Why Make Rare Isotopes?

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2 Outline Use and production of radioactive isotopes. Importance of RIBs Challenges in making RIBs Current experiments to make RIBs Current experiments using RIBs

3 Why Make Rare Isotopes? Fill in the Chart of the Nuclides Decay Properties: Half-life, decay energy, branching ratios. Nuclear Properties: Ground and excited state spins, quadrupole moment, energy levels. Study Secondary Reactions Astrophysics: r, s & p processes occur with short lived isotopes. Cross sections for various interactions

4 How To Make Rare Isotopes Ion Beam incident on a target (p,gamma), (p,n), (d,p),(d,n) etc. Neutron Capture (n,gamma), (n,alpha) Fission by products

5 Now What? Radioactive nuclides are stuck in the target or have recoiled into vacuum or another medium. They can be retrieved either chemically or with electromagnetic fields or a combination of both. Chemical Separation: effective if chemistry needs to be done anyway separates elements but not isotopes slow (sometimes) involves a carrier potentially %100 efficient EM Separation: Make a RIB fast transport separates isotopes not isobars carrier free allows secondary reactions not efficient area of current research

6 Example: 14 O We use 14 O to find the branching ratio of the excited state decay vs ground state decay, testing the unitarity of the CKM matrix. This involves finding the shape and amplitude of both beta spectra. Produce 14 O via : 14 N(p,n) 14 O

7 Why a RIB is Better: 14 O Competing reaction 15 N(p,n) 15 O 15 O: comparable endpoint betas and halflife. Chemistry does not separate O isotopes, but a RIB and magnet would deliver 14O and ionized 14N (stable). Carrier CO 2 gas can distort the beta spectra if it gets too thick

8 S-Process Isotopes and 42Si The cross section for (d,p) is related to the neutron capture cross section in S- process reactions. The inverse kinematics of a RIB, d(1,p)2, would allow the differential cross section to be measured for the transfer reaction. This gives a more feasible experiment than direct s-process neutron capture. 42Si can be produced only with a 44S beam. Are there new magic numbers? Is there something fundamentally different about the nuclear force away from stability?

9 RIB Challenges 8 B 6 Li( 3 He,n) 8 B Very poor optics Liouville s THM Rare Isotope Beams cannot be created by simply refocusing recoils with traditional kinematics

10 How to Make RIBs: ISOL(DE), HRIBF Create and implant the desired isotopes in a target. The target is hot enough to effuse the radionuclides into an inert carrier gas. Hot chemistry can be done on the way through interactions with tube walls or filters. Reaccelerate with a second ion source. Slow, only works for longer lived isotopes. Inefficient

11 How to make RIBs: Cyclotron Gas Stopper degrader Eject recoils into an inert gas. As the ions slow through collisions they undergo cyclotron motion around an axial field and are focused towards a small output hole. Most species will retain a +1 charge state in He RF carpet keeps ions from hitting the walls by creating a quadrupole field. A small DC voltage nudges stopped ions along Reacceleration occurs after skimming the stopper gas Helium gas

12 Making RIBs: A1900 Fragement Separator For rare isotope study, create a beam by focusing recoils. This works well for inverse kinematics with large A beams.

13 Using RIBs: Beta NMR Create a polarized RIB by selecting fragments off beam axis Implant the nuclei into a target with a small magnetic field applied to retain polarization. Look for the beta decay asymmetry with different applied RF fields

14 Beta NMR cont. 58Ni(p,2n)57Cu Polarized by proton pickup Measures the strength of the dipole moment Result differs significantly from Shell model calculations

15 Experiments Using RIBs: HELIOS Deuterated Target. RIB hits the target and the proton from the (d,p) reaction is used to get the differential cross section. This gives information about the s-process.

16 Conclusion Rare Isotope Beams are important for Astrophysics, Nuclear models, and spectrographic studies. There are several ways to make RIBs with varying efficiencies depending on the desired use References: 1. M.S. Smith, K.E. Rehm; Ann. Rev. Nucl. Part. Sci., nucl 2001, 51(1), Nuclear Astrophysics with Radioactive Beams 2. P.F. Mantica et al.; PRL Nuclear Magnetic Moment of the 57Cu Ground State 3. R.V.F Janssens; Nature Nuclear Physics: Elusive Magic Numbers 4. G. Bollen et. al.; NIM A A Study of Gas Stopping of Intense Energetic Rare Isotope Beams