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XI International Workshop PST05Tokyo, Japan, November 14-17, 2005

The Sb and HIO3 Aligned Nuclear Targets

for Investigation of Time Reversal Invariance Violation.

A.G.Beda , L.D. Smirnova

Institute of Theoretical and Experimental Physics (ITEP),

Moscow, Russia

e-mail: beda@itep.ru

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Topics

1. Introduction. 2. Aligned targets.

2.1. Nuclear alignment. 2.2. Aligned nuclear targets for PCTV experiments. 3. Outlook.

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Introduction Forward scattering amplitude for slow neutrons can be written in the following way : f(0) = A + BsI + Csp + DspI+ EspI(pI) PV PVTV PCTV where s, I , p are the neutron spin , spin of the target nuclei and neutron momentum respectively.

Investigation of fundamental symmetries violation (spatial parity and time invariance ) in neutron-nuclear interactions is rather perspective due to large enhancement of effects of violation in the compound resonances. 

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Real progress in this field was hampered in the first place by absence of appropriate oriented nuclear targets, by serious methodical problems ( in the case of threefold correlation) and to some extent by insufficient intensity of sources of resonance neutrons.

Now the creation of the two neutron spallation sources (JSNS, Japan and SNS, USA) are in progress. Their intensity will be more than intensity of present sources by a factor 20-30.

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Today the japanese physicists are successful in the development of polarized nuclear target LaAlO3+Nd3+

Real progress in the development of aligned nuclear target is achieved in Russia.

The Sb and HiO3 single crystals are grown and the construction of PTR based dilution refrigerator is developed.

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2. Aligned nuclear targets

2.1. The nuclear alignmentInteraction of nucleus qadrupole moment Q with gradient of electric field eqzz results in splitting of the

ground state over 2I–1 double (± mi) degenerated

substates . ЕQ (mi)= eQqzz [ 3mi

2 - I(I+1)] / 4I(2I-1)

Recall that an ensemble of nuclei with spin I 1 is aligned if the parameter of alignment р2 (I) is nonzero

 р2 (I) = [3 m2 – I (I+1) ] / I (2I–1) Here m2 = ( mi

2 ni) / ni and ni is a population of

substate mi .

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If the spins are in equilibrium at the temperature T0

the distribution of ni over substates is given by

Boltzman law, at T= 0.5 K and NQR ~ 100 MHz

p2equilibr =0.5%

The high degree of nuclear alignment р2 (I) can be

achieved by dynamic nuclear alignment (DNA) method (Atsarkin, Beda et al, 2000) or sometimes by brute force method.

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Dynamic nuclear alignment method (DNA) is similar to dynamic nuclear polarization method (DNP)

DNP DNA

-1/2 3/2 I = 1/2 I = 3/2 +1/2 1/2 n-/n+ = exp(-Em/kT) n+/-3/2/n+/-1/2 = exp(-a/kT) at T = 0.5 K and H = 2.5 T at T = 0.5 K p1

equilibr ~ 0.5% p2equilibr ~ 0.5%

Plus paramagnetic admixture and microwave pumping of nuclear orientation p1

equilibr ~ 100% p2equilibr ~ 100%

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The main problem of the realization of DNA method is the selection of an appropriate compound, which has to meet the following requirements:

1. high content of nuclei of interest, 

2. high quadrupole energy splitting of the nuclear sublevels (NQR frequency > 30 MHz )

3. high energy splitting of the sublevels of the paramagnetic impurities, EPR frequency > 30 GHz

4. possibility of growing large single crystal.

At the first stage, the LuNbO4 + Cr3+ single crystal

was grown, NQR ~ 100 MHz, EPR = 9,7 GHz

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The suitable targets for study TRI violation with the use FC correlation are the nuclei with I 1 having low lying p-wave resonances.

Number of p-wave Natural resonance in theIsotope Abundance Spin range 0-350 eV %

115In 96 9/2 40 121Sb 57 5/2 17 123Sb 43 7/2 6 127I 100 5/2 20

2.2. Aligned nuclear targets

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I2 (eQq0) ni

1/2 0.095 0.95   334 MHz 3/2 0.21 0.97

  643 MHz

 5/2 1 1

P2 = 0.68 0.016

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P2, %

60

40

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0 20 40 60 80 100 T, mK

I2 Sb2O3

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A.L.Barabanov, A.G.Beda, J. Phys. G: Nucl. Part. Phys. 31 (2005) 161-178

pT, pPV

1 10-1 10-2

10-3

10-4 0 5 10 15 20

pT

pPV

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The value of the effect рт is

рт = k l

Factor k includes nuclear characteristics, l is the target thickness in cm.

The statistical error Δ of measurements

Δ = 1/ ( Io S T e –l/λ )1/2,

The necessary condition for observation of the effect

рT /Δ ≥ 3

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Sb single crystal obtained by Chokhralsky method (50 X 40 X 60 mm3)

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Big–sized single crystals (volume about 100 cm3) can be grown from following compound :   Sb I In 

Sb2Te3 HIO3 InAs

Bi0.2Sb1.8Te3 LiIO3 InSb

Bi0.4Sb1.6Te3 TlI-TlBr

GaSb

InSb

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HIO3 LiIO3

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Impressive progress in the field of low temperature technique during the last years was achieved.

The new type of the dilution refrigerator was developed: precooled by a commercial two-stage pulse-tube refrigerator (PTR). No cryoliquids are needed to operate such millikelvin cooler. Such refrigerator makes it possible to carry out the experiments at mK temperatures with good movability, automatic cooling-down, easy handling, low running coast, stable and continuous operation, and no neutron beam loss due to the refilling liquid helium.

It can also provide rather high cooling power which makes possible to cool down the samples of large mass. Now this two stage PTRs are produced in USA (Cryomech), Germany (VeriCold) and Japan (Janis).

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Outlook

1. Application of HIO3 and Sb single crystals opens the way for study of PCTV interactions.

2. The use of pulse tube based dilution refrigerator provides possibility of nuclear alignment by brute force method.

3. The use of HIO3 and Sb targets in the experiments at SNS or JSNS will make possible to discover TRI violation or to decrease the current limit on intensity of PCTV interactions by two orders of magnitude.

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Thank you

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0

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P2, %

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RCP, W

160

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0 20 40 60 80 100 T, mK

HIO3 Sb, 10 RCP - Refrigerator Cooling Power

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Neutron B4C neutron beam absorber 3He - 4He HIO3 plates

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Two stages of experiments

I P

tot = 0 + p2(I) (3(npnI)

2 – 1)D

p1(s)p2(I)s[pI] (pI)

PCTV

1st stage

2nd stage

(3(p I)2