HiRA: Science and Design Considerations

Transcription

1 HiRA: Science and Design Considerations Scientific Program: Astrophysics: Transfer reactions Resonance spectroscopy Nuclear Structure: Inelastic scattering Transfer reactions Resonance spectroscopy Breakup reactions Complex Reactions: Fragmentation Correlations Design Considerations: Resolution issues Angular resolution Energy resolution Mass and charge resolution Timing resolution Angular coverage Dynamic range Flexibility Matching to other devices Cost

2 HiRA High Resolution Array 20 Telescopes 62.3 x 62.3 mm 2 Active Area δθ < ±0.16 ο deg (35 cm) δε < 50 kev 1.5 mm 4 cm Design supports many configurations 1024 pixels per telescope beam Target

3 LASSA: HiRA prototype LASSA- HiRA comparisons: characteristic LASSA HiRA # telescopes 9 20 area/telescope 25 cm 2 38 cm 2 design distance 20 cm cm pitch 3 mm (16) 1.9 mm (32) total # strips electronics CAMAC ASIC E thickness 75 µm 75 µm E thickness 0.5 mm 1.5 mm CsI(Tl) thickness 6 cm 4 cm

4 HiRA project IU: Silicon development: de Souza, Caraley, Davin, Viola WU/SIU: Electronics development: Sobotka, Elson, Engel MSU/Milano/IU: Mechanical design van Goethem, Morris, Moroni, Wallace MSU: CsI(Tl) van Goethem, Wallace, Nett DAQ: MSU/IU Fox, Elson Budget: 0.54MD 0.2MD silicon

5 First studies: masses relevant to the rp-process The rapid proton capture process is a process believed to occur on the surface of an accreting neutron star in a binary system X-ray burst With X-ray telescopes we observe x-ray bursts that are believed to be produced by the rp-process.

6 The rp-process Separation energy defines path S p =(M(Z,N)-M(Z-1,N)-M p )c 2 S α =(M(Z,N)-M(Z-2,N-2)-M α )c 2

7 Single nucleon transfer reactions (p,d),(d, 3 He) 12 Be(p,d) Typical angular distributions Kinematics are forward peaked Measurements are only possible for θ<40 Good angular and energy resolution are required. Can determine an unknown mass via two-body kinematics if other masses are known. Reactions are reasonably matched at fragmentation facilities. Much better matched than (d,p). Can typically measure past the first diffraction maximum. Can provide information about l- transfer.

8 Producing a beam Stable Beams are produced in the Ion Source and accelerated in the K500&K1200 Superconducting Cyclotrons The Primary beam is then incident on a production target producing secondary beams. These beams are then separated using the A1900 Fragment Separator

9 Secondary beams from Kr primary beam If we require a beam intensity of 1 x 10 4 then we could make mass measurements of all the nuclei in yellow here without changing the setting of the fragment separator. This can work to our advantage as we will be able to use some with known masses as calibrations.

10 Possible geometry Hira Strip Array Quadrupoles Focal plane detector S800 Spectrograph with Strip array having Θ <± 0.16 deg. at Θ = 5-28 deg. HiRA covers the solid angle with about 70% efficiency. S800 spectrometer is used to detect binary reaction partner. e.g. for p( 66 As,d) 65 As, 65 As would be detected with 100% efficiency in S800 focal plane. suppresses background from breakup reactions on 12 C in CH 2 target. Experiment can be finished in several days - week using 10 4 ions/s. Device must be able to fit into the S800 chamber.

11 Experimental Challenges for (p,d) mass meas. Need good energy resolution: δe cm 2 δe lab Stop particles in silicons, CsI(Tl) serves mainly to veto fast particles. Need good angular resolution if you want to take advantage of the full solid HiRA solid angle. kinematic broadening increases with angle, move backward angle telescopes away from the target. ~1.9 mm pitch is compromise between wanting good resolution and also low interstrip hit probabilities. Major challenges are good calibrations of the silicon energy and the beam energy. Particle identification via E-E is easy for (p,d). (For elastic, inelastic, you may need TOF.)

12 Silicon energy calibration 228 Th source Silicon detectors CsI(Tl) crystals Calibration with a 228 Th α source (8.7 MeV) and a precision pulser. Source can be mounted between the 75 µm and 1.5 mm silicon detectors. Scheme has been tested with LASSA silicon detectors. It merely requires that that the columns of detectors of the array can be moved apart, one side of each silicon mount be removed and the source inserted.

13 Secondary beam characteristics The Beam spot on the production target also has a finite width. The Beam energy is defined by the momentum acceptance of your fragment separator. Typically on the order of 1-3% p/p

14 Beam position, energy & angle determination One 2 dim. PPAC at the object determines the beam ion s position at the target image Two 2-dimensional PPAC s in the dispersive intermediate image of the the S800 beam line determine the ion s angle and energy. Two removeable PPAC s at the target can check the trajectory reconstruction using the upstream PPAC s

15 Final uncertainties Uncertainties needed to be considered Beam Energy Incident angle of beam on target Target thickness Distance to HiRA (angular resolution) Detector resolution

16 Resonance spectroscopy - Radiative Capture via Coulex High Resolution Strip detector Array p 7 Li E rel 1 2 µ v v ( v v ) Yield (2J+1) Resonances relevant to hot stellar environments. 20 Na, 23 Al, 24 Si, etc. Branching ratios, Spins E.g. 20 Na resonances Energies to 10 kev accuracy.

17 Correlation Technique Experimental correlation function: ( 1 R( E )) rel Y12( E1, E2) = C + Y1 ( E1) Y2 ( E2) Correlation function in thermodynamic limit (Boal, Jennings) R( E R decay rel ) = ( E ) rel R( E = rel ) (2s i 1 coul, background 2π + 1)(2s 2 ( hc) 3 + 1) µ 2µ E ( E ) i ( 2J + 1) exp( E / T ) i + dδ de rel R decay rel rel rel app

18 Radiative Capture via Coulex 0.1 Resolution requirements Resolution <(E rel -<E rel >) 2 > 1/ d=60 cm d=35 cm d=120 cm Uses same geometry Isolated resonances which decay to the g.s. are easiest cases. 14 O { e.g. 13 N(p,γ) } 23 Al {e.g. 22 Mg (p,γ) } Direct capture, e.g. 7 Be(p,γ) is harder E (MeV) rel Need: Excellent angular resolution. governs δe*, 40 kev FWHM has been achieved. Moderate energy resolution Excellent isotopic resolution Good multi-hit capability.

19 Complex Reactions Correlation functions: Imaging of nuclear collisions Resolution requirements identical to that for resonance spectroscopy Need multi-hit capability Fragmentation and L.G.P.T. Investigations of caloric curve Isospin dependence of fragmentation, L.G.P.T., EOS Science of rare isotope production Need excellent broadrange PID Counts Li C Before Correction Before Correction C After Correction A Li After Correction Excellent PID possible With non-planar 75 µm E

20 Scaling behavior ( N, Z ) Y2( N, Z) = CY1 exp( αn + βz) α and β are proportional to difference in isospin asymmetry Appears to be respected by all statistical production mechanisms.