Neutron Activation analysis(NAA) Neutron activation analysis is a multi-, major-, minor-, and trace-element analytical method for the accurate and precise determination of elemental concentrations in materials Sensitivity for certain elements are below nanogram level The method is based on the detection and measurement of characteristic gamma rays emitted from radioactive isotopes produced in the sample upon irradiation with neutrons High resolution germanium semiconductor detector gives specific information about elements
16 Neutron Activation Analysis (NAA) Neutron activation analysis is a multi-, major-, minor-, and trace-element analytical method for the accurate and precise determination of elemental concentrations in materials. Sensitivity for certain elements are below nanogram level. The method is based on the detection and measurement of characteristic gamma rays emitted from radioactive isotopes produced in the sample upon irradiation with neutrons. High resolution germanium semiconductor detector gives specific information about elements
1,A14(t)/g(C) 2. Accelerator Mass Spectrometry 入(A14(0)/g() prior to ams samples were 14C-dated by counting the number of decays required large samples and long analysis times 1977: Nelson et al. and Bennett et al. publish papers in Science demonstrating the utility of attaching an accelerator to a conventional mass spectrometer Principle You cannot quantitatively remove interferring ions to look for one 14C atom among several quadrillion C atoms Instead, you a)destroy molecular ions(foil or gas) b filter by the energy of the ions(detector) to separate the needle in the haystack
2. Accelerator Mass Spectrometry -prior to AMS samples were 14C-dated by counting the number of decays - required large samples and long analysis times -1977: Nelson et al. and Bennett et al. publish papers in Science demonstrating the utility of attaching an accelerator to a conventional mass spectrometer Principle: You cannot quantitatively remove interferring ions to look for one 14C atom among several quadrillion C atoms. Instead, you a) destroy molecular ions (foil or gas) b) filter by the energy of the ions (detector) to separate the needle in the haystack
(c) (e) C)ACCELERATOR enerates 2.5 million volts accelerates c- ions b)INJECTOR MAGNET d TERMINAL separates ions by mass C- ions interact with e)ELECTROSTATIC DEFLECTOR masses 12, 13, and 14 injected stripper gas Ar specific charge of ions selected ( 3*) molecular species CH a)ON SQURCE carbon ions D MAGNETIC SEPARATION by Cs sputtering 13C steered into cup, 14C passes through to solid detector () Berylium Carbon iodine (g) g)SLBARRIER DETECTOR 0 pulse produced is proportional to the energy of ion, can Scale differentiate b/t 14c and other ions count rate for modem sample 100cp meters http://www.physics.arizonaedw/ams/education/ams_principle.htm
a) ION SOURCE generates negative carbon ions by Cs sputtering b) INJECTOR MAGNET separates ions by mass, masses 12, 13, and 14 injected http://www.physics.arizona.edu/ams/education/ams_principle.htm c) ACCELERATOR generates 2.5 million volts, accelerates Cions d) TERMINAL C- ions interact with ‘stripper’ gas Ar, become C+ ions, molecular species CH destroyed e) ELECTROSTATIC DEFLECTOR specific charge of ions selected (3+ ) f) MAGNETIC SEPARATION 13C steered into cup, 14C passes through to solid detector g) Si BARRIER DETECTOR pulse produced is proportional to the energy of ion, can differentiate b/t 14C and other ions count rate for modern sample = 100cps
AMS measurement capabilities Nuclide Half-life Stabl Sample System Sensitivity (years) Isobar material efficiency (% H 12.3 3He TiH2 14 10 B 1.5×10 10 B Beo 01 10-15 14 5730 2 2×10-15 Al 74×10 M g Al2O3 00l-0.1 10-15 3.01×10 AgCh 2×10-15 4l Ca 1.0×10 K Cah 0.01-0.1 10-15 129 1.6×107 129Xe Agl 10-14
AMS measurement capabilities