Experiments towards the Efficient Trapping of Francium

by Seth Aubin

Parity Violation in Francium Group

Students:Eduardo GomezJoshua M. Grossman

Professors:Luis A. OrozcoGene D. Sprouse

A Brief History of Francium at Stony Brook

1991-94: Construction of 1st production and trapping apparatus.

1995: Produced and Trapped Francium in a MOT.

1996-2000: Laser spectroscopy of Francium (8S1/2, 7P1/2,7D5/2,7D3/2, hyperfine anomaly).

2000-2002: construction of new production and trapping apparatus.

10,000 atom Fr MOT

New Apparatus for Producing and Trapping Francium

Objective: Trap 106 Fr atoms

Parity Non-Conservation experiments

Nuclear Anapole measurements

Strategy:

• Increase Production

• Optimize Optical Trapping efficiency

• Improve Neutralizer efficiency

Schematic of New Apparatus

Improved Production

0

2

4

6

8

10

12

14

16

0 500 1000 1500 2000 2500 3000t (s)

Fr

pro

du

cti

on

ra

te (

mill

ion

Fr/

s)

phase transition

beam blocked

16O, 18O, 19F ~100 MeVFr+ ions

Au, Pt target

Improved Fr+ ion extraction New target design

Heated tungsten rod

Optical Trapping Efficiency1. Capture Velocity of MOT

Idea: • Accelerate MOT atoms with laser.

• Measure at what velocity atoms cannot be recaptured by MOT.

b. Velocity Calibration:a. Description

atom cloud

on resonance laser push

0

5

10

15

20

25

0 50 100 150 200 250 300

push time (microseconds)

fin

al v

elo

city

(m

/s

c. Capture Velocity (lower bound):

~18 m/s

MOT

1 mm

Displaced MOT

(External B-field)Laser push

1 mm

2. Number of Bounces (Nbounces)

Atoms rethermalize with cell walls on each bounce.

NMOTNbounces.

Nbounces is determined by exit holes, quality of dry-film coating.

Dry-Film (SC-77) test:

780 nm laser probe

Rb atomic beam

shutter

fast detector

Cell with coating (Rb curing)

0.74

0.76

0.78

0.8

0.82

0.84

0.86

0 10 20 30 40 50time (ms)

flu

ore

sc

en

ce

(a

. u.)

Decay Time = 6.6 ms

Monte-Carlo simulations decay time of 5.2 ms (~100 bounces)

Cell without coating

0.0375

0.04

0.0425

0.045

0 3 6 9 12 15 18 21time (ms)

fluo

resc

ence

(a.

u.)

decay time < 1 ms

Comparison of Neutralizer Materials (at 5 KeV)

~ 300 Celsius

Conclusion

New apparatus for trapping 106 Fr atoms.

Increased Fr production by a factor of 15.

Studied neutralization process.

Probes of capture velocity and coating quality.

Capture velocity of at least 18 m/s.

Just converted apparatus to Francium.