Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 50 (2017)

Development of data-collection and data-analysis systems for time-resolved
ESR experiments
T. L. Tang,*1 K. Tateishi, *1 T. Uesaka,*1 and K. Yamada *1,2
Nuclear magnetic resonance (NMR) is a valuable tool forbiochemistry and medical science. The signal strength ofNMR can be boosted significantly using dynamic nuclear
polarization, which transfers the electron polarization to thatof the nucleus. However, the conventional andwell-understood polarization molecule pentacene1) is notwater solvable, and that limits its biological application.
Various water-solvable pentacene derivatives have beensynthesized (from collaborations) and their molecular
structure needs to be studied via the electron spin resonance(ESR) spectrum. We are developing a data-collection
system to simplify the labor of this task.
The data-collection system is illustrated in Fig. 1. The
sample of pentacene derivative is placed inside a dielectric
microwave chamber with a narrow resonance frequency
band. A pulsed laser2) is fed into the chamber to excite theelectrons from the ground singlet state to the excited tripletstate. The laser also triggers the oscilloscope to record thetime-resolved ESR signal. The strength of an external
magnetic field is fixed for each measurement, but it canvary from 0.0 T to 3.8 T and is controlled by a DC voltage
power supply. The DC voltage is fed to a voltage-to-current
convertor to supply a steady current to the magnetic coil.
The magnitude of the magnetic field is measured using aHall probe. A typical ESR signal is show in Fig. 2.

Fig. 2. Typical ESR signal (light gray). The gray lineindicates the 100 kHz cutoff obtained using a Fouriertransform. The black line is fit to the gray line using Eq. (1).
The fitting uses the region after the dashed line.
The 2-dimensional data (time-resolved signal for eachmagnetic field setting) can be analyzed using a custom-built
cross-platform GUI analysis program. The time-domain
signal has the form݂ሺ‫ݐ‬ሻ ൌ ܽ  ൬െ‫ݐ‬‫ݐ‬൰ െ ܾ  ൬െ ൰ǡሺͳሻܶ௔
ܶ௕where ܽ and ܾ are the relative populations of the energylevels and ܶ௔ and ܶ௕ are the lifetimes of thecorresponding energy levels. The Levenberg—Marquardt
algorithm is used to fit the non-linear function against thetime-resolved signal. The effective magnitude of theelectron polarization isܲൌFig. 1. Illustration of the ESR system.
A custom-built data-collection program with a graphicaluser interface (GUI) sets the control voltage, gets the Hall
probe voltage, obtains the time-resolved ESR signal fromthe oscilloscope, and saves the signal into a file for analysis.
Using the program, the strength of the magnetic field can beswapped and the data-collection process is fully automaticonce the initial setup is done.
12ȁܽȁ െ ȁܾ ȁǤȁܽȁ ൅ ȁܾ ȁሺʹሻThe program also has other functions. It can be used as aplotting tool, for example, to plot the contour of the data.
The program also provides a 2-dimensional Fouriertransform3) and different digital filters for noise elimination,for example, a sharp-cut low/high-pass filter andconventional low/high-pass filter. The filter can be applied
as many times as needed to create filters such as aband-pass filter.
We are now developing a cross-platform GUI databaseprogram. The database stores the properties of the samples
and their measurements. Other denoising methods such as
discrete wavelet transformation will be evaluated.
References
1) K. Tateishi et al.: Angew. Chem. Int. Ed. 52 (2013) 13307.
2) N. Saito et al.: Opt. Lett. 32 (2007) 1965.
3) FFTW3.35, www.fftw.org.

RIKEN Nishina Center
Physics Department, Toho University- 223 -