Study of neutron-nuclear spin correlation terms with a polarized xenon target
J-PARC Center, Kenji Sakai
1. Introduction
A xenon (Xe) is interesting to measure a correlation term s·I of a neutron spin s and a target
nuclear spin I with a polarized Xe target for a verification of a neutron optical theorem (NOPT). It
has been observed the large parity non-conserving (PNC) effect at the p-wave resonance inneutron-nuclear reactions, and it polarizes up to 10−2−10−1 at pressures of 10−1−100 atm by using aspin exchange optical pumping (SEOP) method. We plan to measure the neutron polarizing ability,
spin dependent cross section and neutron spin rotation with polarized Xe, which are predicted todepend on neutron energy En strongly around resonance peaks. As the first step, we would measure
the neutron polarizing ability at a 9.6 eV s-wave resonance peak of 129Xe when unpolarized
neutrons transmit through the polarized Xe cell.
2. ExperimentFig. 1 shows the experimental apparatus in BL10. Pulsed neutron beams transmit throughcollimators, the Xe cell, a metal foil, and are counted by a position sensitive neutron detector(PSND) placed at 14.5 m position apart from the neutron source. For obtaining high count rates, thePSND consists of a Li glass scintillator and multi-anode photomultiplier tube (MAPMT) having
1616 pixels with a 33 mm2 pixel size. The metal foil is used to compensate time fluctuations of thedetector by referring to a 5.2 eV resonance peak of 109Ag. A ratio R between neutron transmissions
with the polarized and unpolarized Xe cell is expressed as R = cosh(NσlρP), where N, σ, l, P, and ρ
denote a number density, neutron cross section, thickness, polarization and spin dependent
parameter of Xe. The Xe cell is polarized by utilizing a SEOP system, where Xe gas is contained in acylindrical glass cell with N2 gas and Rb. Atomic spins of Rb are polarized by a resonance absorptionof circularly polarized laser light,and Xe nuclear spins are polarized

Mirrorby spin exchange with polarized
Rb atoms. Temperature inside an
Al oven is kept between 340 K and795nm Laser light(Circular Pol.)

Pulse neutronsource380 K for obtaining Rb vapor. The
Xe polarization P is monitored bynuclear

magnetic(NMR) system.

DiodeLaser

In-situ SEOP box(40 60  60cm3)

MirrorXe CellPXe

Pickup CoilCollimator
Solenoid Coilresonance

PSND having
1616 pixels with a
33 mm2 pixel size

AlovenRFCoil
Ag foil of 10mthickness

Fig. 1. Experimental apparatus for detecting neutron polarizing ability of Xe

3. Results
In the previous experiment of 2016B0146, we measured the ratio R (=TP/TU0) between neutrontransmissions with the polarized cell at 343 K and unpolarized cell at room temperature, denotedby TP and TU0, with a cylindrical cell (cell-I) in 2.5 cm diameter and 5 cm long and containing thenatural Xe gas of 3 atm pressure, and R (=R−1)10-2 was obtained at the resonance peak of 129Xe
preliminary. In analyzing process, however, we noticed that it might be caused by the Doppler
broadening (DB) effect due to temperatures difference between TP and TU0 measurements. In the1

experiment of 2017B0016, three type transmissions were measured with the polarized andunpolarized cell at 358 K, and the unpolarized cell at room temperature, denoted by TP, TU and TU0.
We used another cell (cell-II) in 3.5 cm diameter and 10 cm long and containing the enriched 129Xe
gas of 1 atm which was predicted to be higher P because decrement of Xe gas pressure suppresses
increment of Rb spin destruction due to effect of binary collisions. Fig. 2 (A), (B) and (C) represent

TU, TU0 as a function of neutron flight time t, and the ratio RD(=TU/TU0) zooming in the 9.6 eV
resonance peak along t axis. Fig. 3 (A), (B) and (C) represent TP, TU and RP(=TP/TU) zooming in theresonance peak. The shape of RD having dips at both sides of the peak should be caused by the DB
effect due to temperature difference. In contrast, the shape of RP couldn’t be explained by the DB
effect only because it didn’t have dips and both of TP and TU were measured at same temperature.
Although a new NMR system for the cell-II operated in this experiment, P could not be decided by
NMR signal because the NMR system had not been calibrated yet. If RP (=RP−1) 0.02 in Fig. 3 (C)is caused by P, the value of P would be 0.3 or 0.1 by assuming total angular momentum J=1 or J=0.
4. Conclusion
We noticed that R 10-2 obtained with the cell-I in the previous experiment might be caused by
the DB effect due to temperature difference. For demonstrating it, RD and RP were measured withthe cell-II. The shape of RD in Fig. 2 (C) was consistent roughly with evaluation by the DB effect. Incontract, we consider that the shape of RP in Fig. 3 (C) should be caused by P. Although we also
attempted to measure RD and RP with the cell-I and its calibrated NMR system for checking theprevious result, enough statistics couldn’t be obtained because beam operation terminated more(A)Transmission TU

9.6eV（129Xe）

Unpolarized 129Xe（T=358K）

TP (Count)

TU (Count)than half a day during this measurement. Preparation for verifying the values of RP are in progress.

5.2eV（109Ag）(A)Transmission TP

9.6eV（129Xe）(B) TransmissionTU0

9.6eV（129Xe）

Unpolarized（T=298K）(B) Transmission TU

9.6eV（129Xe）

5.2eV（109Ag）t (sec)

Unpolarized 129Xe（T=358K）

5.2eV（109Ag）t (sec)(C) Ratio RD

RP (= TP /TU)

R (= TU /TU0)

5.2eV（109Ag）t (sec)

129Xe

TU (Count)

TU0 (Count)t (sec)

Polarized 129Xe（T=358K）

9.6eV（129Xe）t (sec)(C) Ratio RP

9.6eV（129Xe）t (sec)

Fig. 2 (A) TU and (B) TU0 with unpolarized Xe at 358 K Fig. 3 (A) TP (B) TU with polarized and unpolarized Xe at358 K, as a function of flight time t, and (C) RP(=TP/TU)
and 298 K as a function of t, and (C) RD (=TU/TU0)
zooming in 9.6 eV resonance peak along t axis.
zooming in 9.6 eV resonance peak along t axis.

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