The Next Generation Beam Neutron Lifetime Experiment F . E. - - PowerPoint PPT Presentation

The Next Generation Beam Neutron Lifetime Experiment

F . E. Wietfeldt Tulane University

Our Plan

Based on Sussex-ILL-NIST beam neutron lifetime program using quasi-Penning proton trap. More than 30 years experience with this program; many systematics thoroughly studied and understood.

Our Plan

Based on Sussex-ILL-NIST beam neutron lifetime program using quasi-Penning proton trap. More than 30 years experience with this program; many systematics thoroughly studied and understood. Goal #1: Further explore, cross check, and reduce all systematic uncertainties to the 10 level

• 4

Our Plan

Based on Sussex-ILL-NIST beam neutron lifetime program using quasi-Penning proton trap. More than 30 years experience with this program; many systematics thoroughly studied and understood. Goal #1: Further explore, cross check, and reduce all systematic uncertainties to the 10 level

• 4

Goal #2: Reduce the neutron lifetime uncertainty, using the beam method, to < 0.2 s

Brief Review of the 2005 NIST Beam Neutron Lifetime Experiment and 2013 Update

Brief Review of the 2005 NIST Beam Neutron Lifetime Experiment and 2013 Update

proton counting rate: Rp = εp AbeamLdet τn

Z φ(v)

v dv neutron counting rate: Rn = εthAbeamvth

Z φ(v)

v dv

Brief Review of the 2005 NIST Beam Neutron Lifetime Experiment and 2013 Update

proton counting rate: Rp = εp AbeamLdet τn

Z φ(v)

v dv neutron counting rate: Rn = εthAbeamvth

Z φ(v)

v dv

τn = RnεpLdet Rpεthvth

neutron beam proton detector alpha, triton detector precision aperture B = 4.6 T Li deposit

6

trap electrodes door closed (+800 V) mirror (+800 V)

τ = Rnε pLdet Rpεthvth

neutron beam proton detector alpha, triton detector precision aperture B = 4.6 T Li deposit

6

trap electrodes door closed (+800 V) mirror (+800 V)

τ = Rnε pLdet Rpεthvth

neutron beam proton detector alpha, triton detector precision aperture B = 4.6 T Li deposit

6

trap electrodes door closed (+800 V) mirror (+800 V)

Ldet = nl + Lend

τ = Rnε pLdet Rpεthvth

neutron beam proton detector alpha, triton detector precision aperture B = 4.6 T Li deposit

6

trap electrodes door closed (+800 V) mirror (+800 V)

Ldet = nl + Lend

# trap electrodes

τ = Rnε pLdet Rpεthvth

neutron beam proton detector alpha, triton detector precision aperture B = 4.6 T Li deposit

6

trap electrodes door closed (+800 V) mirror (+800 V)

Ldet = nl + Lend

# trap electrodes length of electrode + spacer

τ = Rnε pLdet Rpεthvth

neutron beam proton detector alpha, triton detector precision aperture B = 4.6 T Li deposit

6

trap electrodes door closed (+800 V) mirror (+800 V)

Ldet = nl + Lend

# trap electrodes length of electrode + spacer total effective end region length

τ = Rnε pLdet Rpεthvth

neutron beam proton detector alpha, triton detector precision aperture B = 4.6 T Li deposit

6

trap electrodes door closed (+800 V) mirror (+800 V)

Ldet = nl + Lend

# trap electrodes length of electrode + spacer total effective end region length

Rp Rn = τ −1 ε p εthvth ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ nl + Lend

( )

Proton Trap

1 10 100 1000 Counts 600 500 400 300 200 100 ADC Channel (7.47 ch. = 1 keV) Prot

• ton
• n Pulse Height Sp

Spectrum ( (32.5 .5 kV; 2 kV; 20 µ µg/cm /cm

2 Au)

Au) 32.5 keV

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

2 Au)

• 40x10
• 6
• 20

20 40 Residuals 11 10 9 8 7 6 5 4 3 2 Electrode Number

4.0x10

• 3

3.5 3.0 2.5 2.0 1.5 Proton-Bkdg/Alpha 11 10 9 8 7 6 5 4 3 2 Electrode Number Nor

• rma

malized Prot

• ton
• n Cou
• unts vs. Trap Length

( (32.5 .5 kV; 2 kV; 20 µ µg/cm /cm

2 Au)

Au)

• 40x10
• 6
• 20

20 40 Residuals 12:00 AM 9/29/00 12:00 AM 9/30/00 12:00 AM 10/1/00 12:00 AM 10/2/00 12:00 AM 10/3/00 Date/Time

Fit of Rp Rn

• vs. number

trap electrodes

910 905 900 895 890 885 880 measured lifetime (s) 30x10

• 3

25 20 15 10 5 backscatter fraction

extrapolated result (stat. error only) 886.8 ± 1.2 s

27.5 kV 30 kV 32.5 kV

Lifetime vs. Backscatter

1/v neutron counter

neutron detection efficiency: εth = σ th 4π Ω x,y

( )

∫ ∫

ρ x,y

( )θ x,y ( )dxdy

1/v neutron counter

neutron detection efficiency: εth = σ th 4π Ω x,y

( )

∫ ∫

ρ x,y

( )θ x,y ( )dxdy

1/v neutron counter

Si detector solid angle

neutron detection efficiency: εth = σ th 4π Ω x,y

( )

∫ ∫

ρ x,y

( )θ x,y ( )dxdy

1/v neutron counter

Si detector solid angle areal density of Li foil

neutron detection efficiency: εth = σ th 4π Ω x,y

( )

∫ ∫

ρ x,y

( )θ x,y ( )dxdy

1/v neutron counter

Si detector solid angle areal density of Li foil neutron beam density

Error Budget 2005: τ = 886.3 ± 3.4 s

n

Source of correction Correction (s) Uncertainty (s)

6LiF deposit areal density

2.2

6Li cross section

1.2 Neutron detector solid angle 1.0 Absorption of neutrons by 6Li +5.2 0.8 Neutron beam profile and detector solid angle +1.3 0.1 Neutron beam profile and 6Li deposit shape −1.7 0.1 Neutron beam halo −1.0 1.0 Absorption of neutrons by Si substrate +1.2 0.1 Scattering of neutrons by Si substrate −0.2 0.5 Trap nonlinearity −5.3 0.8 Proton backscatter calculation 0.4 Neutron counting dead time +0.1 0.1 Proton counting statistics 1.2 Neutron counting statistics 0.1 Total −0.4 3.4

• J. S. NICO et al.

PHYSICAL REVIEW C 71, 055502 (2005)

Error Budget 2005: τ = 886.3 ± 3.4 s

n

Source of correction Correction (s) Uncertainty (s)

6LiF deposit areal density

2.2

6Li cross section

1.2 Neutron detector solid angle 1.0 Absorption of neutrons by 6Li +5.2 0.8 Neutron beam profile and detector solid angle +1.3 0.1 Neutron beam profile and 6Li deposit shape −1.7 0.1 Neutron beam halo −1.0 1.0 Absorption of neutrons by Si substrate +1.2 0.1 Scattering of neutrons by Si substrate −0.2 0.5 Trap nonlinearity −5.3 0.8 Proton backscatter calculation 0.4 Neutron counting dead time +0.1 0.1 Proton counting statistics 1.2 Neutron counting statistics 0.1 Total −0.4 3.4

can be significantly reduced by an absolute calibration

• f the

1/v neutron counter

• J. S. NICO et al.

PHYSICAL REVIEW C 71, 055502 (2005)

Absolute neutron flux measurement to < 0.1% precision

• 3He gas scintillation chamber (Tulane, NIST) - in construction/testing
• neutron radiometer (Indiana, Michigan) - under development
• 10B alpha-gamma device

now working at NIST 0.06% precision recently achieved! (Andrew Yue, NIST)

Neutron fluence monitor

The Alpha-Gamma device

Monochromatic neutron beam HPGe detector

Alpha-Gamma device

PIPS detector with aperture

Totally absorbing

10B target foil

HPGe detector

Absolute neutron flux measurement to < 0.1% precision

• 3He gas scintillation chamber (Tulane, NIST) - in construction/testing
• neutron radiometer (Indiana, Michigan) - under development
• 10B alpha-gamma device

now working at NIST 0.06% precision recently achieved! (Andrew Yue, NIST)

Neutron fluence monitor

The Alpha-Gamma device

Monochromatic neutron beam HPGe detector

Alpha-Gamma device

PIPS detector with aperture

Totally absorbing

10B target foil

HPGe detector

2013 improved result: τ = 887 .7 ± 2.3 s

n

900 895 890 885 880 875 870 neutron lifetime (s) 2015 2010 2005 2000 1995 1990 year

neutron lifetime results since 1990

beam method UCN bottle τn = 879.6 ± 0.6 s τn = 888.0 ± 2.1 s

THE NEXT GENERATION

BEAM NEUTRON LIFETIME

Source of correction Correction (s) Uncertainty (s)

6LiF deposit areal density

2.2

6Li cross section

1.2 Neutron detector solid angle 1.0 Absorption of neutrons by 6Li +5.2 0.8 Neutron beam profile and detector solid angle +1.3 0.1 Neutron beam profile and 6Li deposit shape −1.7 0.1 Neutron beam halo −1.0 1.0 Absorption of neutrons by Si substrate +1.2 0.1 Scattering of neutrons by Si substrate −0.2 0.5 Trap nonlinearity −5.3 0.8 Proton backscatter calculation 0.4 Neutron counting dead time +0.1 0.1 Proton counting statistics 1.2 Neutron counting statistics 0.1 Total −0.4 3.4

2005 Error Budget

Source of correction Correction (s) Uncertainty (s)

6LiF deposit areal density

2.2

6Li cross section

1.2 Neutron detector solid angle 1.0 Absorption of neutrons by 6Li +5.2 0.8 Neutron beam profile and detector solid angle +1.3 0.1 Neutron beam profile and 6Li deposit shape −1.7 0.1 Neutron beam halo −1.0 1.0 Absorption of neutrons by Si substrate +1.2 0.1 Scattering of neutrons by Si substrate −0.2 0.5 Trap nonlinearity −5.3 0.8 Proton backscatter calculation 0.4 Neutron counting dead time +0.1 0.1 Proton counting statistics 1.2 Neutron counting statistics 0.1 Total −0.4 3.4

2005 Error Budget

neutron counting

Source of correction Correction (s) Uncertainty (s)

6LiF deposit areal density

2.2

6Li cross section

1.2 Neutron detector solid angle 1.0 Absorption of neutrons by 6Li +5.2 0.8 Neutron beam profile and detector solid angle +1.3 0.1 Neutron beam profile and 6Li deposit shape −1.7 0.1 Neutron beam halo −1.0 1.0 Absorption of neutrons by Si substrate +1.2 0.1 Scattering of neutrons by Si substrate −0.2 0.5 Trap nonlinearity −5.3 0.8 Proton backscatter calculation 0.4 Neutron counting dead time +0.1 0.1 Proton counting statistics 1.2 Neutron counting statistics 0.1 Total −0.4 3.4

2005 Error Budget

neutron counting proton counting

Source of correction Correction (s) Uncertainty (s)

6LiF deposit areal density

2.2

6Li cross section

1.2 Neutron detector solid angle 1.0 Absorption of neutrons by 6Li +5.2 0.8 Neutron beam profile and detector solid angle +1.3 0.1 Neutron beam profile and 6Li deposit shape −1.7 0.1 Neutron beam halo −1.0 1.0 Absorption of neutrons by Si substrate +1.2 0.1 Scattering of neutrons by Si substrate −0.2 0.5 Trap nonlinearity −5.3 0.8 Proton backscatter calculation 0.4 Neutron counting dead time +0.1 0.1 Proton counting statistics 1.2 Neutron counting statistics 0.1 Total −0.4 3.4

2005 Error Budget

neutron counting proton counting

Source of correction Correction (s) Uncertainty (s)

6LiF deposit areal density

2.2

6Li cross section

1.2 Neutron detector solid angle 1.0 Absorption of neutrons by 6Li +5.2 0.8 Neutron beam profile and detector solid angle +1.3 0.1 Neutron beam profile and 6Li deposit shape −1.7 0.1 Neutron beam halo −1.0 1.0 Absorption of neutrons by Si substrate +1.2 0.1 Scattering of neutrons by Si substrate −0.2 0.5 Trap nonlinearity −5.3 0.8 Proton backscatter calculation 0.4 Neutron counting dead time +0.1 0.1 Proton counting statistics 1.2 Neutron counting statistics 0.1 Total −0.4 3.4

2005 Error Budget

neutron counting proton counting

Proton Counting Statistics

Proton Counting Statistics

Want 200x increase in proton trapping rate Bigger, longer trap and magnet, larger neutron beam

Proton Counting Statistics

Want 200x increase in proton trapping rate Bigger, longer trap and magnet, larger neutron beam

2005 NIST BL3 factor beam diameter 7 mm 35 mm 25 effective trap length 300 mm 600 mm 2 relative neutron flux* 1 4 4

Net: 200

*based on MCNP calculation using optimized collimation at NIST NG-C end position

Source of correction Correction (s) Uncertainty (s)

6LiF deposit areal density

2.2

6Li cross section

1.2 Neutron detector solid angle 1.0 Absorption of neutrons by 6Li +5.2 0.8 Neutron beam profile and detector solid angle +1.3 0.1 Neutron beam profile and 6Li deposit shape −1.7 0.1 Neutron beam halo −1.0 1.0 Absorption of neutrons by Si substrate +1.2 0.1 Scattering of neutrons by Si substrate −0.2 0.5 Trap nonlinearity −5.3 0.8 Proton backscatter calculation 0.4 Neutron counting dead time +0.1 0.1 Proton counting statistics 1.2 Neutron counting statistics 0.1 Total −0.4 3.4

2005 Error Budget

neutron counting proton counting

Proton Backscatter Extrapolation

Proton Backscatter Extrapolation

910 905 900 895 890 885 880 measured lifetime (s) 30x10

• 3

25 20 15 10 5 backscatter fraction

extrapolated result (stat. error only) 886.8 ± 1.2 s

27.5 kV 30 kV 32.5 kV

2005 NIST:

Proton Backscatter Extrapolation

910 905 900 895 890 885 880 measured lifetime (s) 30x10

• 3

25 20 15 10 5 backscatter fraction

extrapolated result (stat. error only) 886.8 ± 1.2 s

27.5 kV 30 kV 32.5 kV

2005 NIST: BL3:

Larger detector, variable field expansion eliminate this effect (Monte Carlo)

Source of correction Correction (s) Uncertainty (s)

6LiF deposit areal density

2.2

6Li cross section

1.2 Neutron detector solid angle 1.0 Absorption of neutrons by 6Li +5.2 0.8 Neutron beam profile and detector solid angle +1.3 0.1 Neutron beam profile and 6Li deposit shape −1.7 0.1 Neutron beam halo −1.0 1.0 Absorption of neutrons by Si substrate +1.2 0.1 Scattering of neutrons by Si substrate −0.2 0.5 Trap nonlinearity −5.3 0.8 Proton backscatter calculation 0.4 Neutron counting dead time +0.1 0.1 Proton counting statistics 1.2 Neutron counting statistics 0.1 Total −0.4 3.4

2005 Error Budget

neutron counting proton counting

Proton Trap Nonlinearity

Proton Trap Nonlinearity

5.0 4.5 4.0 3.5 3.0 axial magnetic field (T) 50 40 30 20 10 axial position (cm)

downstream upstream electrode positions

Trap Magnetic Field

800 600 400 200 potential (V) 50 40 30 20 10 axial position z (cm)

Trap Electrostatic Potential (10 electrodes)

1.000 0.995 0.990 0.985 0.980 0.975 0.970 p/n correction factor 10 9 8 7 6 5 4 3 trap length (electrodes)

Correction Cactors from Monte Carlo Calculation

2005 NIST

8% nonuniformity

Proton Trap Nonlinearity

5.0 4.5 4.0 3.5 3.0 axial magnetic field (T) 50 40 30 20 10 axial position (cm)

downstream upstream electrode positions

Trap Magnetic Field

800 600 400 200 potential (V) 50 40 30 20 10 axial position z (cm)

Trap Electrostatic Potential (10 electrodes)

1.000 0.995 0.990 0.985 0.980 0.975 0.970 p/n correction factor 10 9 8 7 6 5 4 3 trap length (electrodes)

Correction Cactors from Monte Carlo Calculation

2005 NIST

8% nonuniformity

BL3 ΔB/B < .001 over 60 cm proton trapping region

Proton Trap Nonlinearity

5.0 4.5 4.0 3.5 3.0 axial magnetic field (T) 50 40 30 20 10 axial position (cm)

downstream upstream electrode positions

Trap Magnetic Field

800 600 400 200 potential (V) 50 40 30 20 10 axial position z (cm)

Trap Electrostatic Potential (10 electrodes)

1.000 0.995 0.990 0.985 0.980 0.975 0.970 p/n correction factor 10 9 8 7 6 5 4 3 trap length (electrodes)

Correction Cactors from Monte Carlo Calculation

2005 NIST

8% nonuniformity

BL3 ΔB/B < .001 over 60 cm proton trapping region Other contributions:

• trap metrology
• beam divergence

are small, < 0.1 s

Source of correction Correction (s) Uncertainty (s)

6LiF deposit areal density

2.2

6Li cross section

1.2 Neutron detector solid angle 1.0 Absorption of neutrons by 6Li +5.2 0.8 Neutron beam profile and detector solid angle +1.3 0.1 Neutron beam profile and 6Li deposit shape −1.7 0.1 Neutron beam halo −1.0 1.0 Absorption of neutrons by Si substrate +1.2 0.1 Scattering of neutrons by Si substrate −0.2 0.5 Trap nonlinearity −5.3 0.8 Proton backscatter calculation 0.4 Neutron counting dead time +0.1 0.1 Proton counting statistics 1.2 Neutron counting statistics 0.1 Total −0.4 3.4

2005 Error Budget

neutron counting proton counting

Neutron Beam Halo

Neutron Beam Halo

Due to neutron beam + readout hysteresis

2005 NIST

Neutron Beam Halo

Due to neutron beam + readout hysteresis

2005 NIST BL3 Recent studies: readout hysteresis >90% of effect So with much larger (10 cm dia.) proton detector this will be negligible

Source of correction Correction (s) Uncertainty (s)

6LiF deposit areal density

2.2

6Li cross section

1.2 Neutron detector solid angle 1.0 Absorption of neutrons by 6Li +5.2 0.8 Neutron beam profile and detector solid angle +1.3 0.1 Neutron beam profile and 6Li deposit shape −1.7 0.1 Neutron beam halo −1.0 1.0 Absorption of neutrons by Si substrate +1.2 0.1 Scattering of neutrons by Si substrate −0.2 0.5 Trap nonlinearity −5.3 0.8 Proton backscatter calculation 0.4 Neutron counting dead time +0.1 0.1 Proton counting statistics 1.2 Neutron counting statistics 0.1 Total −0.4 3.4

2005 Error Budget

neutron counting proton counting independent

• f neutron

spectrum

Absolute Neutron Fluence Measurement

Absolute Neutron Fluence Measurement

Alpha-Gamma Method:

Source of uncertainty Fractional uncertainty Neutron counting statistics 3.1 × 10−4 ↵-source calibration of AG ↵-detector 2.7 × 10−4 attenuation in B4C target 2.5 × 10−4 Neutron beam wavelength 2.4 × 10−4 attenuation in thin 10B target 1.3 × 10−4

λmono 2

contamination of beam 1.0 × 10−4 Neutron backscatter in monitor substrate 3.9 × 10−5 AG ↵ solid angle for beam spot 2.7 × 10−5 Detector dead time 2.4 × 10−5 Neutron loss in Si substrate 1.8 × 10−5 Neutron absorption by 6Li 1.2 × 10−5 Self-shielding of 6Li deposit 6.0 × 10−6 Neutron monitor solid angle for beam spot 4.5 × 10−6 production in thin 10B target Si subtrate 3.2 × 10−6 Monitor misalignment w.r.t. beam 2.0 × 10−6 Neutron scattering from B4C 3.3 × 10−7 Total 5.7 × 10−4

2013 result error budget

counting statistics reduced using new geometry can be done better <0.01% achieved previously at NIST

Absolute Neutron Fluence Measurement

Alpha-Gamma Method:

Source of uncertainty Fractional uncertainty Neutron counting statistics 3.1 × 10−4 ↵-source calibration of AG ↵-detector 2.7 × 10−4 attenuation in B4C target 2.5 × 10−4 Neutron beam wavelength 2.4 × 10−4 attenuation in thin 10B target 1.3 × 10−4

λmono 2

contamination of beam 1.0 × 10−4 Neutron backscatter in monitor substrate 3.9 × 10−5 AG ↵ solid angle for beam spot 2.7 × 10−5 Detector dead time 2.4 × 10−5 Neutron loss in Si substrate 1.8 × 10−5 Neutron absorption by 6Li 1.2 × 10−5 Self-shielding of 6Li deposit 6.0 × 10−6 Neutron monitor solid angle for beam spot 4.5 × 10−6 production in thin 10B target Si subtrate 3.2 × 10−6 Monitor misalignment w.r.t. beam 2.0 × 10−6 Neutron scattering from B4C 3.3 × 10−7 Total 5.7 × 10−4

2013 result error budget

counting statistics reduced using new geometry can be done better <0.01% achieved previously at NIST

need a factor of 6 better for BL3

Absolute Neutron Fluence Measurement

Alpha-Gamma Method: new apparatus

Absolute Neutron Fluence Measurement

A 3He gas scintillation absolute neutron counter

(Tulane, NIST)

TPB acrylic 25 cm 13 cm PMT 1 atm He + N

5 mm dia, 5A neutron beam .004" Al window PMT PMT PMT PMT

Design features:

• absolute neutron counting to 99.95%
• 3He gas scintillates in XUV (70-90 nm)
• >50 kHz pulse counting rate
• XUV downshifted to visible by TPB
• >30 photoelectrons/neutron capture
• 1-10 torr N2 quenches long-lived triplet dimers

construction / testing now in progress

Absolute Neutron Fluence Measurement

A 3He gas scintillation absolute neutron counter

(Tulane, NIST)

TPB acrylic 25 cm 13 cm PMT 1 atm He + N

5 mm dia, 5A neutron beam .004" Al window PMT PMT PMT PMT

Design features:

• absolute neutron counting to 99.95%
• 3He gas scintillates in XUV (70-90 nm)
• >50 kHz pulse counting rate
• XUV downshifted to visible by TPB
• >30 photoelectrons/neutron capture
• 1-10 torr N2 quenches long-lived triplet dimers

construction / testing now in progress

current goal is < 0.05% precision

Source of correction Correction (s) Uncertainty (s)

6LiF deposit areal density

2.2

6Li cross section

1.2 Neutron detector solid angle 1.0 Absorption of neutrons by 6Li +5.2 0.8 Neutron beam profile and detector solid angle +1.3 0.1 Neutron beam profile and 6Li deposit shape −1.7 0.1 Neutron beam halo −1.0 1.0 Absorption of neutrons by Si substrate +1.2 0.1 Scattering of neutrons by Si substrate −0.2 0.5 Trap nonlinearity −5.3 0.8 Proton backscatter calculation 0.4 Neutron counting dead time +0.1 0.1 Proton counting statistics 1.2 Neutron counting statistics 0.1 Total −0.4 3.4

2005 Error Budget

neutron counting proton counting depend on neutron spectrum

Need a precise measurement of the in situ neutron velocity spectrum

Need a precise measurement of the in situ neutron velocity spectrum Dedicated time-of-flight spectrometer

Source of correction Correction (s) Uncertainty (s)

6LiF deposit areal density

2.2

6Li cross section

1.2 Neutron detector solid angle 1.0 Absorption of neutrons by 6Li +5.2 0.8 Neutron beam profile and detector solid angle +1.3 0.1 Neutron beam profile and 6Li deposit shape −1.7 0.1 Neutron beam halo −1.0 1.0 Absorption of neutrons by Si substrate +1.2 0.1 Scattering of neutrons by Si substrate −0.2 0.5 Trap nonlinearity −5.3 0.8 Proton backscatter calculation 0.4 Neutron counting dead time +0.1 0.1 Proton counting statistics 1.2 Neutron counting statistics 0.1 Total −0.4 3.4

2005 Error Budget

neutron counting proton counting

BL3

A Next Generation Beam Neutron Lifetime Experiment

10 cm dia. segmented Si detector (Nab, UCNB)

Goals: 1) Control and reduce all systematics at the <0.1 s level 2) Reduce the beam neutron lifetime uncertainty to < 0.2 s

BL3

6 5 4 3 2 1 B (T) 2.0 1.5 1.0 0.5 0.0 u (m) magnet coils 10° bend proton trap detector

BL3

4.54 4.53 4.52 4.51 4.50 4.49 4.48 B (T) 100 80 60 40 u (cm)

62 cm

< 0.001 uniform B field region

Proton Backscatter

0.10 0.08 0.06 0.04 0.02 0.00 backscatter missed fraction 20 15 10 5 p detector translation (cm)

• 10
• 5

5 10 cm

• 10
• 5

5 10 cm +13 cm

• 10
• 5

5 10 cm

• 10
• 5

5 10 cm +13 cm

• 10
• 5

5 10 cm

• 10
• 5

5 10 cm +6 cm

• 10
• 5

5 10 cm

• 10
• 5

5 10 cm +6 cm

• 10
• 5

5 10 cm

• 10
• 5

5 10 cm 0 cm

• 10
• 5

5 10 cm

• 10
• 5

5 10 cm 0 cm

First Hit Second Hit

BL3 Systematic Improvements

Proton Counting:

• larger detector area (30x)
• pixellated detector
• variable field expansion by detector translation (backscatter correction)
• <0.01% magnetic field uniformity in trap region
• trim coils to test variations in field uniformity

Neutron Counting:

• precision neutron spectral flux measurement
• improved alpha-gamma geometry
• multiple independent absolute flux calibrations

Summary

• >30 years experience with the Sussex-ILL-NIST beam neutron lifetime

program.

• With a larger beam, magnet, and trap of design similar to the existing

apparatus, proton counting statistics can achieve < 0.1 s uncertainty

• With achievable technical improvements (no high-risk R&D), known

systematic effects can be reduced to < 0.1 s.

• As before, neutron counting systematics are the most challenging part.
• Estimated capital cost is approx. $2M (DOE + NSF)
• Timetable: 2015: proposal

2016-2017: funding 2017-2020: design/construction 2020+ commissioning at NIST.