Making an Exotic Beam with MARS : Part 1. Brian Roeder Cyclotron Institute Texas A&M Univ. 22 June 2009

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1 Making an Exotic Beam with MARS : Pat 1 Bian Roede Cycloton Institute Texas A&M Univ. June 009

2 Oveview Motivation: Why do we need to make an exotic beam? In-flight Poduction of exotic beams Reaction Mechanisms Why we need MARS? Review of chaged paticle motion in E and fields. Concept of Magnetic Rigidity o Bρ. Concept of Velocity Filte v = E/B. Paticle Identification at the Focal Plane Enegy Loss in Mateials Bethe Bloch Equation Final Selection by the Slits Conclusion Example: Sepaation of 6 Si ( Alex Spiidon ) What we do fo 0 Na ( Alex Spiidon )? July 009 B.T. Roede - MARS Semina

Motivation: Exotic Beam Studies Must MAKE exotic beams via nuclea eactions! Would like to study exotic (adioactive, but paticle stable) nuclei away fom stability (Tea incognita egions).

3 Motivation: Exotic Beam Studies Must MAKE exotic beams via nuclea eactions! Would like to study exotic (adioactive, but paticle stable) nuclei away fom stability (Tea incognita egions). Most nuclea astophysics pocesses that fom heavy elements occu in eactions with exotic nuclei. Many exotic nuclei have shot T ½ (less than 1 day), can not dig them out of the gound, can not make tagets with them. July 009 B.T. Roede - MARS Semina 3

4 Methods of Exotic Beam Poduction (1) ISOL Isotope Sepaation On-Line Stop a light beam in a thick taget, make exotic nuclei inside taget. Sepaate exotic nuclei with chemisty limits beam types Reacceleate nuclei with a post-acceleato to expeiments TAMU will use technique simila to this (upgade 011). July 009 B.T. Roede - MARS Semina 4

5 Methods of Exotic Beam Poduction () In-flight Technique MARS and othes Heavy-ion beam on a thin taget of light nuclei, e.g. H, He, Be, etc. (Invese Kinematics) In pinciple, can poduce a beam of any isotope. Limitations: Coss sections decease as you go futhe fom stability. Must wok at high enegy due to negative Q-values (E > 0 MeV/u) Beams ae often not pue! Must use ticks to obtain pue beam. July 009 B.T. Roede - MARS Semina 5

Invese kinematics heavy-ion beam on light mass taget.

6 Invese Kinematics Fowad kinematics light-ion ion beam on heavy mass taget. Most stable beam expeiments done this way. Invese kinematics heavy-ion beam on light mass taget. Get fowad focusing of eaction poducts due to momentum consevation. Heavy-ion poduct keeps most of the kinetic enegy. July 009 B.T. Roede - MARS Semina 6

7 Reaction Mechanisms Diffeent eaction types poduce a nucleus of inteest at diffeent final enegies. Use eaction-type that maximizes poduction of the exotic nucleus! 1. Tansfe eaction Nucleon is tansfeed diectly fom taget to beam o vise-vesa. E final = E initial + Q.. Fusion Evapoation Fom a compound nucleus, poduct evapoates nucleons as it de-excites v final = v cm. 3. Pojectile Fagmentation ( > 30 MeV/u ) nucleons shaved off of heavy-ion pojectile v final = v pojectile. July 009 B.T. Roede - MARS Semina 7

8 Why do we need MARS? Can not pick and choose nuclei poduced; can only choose initial eaction of beam + taget. The most exotic nuclei (the futhest fom stability) ae often poduced at the lowest ate poduce nuclei close to stability at highe ates. Need a way to sepaate eaction poducts we do want fom those we don t want and then make that into a beam MARS! July 009 B.T. Roede - MARS Semina 8

9 MARS MARS Momentum Achomat Recoil Sepaato. Sepaates Reaction Poducts in two ways: Magnetic Rigidity Selection ( Bho ) Velocity Selection (Velocity o Wien Filte) Block out unwanted ions by closing position slits along the way. R.E. Tibble et al. Nucl. Inst. and Meth. A85, Pg. 441 (1989). R.E. Tibble et al. Nucl. Inst. and Meth. B56/57, Pg. 956 (1991). July 009 B.T. Roede - MARS Semina 9

10 Oveview of MARS Moe details in talk by Alex S. July 009 B.T. Roede - MARS Semina 10

11 Magnetic Rigidity - Basics A chaged paticle (ion) in a magnetic field moves in a cicle accoding to the Loentz foce. F centipetal Mv ρ Mv ρ Mv q = = F Magnetic = q( v B) qvb = Bρ Right-Hand Rule Definition of Magnetic Rigidity! *Fo a magnetic sepaato, Bρ = constant povides selection in p/q! * Magnetic Fields (static) do no Wok! (ΔE = 0) July 009 B.T. Roede - MARS Semina 11 ẑ xˆ ŷ

12 Example Simple Mass Sepaato V B B oz ˆ Mass sepaation condition: this case Halliday and Resnick, Fundamentals of Physics 3 d d edition (1988) = (1) 1 () mv mv = Bρ q v = qv = qv m ( 3) x = ρ m V = q Bρ July 009 B.T. Roede - MARS Semina 1

13 Bρ constant B m V = Bρ q Mv ρ = q( v B) Paticle Mass m and chage +q cuves to ight (+x diection) with adius ρ. Paticle Mass m and chage +q cuves to ight (+x diection) with adius ρ. Sepaated in position! Paticles Mass m and chage +q (and nm and +nq) cuve to ight with same adius ρ can not be sepaated in position! July 009 B.T. Roede - MARS Semina 13

Bρ constant B and ρ mv = q Bρ Magnet has fixed ρ and opening gap. Once B is set, only paticles with pope mv/q (± opening gap) get though magnet, othes hit walls (bending adius too lage o too small).

14 Bρ constant B and ρ mv = q Bρ Magnet has fixed ρ and opening gap. Once B is set, only paticles with pope mv/q (± opening gap) get though magnet, othes hit walls (bending adius too lage o too small). Paticles with highe mv/q moe igid Paticles with lowe mv/q less igid Adjusting B field fo eaction poduct of inteest in mv/q allows it to pass, othes can be blocked with slits, etc. July 009 B.T. Roede - MARS Semina 14

15 Velocity ( Wien ) Filte E( yˆ) B(ˆ) x Σ F = 0 qe = v = Fo a paticle moving along the z-axis, E-field deflects downwad (- y) and B-field (+ x) deflects upwad (+y). Paticle must be taveling at pope velocity to emain undeflected (foces balance). How does this help isotope selection? qvb July 009 B.T. Roede - MARS Semina 15 E B Halliday and Resnick, Fundamentals of Physics 3 d d edition (1988)

16 Change y position as q/m Suppose only E-field : Equations of Motion: E F a Z y y = qe = ma = = qe m vt = at qez = mv ( yˆ) = qe ( yˆ) ( yˆ) July 009 B.T. Roede - MARS Semina 16

17 Change y position as q/m Now add in v = E 0 /B 0 : Amount of Deflection If v < E 0 /B 0 If v > E 0 /B 0 F F E E > < F F B B y = q m yˆ + yˆ B 0 E Z 0 deflection deflection Ions with diffeent q/m ae sepaated in y! Allows Paticle Identification (PID) in focal plane (with enegy loss in detecto). July 009 B.T. Roede - MARS Semina 17

18 Enegy Loss in Taget Detecto de dx q v Bethe-Bloch fomula enegy loss in mateial (silicon detecto) popotional to squae of (q/v) independent of mass. Enegy-loss in mateials can be calculated with pogams (e.g. SRIM/TRIM, LISE) If v is simila fo all ions afte velocity filte, then - de/dx q. July 009 B.T. Roede - MARS Semina 18

19 Paticle Identification 4 Mg + 9 Be Paticles sepaated on y axis by enegy loss. Paticles sepaated on x axis by position in y. Fo diffeent q/m, paticles ae in diffeent hypebolas. July 009 B.T. Roede - MARS Semina 19

20 Final Selection by the Slits p( 46 Ti, 46 V)n Cente ion of inteest (seconday beam) in y by matching Bρ of D3 to velocity v selected by velocity filte See Alex s talk. Block out othe ions by closing vetical ( y ) slits in font of taget detecto. July 009 B.T. Roede - MARS Semina 0

21 Conclusion Can make an exotic beam to study nuclei fa fom stability with eactions in Invese Kinematics Can make a seconday beam of an isotope of inteest by sepaation in p/q (magnetic igidity) and q/m (velocity filte). Limitations : Must be able to conduct expeiments with highe enegy beams o degade enegy of beam to desied enegy. Beams with vey simila o equal Bρ can not be sepaated in position (need enegy loss technique). Questions? July 009 B.T. Roede - MARS Semina 1

21 MAGNETIC FORCES AND MAGNETIC FIELDS

21 MAGNETIC FORCES AND MAGNETIC FIELDS CHAPTER 1 MAGNETIC ORCES AND MAGNETIC IELDS ANSWERS TO OCUS ON CONCEPTS QUESTIONS 1. (d) Right-Hand Rule No. 1 gives the diection of the magnetic foce as x fo both dawings A and. In dawing C, the velocity