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Nuclear Physics

by: Horace McClure

Nuclear Physics PHY 224B

Horace McClure
GPA 3.82


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This 19 page Class Notes was uploaded by Horace McClure on Tuesday September 8, 2015. The Class Notes belongs to PHY 224B at University of California - Davis taught by Staff in Fall. Since its upload, it has received 48 views. For similar materials see /class/191845/phy-224b-university-of-california-davis in Physics 2 at University of California - Davis.


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Date Created: 09/08/15
neutron prompt an neu Phy 2243 Chapter 202Applications of Nuclear Physics 24 March 2005 unused small interstitial hydrogen atoms cause vacancies in Nb crystal which lead to embrittlement and diminish superconducting abilities in Nb Two techniques for measuring H 0 cold n prompt Y activation analysis PGAA my process nondestructive chemical formshape not important matrix independent entire sample analyzed fast simultaneous for different isotopes 0 n incoherent scattering NIS incoherent scattering cross section of hydrogen gtgt absorption cross section higher sensitivity and faster detection of H than PGAA but signal is not speci c to H hence a Hless sample is needed to account for n scattering by other elements 2 Questions to Does the acid treatment of the niobium introduce a measurable amount of hydrogen Can vacuum heating remove hydrogen Neutron and M o o o o scatterin a a a g Q kf ki Owghg Q tlnough vector quot o o 7 lkZ i lkr 1Pi 6 IPf 7 re 0 O Q Q 2 do 2 N if E725Q b2 b2 ocoherent scattering o neutron interacts with sample as a whole hydrogen incoherent o incoherent scattering scattering cross 0 neutron interacts with each nucleus independently section is very o scattering is uniform in all Q directions o scattering depends on Q direction 4Nb atomic weight 92906 soft easily shaped low thermal neutron capture cross section At atm Nb has the highest critical temperature of the elemental superconductors 93 K remains a superconductor even when inside high B eld treated with acid to remove surface impurities operating temperatures 2 K ltT lt 42 K drop in superconductor s Qvalue observed at 75 K ltT lt I30 K attributed to hydride precipitation reactance resistance stored energyenergy REEL l H m EMS EACKSCA39I F 3U m SANS 1 neutron guides PHYSICS 311 m SANS 2 NIST Cold Neutron Research Guide Hall httpwwwncnrnistgovinstrumentscoldinstrhtm 7 neutron is captured photon is promptly emitted with energy related to binding energy of added neutron Mw um 4 mm drying heating nucleus 500 l i Y energies ID element species 74quot 39 Y intensities gives Concentrations I 21 7S 2200 2225 Wu example result i Signal l i x 3 v 5 fl 5 s Jr39V39 quotquotw quot Jih39 quotl 39V J39M 39I Energy k2V bismuth germanate BGO Compton suppressor Neutron guide end View Ge gamma detector Fig lzcold neutron PGAA spectrometer PGAA aircraft industry 0 hydrogen embrittlement of titanium alloy jet engine turbine blades 0 hydrogen mass fraction of hydrogendoped titanium alloy standard reference mateiral hydrogen in semiconductors and related materials quartz germanium thin lms on silicon wafers entirely of carbon taking the form of hyd rogen 39n funerenes a hollow sphere elVlipsohid gogr PGAA small angle neutron scattering SANS is used to study hydrogen impurity and pore size in nanocrystalline metals 2D neutmn detectm Sample beam scattered 39 incident beam E 0 measure large objects IIO3 um SANS httpwwwncnrnistgovprogramssans NIS Cd aperture Be filter 9 mm diameter Neutron beam removed n below 4 Cd sleeve angstroms 3He detector Fig2 NIS measurement setup Calibration using polypropylene lms are done with this same setup I 2 information required I scattered neutron signal from sample 2 blank measurement 3 calibration of neutron signal vs hydrogen concentration each sample measured for 6 mins Methd 39 5 slabs of ultrapure niobium each IO g degassed atJefferson Lab by heating in hot vacuum furnace for 6 h to remove hydrogen designed to operate at I039E torr extending from the top of each niobium insert are a series of notches which are bent over to seperate inserts together both spectra show a peak at 2223 keV similar magnitudes Counts EquivalentAto 029 t 002 atom traction hydrogen Equivalent to 029 1 002 atom iraction hydrogen IlllI 2250 2300 N 1 0 0 200 Energy keV Fig 3 PGAA spectrum H energy region of Nb sample 4 after Ist vacuum heating top and then after acid treatment bottom l5 Counts smaller 2223 llteV peak 16 10 5 1 5 Equivalent to 018 t 001 15 10 0 atom fraction hydrogen 14 10 5 13 10 5 12 1D 5 Nb 4 5 Equivalent to 057 t 002 11 10 atom fraction hydrogen 39 1 1n 5 9 1o 4 a 10 4 I I 2150 00 k V 2250 2300 Energy e large 2223 keV peak Fig 4Top PGAA spectrum H energy region of Nb sample 4 after the 2quotd vacuum heating Bottom PGAA spectrum of Nb sample 5 after 2quotd degassing and 2quotd acid treatment 6 Change in E39 c once39ntra u bh at H 100 at Nb l a 4mm 39 94le l l 5me ems T g E 1 mm I itm 5 u m an 6 eh m a E E a E 5 E E lm 4 m a m 47 E E a E 3 Treatment Condition Fig 5The change in H concentration in Nb samples 4 left and 5 right relative to that after the lst degassing as determined by PGAAThe results obtained after the lst H loading are expressed as the upper limit since the changes observed are within the measurement uncertainty The signi cant changes occurred only after the 2nd degassing for 4 and 2nd H loading for 5 PGAA uncertainties are 2s based on propagation of counting statistics and uncertainties in element sensitivities NIS uncertainties are 2s based on the propagation of uncert7ainty in the polypropylene lm thickness Conclusin 0 amount of H did not show correlation with time or temperature of initial degassing 0 H content was not correlated with duration of initial acid treatment 0 signi cant gain of H in sample 5 after 2ncl vacuum heating and 2nd acid treatment 0 800 celsius heat removed strongly bound hydrogen activating sites where H can be picked up by Nb upon subsequent acid treatment Answers Does acid treatment of Nb introduce a measurable amount of H 2 Can vacuum heating remove H answers 0 NO for lSt cycle of treatment 0 YES for 2nd cycle


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