Accelerator Applications DAVID COHEN  Australian Nuclear Science and Technology Organisation  Lucas Heights, Sydney, Australia  Overview -   Ion - atom interactions -     Ion transport -      IBA Techniques -      Accelerators at ANSTO -      IBA applications

e- What is an ion ? Atom electron ejected proton - H+ alpha - He2+ gases - Ne+ metal - Ti2+

Ion Energy  E = q*V  for example for 12 MV acceleration voltage,  H+ ion gives 12 MeV Cl10+ ion gives 120 MeV Ion Currents  I = Q/t Charge Q = qe  N/t = I/(qe) is number of ions/ sec  1 pA = 6x106 ions/sec (q=1)  100 µA = 6x1014 ions/sec (q=1)

Ion Acceleration & Transport T = transport, focus T Neg Ion Source Accelerator +Va, q+ Target Detector 1MV-1GV 10-100kV Ei+(1+q)Va Vi, Ei If Vi = 50 kV, q = 4+ Va = 8 MV Then Etarget = 40.05 MeV

Beam Power  P = I*V=Q*V/t For example, 1 µA of protons from a 3 MV accelerator will produce 3W of power in the target over the beam area. Potential for large power into small spots. Ion Velocity v = 1.384x109 *sqrt(E/M) cm/s (v/c) = 0.046*sqrt(E/M) (v/vo) = 6.30*sqrt(E/M)  where E in MeV and M in amu 1 MeV proton 4.6% of c 120 MeV 36Cl ion 8.4% of c

Is a Pb atom bigger than H atom? Shell radius an = 0.53*(n2/Z)  0.5 Å   Nuclear radius R = 1.2*10-5 A1/3  10-5 Å, 5 orders of magnitude – like marble in the middle of several football fields. 2e- Atom K L1-3 8e- Pb, A=207 R = 7.1*10-5 Å H, n=1, Z=1 an = 0.53 Å Pb, n=6, Z=82 an = 0.23 Å Pb atom actually sits inside an H atom!!

Ion Velocity For atomic electrons, (v/c) = Z/(137n)  where n is the principal quantum number.  For H K shell (v/c) = 0.7% For Pb K shell (v/c) = 60%, relativistic! So ion velocities from accelerators comparable with loosely bound electron velocities.   velocity matching optimises the interact!!

Atomic Sizes of Interacting Ions For H and He on Pb their K shells are outside the Pb atomic radius so the charge state of the ion is not important in the interaction process.   There are two distinct regions, inside/ outside the atom (effective charge changes) Distance of closest approach d is small,   d(Å) = 2Z1Z2/{M1M2(v/vo)2/(M1+M2)}  e.g. for 1 MeV protons on Au d = 0.002 Å

Ion-Atom Collision Time Scales Collision times << Lifetimes of states. Ion has been and gone before the vacancy decays. (ii) Max ionisation cross sections for velocity matching of removed electron and bombarding ion.

How Far Does an Ion Travel ? Charged particles interact with matter through the electron cloud and the nucleus. The electron cloud acts as a drag force on the ion slowing it down and reducing its energy - this is called electronic stopping. Eventually the ion energy becomes low enough for the ion to have a reasonable chance of interacting directly with the target nucleus - this is called nuclear stopping. The range of an ion is the integral of the stopping power over all energy losses.

Proton in carbon, p in Si For alphas in carbon, He in Si Electronic stopping power is proportional to Z2 for the same velocity ion. SI(E1) = (ZI/Zp)2*Sp(E1/MI) He in Si

p in Si He in Si The corresponding ranges are: For protons in carbon, For alphas in carbon, He in Si The ion range RI is inversely proportional to Z2 for the same velocity ion. RI(E1) = (Zp2MI/ZI2)*Rp(E1/MI)

Transporting/ Bending Charged Particles Range of MeV ions in materials is short – 10’s of microns Need evacuated tubes, pressures < 1mPa to transport ions Bent by E, B fields F = Q (E + vxB) E fields  10’skV/ cm for MeV ions B fields  1-5 kG for light MeV ions (H, He)  5-15 kG for heavy MeV ions (Cl, I) Require high voltages and large magnets

Ion Rigidity and Ion Filters For magnets ions with the same (ME/Q2) experience the same force. Wien filter has perpendicular magnet and electrostatic field. For protons, M=1, E=2MeV, Q=1 and (ME/Q2) = 2 For He2+ M=4, E=2 MeV, Q=2 and (ME/Q2) = 2 also.

ANSTO Accelerators 3 MV Van de Graaff Accelerator (retired 2005) single ended machine Belt 10 MV Van de Graaff Tandem ANTARES double ended machine – Tandem-external ion source Chains 2 MV HVE Tandetron solid state power supply double ended machine - external ion source

Van de Graaff Principle

Tandem Accelerator

ANTARES Accelerator 10 MV HVE Tandem. 3 ion sources for H-U. 2 IBA beamlines, heavy ion microprobe, heavy ion ERDA, RToF. 3 AMS beamlines,small sample, actinides, 10Be, 26Al, 14C. 10 MV

10 MV Tandem ANTARES AMS 14C, 10Be, 26Al Actinides IBA Microprobe PIXE, RBS ToF ERDA

High Energy Beam Hall at ANSTO Tandem

STAR Accelerator 2MV HVE Tandetron 2 Duoplasmatron ion sources for H, He 1 Sputter ion source for heavy ions. 2 IBA beamlines, PIXE, PIGE, RBS, PESA, ERDA 14C AMS

Accelerator Based Ion Beam Techniques 2MV STAR Accelerator PIXE, PIGE, RBS, ERDA beamline Beams of high energy ions (p, He, C….) fired into sample surfaces. Interactions with e- X-rays PIXE (Al-U) nucleus  -rays PIGE (Li, F, Na..)  scattered and recoiled particles RBS,ERDA,RToF (H, C, N, O,..) IBA techniques cover Periodic Table (H to U). Very sensitive (µg/g) on small samples (pg). Fast (<5mins), essentially non destructive as counting individual atoms/ ions/ photons. Have between 100-120 external visitors/ year Interact with all 37 Australian Universities

Direct Ionisation – what is it? The max energy Emax that an ion of mass M1 and energy E1 can transfer to an ion M2, at rest is:- Emax = 4M1M2E1/(M1+M2)2 If M1>>M2 then, Emax = 4M2E1/M1 For a 3MeV proton on an electron Emax = 6.5 keV this has major consequences for ion induced secondary electron bremsstrahlung! Holes, X-rays, Lifetimes

X-ray Transitions Allowed E1 transitions l = ±1, j = 0,±1 Number of electrons per sub-shell = 2(2l+1) Observable X-ray transitions for high resolution systems, K  8, L  25, M  40.

CuK Shell X-ray Spectrum PbL Shell X-ray Spectrum 2.6 MeV protons.

Typical PIXE X-ray Spectrum Taken in air - note argon peak.

Blank Spectrum 2.6 MeV protons on Teflon, note bremsstrahlung cutoff at (4*2600/1836)= 5.7 keV

Yield Equations for PIXE

Thick target yields for proton induced K and L shell ionisation

Minimum Detectable Limits

IBA Applications on ANTARES and STAR Taylor the ion beam energy and mass to suit the problem, Fine particle air pollution – source fingerprinting, long range transport, climate change. Heavy ion microscopy – hyper-accumulating plants, IBIC studies, microdosimetry. Materials characterisation – thin films, monolayers, multilayers, surface modification, implantation.

Hybantus Floribundus subsp. floribundus Leaf sections for Ni accumulator ICP-AES Ca 2.0 % K 1.7 % Ni 0.8 % 100 µm palisade K Ca adaxial epidermis Ni 100 µm vascular tissue adaxial epidermis Hybantus Floribundus subsp. floribundus Takes up to 4% Ni by dry weight

Aerosol Sampling Project

Four techniques cover most of the periodic table from H to U

IBA Aerosol Characterisation in Asia Cheju Is. Manila Sado Is. Dust S Hong Kong Hanoi NASA satellite 11 April 2001, major Gobi desert dust storm.

Source: Zhao, Y. , Wang, S. , Duan, L. , Lei, Y. , Cao, P. , Hao, J Source: Zhao, Y., Wang, S., Duan, L., Lei, Y., Cao, P., Hao, J. Primary Air Pollutant Emissions of Coal-fired Power Plants in China: Current Status and Future Prediction, Atmospheric Environment (2008), doi: 10.1016/j.atmosenv.2008.08.021

Dust over the Sea of Japan 8 April 2006

Dust from Gobi Desert over Korea, Japan 16 March 2009 Dust Korea Japan Cheju Is NASA satellite photo

Hanoi Soil 2001-08, Hourly 7 Day Back Trajectories

Obsidian glass, axe head PIXE and Archaeology Obsidian glass, axe head

Summary Accelerator based ion beam analysis (IBA) techniques are:- Fast (5mins) Non destructive Very sensitive (µg/g) Multi-elemental (H to U) Can analyse very small samples (pg-µg)