02 PTR-16 • Single channel version in parallel with JSR-14 • Copy output of PTR-02 used JSR-14 JCC-31

13. Comparison results • Good agreement with JSR-14 results • Data without deadtime correction • At high count rate multichannel version compensates for impulse loss resulting from merging of preamplifier signals

14. Virtual source Virtual source is a toolfor replaying impulse trains recorded with a list mode device.It opens new possibilities for NCC Virtual source Computer with impulse train library • Can feed any standard data acquisition unite.g. JSR-14, AMSR, PTR • Replaces real source and detector • Extendable impulse train library • Replays list mode data and software-generated artificial pulse trains Data acquisition unit

15. Replacing real source and detector • High efficiency detectors are difficult to move because of their large mass • Transporting radioactive sources especially nuclear ones involves a lot of administration With a virtual source neither a source nor a detector nor paperwork is needed for neutron coincidence training. • The virtual source system can be transported like a laptop and no paperwork is needed • Great freedom in establishing training sites because some training can be performed without any real sources

16. Virtual source applications • Training and Educational Tool for NCC • Demonstrating basic features of coincidence spectra by artificially generated impulse trains • Easy transport gives more freedom in selecting and preparing training sites • Virtual source library gives the possibility of investigating sources that trainees would not have access to or not present at the training site • No radiation hazard • Service generator • Signal generator and virtual neutron detector in one small unit • No real sources are needed for instrument testing • The same random pulse train can be reproduced many times

17. Classroom use of virtual source • Four identical output channels • Teams connected in star topologyare independent of each other • Additional teams can be lined up through the copy output of PTR-02

18. Exercises with virtual source Demonstrating the basics of neutron coincidence counting • Three-stage exercise plan with software-generated periodic, burst and random impulse trains • Several simple tasks at each stage Analyzing real spectra • Introduction to most frequent sources • Application of basic knowledge to real measurements Determining the type of unknown source • Application of D/S-method of IKI

19. Distribution basics Every stage demonstrates some basic characteristics of the distributions Follow-up Multiplicity Rossi-alpha • Periodic: multiplicity depends on gate width, building-up of Rossi-alpha Periodic • Burst: interpreting follow-up distribution, predelay Burst Random • Random: variants of multiplicity spectrum

20. Analyzing real spectra • Getting familiar with basic source types • Basic impulse train library • Impulse trains measured in other laboratories can be added to library PuBe Cf-252 Follow-up Multiplicity Rossi-α

21. Identifying unknown source Application of D/S method developed in IKI Reference sources • Data acquisition • Calculation of coincidence rates • Setting up classification diagram • Unknown sample • Data acquisition • Calculation of coincidence rates • Determining source kind from D/S value

22. Exercises – completion Real source handling is required • No sample handling exercise • Using of detector Virtual source reduces training costs • Basic training can be held in a simple classroom • Training in the laboratory is shorter • Trainees are better prepared when measuring with real sources

23. Conclusion • List mode measuring is emphasized in IAEA R&D objectives • Laboratory prototype available • Multichannel prototype extends measuring capability into million cps range • Virtual source is a spin-off product of list mode • Application of virtual source in training • Cost reducing • No radiation hazard

24. Thank you for your attention! www.iki.kfki.hu/radsec/research huszti@iki.kfki.hu