Production and Separation of Radioactive Beams. Mg and 20 Na with MARS

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1 Production and Separation of Radioactive Beams 20 Mg and 20 Na with MARS Gopal Subedi, Colby College REU 2009, Cyclotron Institute, TAMU Advisor: Dr. Robert E. Tribble August 23,

2 Overview Motivation MARS: what? why? working mechanism. Some terminologies. REU group experiment 20 Na production, separation, setup, decay, etc. 20 Mg experiment (production and separation): steps, results, data analysis Conclusion. 2

3 Motivation (1) Heavy elements formed by reactions with exotic nuclei in nuclear astrophysical processes. Interested in studying exotic nuclei away from stability. Make exotic beams via nuclear reactions in the laboratory. 3

This experiment is very hard to conduct directly in the labs.

4 Motivation (2) Breakout from the hot CNO cycle if 19 Ne + p 20 Na* into the rp process. Interested in the reaction rate of 19 Ne(p,γ) 20 Na in stars. This experiment is very hard to conduct directly in the labs. Use indirect methods in lab using facilities like MARS. 20 Mg β-delayed proton emission 20 Na* Source: cococubed.asu.edu Source: O.Sorlin, Nuclear data for unstable isotopes, Nucl.phys,

5 Some terms: Inverse Kinematics: method used for our experiment. Heavy-ion beam on light mass target. Get forward focused products. Transfer reaction: Nucleon is transferred directly from target to beam or vice-versa. Fusion-Evaporation: Form a compound nucleus and the product ejects nucleons as it de-excites. Projectile Fragmentation: nucleons are stripped off of heavy-ion projectile. 5

6 Why MARS? Helps us separate exotic nuclei. Produce highly pure beams (~90 %) by getting rid of unwanted reaction products (less background). Separates Reaction products in two ways: Magnetic rigidity selection (Brho): Mv/q = Bρ Velocity Selection 6

7 20 25 A MeV 7

8 WORKING MECHANISM OF MARS Primary beam of MeV/u from K500. Reaction ( 20 Ne + 3 He/ 20 Ne + 1 H 2 ) in the gas cell to get the secondary beam 20 Mg or 20 Na. Separate the beam by the magnetic rigidity, p/q = Bρ using dipole D1 and D2. Stop the primary beam with a Faraday cup in the coffin. The slits (2h) in the coffin define the momentum acceptance of the spectrometer. Get a parallel beam into the velocity filter with the help of quadrupole, Q3 and dipole D2 (which together make a momentum achromat). Make mass selection, m/q in the y-direction with the help of velocity filter and dipole D3. 8

9 REU Group Experiment: 20 Na production, separation and its β-delayed alpha and gamma decay Produce 20 Na with (p,n) charge exchange reaction with 20 Ne + 1 H 2. Primary beam: MeV/u from K500 cyclotron. Secondary beam: 20 Na Gas target: H 2 at LN 2 temp (77K) and P = 2.0 atm. Three different groups, each with 4 students performing the experiment at different shifts. 9

10 Results: 20 Na production and separation Productivity: 1860 evts/nc Purity ( 20 Na/total): ~ 91% Productivity: 2691 evts/nc Purity: ~ 93% Productivity: 2011 evts/nc Purity: ~ 87% 10

11 Experimental setup for the 20 Na decay After separation, 20 Na was implanted in detectors: thick and thin thermocooler OD Φ=150 mm Energy degrader (rotating, motorized) 275 mm connectors 64 mm >110 mm Φ=80 mm 18 dia chamber α-detector v. thin Si strip 65 μm β-detector thick Si det 1 mm γ-detector HPGe 70% effic 11

12 Results: 20 Na decay ms 20 Na beta α + β implanted in thick β-det α 4.4 MeV (2.8%) β 2.1 MeV (16%) 4.7 MeV 16 O MeV MeV (79 %) 20 Ne Source: M.Huyse et al, Nucl. Phys. A 588, Pg 313c (1995) γ-rays spectrum β α + β implanted in thin α-det 511 kev MeV 1633 kev MeV 12

13 20 Na experiment summary Good production rate obtained, 2 million pps as opposed to 50/sec. Observed alpha, α+β spectrum and gamma spectrum. Observed 20 Na 20 Ne* gamma spectrum in γ singles mode. Saw 1633 kev gamma line. Other higher energy 20 Ne* gamma lines were difficult to observe due to low detection efficiency (could be improved with Betagamma coincidence requirement). 13

14 Before the 20 Mg experiment LISE predictions Production of 20Mg by LISE predictions cross section Mg + 9Be 20Ne + 3He p rod. rate Mg + 9Be 20Ne + 3He beam energy (MeV/u) beam energy (MeV/u) Used LISE to compare projectile fragmentation reaction of 24 Mg + 9 Be and fusion evaporation of 20 Ne + 3 He. LISE s prediction better production of 20 Mg with 20 Ne MeV/u. Used LISE s prediction to conduct the experiment and compare the results. 14

15 Production and separation of 20 Mg- steps MARS at 5. MARS set for the secondary beam using the values from the Marsinator for the fusion-evaporation. Started to see 20 Mg beam at D 12 = 402A. MARS set for secondary beam with values from the Marsinator. Scanned D 3 to identify 20 Mg. Found 10 C and 20 Mg at D 3 = 109A. Scanned D 12 to maximize 20 Mg production. Different Q1, Q2, Q3 for different D 12 scans to improve transport efficiency. Found best yield 20 Mg in the center at D 12 = 442 A and D 3 = 122 A. Close slits to filter out the impurities. 15

16 Energy Results: 20 Mg production and separation D3= 130 A D3 = 119 A D3 =109 A y position q/m ratio 20Mg from 20Ne(3He,3n) in inverse kinematics on 3He gas Production: pps Purity (20 Mg /10 C) : ~ 9% 16

17 Data analysis of 20 Mg LISE predictions Experimental Results prod rate(evts/uc) Mg 10C p rod rate (evts/uc) Runs , 107, 108 Runs , 106 momentum (MeV/c) momentum (MeV/c) LISE predicted that 20 Mg production is maximum at around 3580 MeV/c. Experimental data found that the highest rate was at about 3900 MeV/c. Some combination of fusion-evaporation and transfer reactions?? 17

18 Observations for 20 Mg Observe that for p = 1.5 atm and slit # 2= ± 1.0 cm, prod ( 20 Mg) ~ 20 evts/µc and 10 C ~222 evts/µc. With p = 3.0 atm and slit # 2 = ± 1.5 cm, expect 20 Mg ~ pps and 10 C ~ pps. Used 5 mil Al degrader before the target to make the MeV/u. No improvement with the degrader. Best was 5 evts/µc. 18

19 Something to remember The production rate of a RNB is related as follows: N( 20 Mg) = σ I N efficiency of transport where, σ is the production cross section in barns (1 barn= cm 2). It is reaction dependent. I is the intensity of the primary beam in pps and N is the target thickness in atoms cm -2. dσ/dp (differential cross section) is a function of momentum (or rigidity ), which is dependent on 20 Mg production mechanism. Note that dp > the MARS acceptance. The best production rate is found at the maximum of the dσ/dp distribution. 19

20 Conclusions: 20 Mg experiment and beyond Projectile fragmentation of 24 Mg MeV/u done in February yielded 10 pps of 20 Mg with 600 pps of 10 C; about 6% purity. In June: 20 Ne MeV/u pps of 20 Mg (20 evts/uc). Purity: ~ 9% Overall, production of 20 Mg was better with fusion-evaporation reaction of 20 Ne + 3 He because higher beam currents were available for 20 Ne. This known, β- delayed proton decay of 20 Mg will be studied in November by MARS group at TAMU in collaboration with people from University of Edinburgh, UK. 20

21 References Sorlin, O Nuclear data for unstable isotopes. Institut de Physique, F Orsay, France. Tribble, R.E., Gagliardi, C.A and W. Liu MARS: a status report. Nuclear Instruments and Methods in Physics Research B56/57: Woods, P.J., Davinson., G.T. Lotay (Univ of Edinburgh) and MARS group (Cyclotron, TAMU). Measurement of β-p emission from 20Mg, and the breakout from the hot CNO cycles. O.B.Tarasov, et al. Development of the program LISE. Nucl Phys. A 746, pg. 411(2004). M. Huyse, et al. Nuclear Reactions of Astrophysical Interest with Radioactive Beams. Nucl. Phys. A 588, pg.313c, (1995). Talks to the REU group by: Brian, Matt, Alex. 21

22 Acknowledgements Thanks to Prof. Sherry Yennello and the REU selection team for giving me the opportunity to participate in the program. Thank you to Dr. Robert Tribble for serving as my advisor. Thank you to Dr. Livius Trache, Dr. Brian Roeder and Dr. A. Banu for guiding me throughout the summer research. Thanks also to all the members of MARS group. 22

MARS status report for : Development of rare isotope beams of 25 Si, 6 He, 9 Li, 23 Si, and 22 Si

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