U.S. patent number 3,771,054 [Application Number 05/253,667] was granted by the patent office on 1973-11-06 for method and apparatus for observing transient gyromagnetic resonance.
This patent grant is currently assigned to Varian Associates. Invention is credited to James S. Hyde.
United States Patent |
3,771,054 |
Hyde |
November 6, 1973 |
METHOD AND APPARATUS FOR OBSERVING TRANSIENT GYROMAGNETIC
RESONANCE
Abstract
Gyromagnetic resonance spectrometers and methods of operating
same are disclosed wherein gyromagnetic resonance of a sample of
matter is excited and detected at a first electron resonance
condition repetitively and abruptly purturbating said sample of
matter to produce a train of transient resonance responses after
said purturbation is removed. Establishing a second electron
resonance condition within the sample. The transient response is
detected as a function of the relatively slow changes in the
electron resonance condition to obtain an output transient
resonance spectrum.
Inventors: |
Hyde; James S. (Stockholm,
SW) |
Assignee: |
Varian Associates (Palo Alto,
CA)
|
Family
ID: |
22961210 |
Appl.
No.: |
05/253,667 |
Filed: |
May 15, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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29916 |
Apr 20, 1970 |
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Current U.S.
Class: |
324/316 |
Current CPC
Class: |
G01R
33/62 (20130101) |
Current International
Class: |
G01R
33/62 (20060101); G01n 027/78 () |
Field of
Search: |
;324/.5R,.5A,.5AC |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lynch; Michael J.
Parent Case Text
This is a continuation of application Ser. No. 29,916 filed Apr.
20, 1970, now abandoned.
Claims
I claim:
1. A method for obtaining a display of changes in purturbation
induced transients of electron cyromagnetic resonance as a function
of electron resonance condition, the steps comprising:
a. continuously exciting and detecting electron gyromagnetic
resonance of a sample of matter at a first electron resonance
condition;
b. applying an abrupt purturbation to said sample of matter and
commencing periodic sampling and storage of electron gyromagnetic
resonance signal at predetermined intervals;
c. discontinuing application of said abrupt purturbation to said
sample while continuing said periodic sampling and storage of said
electron gyromagnetic resonance signal;
d. establishing a second electron resonance condition and
continuously exciting and detecting electron gyromagnetic resonance
of said sample of matter at said second electron resonance
condition;
e. repeat steps (b)
f. repeat step (c)
g. compare the detected signals of steps (b) and (c) respectively
with the detected signals of steps (e) and (f) and
h. display the comparison determined in step (g) as a function of
electron resonance condition.
2. The method of claim 1 wherein steps (b) and (c) are repeated a
plurality of times for each electron resonance condition in order
to obtain signal-to-noise improvement by time-averaging.
3. The method of claim 1 wherein the abrupt purturbation of step
(b) is an induced temperature jump.
4. The method of claim 2 wherein the abrupt purturbation of step
(b) is an induced temperature jump.
5. The method of claim 1 wherein the abrupt purturbation of step
(b) is radiation at optical wavelengths.
6. The method of claim 2 wherein the abrupt purturbation of step
(b) is radiation at optical wavelengths.
7. The method of claim 1 wherein the abrupt purturbation of step
(b) is a step in the phase of a microwave pumping source, said
microwave source being at the frequency associated with the
electron resonance condition.
8. The method of claim 2 wherein the abrupt purturbation of step
(b) is a step in the phase of a microwave pumping source, said
microwave pumping source being at the frequency associated with the
electron resonance condition.
9. The method of claim 1 wherein the abrupt purturbation of step
(b) is a step in the amplitude of a microwave pumping source, said
microwave pumping source being at the frequency associated with the
electron resonance condition.
10. The method of claim 2 wherein the abrupt purturbation of step
(b) is a step in the amplitude of a microwave pumping source, said
microwave pumping source being at a frequency associated with the
electron resonance condition.
11. The method of claim 1 wherein the abrupt purturbation of step
(b) is a step in the amplitude of a microwave pumping source, said
microwave pumping source being at a frequency different from the
frequency associated with said electron resonance condition.
12. The method of claim 2 wherein the abrupt purturbation of step
(b) is a step in the amplitude of a microwave pumping source, said
microwave pumping source being at a frequency different from the
frequency associated with said electron resonance condition.
13. In apparatus for observing electron paramagnetic resonance
including a means for holding a sample of matter under test in a
polarizing magnetic field and a means for applying an RF magnetic
field at a frequency to excite an electron resonance condition in
said sample and to detect gyromagnetic resonance of said sample,
the improvement comprising
means to periodically purturbate said sample;
means to sample and store said detected gyromagnetic resonance
signals following the discontinuance of said purburbation;
means to step through differing values of electron resonance
condition of said sample responsive to each cycle of said
programmer;
programmer means for synchronizing said purturbation of said sample
and said sampling and storage of said detected gyromagnetic
resonance signal and said stepping of said electron resonance
condition;
means to compare the stored gyromagnetic resonance signals for each
said step of said electron resonance condition; and
means for displaying said comparison of said detected gyromagnetic
resonance signals as a function of electron resonance
condition.
14. The apparatus of claim 13 wherein the means to abruptly
purturbate is a flash lamp having radiation in the visible
wavelengths.
15. The apparatus of claim 13 wherein the means to abruptly
purturbate is a heater.
16. The apparatus of claim 14 wherein the means to abruptly
purturbate is a microwave pumping source including means to phase
switch energy from said source which impinges upon said sample.
17. The apparatus of claim 14 wherein the means to abruptly
purturbate is a microwave pumping source including means to
amplitude step energy from said source which impinges upon said
sample.
18. Apparatus for observing purturbation-induced transients in the
electron gyromagnetic resonance of a sample of matter
comprising,
programming means;
means for continuously exciting electron gyromagnetic resonance of
said sample of matter at selected electron resonance conditions;
said electron resonance conditions being responsive to said
programming means;
means for abruptly and periodically purturbating said sample and
for discontinuing said purturbations responsive to said programmer
means;
means for detecting said gyromagnetic resonance signal at a
predetermined time interval after discontinuance of said
purturbation, said detected signal being said transient in the
electron gyromagnetic resonance;
means for comparing said detected transient gyromagnetic resonance
signal at a first selected electron resonance condition to a
corresponding detected transient gyromagnetic resonance signal at a
second selected electron resonance condition, and means to display
said comparison of corresponding detected signals.
19. The apparatus of claim 18 wherein said means for comparing
includes means for separating each said detected transient into its
component frequencies.
20. The apparatus of claim 18 wherein said means for comparing
includes means for sample and storage of the amplitude of said
detected gyromagnetic resonance signal.
21. The apparatus of claim 20 wherein means for comparison further
includes a time constant calculator and wherein said display means
includes means for displaying said time constants as a function of
electron resonance condition.
22. The apparatus of claim 18 wherein said means for comparing
includes means for periodic sample and storage of the amplitudes of
said detected gyromagnetic resonance signal to time-average a
plurality of detected transient signals for each value of electron
resonance condition.
Description
DESCRIPTION OF THE PRIOR ART
Heretofore, pulsed electron-electron double resonance experiments
have been performed wherein one part of an electron paramagnetic
resonance spectrum was irradiated with a pulsed source of microwave
energy while the resulting transient response was observed at a
certain portion of the spectrum. Such an experiment is disclosed in
Volume 115 of the Physical Review, page 986, appearing in 1959;
Volume 118 of the Physical Review, page 939, appearing in 1960; and
Volume 129 Physical Review, page 2,441 appearing in 1963.
It is also known that an electron spin resonance spectrum of a
sample can be obtained by pumping the spectrum with a relatively
strong RF pump field to saturate resonance of the spectrum while
simultaneously probing the spectrum under analysis with weak RF
detector field applied at a different frequency, such spectrometer
and method of operating same is disclosed in Physical Review,
Volume 135, No. 1a of July, 6, 1964, at page A247.
SUMMARY OF THE PRESENT INVENTION
The principal object of the present invention is the provision of
improved method and apparatus for observing transient gyromagnetic
resonance.
One feature of the present invention is the provision of exciting
and detecting gyromagnetic resonance of a sample of matter, and
while detecting such resonance, repetitively and abruptly
purturbating and removing said purturbation on said sample to
produce a train of transient responses in the detected resonance of
the sample, changing the electron resonance condition within the
sample with a time rate of change slower than the abrupt
purturbations, and detecting the changes in the transient resonance
response as a function of changes in the electron resonance
condition.
Another feature of the present invention is the same as the
preceding feature wherein the purturbation includes one or more of
the following conditions: irradiation of the sample either in the
optical or radio frequency spectrum, temperature of the sample,
electrical current passing through the sample, and phase of the RF
energy applied to the sample.
Another feature of the present invention is the same as any one or
more of the preceding features wherein the electron resonance
condition, which is changed at a relatively slow rate, is a
function of the polarizing magnetic field intensity or the
frequency of an alternating RF field applied to the sample to
excite resonance.
Another feature of the present invention is the same as any one or
more of the preceding features wherein the changes in the transient
response due to the relatively slow changes in the electron
resonance condition are separately detected for different transient
components, if any, present in the transient resonance response,
and at least one of the transient components is selected and
detected as a function of the change in the electron resonance
condition.
Other features and advantages of the present invention will become
apparent upon a perusal of the following specification taken in
connection with the accompanying drawings wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram of a gyromagnetic resonance
spectrometer incorporating features of the present invention,
FIG. 2 is a schematic block diagram, similar to the block diagram
of FIG. 1, depicting an alternative embodiment of the present
invention,
FIG. 3 is a plot of the detected resonance signal as a function of
time for the spectrometer system of FIG. 2,
FIG. 4 is a schematic block diagram of an electron paramagnetic
resonance spectrometer incorporating features of the present
invention,
FIG. 5 is a schematic block diagram depicting an alternative
spectrometer embodiment incorporating features of the present
invention,
FIG. 6 is a schematic block diagram of further electron
paramagnetic resonance spectrometer incorporating features of the
present invention,
FIG. 7 is a plot of resonance signal amplitude versus time
depicting the transient output signal obtained in a portion of the
spectrometer of FIG. 6,
FIG. 8 is a plot of three output spectra derived from the
spectrometer FIG. 6 and depicting different frequency components of
the composite transient resonance responses,
FIG. 9 is a schematic circuit diagram, partly in block diagram
form, depicting a portion of the spectrometer of FIG. 6 delineated
by line 9--9, and
FIG. 10 is a schematic block diagram of an electron paramagnetic
spectrometer incorporating features of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, there is shown an electron paramagnetic
resonance spectrometer 1 incorporating features of the present
invention. The spectrometer 1 includes a sample probe structure 2
having a gyromagnetic resonance sample material disposed in RF
magnetic field exchanging relation with a resonant circuit for
exciting and detecting gyromagnetic resonance of the sample
material. The resonant circuit comprises a cavity resonator having
a light transmissive wall portion for irradiation of the sample by
a flash lamp 3. A magnet having pole pieces 4 and 5 produced an
intense DC magnetic field within the sample. Each line in an EPR
sample spectrum represents an electron resonance condition obtained
by establishing the exciting frequency and polarizing field such
that gyromagnetic resonance occurs.
A gyromagnetic resonance exciter and detector is coupled to the
resonant circuits within the probe 2 for exciting and detecting
gyromagnetic resonance of the sample material. The gyromagnetic
resonance exciter and detector 6 supplies a radio frequency
magnetic field to the sample at an angle to the polarizing magnetic
field, the frequency of the radio frequency magnetic field being
such as to produce gyromagnetic resonance of the gyromagnetic
bodies within the sample material for the particular value of the
polarizing field. The resonance of the sample is detected in the
gyromagnetic resonance exciter and detector and the transient
resonance signals are fed by a coupling capacitor 7 to the input of
a multichannel sample and storage unit 8.
In a typical example of the present invention, the gyromagnetic
resonance bodies are electrons, the radio frequency magnetic field
has a frequency on the order of 10 GH.sub.z and as an aid in
detecting resonance, the magnetic field is modulated at a
relatively high frequency, such as 100 KH.sub.z to permit
synchronous detection of the 100 KH.sub.z component in the
resonance signal. Alternatively, if the transient response to be
investigated is sufficiently rapid, magnetic field modulation may
be eliminated since low frequency noise components of the response
distorted by the detector will not pass the coupling capacitor.
A pulse programmer 9 produces a train of output pulses which are
fed to a trigger 11 which in turn produces a train of trigger
pulses fed to the flash lamp 3 such as an xenon flash tube, which
produces an output train of purturbating light flashes which are
applied to the sample gyromagnetic resonance material within the
polarizing magnetic field H.sub.o. In a typical example, output
flashes from lamp 3 have a repetition rate of 10 per second, each
flash from the lamp having a duration, of 10 microseconds. Each
flash from the lamp 3 produces a corresponding transient change in
the continuously detected resonance of the sample material if the
sample is light sensitive. Thus, a train of transient resonance
responses is obtained in the output of the gyromagnetic resonance
exciter and detector which is coupled to the input of the
multichannel sample and storage 8. Each transient response in the
train of transient responses has a characteristic envelope such as
depicted by curve 12 of the waveform diagram (a). The multichannel
sample and storage unit 8 is synchronized with each transient
response via an input from the pulse programmer 9. The multichannel
sample and storage unit 8 samples each transient response signal 12
at a number of time displaced intervals indicated at t.sub.1,
t.sub.2, t.sub.3 . . . . t.sub.N. Each sampled response amplitude
is stored in a separate respective channel of the multichannel
storage unit 8. After one or more of the transient responses 12 has
been sampled and stored in the multichannel sample and storage
unit, the outputs of the respective channels are fed into the input
of an integrator 13 which integrates the output of each of the
channels to obtain a total output which is fed to one input of a
recorder 14.
After one or more of the transient responses 12 has been integrated
by the integrator 13, the pulse programmer 9 sends a pulse to the
integrator, thereby discharging same, and also at the same time
sends a pulse to a magnetic sweep circuit 15 which produces an
output to a magnet control unit 16 for changing the magnitude of
the polarizing magnetic field H.sub.o to a new value slightly
different from the intensity of the polarizing magnetic field in
the sample used to derive the first train of transient responses,
thereby changing the electron resonance condition. At the same
time, a sample of the output of the magnetic sweep circuit 15 is
fed to the recorder 14 for recording the output of the integrator
13. The pulse programmer 9 periodically advances the magnetic field
intensity until the magnetic field intensity has been swept in a
successive number of discrete steps through the electron resonance
condition spectrum of the sample under analysis. The result is a
recorded output spectrum of the transients of resonance lines which
are sensitive to light. Other resonance lines in the sample which
are not sensitive to light would be suppressed in the recorded
spectrum.
If the multichannel sample and storage unit 8 is set to accumulate
the output of a number of transient responses before the pulse
programmer 9 advances the magnetic field, a time average of the
output transient responses is obtained, thereby improving the
signal to noise ratio of the final output recorded spectrum. One
advantage of the spectrometer of FIG. 1 is that, provided the
alternative of no magnetic field modulation is employed, the
recorded resonance lines are pure absorption mode resonance and not
"derivative like" first harmonic output signals of a phase
sensitive detector.
As an alternative to sweeping the magnetic field, the output of the
pulse programmer 9 may be applied for changing the frequency of the
exciting radio frequency magnetic field applied to the sample. This
changes the electron resonant condition in the same manner as a
change in the magnetic field.
As still another alternative to the spectrometer of FIG. 1, the
flash lamp 3 need not irradiate the sample material with optical
radiation but the purturbation may be a pulsed microwave source
which sharply raises the temperature of the sample material due to
dielectric heating within the sample. As another alternative the
flash lamp 3 may be replaced by an electrical discharge device for
producing a pulse or step of current or voltage through the sample
material within the probe 2. In each of the above alternatives, the
transient response in the detected resonance of the sample material
in response to the abrupt purturbation in the temperature, the
current, voltage or the like applied to the sample is detected and
fed to the multichannel sample and storage unit 8 for analysis as
above described. In each of the aforementioned alternatives, the
recorded output spectrum, obtained from recorder 14, comprises a
spectrum of the transients of resonance line signals which are
sensitive to the resonance affecting purturbation such as light,
temperature, phase of the RF, voltage, current, etc.
In another alternative embodiment of the spectrometer of FIG. 1,
the multichannel sample and storage unit 8 may be deleted and the
output of the coupling capacitor 7 merely fed to the input of the
integrator 13 for integrating the area under curve 12. The pulse
programmer 9 would discharge the energy of the integrator 13 after
integration of each of the output transient responses and before
advancing to the magnetic field via the magnetic sweep circuit
15.
In another embodiment of the spectrometer of FIG. 1, the
multichannel sample and storage unit 8 takes only a selected one
sample out of each transient resonance response 12, such sampling
time may be arbitrarily chosen as any one of the channels of the
sample and storage unit 8. This representative channel is then
employed for sampling each successive transient resonance response
12 and the sampled output is stored for a succession of transient
resonance responses 12 for a given electron resonance condition.
The sampled amplitudes are accumulated in the selected channel to
obtain a time average and the accumulated total is read out
directly to the recorder 14 without the necessity of integrator
13.
Referring now to FIG. 2, there is shown an alternative spectrometer
of the present invention. The spectrometer of FIG. 2 is essentially
the same as that of FIG. 1 with the exception that the coupling
capacitor 7 between the gyromagnetic resonance exciter and detector
6 and the input to the multichannel sample and storage unit 8 has
been deleted such that an output including the DC resonance is fed
to the multichannel storage unit 8 with the transient response
superimposed thereon, as shown in FIG. 3. This configuration
employs magnetic field modulation and phase sensitive detection.
This resonance signal is characterized by a more or less continuous
DC resonance signal level with the transient response superimposed
thereon, there being a transient resonance response following each
of the pulses of the lamp 3.
The multichannel sample and storage unit 8 is synchronized by the
pulse programmer 9 in such a manner that the sampling times for the
output resonance signal, t.sub.1, t.sub.2, t.sub.3 . . . . t.sub.N,
start slightly before the initiation of the light flash from lamp 3
and continue for a time after the transient response has returned
to the DC level. A number of the transient responses are sampled
and stored in the storage unit 8 such that the results for the
various channels are accumulated in order to obtain a time averaged
output having improved signal to noise ratio. Alternatively, each
transient output may be sampled and read directly to the output of
the multichannel sample and storage unit 8.
Certain ones of the selected storage channels, corresponding to
measurements of the resonance signal before initiation of the flash
are fed to a Y-axis of a first recorder 14 for recording as a
function of the magnetic field intensity. Certain others of the
channels corresponding to the transient response are read out to
the Y-axis of a second recorder 14', and a third number of channels
corresponding to the period following the transient response are
read out and fed to the Y-axis of a third recorder 14". The result
is three separate recorded output spectra (a), (b), (c). By
comparison of the output spectra (a), (b), and (c) valuable
information is obtained concerning the transient response of the
sample material to the pulsed irradiation.
As in the spectrometer of FIG. 1 the flash lamp may be replaced by
any one of a number of other devices for changing the resonance
affecting conditions over the sample in a transient and abrupt
manner. Suitable alternatives for the flash lamp 3 include a pulsed
microwave source, or a pulse of current or voltage through the
sample material. As an alternative to the use of N number of
graphic recorders 14 the resonance data output of the multichannel
sample and storage unit 8 may be stored on a tape recorder or in a
computer memory and displayed at a later time on a graphic recorder
or printed out in digital form.
Referring now to FIG. 4, there is shown an alternative electron
paramagnetic resonance spectrometer incorporating features of the
present invention. The spectrometer of FIG. 4, is essentially the
same as the spectrometers of FIGS. 1 and 2 with the exception that
the flash lamp 3 is replaced by a microwave source 21 and the
amplitude of microwave radiation applied to the sample is not
altered but instead the phase of the microwave energy is abruptly
and repetitively shifted by a relatively large phase angle, as of
180.degree., to produce a train of transient responses in the
resonance of the sample being monitored. More particularly, the
microwave source 21 supplies microwave energy at a frequency of
f.sub.1 suitable for excitation of gyromagnetic resonance of a
sample of material under analysis. A typical spectrum for such a
sample is shown by waveform A. The microwave energy is fed into a
three port circulator 22 having a diode switch placed one quarter
of a wave length from a shorted end of a waveguide attached to one
port of the circulator such that when the diode 24 is fired by the
output of the trigger 11, the microwave energy, instead of being
reflected from the shorted end of arm 23 is reflected from the
diode 24, such that now the phase of the wave energy passing out of
the circulator to the sample is abruptly shifted by
180.degree..
The probe structure 2 includes a bimodal cavity having the sample
material disposed in a region common to two orthogonal modes of
osciallation, one of the modes being the pumping mode and being
connected to the output of the circulator 22. The other mode of the
cavity is coupled to the gyromagnetic resonance exciter and
detector 6 which excites resonance of the sample material at either
the same frequency of the microwave source, namely f.sub.1 or at
any other frequency f.sub.2 suitable for excitation of gyromagnetic
resonance within the spectrum of the sample under anaylsis.
The abrupt change in the phase of the pumping energy applied to the
sample produces a transient response in the resonance of the line
being detected and the transient response is coupled via coupling
capacitor 7 to the multichannel sample and storage unit 8. As in
the previous spectrometer embodiments, the sampled transient
resonance responses can be time averaged and integrated or merely
time averaged or merely sampled, with the output being fed to the
Y-axis of the X-Y recorder 14 for recording against the sweep of
the electron resonance condition to obtain an output spectrum of
the transient responses produced by the train of abrupt changes in
the phase of the microwave energy employed for pumping the
sample.
Referring now to FIG. 5 there is shown a gyromagnetic resonance
spectrometer similar to that of FIG. 4. The apparatus is
essentially the same as that of FIG. 4 with the exception that the
phase of the microwave energy applied for pumping the sample is not
changed but rather the amplitude of the microwave energy applied
for RF pumping of the sample is changed abruptly from a first RF
level of sufficient amplitude to produce saturated resonance of a
spectral line of the sample to a much lower amplitude, such as 30
db below the saturation RF amplitude to produce a transient
resonance response in the excited and detected gyromagnetic
resonance of the sample.
Gyromagnetic resonance exciter and detector 6 excites resonance of
a line of the resonance sample, namely f.sub.2. The resonant sample
is purturbated by pulsing the pump power which is of radiofrequency
f.sub.1 and the train of transient responses produced in the
detected resonance is coupled via coupling capacitor 7 to the input
of a single channel sample storage unit 8. The microwave energy at
f.sub.1 from microwave source 21 is pulsed to the lower level by
means of diode switch 25 in response to the output of trigger
11.
Each transient response, indicated by curve 12 of waveform (b), is
sampled at some predetermined point, such as point t.sub.d which is
selected by means of a pulse derived from pulse programmer 9 and
delayed by a suitable delay time t.sub.d in time delay 20
corresponding to the desired sampling time t.sub.d following
initiation of each transient response. A plurality of successive
transient responses are sampled at the same point and the sampled
amplitude is accumulated in the single channel sample and storage
unit 8. The accumulated total, which corresponds to a time average
of the transient resonance response is fed to the Y-axis of the X-Y
recorder 14 for recording as a function of the difference between
the frequency of the pumping source and the resonance exciting and
detecting frequency. Either the detecting frequency or,
alternatively, the frequency of the pumping source is swept in
accordance with the output of the pulse programmer 9. More
particularly, sweep circuit 15' changes the tuning of the receiver
mode cavity or, alternatively, the pumping mode cavity in the
bimodal cavity portion of the probe 2. An electro-mechanical
frequency control 25 also causes the microwave source 6 or,
alternatively, 21 to shift frequency to track the tuning of the
bimodal cavity such that the frequency f.sub.1 of the microwave
source 21 or, alternatively, the frequency f.sub.2 of the
gyromagnetic resonance exciter and detector 6 shifts across the
spectrum of the sample under analysis.
The result is an output spectrum of improved resolution as compared
to that obtained from a conventional electron spin spectrometer.
The spectrum is a pure absorption spectrum due to the transient
nature of the resonance signals being recorded. All the reasons for
the substantial improvement in resolution of the output spectrum
are not fully understood. In a typical example, the abrupt change
in the RF level of the microwave source as fed to the bimodal
cavity for pumping the sample, shifts from the high intensity
saturation level to the non-saturation low intensity level in
approximately 100 nanoseconds, as before, the repetition rate for
the abrupt change in RF level is approximately 10 per second. Upon
the termination of each transient output signal the RF level is
returned via pulse programmer 9 and trigger 11 to the high
intensity level and the RF level remains at the high intensity
level for sufficiently long time for saturation of the sample to
reach equilibrium. Typically this is on the order of 100
microseconds.
In an alternative embodiment of the purturbation spectrometer of
FIG. 5, the frequency f.sub.1 of the pumping microwave source is
approximately the same as or, alternatively, coherent with or,
alternatively, different from the frequency f.sub.2 of the
gyromagnetic resonance exciter and detector 6 and the applied
polarizing magnetic field is swept by the pulse programmer. The
resulting transient response is obtained as previously and
displayed on the graphic recorder 14 as a function of the
polarizing magnetic field.
Referring now to FIG. 6 there is shown an alternative gyromagnetic
resonance spectrometer incorporating features of the present
invention. The spectrometer of FIG. 6 is substantially the same as
that of FIG. 4 with the exception that the intensity of the
microwave source is pulsed, as previously disclosed spectrometer of
FIG. 5. The resultant train of transient output resonance signals
are fed via coupling capacitor 7 to the input of a transient
analyzer 26 which separates transients having different time
constants. The separated output transient components from transient
analyzer 26 are fed to separate integrators 27 and 28' for
integrating the separated transient components. The integrated
outputs are fed to separate recorders 14 and 14' for recording
separately the separated transient signals. After the analysis of
each transient output signal, the pulse programmer 9 pulses the
magnetic sweep current 15 to change the electron resonance
condition to observe the transient resonance of a different portion
of the spectrum of the sample under analysis. A sample of the sweep
circuit output is fed to the X axis of the respective recorders 14
and 14' to obtain seprate output spectra as shown by spectra 2 and
3 of FIG. 8. The conventional ordinary electron spin resonance
spectrum is shown by spectrum 1 of FIG. 8.
Referring now to FIGS. 7 and 9 the transient analyzer 26 will be
more fully disclosed. Each transient output from the output of
gyromagnetic resonance exciter and detector 6 may comprise a signal
having a transient envelope of decaying amplitude as shown by curve
31 of FIG. 7. Curve 31 represents a composite transient signal,
such as that produced by super-position of a short transient signal
32 and a long transient signal 33. The transient analyzer 26
comprises a parallel connection of a high pass filter 34 and a low
pass filter 35. High pass filter comprises a series capacitor 36
and shunt resistor 37, whereas the low pass filter 35 comprises
series inductance 38 and shunt resistor 39. High pass filter 34
separates the short transient component from the composite
transient resonance signal 31 and feeds the short transient to the
first integrator 27. The low pass filter 35 separates the long
transient output signal 33 from the composite resonance signal 31
and feeds long transient component to the second integrator 28.
As an alternative to analyzer 26, the composite transient signal is
decomposed into the sum of two or more transient exponential
functions in a digital computer. The separated exponential
functions may then each be integrated independently in the computer
by digital techniques and the output converted to analog form and
recorded on an X-Y recorder to obtain the output spectra 2 and 3 of
FIG. 8. The spectrometer of FIG. 6 is especially useful for
separating the spectra of two gyromagnetic groups having overlying
spectrums. For example, electrons in the resonance sample may be
related to two radical systems having overlying resonance spectra.
The spectra are readily separated according to their time
constants.
Referring now to FIG. 10 there is shown an alternative spectrometer
embodiment of the present invention. The spectrometer of FIG. 10 is
essentially the same as that of FIG. 6 with the exception that the
output of capacitor 7 is fed to the input of a multichannel sample
and storage 8 which samples each transient resonance response, 12
as indicated in waveform (a), at a number of time displaced
sampling points with each sampling point corresponding to a
specific channel of the sample and storage 8. Successive transient
resonance responses for a given electron resonance condition, i.e.,
magnetic field intensity, are accumulated in the multichannel
sample and storage 8 for time averaging to improve the signal to
noise ratio. Periodically the output of the multichannel sample and
storage unit 8 is fed to the input of a time constant calculator
41, such as a digital computer, which measures the response in the
first channel, that response being A, and utilizes this value of A
to calculate a value B which is 1/e A. The computer then compares
the calculated value B with the measured values in the various
channels to arrive at the time constant T, i.e., the time at which
the signal amplitude has decayed to the value of B. The computer
then generates a voltage proportional to T and this time constant T
is recorded on the Y-axis of recorder 14 as a function of the
magnetic field intensity derived from the output of magnetic sweep
circuit 15 to obtain an output spectrum of the sample under
analysis. In the spectrum, the separate line signals have
amplitudes in variable accordance with the time constants of the
various lines.
Since many changes could be made in the above construction and many
apparently widely different embodiments of this invention could be
made without departing from the scope thereof, it is intended that
all matter contained in the above description or shown in the
accompanying drawings shall be interpreted as illustrative and not
in a limiting sense.
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