A Path to a 0.1s Neutron Lifetime Measurement Using the Beam Method - PowerPoint PPT Presentation

A Path to a 0.1s Neutron Lifetime Measurement Using the Beam Method F. E. Wietfeldt Tulane University

The beam neutron lifetime method Γ = − dN dt = N neutron decay rate: τ

The beam neutron lifetime method Γ = − dN dt = N neutron decay rate: τ N = ρ n V det = φ ⎛ ⎞ ⎜ ⎟ A beam L det neutrons in detection volume : V det ⎝ ⎠ v

The beam neutron lifetime method Γ = − dN dt = N neutron decay rate: τ N = ρ n V det = φ ⎛ ⎞ ⎜ ⎟ A beam L det neutrons in detection volume : V det ⎝ ⎠ v φ ⎛ ⎞ τ = A beam L det neutron lifetime: ⎜ ⎟ ⎝ ⎠ Γ v

φ ( v ) τ = A beam L det ∫ for a “white” neutron beam: dv Γ v

φ ( v ) τ = A beam L det ∫ for a “white” neutron beam: dv Γ v v th σ abs = σ th neutron absorption cross section in thin “1/v” counter: v v th = 2200 m/s reference thermal neutron velocity

φ ( v ) τ = A beam L det ∫ for a “white” neutron beam: dv Γ v v th σ abs = σ th neutron absorption cross section in thin “1/v” counter: v v th = 2200 m/s reference thermal neutron velocity φ ( v ) ∫ R n = ε th A beam v th neutron count rate: dv v

φ ( v ) τ = A beam L det ∫ for a “white” neutron beam: dv Γ v v th σ abs = σ th neutron absorption cross section in thin “1/v” counter: v v th = 2200 m/s reference thermal neutron velocity φ ( v ) ∫ R n = ε th A beam v th neutron count rate: dv v

φ ( v ) τ = A beam L det ∫ for a “white” neutron beam: dv Γ v v th σ abs = σ th neutron absorption cross section in thin “1/v” counter: v v th = 2200 m/s reference thermal neutron velocity φ ( v ) ∫ R n = ε th A beam v th neutron count rate: dv v

φ ( v ) τ = A beam L det ∫ for a “white” neutron beam: dv Γ v v th σ abs = σ th neutron absorption cross section in thin “1/v” counter: v v th = 2200 m/s reference thermal neutron velocity φ ( v ) ∫ R n = ε th A beam v th neutron count rate: dv v R p = ε p Γ charged particle count rate:

φ ( v ) τ = A beam L det ∫ for a “white” neutron beam: dv Γ v v th σ abs = σ th neutron absorption cross section in thin “1/v” counter: v v th = 2200 m/s reference thermal neutron velocity φ ( v ) ∫ R n = ε th A beam v th neutron count rate: dv v R p = ε p Γ charged particle count rate: τ = R n ε p L det R p ε th v th

φ ( v ) τ = A beam L det ∫ for a “white” neutron beam: dv Γ v v th σ abs = σ th neutron absorption cross section in thin “1/v” counter: v v th = 2200 m/s reference thermal neutron velocity φ ( v ) ∫ R n = ε th A beam v th neutron count rate: dv v R p = ε p Γ charged particle count rate: τ = R n ε p L det R p ε th v th most challenging

1400 neutron lifetime results current 1300 1200 neutron lifetime (s) 1100 1000 900 beam method 800 UCN bottle magnetic trap 700 1950 1960 1970 1980 1990 2000 2010 year

900 neutron lifetime results since 1990 895 890 neutron lifetime (s) 885 880 875 recent revisions beam method UCN bottle 870 1990 1995 2000 2005 2010 year

900 neutron lifetime results since 1990 895 890 neutron lifetime (s) 885 τ n = 880.0 ± 0.6 s 880 2 = 14.0/6 (3%) χ ν 875 beam method UCN bottle 870 1990 1995 2000 2005 2010 year

900 neutron lifetime results since 1990 895 τ n = 887.3 ± 2.8 s 890 neutron lifetime (s) 885 880 τ n = 879.6 ± 0.6 s 875 beam method UCN bottle 870 1990 1995 2000 2005 2010 year

900 neutron lifetime results since 1990 895 τ n = 887.3 ± 2.8 s 890 neutron lifetime (s) 885 Δτ n = 7.7 ± 2.9 s 880 τ n = 879.6 ± 0.6 s 875 beam method UCN bottle 870 1990 1995 2000 2005 2010 year

900 neutron lifetime results since 1990 895 τ n = 887.3 ± 2.8 s 890 neutron lifetime (s) NIST beam neutron lifetime experiment 885 Δτ n = 7.7 ± 2.9 s 880 τ n = 879.6 ± 0.6 s 875 beam method UCN bottle 870 1990 1995 2000 2005 2010 year

Measurement of the Neutron Lifetime Using a Proton Trap J.S. Nico, M.S. Dewey, and D.M. Gilliam National Institute of Standards and Technology F. E. Wietfeldt Tulane University X. Fei and W.M. Snow Indiana University G.L. Greene University of Tennessee J. Pauwels, R. Eykens, A. Lamberty, and J. Van Gestel Institute for Reference Materials and Measurements, Belgium

NIST Center for Neutron Research Cold Neutron Guide Hall NEW! neutron NG-C high flux interferometer end position - curved SM guide NG6 end position 0.50 nm test beam Fundamental Neutron Physics Program: • 30 postdocs • 31 Ph.D. theses 0.89 nm UCN • 40 graduate students • >50 undergraduate students • 41 collaborating institutions

alpha, triton detector precision proton B = 4.6 T aperture detector neutron beam 6 Li mirror trap electrodes door closed deposit (+800 V) (+800 V)

alpha, triton detector precision proton B = 4.6 T aperture detector neutron beam 6 Li mirror trap electrodes door open deposit (+800 V) (ground)

alpha, triton detector precision proton B = 4.6 T aperture detector neutron beam 6 Li mirror trap electrodes door closed deposit (+800 V) (+800 V)

alpha, triton detector precision proton B = 4.6 T aperture detector neutron beam 6 Li mirror trap electrodes door closed deposit (+800 V) (+800 V)

alpha, triton detector precision proton B = 4.6 T aperture detector neutron beam 6 Li mirror trap electrodes door closed deposit (+800 V) (+800 V) τ = R n ε p L det R p ε th v th

alpha, triton detector precision proton B = 4.6 T aperture detector neutron beam 6 Li mirror trap electrodes door closed deposit (+800 V) (+800 V) τ = R n ε p L det L det = nl + L end R p ε th v th

alpha, triton detector precision proton B = 4.6 T aperture detector neutron beam 6 Li mirror trap electrodes door closed deposit (+800 V) (+800 V) τ = R n ε p L det L det = nl + L end R p ε th v th # trap electrodes

alpha, triton detector precision proton B = 4.6 T aperture detector neutron beam 6 Li mirror trap electrodes door closed deposit (+800 V) (+800 V) τ = R n ε p L det L det = nl + L end R p ε th v th # trap electrodes length of electrode + spacer

alpha, triton detector precision proton B = 4.6 T aperture detector neutron beam 6 Li mirror trap electrodes door closed deposit (+800 V) (+800 V) τ = R n ε p L det L det = nl + L end R p ε th v th total effective # trap electrodes end region length length of electrode + spacer

alpha, triton detector precision proton B = 4.6 T aperture detector neutron beam 6 Li mirror trap electrodes door closed deposit (+800 V) (+800 V) τ = R n ε p L det L det = nl + L end R p ε th v th total effective # trap electrodes end region length length of electrode + spacer ε p ⎛ ⎞ R p ( ) = τ − 1 ⎟ nl + L end ⎜ ε th v th ⎝ ⎠ R n

Proton Trap

1000 Prot oton on Pulse Height Sp Spectrum 2 Au) (32.5 ( .5 kV; 2 kV; 20 µ µg/cm /cm Au) 100 Counts 10 32.5 keV 1 0 100 200 300 400 500 600 ADC Channel (7.47 ch. = 1 keV)

Proton Arrival Time Spectrum 1000 2 Au) (32.5 kV; 20 µg/cm 3 Electrodes 4 Electrodes 100 5 Electrodes Counts 6 Electrodes 7 Electrodes 8 Electrodes 9 Electrodes 10 Electrodes 10 1 0 100 200 300 400 500 TDC Channel (6.25 ch/µs)

-3 4.0x10 Nor orma malized Prot oton on Cou ounts vs. Trap Length 2 Au) ( (32.5 .5 kV; 2 kV; 20 µ µg/cm /cm Au) 3.5 Proton-Bkdg/Alpha 3.0 2.5 2.0 1.5 2 3 4 5 6 7 8 9 10 11 Electrode Number Fit of R p 40 vs . number 20 R n Residuals 0 trap electrodes -20 -6 -40x10 2 3 4 5 6 7 8 9 10 11 Electrode Number 40 20 Residuals 0 -20 -6 -40x10 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 9/29/00 9/30/00 10/1/00 10/2/00 10/3/00 Date/Time

Lifetime vs. Backscatter 910 905 extrapolated result 886.8 ± 1.2 s measured lifetime (s) 900 (stat. error only) 895 27.5 kV 890 30 kV 32.5 kV 885 880 -3 0 5 10 15 20 25 30x10 backscatter fraction

1/v neutron counter

1/v neutron counter neutron detection efficiency: ε th = σ th ( ) ( ) θ x , y ( ) dxdy ∫ ∫ Ω x , y ρ x , y 4 π

1/v neutron counter neutron detection efficiency: ε th = σ th ( ) ( ) θ x , y ( ) dxdy ∫ ∫ Ω x , y ρ x , y 4 π Si detector solid angle

1/v neutron counter neutron detection efficiency: ε th = σ th ( ) ( ) θ x , y ( ) dxdy ∫ ∫ Ω x , y ρ x , y 4 π Si detector solid angle areal density of Li foil

1/v neutron counter neutron detection efficiency: ε th = σ th ( ) ( ) θ x , y ( ) dxdy ∫ ∫ Ω x , y ρ x , y 4 π Si detector solid angle areal density of Li foil neutron beam distribution

Error Budget

Error Budget can be significantly reduced by an absolute calibration of the 1/v neutron counter