[Paper Review] Chemically-polarized material for nuclear and particle physics

Benjamin G. Collins, Daniel P. Watts+7 more|arXiv (Cornell University)|Mar 6, 2026

Advanced NMR Techniques and Applications0 citations

TL;DR

The paper tests SABRE-polarized material as a room-temperature, chemically hyperpolarized target for nuclear/particle experiments by measuring beam-induced depolarization and radiation tolerance at MAMI, with promising resistance to depolarization and high-dose irradiation.

ABSTRACT

Spin-polarized solid targets have underpinned many recent key advances in nuclear and particle physics, yet traditional methods to produce them face significant limitations due to the high cost and demanding cryogenic and magnetic field requirements. These factors constrain experimental geometries and present challenges in intense radiation environments where depolarization and materials damage can occur. We present the first results assessing the capabilities of the chemical hyperpolarization (ChHP) method Signal Amplification By Reversible Exchange (SABRE) to act as the polarization method to produce targets or active detector media. We show by using in-beam measurements that there is no depolarizing effect observed with the SABRE-polarized material in the A2 photon beam at the Mainzer Mikrotron (MAMI), as well as showing the resilience of such media to radioactive doses of up to \SI{3}{\kilo\gray}. We also illustrate the capabilities for using SABRE-polarized material as a scintillation or Cherenkov detector.

Motivation & Objective

• Motivate the need for alternative polarized targets that withstand high beam intensities and radiation.
• Assess whether SABRE-polarized material experiences depolarization when exposed to an A2 photon beam.
• Evaluate radiation damage and changes to T1 and polarization after high-dose exposure (~3 kGy).
• Explore potential of SABRE-polarized material as scintillation/Cherenkov detector media.
• Discuss implications for scalable, low-cost, magnet-free polarized targets in future experiments.

Proposed method

• Prepare SABRE-compatible substrates and form active SABRE catalysts in solution.
• Polarize in a 6 mT Halbach array and transfer to a benchtop MRI system for NMR-based polarization decay measurements.
• Expose polarized samples to the A2 photon beam and compare beam-on vs control decay profiles.
• Quantify depolarization via T1 comparisons, ratios of decay rates, and logarithmic differential analysis.
• Irradiate a replicate sample with ~3 kGy near the beam dump and compare pre-/post-irradiation T1 and polarization.
• Assess optical performance as potential scintillation detectors in mixtures with liquid scintillators.

Figure 1 : a) Spin-order transfer during SABRE, converting p - $\text{H}{\vphantom{\text{X}}}_{\smash[t]{\text{2}}}$ to o - $\text{H}{\vphantom{\text{X}}}_{\smash[t]{\text{2}}}$ and an initially unpolarized spin to a polarized spin. The active SABRE catalyst shown here is of the form $\text{[}\text{

Experimental results

Research questions

• RQ1 Does SABRE-polarized material exhibit beam-induced depolarization under A2 photon beam exposure at MAMI?
• RQ2 Is SABRE polarization robust against high radiation doses (~3 kGy) near an electron beam dump?
• RQ3 Are there substrate-dependent depolarization effects for SABRE materials in beam environments?
• RQ4 Can SABRE-polarized material function as a scintillation or Cherenkov detector medium without substantial loss of performance?
• RQ5 What are the implications of SABRE benefits (room-temperature operation, rapid polarization) for future high-intensity polarized targets?

Key findings

• No significant depolarization observed for SABRE substrates under A2 photon beam (10 nA) across substrates 3,5-dcpy, 3,5-dbpy, and 2,6-dcpz.
• Measured T1 values before/after beam are consistent with control runs within uncertainties (examples: 3,5-dcpy, 170→160 s; 3,5-dbpy, 104→87 s; 2,6-dcpz, 170→141 s).
• Ratio analysis (R_n) of beam-on vs control decay rates remained within unity within 1σ for all substrates (e.g., 3,5-dcpy: 1.01×1.10 before, 1.00×1.13 after).
• Irradiation at ~3 kGy caused only marginal changes in T1 and polarization (before: 121 s, 1; after: 126 s, 0.87), with post-irradiation polarization consistent within error margins.
• Liquid-based SABRE materials show potential for continuous replenishment and self-repair against beam heating, enabling higher beam robustness than traditional solid targets.
• Initial fluorescence studies suggest SABRE substrates can retain substantial scintillation output when mixed with liquid scintillators, supporting detector media applications.

Figure 2 : Diagram of the experimental procedure. a) Prepare sample and fill with p - $\text{H}{\vphantom{\text{X}}}_{\smash[t]{\text{2}}}$ . b) Transfer to Halbach array and shake for $45\text{\,}\mathrm{s}$ . c) Transfer to MRI system and start acquisition. d) Vacate hall and turn on photon beam.