1. Backscattering on Pulsed Sources
a personal account
Colin Carlile, Uppsala University

2. I first met him in 1972 at a H in M meeting
Bert Alefeld
I first met him in 1972 at a H in M meeting
meV resolutions
100 times better !!!

3. The main message “A Better Mousetrap”
"If a man can write a better book,
preach a better sermon,
or make a better mousetrap than his neighbor,
though he builds his house in the woods,
the world will make a beaten path to his door”
Ralph Waldo Emerson 1855

4. Key People – why are they all German?

5. The original idea for IRIS
A telex from George Stirling in 1975
“an outline design of an instrument to cover IN5”
Coffee talks with Reinhard Scherm and Julia Higgins
“IN10 on the end of a guide” said Reinhard

6. “IN10 on the end of a long guide”
The concept
“IN10 on the end of a long guide”

7. The name
IRIS – the Goddess of the Rainbow
’igh
resolution
inelastic
spectrometer

8. ISIS The IRIS beamline First neutrons 16th December 1984 Inauguration
1st October 1985
The IRIS beamline

9. The neutron minefield
ISIS is for thermal/epithermal; ILL is for cold/thermal
There are no cold neutrons on pulsed sources
No guide bunches on spallation sources
Build a machine that will be
a stepping stone to IN5

10. What was the driving force?
Not to spend 10 years of my life making a pale imitation of IN5
“No cold neutrons” so a back end moderator (50% down)
So couple the moderator to the reflector
Get as close to the moderator as possible
Maximise the guide area
Get very close to a line of sight [1.1 L0]
Shield the guide closely – no gaps
Avoid backscattering analyser geometry
Avoid silicon (Bert Alefeld again)

11. “No
cold
neutrons”

12. Maximise intensity,
strengthen shielding

13. Use pyrolytic graphite
Go off backscattering,
Use pyrolytic graphite

14. The Analyser Layout

15. What happened? There were lots and lots of cold neutrons
…and 0.5mm cadmium would stop the beam !
…and create many gammas
The underlying background was terrible !! 120:1
…we cooled the graphite & it worked 4000:1
The first detector (glass scintillator) was gamma sensitive
…and so was the second detector
We installed a radial collimator
We installed a second disc chopper to suppress earlier pulses
We installed a beryllium filter
We went for higher resolution using mica (Axmann’s RXS)
We installed a diffraction detector
We employed Devinder Sivia (Mr Bayes)to professionalise peak guessing
We added a second guide so that we could maximise everything & build OSIRIS
It was 10 years before a first “science” paper came out

16. We could see the fast neutrons from
beam loss at proton injection and extraction

17. We cooled
the graphite

18. Close to a
“final” layout

19. Some Science Tribromomesitylene 3 inequivalent CH3 groups in a plane
----
Single crystal
tunnelling spectroscopy
Jean Meinnel’s group

20. Some Science Ammonia absorption in caesium-intercalated graphite ----
Simultaneous
tunnelling spectroscopy
and diffraction
John White’s group

21. Some Science Methyl pyridine A standard tunnelling line ----
The benefits of resolution

22. Some Science
Powder Diffraction

23. 2nd Generation
OSIRIS

24. So that’s the IRIS story up to 1999…
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