William A. Peters

August 8, 2009ANL 1

D“Surrogate”reaction

db

B*

Aa

“Desired” reaction

Cc

Compound nucleus

different decay modes

August 8, 2009ANL 2

Fission vs. neutron captureRecent capture/fission ratio work shows promise. J. M. Allmond et al., Phys. Rev. C 79, 054610

(2009). Short-lived isotopes

Important for stewardship and basic science. Astro-physical reactions Nuclear reactors and device modeling Stockpile and waste storage

August 8, 2009ANL 3

August 8, 2009ANL 4

xp

xpx

CN

EN

ENEG

Compound nucleus decay becomes independent of spin and parity.

WE(E) =

CN(E) . G(E)

No sum over J,π!

(Ex ) CN

J , (Ex , J, )G

CN (Ex , J, )

First factor can be calculated. Second factor is difficult.

Requires W-E limit of H-F. Measure one reaction relative to

another. Reduces systematic uncertainties. No need to measure singles rate.

August 8, 2009ANL 5

)(

)(

)()()(

)()()(

)(

)()2(

)1(

)1()2()2(

)2()1()1(

)2(

)1(

xp

xp

xpxpxCNn

xpxpxCNn

xn

xn

EN

EN

ENENE

ENENE

E

E

Assumes Np1/Np2 cancel

August 8, 2009ANL 6

18.5 MeV deuteron beamfrom cyclotron

• Targets: two isotopically enriched metallic foils of 171Yb (0.981 mg/cm2) and 173Yb (0.502 mg/cm2)

• 3 Si detectors for particle detection (STARS):

dE: 500 m, 48 rings, 16 sectors

E1: 1000 m, 24 rings, 8 sectors

E2: 1000 m, 16 rings, 16 sectors

angular range covered: 44° to 73°

• 6 Ge clover detectors to detect coincident -rays (LiBerACE)

August 8, 2009ANL 7

Not in W-E limit Resolution not as good as n,γ Try to selectively match neutron capture

spin distribution Singles rate might not cancel Ratio seems consistent above 100 keV

August 8, 2009ANL 8

Needed for short lived isotopes (<100 days).

A reliable method and analysis could start an exciting new campaign of capture measurements.

August 8, 2009ANL 9

View of (d,pγ) components

8 Silicon(ORRUBA) detectors

4 Germanium clovers

Target manipulator

Cubic chamber

Beam direction

High-ratediamond detector

-J. CizewskiAugust 8, 2009 10ANL

ORRUBA + Gammasphere – chamber conceptORRUBA + Gammasphere – chamber concept

28°

175mm

214mm

145mm

Feed-throughs

BGO

-S. Pain

Original design by Charles Reed, first used by Micah Johnson

August 8, 2009ANL 12

73As/74As = 1/2 σ74(n,2n) Фn (D.Vieira)

Isotope ratios measured after event (n,2n) reactions most important (n,γ) reactions can effect results

August 8, 2009ANL 13

Deuterated plastic target 400 μg/cm2

75As at 530 MeV Tandem voltage near 24 MV Beam rate was 10^7 pps 1 week of beam time Trigger on ORRUBA (proton) singles

August 8, 2009ANL 14

Gamma Spectrum (keV)

Spectrum not Doppler corrected

165 511

Partial level scheme (from ENDSF) of 76As used to identify successful (d,pγ) events. Quoted branching are from (n,γ) experiments.

August 8, 2009ANL 15

Doppler corrected6 keV FWHM

August 8, 2009 16ANL

Carbon target CD2 target

August 8, 2009ANL 17

Sn=7.33 MeV

Fusion on carbon dominates background Resolution poor Still need to gate on γ-rays Will G(E) match n,γ?

August 8, 2009ANL 18

Can n,γ CN be mimicked by surrogates? Can d,pγ work in inverse kin? Will another reaction work for rare isotopes? Must we give up on ratio method if W-E not met? Can we calculate spin mismatch of d,pγ-n,γ? How to deal with deformed nuclei?

August 8, 2009ANL 19

Use n-rich beams. Tag on d,p recoils.

Timing Recoil separator Pure target

Increase resolution and acceptance.

Improved signal to noise for gammas.

Improved resolution with more space for ORRUBA.

Beam energy range better for d,pg. More n-rich beams available. Might work with less beam.

August 8, 2009ANL 20

Rutgers University. J. Cizewski, R. Hatarik, P. O’Malley

University of Tennessee K. L. Jones, K. Schmitt, R. Kapler, B. Moazen, A. Chae, S.

Pittman Louisiana State University

J.C. Blackmon Tennessee Technological University

R.L. Kozub LANL

D. Vieira, M Jandel, J.B. Wilhelmy ORAU

C. Matei LLNL

A. Becker, C. Y. Wu, J. Escher, F. Dietrich ORNL

D.W. Bardayan, S.D. Pain, M.S. Smith, D. Stracener

August 8, 2009ANL 21

Measure 75As d,pγ for benchmark. Develop 73,74As beams at HRIBF. Use benchmark for ratio measurements

to radioactive As isotopes.

August 8, 2009ANL 22

Measured (n,γ) cross section (from NNDC) to compare to surrogate (d,pγ).

August 8, 2009ANL 23

Proton energy (a.u.)

PRELIMIN

ARY

PRELIMIN

ARY

165 keV

511 keV

August 8, 2009ANL 24

-J. Escher

a

bc

dJ distributions

considered

PRELIMIN

ARY

PRELIMIN

ARY

August 8, 2009ANL 25

75As+12C 530 MeV

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

80.00 100.00 120.00 140.00 160.00 180.00

Lab Angle (deg)

Pro

ton

En

erg

y (

MeV

)

EvapOR calculations show high energy protons come out at back angles from C-fusion. –J. Cizewski

August 8, 2009ANL 26

Diamond beam-rate detector was tested for activation. Beta-gamma analysis confirmed 82Sr, 85Sr, and 83Rb.

August 8, 2009ANL 27

Multi-crystal350 um thickGold plated1.0” diameter0.1 ns timing10^8 pps limit

August 8, 2009ANL 28

Preceded by large-bore quadNo need to tune past first set of slitsInstall Silicon stack for id (need rate less than 10 kHz).Will have more trouble with unreacted beam than C-fusion

150

650

1150

1650

2150

2650

3150

3650

4150

3 53 103 153 203

Cro

ss s

ecti

on

(m

b)

Neutron energy (keV)

171Yb 173Yb

August 8, 2009ANL 29

Using 4-2 transition

Known neutron capture cross sections for 171Yb and 173Yb from K. Wisshak et al., Phys Rev C 61, (2000) 065801.

0+2+4+

6+

J

August 8, 2009 30ANL

Intensity ratios of the 4+ 2+ and 6+ 4+ different for 171Yb (1/2-) and 173Yb (5/2-)

Calculated by DICEBOX

R. Hatarik

Subtract 6+ feeding of 4+ to get spin distribution closer to (n,)