1. The HD target JLab12 Collaboration Meeting Annalisa D’Angelo
Alessia Fantini, Carlo Schaerf and Valentina Vegna
University of Rome Tor Vergata and INFN Roma Tor Vergata
Roma- October 19th 2009

2. Outline
- Principles of HD frozen-spin target production and properties of Hydrogen isotopes molecules
- Optimization of orto-H2 and para-D2 concentrations HD gas distillation
HD gas analysis  gas chromatography high resolution HD gas analysis  Raman Scattering
Improvements on Raman Set-up
Target condensation and NMR set-up
Target polarization  New Building construction
Target transportation and New In-beam cryostat

3. Determination of orto-H2 and para-D2 concentrations
in HD gas using Raman Scattering
HD frozen-spin target advantages:
Fraction of free protons exceeds any other polarized target
 High dilution factors
H and D may be independently polarized and their polarization
may be independently reversed 
proton and neutron polarization
H and D may reach a high degree of polarization:
95 % for H 70% for D
In the frozen-spin condition targets may be cold-transported,
stored and used in beams under simple environment:
(B = 7 Tesla ,T=4k B=1 Tesla , T=0.5K)
storage experiment
HD frozen-spin target main disadvantage:
- long production cycles  R&D

4. Why HD : properties of hydrogen isotopes
Homo-nuclear molecules: H2 (D2) wave-functions must be symmetric (anti-symmetric) under nuclear exchange
Hetero-nuclear molecules (HD) do not obey any symmetry constraint
Nuclear Exchange  space inversion for electrons and nuclear spatial coordinates
e (-1)L symmetric in the ground state (L=0)
V symmetric in the ground state ( =0)
Rotational levels ER= b0 J(J+1) symmetry is given by (-1) J
Always symmetric in
the ground state
Nuclear spins: H2 (Ip =1/2) Spins couple to I = 0 (anti-symmetric)
I=1 (symmetric)
D2 (Id =1) Spins couple to I = 0,2 (symmetric)
I=1 (anti-symmetric)
J= even Symmetric J = odd Anti-symmetric
The H2 and D2 molecules are in I=0 ground state and may not be polarized
I=1 molecular states may be polarized
- not the molecular ground states
- associated to J odd rotational states
- meta-stable
H2 wave-function must be
anti-symmetric :
I = couples to J even (para-H2)
I= couples to J odd (orto-H2)
D2 wave-function must
be symmetric :
I = 0,2 couples to J even (orto-D2)
I= couples to J odd (para-D2)
Nuclei in HD molecules may be polarized in the ground state

5. 1) Brute force: High field/low temperature
HD frozen-spin target principle of operation:
brute force and a gentle touch
1) Brute force: High field/low temperature
By A. Sandorfi
High field B= T and
low temp T=10-15 mK
align spins with magnetic field
Maximum equilibrium polarization
PH =
PD = 0.3

6. 2) Gentle touch: longitudinal relaxation time switch mechanisms.
HD frozen-spin target principle of operation:
brute force and a gentle touch
2) Gentle touch: longitudinal relaxation time switch mechanisms.
T1H = minutes if orto-H2 concentration10-3
T1H = months if orto-H2 concentration10-6 H D
Direct spin-lattice relaxation is suppressed
T1H increases while orto-H2
concentration in HD decreases
T1H and T1D
very high for pure HD gas
T1H depends on orto-H2
concentration in HD
Cross-relaxation
spin-spin
interaction
spin-lattice
relaxation is suppressed H
Efficient
spin-lattice
relaxation H
Para-H2
I=0,J=0
ground state
Orto-H2
I=1,J=1
impurities
T1H spin-lattice relaxation switch
Decay 6.8 days
T=172 K
AGING

7. 2) Gentle touch: longitudinal relaxation time switch mechanisms.
HD frozen-spin target principle of operation:
brute force and a gentle touch
2) Gentle touch: longitudinal relaxation time switch mechanisms. H D
Direct spin-lattice relaxation is suppressed
T1D depends on para-D2
concentration in HD
T1D increases while para-H2
concentration in HD decreases
T1H and T1D
very high for pure HD gas
Cross-relaxation
spin-spin
interaction
spin-lattice
relaxation is suppressed D
Efficient
spin-lattice
relaxation D
Para-D2
I=1,J=1
impurities
Orto-D2
I=0,2 J=0
ground state
T1D spin-lattice relaxation switch
Decay 18.6 days
T=86 K D
AGING

8. HD polarization: relaxation time T1H

9. HD distillation Commercial HD contains  98% HD 1.5% H2 ≤0.5% D2
Distillation process developed
By Steve USC
12 moles in the batch

10. HD distillery operation
6-7 moles may be distilled in three weeks reducing the orto-H2 and para-D2 contaminants by a factor 10
By Steve USC

11. Gas chromatography: measurement of the thermal conductivity difference with respect of Neon gas carrier, as a function of retention time
Varian CP-3800 GC
Retention time is a function of the molecular mass and spin.
Double distillation is necessary to reduce the contamination content by two orders of magnitude.
The GC resolution limit is  0.1%
By Steve USC

12. Problems HD gas stored in high pressure
tanks tends to dissociate and recombine in H2 and D2 species,
at a rate of 0.14% /month
There are indications that after aging the para-H2  orto-H2 conversions occurs with a very long time constant
in normal conditions.
Accurate measurement of
orto-H2 and para-D2 content
in the HD is highly desirable

13. Raman spectroscopy: laser scattering from rotational states
Connects orto- to orto- and para- to para- molecular states
J=2

14. Raman set-up
Argon Ion Laser
Beam expander

15. Concentration
Measurement
< 0.5% D2 in H2
 (cm-1)

16. Exponential dependence from
Raman lines intensity: Temperature dependence
Partition function
I = Laser Intensity
A() = spectral response function
f(J) = an-harmonicity correction
= anisotropic matrix element
N = total number of molecules
gs(J) = nuclear spin multiplicity
Constant C
where
Exponential dependence from
1/ gas Temperature
CN and T may be extracted from a fit to data

17. Dominant H2   J
Iexp
(c/s)
Iexp
467.65
0.21 1
1391.5
0.2 2
200.74 3
132.15  

18. Main H2 gas content Log A = ( 2.764  0.002 ) counts/sJ
Iexp(J)Iexp (counts/s)
Ifit(J)Iexp (J)
(counts/s)
467.650.2
0.1 1
0.2
0.2 2
0.2
0.03 3
0.2
0.02 4 -
0.0009 5
0.0001 6
(  )10-2 7
(  )10-3
E(J)/KB (K-1)
Log A = (  ) counts/s
T = (286.4  0.2) K
Itot exp = ( 0.8) counts/s
Itot fit = ( 0.4) counts

19. Extraction of analysis for different H2 speciesJ
para-H2
CNeven/ CNtot= 0.0005
orto-H2 J
CNodd/ CNtot= 0.0005 J

20. D2 contaminant J (counts/s) 1 2 3 4 Iexp(J)Iexp 1.27 0.16
 (cm-1) J
Iexp(J)Iexp
(counts/s) 1
1.27 0.16 2
2.15 0.15 3
0.68 0.12 4
0.35 0.12
 (cm-1)
 (cm-1)
 (cm-1)

21. D2 gas content Log A = ( -1.1  0.1 ) counts/s T = (294  30) KJ
Iexp(J)Iexp (counts/s)
Ifit(J)Iexp (J)
(counts/s) -
0.21 1
1.270.16
1.34 0.21 2
2.15 0.14
2.13 0.23 3
0.680 0.12
0.57 0.06 4
0.34 0.12
0.43 0.04 5
0.060 0.006 6
0.024 0.002 7 
Log A = ( -1.1  0.1 ) counts/s
T = (294  30) K
E(J)/KB (K-1)
I tot= (6.57 0.71) counts/s

22. D2/H2= (0.00290.0003) H2 temperature Fit I tot= (6.460.69) C/s
D2 temperature

23. Extraction of analysis for different D2 speciesJ
orto-D2
CNeven/ CNtot= 0.660.03
para-D2 J
CNodd/ CNtot= 0.330.03
CND2/ CNH2 = (0.0030.001) J

24. Progress on Raman Analysis:
Raman spectroscopy works.
Sensitivity is being upgraded from to 10-5:
New Laser  15 W on the green line repaired
New cell with lower inner volume and non-magnetic windows done
New beam expander mounted
Second mirror available to be mounted
PM instead of CCD will be done in November
New measurements:
- 0.3% D2 in H2 being repeated to check improvements
Commercial HD gas analysis
Absolute normalization: 50% H2-HD, H2 -D2, H2-HD mixtures – precise gauge.
Real HD sample – sent from JLAB  next weeks

25. HD-ice target production: condensation
Target :  = 15 mm x50 mm
Material: solid HD
HD Gas is condensed
in a production Dewar
were equilibrium temperature NMR
is also performed.
It has been found that HD must
be condensed at HIGH PRESSURE
(30 atm) to avoid formation of
holes in the HD crystal.
The Rome group has been asked
to develop a new production Dewar
allowing:
High pressure production of HD
NMR measurements with
sweeping frequency and fixed magnetic field

26. HD-ice target production: polarization
HDice Target Lab: renovated test lab annex
condense HD gas  liquid  solid at 16 K
calibrate pol- NMR at T=2 K and B= 0.2 T
transfer to dilution refrigerator & polarize at T and 12 mK
hold at high-field low temp. for > 3 months
transfer to 8 T/1.6 K storage Cryostat

27. HD-ice target production: run the experiment
Hall-B
move to Hall B
transfer to In-Beam Cryostat (IBC)
move spins HD as needed
roll IBC into Clas
run the experience
P(H) = 75% P(D)=40%
Dilution factors: ½ 1
T1 (1/e relaxation time  years)

28. HD ice Time Line: 1st Occupancy of HDice Lab: Nov/09
IBC test with polarized HD (in HDice Lab): July/10
IBC installed in CLAS/ Hall-B: Sept/10
Start of g14/E06-101( ) 27/9/10
Test of Apr /10
Start of ET- 1/E / /Nov/11