GB2163257A

GB2163257A - Modified magnetic resonance apparatus

Info

Publication number: GB2163257A
Application number: GB08420781A
Authority: GB
Inventors: Leonard Arthur Freeman
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-08-15
Filing date: 1984-08-15
Publication date: 1986-02-19
Also published as: GB8420781D0

Abstract

A specimen, placed in a magnetic field is additionally subjected to an intensity-modulated beam of either electrons or electromagnetic radiation (eg light), and the intensity of the beam after reflection from, or transmission through, the specimen is monitored. Magnetic resonance may be observed by varying the modulation frequency, while simultaneously monitoring changes in the intensity of the beam after its interaction with the specimen. Means are provided for scanning the beam controllably over the specimen, thereby allowing an image of the specimen with good spatial resolution to be obtained from the transmitted or reflected beam.

Description

SPECIFICATION Modified magnetic resonance apparatus This invention relates to the field of magnetic resonance, and its two principal divisions of nuclear magnetic resonance (N.M.R.) and electron spin resonance (E.S.R.).

Magnetic resonance is a well established technique, used in Chemistry and allied fields.

The physical principles underlying this technique are that, when a material is placed in a strong magnetic field, H, then there are created magnetic quantum levels, between which the absorption or emission of radiation can occur. These levels are-for a given magnetic field-characteristic of the material. The relation between the frequency of the absorbed (or emitted) radiation is given by.

hf=gflH (1) where "h" is Planck's constant, "f" is the frequency, and the other symbols have their usual meanings.

For a review of the method and techniques, see: 1) 'Electron Spin Resonance' by Charles P.

Poole Jr. Wiley-lnterscience publication. John Wiley and Sons, 1983.

2) 'The theory of nuclear magnetic resonance.' by l.V. Aleksandrov. Edward Arnold, London 1966.

In both methods, a specimen is placed in a (usually) strong magnetic field, H, and then subjected to electro-magnetic radiation. At frequency 'f' as in equation (1), some of this incident radiation is absorbed. N.M.R. usually employs radio frequency (RF) radiation whereas E.S.R. uses the higher frequencies associated with microwave radiation.

In these studies it is normal to apply the required radiation directly, that is to use a radio or microwave frequency that satisfies equation (1) at the frequency 'f' For this reason the specimen is usually placed inside a RF coil or a microwave cavity.

According to the present invention, described herein, the RF or microwave radiation is applied in a totally different way. It is applied by using much higher frequency electromagnetic radiation (e.g. infra-red or visible light, etc) to irradiate the specimen. This higher frequency, higher energy radiation is modulated in intensity at a lower RF or microwave frequency, and then the intensity of the transmitted or reflected radiation from the specimen is measured.

By suitable variation of the modulation frequency (or the magnetic field, or both) the transition defined by equation (1) may then be observed.

There is no necessity, in this invention, to use the RF or microwave radiations that are common in either N.M.R. or E.S.R. repectively. Instead one could, for example, use a visible light beam modulated in intensity at 20 MHz, corresponding to 'f'.

A completely separate method of applying the radiation at frequency 'f' is the use of an intensity-modulated corpuscular beam (e.g. of electrons), modulated at frequency 'f'.

The use of either method of irradiating the sample (electromagnetic radiation or corpuscu lar beam) means that higher spatial resolution is possible. This in turn allows the application of microscopic techniques and two dimensional imaging.

1. A method of detecting magnetic resonance in materials wherein the material or specimen to be examined is placed in a magnetic field, H, and subjected to a beam, of either corpuscles (eg electrons) or alternatively electromagnetic radiation (eg infra red, visible light or ultra violet radiation). Means are provided such that the energy of the corpuscles or photons comprising this beam have a fundamental wavelength associated with them whose mean value is less than 0. 1 mm, and means are also provided to modulate the intensity of the beam at high frequency before impinging on the specimen.Additionally a detector system is provided to monitor or measure the intensity of the modulated beam after it has been transmitted through, or reflected from, or both transmitted through and reflected from the specimen under examination, thereby enabling magnetic resonance phenomena to be observed as changes in the detected intensity (dependent on the specimen) that occur while the frequency of modulation of the beam is varied in a controlled manner, or the magnetic field intensity 'H' is varied in a controlled manner, or both the modulation frequency and 'H' are simultaneously varied. The magnetic field 'H' is effected by means of a permanent magnet or electromagnet, or a combination of both of these.

2. A method of detecting magnetic resonance as claimed in claim 1 wherein the beam is further modulated, either in intensity (as in amplitude modulation in radio systems) or in frequency (as in frequency modulated radio systems), at a much lower (eg audio) frequency than the modulation frequency referred to in claim 1, and wherein the detector system can, after appropriate demodulation of its input signal, monitor changes in this lower audio frequency.

3. A method of detecting magnetic resonance as claimed in claim 1 wherein the magnetic field 'H' is varied in strength (by less than 10%) at a lower frequency (eg audio frequency) than the modulation frequency of claim 1 and wherein the detector system can, after appropriate demodulation of its input signal monitor changes in this lower fre

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Modified magnetic resonance apparatus This invention relates to the field of magnetic resonance, and its two principal divisions of nuclear magnetic resonance (N.M.R.) and electron spin resonance (E.S.R.). Magnetic resonance is a well established technique, used in Chemistry and allied fields. The physical principles underlying this technique are that, when a material is placed in a strong magnetic field, H, then there are created magnetic quantum levels, between which the absorption or emission of radiation can occur. These levels are-for a given magnetic field-characteristic of the material. The relation between the frequency of the absorbed (or emitted) radiation is given by. hf=gflH (1) where "h" is Planck's constant, "f" is the frequency, and the other symbols have their usual meanings. For a review of the method and techniques, see: 1) 'Electron Spin Resonance' by Charles P. Poole Jr. Wiley-lnterscience publication. John Wiley and Sons, 1983. 2) 'The theory of nuclear magnetic resonance.' by l.V. Aleksandrov. Edward Arnold, London 1966. In both methods, a specimen is placed in a (usually) strong magnetic field, H, and then subjected to electro-magnetic radiation. At frequency 'f' as in equation (1), some of this incident radiation is absorbed. N.M.R. usually employs radio frequency (RF) radiation whereas E.S.R. uses the higher frequencies associated with microwave radiation. In these studies it is normal to apply the required radiation directly, that is to use a radio or microwave frequency that satisfies equation (1) at the frequency 'f' For this reason the specimen is usually placed inside a RF coil or a microwave cavity. According to the present invention, described herein, the RF or microwave radiation is applied in a totally different way. It is applied by using much higher frequency electromagnetic radiation (e.g. infra-red or visible light, etc) to irradiate the specimen. This higher frequency, higher energy radiation is modulated in intensity at a lower RF or microwave frequency, and then the intensity of the transmitted or reflected radiation from the specimen is measured. By suitable variation of the modulation frequency (or the magnetic field, or both) the transition defined by equation (1) may then be observed. There is no necessity, in this invention, to use the RF or microwave radiations that are common in either N.M.R. or E.S.R. repectively. Instead one could, for example, use a visible light beam modulated in intensity at 20 MHz, corresponding to 'f'. A completely separate method of applying the radiation at frequency 'f' is the use of an intensity-modulated corpuscular beam (e.g. of electrons), modulated at frequency 'f'. The use of either method of irradiating the sample (electromagnetic radiation or corpuscu lar beam) means that higher spatial resolution is possible. This in turn allows the application of microscopic techniques and two dimensional imaging. CLAIMS

3. A method of detecting magnetic resonance as claimed in claim 1 wherein the magnetic field 'H' is varied in strength (by less than 10%) at a lower frequency (eg audio frequency) than the modulation frequency of claim 1 and wherein the detector system can, after appropriate demodulation of its input signal monitor changes in this lower fre quency.

4. A method of detecting magnetic resonance as described in claim 1 and claim 2 and claim 3.

5. A method of detecting magnetic resonance as described in claim 1 or claim 2 or claim 3 or claim 4 wherein means are provided to move the modulated beam in a controlled manner over the specimen under examination while simultaneously monitoring or recording or both monitoring and recording the intensity of the detected signal, and further means are provided to display this signal as a two dimensional image of the specimen, employing general methods comparable to those used in scanning electron microscopy.

6. A method of detecting magnetic resonance wherein a Scanning Electron Microscope or Scanning Transmission Electron Microscope is employed, such microscope employing appropriate modification as described in one of the 5 other claims herein listed.