1. RickFEST -16/06/2008

3. Andy Sunyar - Brookhaven National Lab. - 1967

4. The Neutron Capture reaction 1.Classic Compound Nucleus Reaction 2.Not subject to the Coulomb barrier 3.Very high fluxes of neutrons available - HFBR or ILL Reactor. - At lLL targets in 5 x 10 14 ncm -2 s -1 -HFBR produced external beams of various types 4.E(exc.) = S N +E N –E γ + E R obtained from the primaries Primary Gamma ray Secondary Gamma ray

5. 1.Typically the neutron capture cross-section falls off as 1/v with increasing energy 2.However superimposed on this we have resonances when the total energy coincides with the energy of a discrete state in the compound nucleus Neutron capture cross-section as a function of neutron energy for a typical medium or heavy nucleus Note: logarithmic scales Neutron Capture Cross-section

6. Porter-Thomas Distribution Distribution of PRIMARY gamma-ray energies from 1, 3 and 10 resonances.  For 1 resonance most probable reduced intensity is zero  As we approach an infinite number of resonances the distribution becomes a Gaussian of width [2/(no.of resonances)]. In this situation we should see all primary gamma rays of low multipolarity. Failure to do so would be significant (Average Resonance Capture = ARC at HFBR)

8. Basic interest was the nature of the Gamma band in deformed nuclei 4+ 5+ 3+ 2+ Attempt No.1:- Measure intensities of “stopover” and crossover transitions and use ALAGA rules to deduce E2 intensities

9. Dumond’s exact focussing bent crystal diffraction Spectrometer. GAMS 1, II and III are All spectrometers of this type. GAMS ii and III operated together With diffraction in opposite senses So that zero error in diffraction angle cancelled. GAMS I – 5.8m radius Gams II/III – 24m radius

10. Through Tube

11. 167 Er(n,γ) 168 Er GAMS 1 Diffraction spectrometer – spectrum in 2 nd,3 rd,4 th and 5 th order Note:-In 3 rd order we are looking at ~ 14 keV

12. Spectrum in 3 rd Order from GAMS1.( 4+ - 2+) is 10 4 times more intense than its neighbour 167 Er(n,γ) 168 Er

13. (g k – g R ) Q 0 (2) is constant within the band Conclusion Main point for our story – we had seen how rich the spectrum was!!

14. Attempt No.2:- Internal Conversion using the L- Subshell ratios. 74.63 keV, 3+ - 2+ 122.83 keV, 5+-4+ Transitions in the gamma- band of 168 Er. The BILL Spectrometer – Double-focussing π√2 spectrometer

15. The Results – gamma band transitions Conclusion:- M1 admixtures remarkably constant in these nuclei. Best explanation – they are due to slightly different deformations for neutrons and protons

16. GAMS 1, II and III Dumond type spectrometers BILL – Double focussing beta spectrometer Average Resonance Capture – 2 and 24 keV Complete level scheme up to ~ 2.5 MeV

17. Porter-Thomas Distribution Distribution of PRIMARY gamma-ray energies from 1, 3 and 10 resonances.  For 1 resonance most probable reduced intensity is zero  As we approach an infinite number of resonances the distribution becomes a Gaussian of width [2/(no.of resonances)]. In this situation we should see all primary gamma rays of low multipolarity. Failure to do so would be significant (Average Resonance Capture = ARC at HFBR)

18. Average Resonance Capture at the HFBR Neutron spectrum In practice we create a beam of neutrons with a broad band of energies, which spans many resonances. In this situation the reduced primary gamma-ray intensities[I/E γ 5 ] vary only a little and reflect the multipolarity of the transition. Sc filter at HFBR  At HFBR 2 and 24.3 keV filters with a Ge pair spectrometer to detect primary gamma rays.

19. GAMS 1, II and III Dumond type spectrometers BILL – Double focussing beta spectrometer Average Resonance Capture – 2 and 24 keV Complete level scheme up to ~ 2.5 MeV 2 keV I(2 keV) I(24 keV)

21. This comprehensive level scheme is an Ideal tool for testing nuclear models and Arima and Iachello had just introduced the Interacting Boson model, where the nucleus is regarded as an inert core plus the valence particles regarded as bosons. Initially only s (L =0) and d (L=2) bosons were considered. H = – kQ.Q –k / L.L + k // P.P Rick, Dave Warner and Walter Davidson took this model and applied it to 168 Er with great success. This exploration of algebraic models became Rick’s preoccupation over the next decade or more and we will hear more about that from Alison in the next talk. See Warner,Casten and Davidson,PRC24(1981)1713

22. Comparison of the level scheme with calculations in IBA -1 Warner,Casten and Davidson, PRC24 (1981) 1713

23. Gamma-Ray Induced Doppler Broadening - GRID New opportunities arose at ILL with GAMS 4 and GAMS 5 – diffraction devices but now flat crystal Spectrometers. The nucleus recoils when it emits a gamma ray so when a Secondary gamma is emitted It will be Doppler broadened by an amount dependent on the lifetime of the state. The example shown is the 1112keV transition in the decay of the 3 1 + state In 152 Sm. Rick and Hans Borner also applied it to 168 Er.

26. Measurements at ILL of the L- and M-subshell ratios of the pure E2 (2+ - 0+) transition in 168 Er Raw Spectrum

28. The Reactor Antineutrino Spectrum and Non-Proliferation Meanwhile  Interest in measuring (anti)neutrino masses was high. To establish the initial spectrum for such measurements we used BILL to determine the cumulated beta spectrum from 235 U, 239 Pu and 241 Pu – the main sources of antineutrinos. p n + e- + νSo we can convert this to the Antineutrino spectrum.

30. Same thing for 241 Pu As a reactor runs it breeds Pu. Since The neutrino spectra are different for the three isotopes we can monitor State of the fuel by continuously measuring the spectrum. If every reactor had a suitable detector close by and the signals went directly to the IAEA in Vienna then this could become an established part of non-proliferation Treaties.

31. Search for Mono-energetic positrons from 152m Eu  Nuclear transition takes place whilst an inner shell vacancy is present.  If E(tr) exceeds 2m 0 c 2 – B(e-) then electron can go directly into the vacancy and we are left with a Mono-energetic positron.  For K shell E(e+) = E γ - 2m 0 c 2 + B(e-)  Probability depends on relative lifetimes of K vacancy and nuclear state.  Τ > 3.5 x 10 -15 s for 1511 keV level Colvin, Schreckenbach and Gelletly, J.Phys.G11(1985)L227

32. Approximate focussing arrangement of the Cauchois Spectrograph. Cauchois Geometry

33. Could one combine our active stopper with a diffraction device – in Cauchois Geometry? Active stopper = extended source Bent crystal Multi-strip detector Fitted to focal circle.

34. Could we use a thin active stopper and use it as the source for a beta spectrometer? Below is one I prepared earlier. Second step was to fill the focal plane with a continuous pixellated detector. Main point – We should not blindly follow the same approach that was successful for twenty years.

37. Cocoyoc - 2000

38. Behind every good man there is a better woman

40. Preparing the next Generation-----and the next talk.