Intense beams of n e emitters produced with the ISOL method

1. Intense beams of ne emitters produced with the ISOL method Neutrino factory working group meeting CERN, 22 August 2001 http://cern.ch/ukoester/betabeam.ppt Ulli Köster, EP-ISOLDE

2. A bit of history 1951: First ISOL beams at Niels Bohr Institute (Copenhagen) ISOL beams of 89-93Kr Study of ne-b angular correlation by recoil detection. Ulli Köster, EP-ISOLDE

3. To remember: • ISOL method is approved technique since 50 years • ISOL method allows to use “thick” targets • noble gases are very suitable for ISOL method • primary beam does not need to hit the ISOL target directly • radioactive ion beams (RIB) might be useful for neutrino physics Ulli Köster, EP-ISOLDE

4. Optimize RIB intensity All steps of the separation chain need to be optimized! Ulli Köster, EP-ISOLDE

5. Maximize signal from RIB Requirements: 1. Powerful driver accelerator 2. High production cross-sections and “thick” target (in mol/cm2) 3. High efficiency for release from target 4. High ion source and transport efficiency 5. Rapid transport to avoid decay losses 6. High detection efficiency by the “end user” 7. Introduce selective steps to provide “pure” beams (free from isobaric contaminations) Ulli Köster, EP-ISOLDE

6. Suitable b- emitters Ulli Köster, EP-ISOLDE

7. Suitable b+ emitters Ulli Köster, EP-ISOLDE

8. “Easy” ISOL elements Elements compatible with a “cold-body” ECR ion source Ulli Köster, EP-ISOLDE

9. 6He production by spallation target(p,X)6He • Higher production from heavier targets. • Rise of multifragmentation cross-sections saturates around 10 GeV proton energy. Ratio s/E peaks at 2-6 GeV. • Silberberg & Tsao, semi-empirical model, Phys. Rep. 191 (1990) 351. • Exp. values: M. Gloris et al., NIM A463 (2001) 593. Ulli Köster, EP-ISOLDE

10. 6He production by spallation 1. Spallation scenario: • 80 cm long UCx/graphite target (200 g/cm2 U) • 100 mA of 2.2 GeV proton beam • production rate: 1.8E13 per s • beam heating 30 kW (radiation cooled <50 W/cm2) • target lifetime? 2. Spallation scenario: • 40 cm long Hg jet (droplets) with 75% average density • 100 mA of 2.2 GeV proton beam • production rate: 2.7E13 per s • beam heating 50 kW • extraction efficiency? Ulli Köster, EP-ISOLDE

11. 6He production by 9Be(n,a) • 9Be(n,a)6He reaction favorable: • Threshold: 0.6 MeV • Peak cross-section 105 mb • Good overlap with evaporation part of spallation neutron spectrum: n(E)E*exp(-E/Ee) • Ee: 2.06 MeV for 2 GeV p on Pb G.S. Bauer, NIM A463 (2001) 505 • BeO very refractory s9Be(n,a)6He EXFOR data • 6Li(n,p)6He reaction less interesting: • Threshold: 2.7 MeV • Peak cross-section 35 mb • Li compounds rather volatile Ulli Köster, EP-ISOLDE

12. 6He production by 9Be(n,a) Converter technology: J. Nolen et al., NPA, RNB-5, in press. Layout very similar to planned EURISOL converter target aiming for 1015 fissions per s. Ulli Köster, EP-ISOLDE

13. 6He production by 9Be(n,a) 3. Converter scenario: • 60 cm long liquid Pb or water-cooled W converter • 100 mA of 2.2 GeV proton beam • about 20 to 40 neutrons produced per incident proton (dependent on converter diameter, see: G.S. Bauer, NIM A463 (2001) 505) • thereof about half in suitable angle and energy range • BeO fiber target in 5 cm thick concentric cylinder around • packed to 10% theoretical density (very conservative) • production rate: roughly 4E13 per s (requires MC calculation!) Ulli Köster, EP-ISOLDE

14. Oxide fiber targets Oxide fiber targets: • high open porosity  fast release • intrinsic stability of fiber structure reduces sintering problems • excellent on-line performance of commercial zirconia and ceriafelt • “homemade” production of titania and thoriafelt by fossilization process Ulli Köster, EP-ISOLDE

15. Release efficiency • SPIRAL graphite target (6 kW beam power) 50 % for 18Ne, 90% for 19Ne, 40% for 34Ar, 47% for 35Ar N. Lecesne et al., NIM B126 (1997) 141 • with optimized graphite: 100% for 6He and 35Ar F. Landré-Pellemoine et al., NPA, RNB-5, in press. • 20% total efficiency (release & ionization) for 14O S. Gibouin et al., to be published • To come: TARGISOL optimization Ulli Köster, EP-ISOLDE

16. Ionization efficiency • Standard ISOLDE ion source: FEBIAD very low efficiency for light elements with I.P.>14 eV • various 1+ ECRIS: 72% for 19Ne (M. Oyaizu et al., RSI 69 (1998) 770.) 90% for Ar with “Picogan” (P. Sortais, priv. comm.) • start with efficient 1+ ion source and strip to reach final q/A: fast and efficient, but separate bunching required • ECRIT (bunch width, efficiency?) N. Chauvin et al., NIM A419 (1998) 185. • pulsed gating potential method (M. Oyaizu, see above) Ulli Köster, EP-ISOLDE

17. Production of b+ emitters • spallation of close-by target nuclides: 18,19Ne from MgO and 34,35Ar in CaO production rates of about 1E12/s (with 100 mA proton beam, cross-sections of some mb and a 1 m long oxide target of 10% theoretical density) • alternatively use (a,n) and (3He,n) reactions: 12C(3,4He,n)14,15O, 16O(3,4He,n)18,19Ne, 32S(3,4He,n)34,35Ar (intense 3,4He beams of several 10 MeV are required) Ulli Köster, EP-ISOLDE

18. Summary 1. 6He beams with intensity >1013 ions/s can be produced by conservative extrapolation of conventional ISOL technology. 2. Suitable b+ emitters can be produced by conservative extrapolation of existing ISOL technology with intensities of some 1011-1012 ions/s. 3. Further enhancements possible by dedicated target optimization. 4. These beams are dc or have a long bunch length (some ms), extreme bunching (ms) requires further developments! Ulli Köster, EP-ISOLDE

19. Polarized RIBs? • Switching the longitudinal beam polarization allows to change the angular asymmetry of the n-emission direction in the center-of-mass frame. • Requires isotopes with I > 0! • High degree of polarization reachable by collinear optical pumping. Feasible for Li, Ne, Na, Ar, etc. e.g.S.A. Ahmad, Hyp. Int. 74 (1992) 241 • Nice feature, but physics application? Ulli Köster, EP-ISOLDE