epr spectrometer & dosimetry

8/10/2019 EPR Spectrometer & Dosimetry

1/43

EPR spectrometer & dosimetry

in Hokkaido University

()

2014.09.16Kwon Choi


2/43

Lets say about EPR

Which exist around nucleus

Unpaired electrons

Electron Paramagnetic Resonance


3/43

Lets say about EPR

Paramagnetismisa form of magnetism whereby certain materialsare attractedby an externally applied magnetic field,and form internal, induced magnetic fieldsin the direction ofthe applied magnetic field. () Paramagnetic properties aredue to the presence of some unpaired electrons, (.)

(from Wikipedia )

Electron Paramagnetic ResonanceWhich you may not be familiar with


4/43

Lets say about EPR

In other word, align their directioninto the direction of the extenalmagnetic field.



5/43

Lets say about EPR


Form induced magnetic field

Up spin and down spin electrons have different energy states.ThisEnergy Splittingis determined by the strength of theexternal magnetic field.

=geBB0

ge: g factor, 2.00231930436153 (a.u.)for electron

B: Bohr magneton, 9.274009681024 (a.u.)


6/43

Lets say about EPR

Electron Paramagnetic ResonanceResonance absorption

Absorption of electromagnetic energyat a certain frequencyin a static external magnetic fieldby a quantum excitation of the material


7/43

Lets say about EPR

Electron Paramagnetic ResonanceResonance absorption

Energy

Absorption of theelectromagneticenergy

E =

Release of theenergy (heat, light)

Excitation of electrons Relaxation

The electromagnetic energywith the energy equal to the energy splitting of electrons,= E = geBB0 makes the resonance


8/43

2. Population distribution of electrons between two energy levels :

(Boltzmanns equation)

T : temperaturek : Boltzmann constant

1. Under the resonance :

The population of the lower level is greaterthan thatof the upper level.

Net energy absorption

http://encyclopedia2.thefreedictionary.com/Electron+Paramagnetic+Resonance+EPR

Energyemission

Energyabsorption

Both transitions with

same probability

=#

# <

How energy absorption occur

E = -1

0

E =1

0


9/43


10/43

The frequency of EM wave is determined by the utility.

Frequency => Energy splitting (Better signal)Dielectric loss (Heat loss)

Skin depth (Lower penetration)


11/43

= ( 20

)1/

: Resistivity of material0: dielectric constant: Frequency

Skin depth,

How deep the electromagnetic wave can penetrate

The frequency of EM wave is determined by the use.



Dielectric lossIn water


12/43

= ( 20

)1/


Skin depth,


At 1 GHz

(L-band)

Resistivity

(m)

Skin depth

(cm)Muscle 0.8 1.5

Liver 1 1.7

Fat 7-12 4-6

Bone 10-25 5-8

Brain 1 1.7






13/43

= ( 20

)1/


Skin depth,


At 1 GHz

(L-band)

Resistivity

(m)

Skin depth

(cm)Muscle 0.8 1.5

Liver 1 1.7

Fat 7-12 4-6

Bone 10-25 5-8

Brain 1 1.7





Under L-band (1-2 GHz) isappropriate for the use in vivo.


14/43

=geBB0

External magnetic field / mT

Because of the magneticmodulation

-> Basic form of an EPR signal

For

Microwave

Variant frequency of EM wave isused by the use.



15/43

=geBB0


Because of the magneticmodulation

-> Basic form of an EPR signal

Microwave

Variant frequency of EM wave isused by the use.


16/43

What can we observe with EPR?

Flaw of the

optic fiber

New material

(Ion liquid)

Process ofchemical

reaction fromUV irradiation

Tooth enamel ofthe irradiatedhuman

In vivo brain

/ tumor

How did radicals form in observed objects?

Elapse of timeMix the stableradical into thenew material

Unstable radicalsare formed bythe break of

chemical bonds

Stable radicals areformed in the

tooth enamel

Quantity ofradicals,relationship withthe amount ofradiation

Quantity ofradicals,distribution,relationship withtumor

Inject stable radicalsinto the vessel orregion of interest

What information do you want?

Quantity,distribution,location andquantity of flaw,

Interactionbetween stableradical and newmaterial

Dynamics(Change ofstructure,quantity,characteristicswith the timeelapse

Enamel


17/43

What can we observe with EPR?

Flaw of the

optic fiber

New material

(Ion liquid)

Process ofchemical

reaction fromUV irradiation

Tooth enamel ofthe irradiatedhuman

In vivo brain

/ tumor

How did radicals form in observed objects?

Elapse of timeMix the stableradical into thenew material

Unstable radicalsare formed bythe break of

chemical bonds

Stable radicals areformed in the

tooth enamel

Quantity ofradicals,relationship withthe amount ofradiation

Quantity ofradicals,distribution,relationship withtumor

Inject stable radicalsinto the vessel orregion of interest


18/43

Radiation dosimetry using tooth enamel

Requirement

Possibility of radiologic emergency situation(terrorist attack using a nuclear weapon, accident of nuclear power plants)

Need of patients triage (distinguish who may be irradiated)- Who exposed to over certain amount of radiation need rapid care.- Victims with doses starting at about 2 Gy can benefit from urgent

medical treatment.

General publication does not have the proper dosimeter.

EPR tooth dosimetry can be used for triagein situ.

Conventional blood test can be done at remote place that takes time.


19/43

Radiation dosimetry using tooth enamel

Hydroxyapatite contained in teeth and bones-> Suitable probe for dose reconstruction.

- High content of hydroxyapatite- Completely formed in childhood- Once formed never remodelled.

1. Carbonate impurities in hydroxyapatite crystals

Radiationexposure

radicals

(EPR sensitive stable radical as probe)

2. Tooth enamel is preferred for the retrospective dosimetry

-> Co2--radicals are accumulated over 107years


20/43

"Boys, be ambitious!Be ambitious not for money or for

selfish aggrandizement, not for thatevanescent thing which men call fame. Beambitious for that attainment of all that aman ought to be."

Regrettably, today in Korea this goodmaxim is generally used asBoys, be ambitious for fame and money!

, !, ..

William S. Clark Ph.D.


21/43

Farm (Part of the school of agriculture)


22/43

Farm (Part of the school of agriculture)


23/43


24/43


25/43

A little history about thediscovery of

electron paramagnetic resonance


26/43


27/43

Phenomenon called ElectronParamagnetic Resonance (EPR)

Isior Issac Rabi

Nobel Prize in Physics (1944)

Discovery of Nuclear Magnetic Resonance (1938)

Zavoisky was impressed at Rabis discovery, NMRand tried to detect NMR in liquids and solids.


28/43

Tooth dosimetry in Hokkaido University


29/43


30/43

Surface coil resonator for in vivo use


31/43

Surface coil resonator construction


32/43

Surface coil resonator construction

Home-made coaxial tube(Copper / Teflon)

Home made surface coil (Silver)

Sugawara et al, 2014,IEEE


33/43

Data Acquisition Program

In-house program made using Labview

Show the signal of each scan (upper) andintegration of number of those signals (lower)

SNR histogram (right)


34/43

Dosimetery

Synthetic Hydroxyapatite as dosimeter

- Used as a dental graft / implant

- Good substitute of human tooth enamel

Used electronic scale for the normalization of hydroxyapatitesamples

- Hydroxyapatite samples are irradiated different doses.

Irradiated dose

(cGy)

Weight

(g)0 0.254210 0.125530 0.123150 0.1292100 0.1338200 0.127300 0.1253600 0.0845


35/43


36/43

The quantity of radiation-induced radical can be determined relativelyby the peak-to-peak intensity of the spectrum.

External magnetic field / mTpeak-to-peak intensity


37/43

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

39 39.5 40 40.5 41 41.5 42 42.5 43



Too noisy to determine the exactpeak-to-peak intensity


38/43

(mT)

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

39 39.5 40 40.5 41 41.5 42 42.5 43



Too noisy to determine the exactpeak-to-peak intensity

Need of curve fitting


39/43

Curve fitting

Robinson et al., 1998, Journal of Magnetic Resonance

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

39 39.5 40 40.5 41 41.5 42 42.5 43

Including center frequency, linewidth, modulation frequency, Zeeman modulation

Also resulted signal intensity determined with the correction usingnumber of scans, weight of the sample

To determine the signal intensity


40/43

Results

Irradiated dose(cGy)

signal intensity

0 0.01981

10 0.04742

30 0.05276

50 0.05455100 0.06130

200 0.06347

300 0.08646

600 0.112680

0.02

0.04

0.06

0.08

0.1

0.12

0 100 200 300 400 500 600 700

(cGy)

(a.u.)

200 cGy sample didnt show good signal intensity.

As expected, doses under 100 cGy did not show


41/43

Discussion

1. Noise make the spectroscopy difficult.

Contamination of the surface coil is one reason.

Sugawara et al.Improvement of the baseline stability by HCl cleaning of the resonator


42/43

Discussion

2. Too small and various size of hydroxyapatite samples

-> Different amount of effect from the magnetic field of the surface coil

3. Only one sample per each radiation dose


43/43

epr spectrometer & dosimetry

Documents