1. Development of solid hydrogen target in RIKEN RIKEN T. Ohnishi, H. Takeda, T. Suda KEK S. Ishimoto, S. Suzuki RCNP Y. Takahashi ANL I. Tanihata  Introduction  System  Solid hydrogen target with thin film  Windowless solid hydrogen target  Summary

2. Solid hydrogen target for RI beam experiment Introduction High energy and angular resolutions are needed. 1.Thin and flat target 2.Uniform density 3.Low background Windowless solid hydrogen target Solid hydrogen target with thin film Proton elastic scattering, (p, 2p) reactions and etc.. t=1 ～ 5 mm d=20 ～ 30 mm Requirements

3. Previous work TRIUNF, KEK Cooling system: Liquid He system For RI beam Small system: to cover large solid angle and set easily on the beam line Large target: d > 20 mm KEK: t=5 ～ 10 mm, d=10 ～ 20 mm We develop small system and more thinner target. Window less solid hydrogen target TRIUNF: P. E. Knowles,et. al. Nucl. Instr. Meth. A368(1996)604. KEK : S. Ishimoto, el. al. Nucl. Instr. Meth. A480(2002)314.

4. System Gas Flow system Cryostat Vacuum Chamber

5. Cryostat: SUMITOMO RDK-415D Cooling power 1.5W@4K Gas Flow system: Pressure Control Pt-Co resistance thermometer Radiation shield: Copper cylinder Cell 2 nd stage 1 st stage Copper block H2 tube 368mm

6. Solid hydrogen target with thin film 300K G-H2 in/out t=3 mm Stycast-2850FT PtCo thermometer Mylar φ30 mm

7. 300K G-H2 in/out Stycast-2850FT Stycast-1266 PtCo thermometer

8. 11min 20sec P set =60 Torr Result Good result 3min 40sec P start =0.35 atm Solid Liquid Bad result T=3.7K 50 μm Mylar

9. Liquid Solid Void Liquid

10. Keyence LK500 H.R. Mode; 350 +/- 100 mm Linearity; +/- 0.1% of FS Resolution; 10 µm Measurement of thickness Vacuum x L Target LK500

11. t=3 + d = 3.6 mm 3 mm d 25 μm Mylar

12. Experiment R378@RIKEN

13. Windowless solid hydrogen target t=7 He gas 5 atm

15. Result After 10 days H2 Flow Start H2 Flow Stop Plates Release 3 mm cell P chamber (start) ～ 10 -5 Torr

16. Average thickness 2.7 mm Measurement of thickness

17. Experiment Proton elastic scattering Density distribution of unstable nuclei RI beam NaI array MWDC Vacuum chamber Window less solid hydrogen Si Chamber Beam tracker Recoil Proton: 1 ～ 100 MeV Energy resolution < 600 keV(FWHM) RI beam: 200 – 300 MeV/A t = 1 mm

18. Summary We have developed small solid hydrogen target system. 1: Solid hydrogen target with thin film d = 30 mm, t = 3 mm, Mylar 25,50μm Clear solid hydrogen target without void. Thickness measurement. 2: Windowless solid hydrogen target d = 30 mm, t = 3 mm Clear solid hydrogen target without void. Thickness measurement. 10 days operation Next step: More thinner window less target, t = 1 mm