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Experimental Examples CLICK HERE |
System Components CLICK HERE |
The postulate of Pauli in 1924 that certain nuclei posses a spin angular momentum led Gerlach and Stern to experimental confirmation that nuclei had magnetic moments.
In 1939 Rabi first demonstrated resonance absorption of an oscillating electromagnetic field by molecules placed in a constant magnetic field. The first unsuccessful NMR experiment in solid state was performed in 1936 by Gorter. It was successfully done in 1946 independently by 2 groups, Purcell at Harvard and Bloch at Stanford (Nobel Prize in 1952). Later in 1950 Hahn implemented an ingenious idea of replacing continuous wave excitation of polarized nuclei by pulse excitation. In 1951 Arnold went beyond the limits of magnet homogeneity and obtained the first high-resolution spectra discovering 1H chemical shifts. Hahn’s pulse spectroscopy idea matured in the 1960’s when technology allowed Anderson and Ernst the use of computers for Fourier Transformations (for his contribution to modern NMR Ernst received the Nobel Prize in 1991). This allowed one to change time domain to frequency domain in one keystroke.
The age of medical applications started in the early 1970’s after Lautertbur demonstrated the feasibility of using NMR for imaging. Liberated from the obsession of perfect magnetic field homogeneity he deliberately applied gradients to encode the spatial information into an NMR spectrum. This and Damadian’s discovery in 1971 about tissue contrast available through variation of nuclear relaxation times opened Pandora’s box for medical application.
Since its discovery, NMR has proved to be a versatile technique in basic research (Physics, Chemistry, Biochemistry). It found application in Geology (oil and ferrous compounds search), Agriculture and Food Industries (moisture contents and purity measurements), and in Archeology (tracing changes of the Earth’s magnetic field through the ages). Finally materializing under the MRI acronym Magnetic Resonance Imaging; (for “political” reasons the word “nuclear” was removed) Lauterbur’s idea on “Image Formation by Induced Local Interactions” proved to be a perfect modality for clinical noninvasive anatomical and functional imaging. Not surprisingly the 2003 Nobel prize in Medicine was awarded to Chemist Lauterbur and Mansfield, a Physicist who invented modern MR Imaging.
SPECTROMETER DESCRIPTION
Tel-Atomic, Inc. presents a desktop pulse NMR system, the PS-15, that combines all of the sophisticated features that mainframe spectrometers have including:
- Electromagnet with three stage magnetic field stabilization (current, flux, and NMR lock on 19F),
- Broadband transmitter
- Multiphase RF pulses,
- Low-noise quadrature receiver,
- Intuitive software for experiment preparation, experimental data acquisition, storage and processing,
- Collection of modern NMR pulse sequences dedicated for:
- NMR spectroscopy
- nuclear relaxation times measurements (T1, T2, T1σ)
The spectrometer can operate with or without NMR magnetic field stabilization. The NMR stabilizer provides excellent long-term stability of the electromagnet by compensating for thermal drift. This stability is necessary for experiments that require long times (for example multiple signal accumulation, samples with very long relaxation times).
With the NMR flux stabilizer turned off diagnostics like confirming the magnet’s homogeneity (shimming) and adjustment of initial current (I 0 ) of the basic magnet current stabilizer can be performed.
ATTENUATORS
The PS-15 includes 2 attenuators for changing the pulse power. The main attenuator has a range of 0-31.5 dB in 0.5 dB steps. This attenuator changes the power of pulses simultaneously in all channels. This means very accurate adjustment of the exciting pulse. Samples with short relaxation times (solids) need short high-power pulses. For samples with long relaxation times (liquids) long, low-power is more adequate. The Y channel attenuator changes the power of pulses in Y channel only. It is active only during rotating frame experiments. It is used for calibration and selecting of the locking B1 field for T 1ρ measurements.
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goiniometer
The PS-15 also comes with a 360 degree dial attached permanently to the magnet and a rotating sample holder. This can be used for measurements of spectra shape angle dependence in monocrystal samples. 1H NMR spectra of solid samples can give structural information that X-ray crystallography cannot deliver due to poor X-ray scattering on the hydrogen single electron. A gypsum monocrystal is used as an illustration of line split due to proton interaction with the local magnetic dipolar field. |
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The spectrometer operation is controlled by a package of dedicated software for user-friendly assistance during the preparation of an experiment, the actual acquisition of data and later data processing. The software provides a convenient means for the acquisition of any form of nuclear signal related to NMR spectroscopy or relaxometry and its subsequent processing. The software graphic interface consists of three windows: setup, acquisition, and processing.
 Experimental setup window This window is used for the preparation of an experiment . Data obtained during any experiment that is run on the setup window are shown continuously in real time. Any change in setup takes effect immediately on the displayed data. The user can create, save and load his own setups to preserve and retrieve specific settings.  Data acquisition window The final experiment and data storage is performed in the acquisition window. This task requires the definition of the name of the destination binary file, the accumulation number, the variable delay file name if relaxation measurements take place, and any comments the user wants to make about the experiment. During relaxation measurements, amplitudes of consecutive FIDs corresponding to executed interpulse delays are displayed to show the magnetization recovery.  Data processing window This window is used for data viewing and processing. It allows the user to perform the following operations:
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Documentation
An experimental manual, on CD, gives the student full flexibility with respect to the level of involvement and the applications of magnetic resonance spectroscopy one wishes to explore. Twenty plus basic and advanced, as well as instrumentation experiments are included in the experimental manual. Basic experiments include, NMR Specta, and Relaxation experiments. Advanced experiments such as multiple pulse sequences and rotating frames of reference, as well as, angle dependence on spectra shape lets the student explore more deeply into the uses of NMR. Instrumentation experiments are designed to teach the student about NMR instrumentation. A number of samples for use with the experiments in the experimental manual have been included for convenience and ease of use. The student however is not limited to these samples. The number of potential samples (chemical compounds, commercial substances or products) and measurements are practically unlimited.
TEL PS-15 Pulsed NMR System
The complete system includes the PS-15 control unit, electromagnet with integrated probe head, accessories, a CD which includes the software, a 100 page operations manual and the 140 page experimental manual (in PDF format), as well as all connecting cables. The unit is shipped in an exceptionally well built case that can be used for storing the unit.
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TEL PS-15 Pulsed NMR System |
$16,799.00 |
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TEL PS-15 Plused NMR System experimental manual download |
Hard copy of the PS-15 Manual
A printed version of the experimental and operations manual is available. Both the 100 page operating manual and the 140 page experimental manual are contained in a single sturdy 3 ring binder.
| TEL PS-15 Manual | $159.00 |
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The TeslaMeter 2000 comes with complete operating instructions, a transverse probe, and an external power supply. The Zero Gauss Chamber and software are also included.
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Computer requirements and software installation: Computer considerations
For proper operation, data storage and display, the spectrometer winner control program requires an IBM PC AT VGA or compatible computer. The program and factory created files occupy less than 2MB of hard drive total space. Average spectroscopy binary data files need only about 10 Kb of space, but expand as much as 5 times when converted into text files. Average relaxation binary data files occupy about 100 Kb, but collapse to 1 Kb when amplitudes and corresponding delays are extracted for further relaxation time calculations. Processed spectra occupy about 25 Kb. Exact numbers depend on number of data points acquired. Even if intensively used, the software generally needs only moderate space on the hard disk.
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SPECIFICATIONS FOR TEL-PS-15 |
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| Mode | pulse NMR |
| Operational Frequency | 15 MHz (1H) |
| Frequency Stability | ≤ 1 PPM(15Hz or 0.0001%)/ 24h |
| Magnetic Field Source | |
| - magnetic field magnitude | 350 mT |
| - gap | 10.5 mm |
| - pole diameter | 60 mm |
| - homogeneity | ≤ 7 μT/300Hz (0.002%) measured over 0.05cc cylindrical sample (4mm diameter, 4mm length) |
| - field stability (NMR stabilizer) | ≤ 0.1 μT/24hrs |
| - thermal drift. No thermal drift in range | 10°C-35°C |
| Programmer | |
| - pulse width | 0.4μs -50μs |
| - minimum pulse increment | 0.2μs |
| - maximum time delay | 24 h |
| - pulse length stability | ≤ 0.0001%/24h |
| - measurement sequences | factory and user created (see list) |
| RF Square Pulse Modulator | |
| - RF channels | Orthogonal Y, X, -Y, -X |
| RF Transmitter | |
| - RF pulse power | ≤ 15 W (π/2 ≤ 3.0 μs) |
| - RF pulse attenuation | 0-31.5 dB, 0.5 dB step |
| - maximum locking pulse width | 100 ms |
| - locking pulse attenuation | 0-7dB, 1dB step |
| RF Probehead | |
| - solenoid coil dimensions | ID= 5.8 mm; L= 10 mm |
| - recovery (“dead”) time | < 18 μs |
| Receiver | |
| - gain | 60 dB (1 dB step) |
| - detection | amplitude/quadrature (phase-sensitive) |
| - low pass filter band | 300 kHz; 100 kHz, 30 kHz |
| - DC offset | ± 50 % |
| A/D Converter | |
| - type/resolution | flash/8 bits |
| - channels | 2 |
| - dwell time | 0.4 – 400 μs |
| - number of samples | 256-8192 |
| Weight and dimensions WxDxH | |
| - electronic unit | 6.3 kg, 47x26.3 x11 cm |
| - probehead | 0.8 kg, 12x12x2.3 cm |
| - electromagnet | 21 kg, 21x13x18 cm |
| Power Consumption | 110V/220 V; 50/60 Hz; 70 W |
| Communication Port | two way RS 232C |
| Computer Required | IBM PC or compatible, 750MHz recommended |
| Software | MS Windows operated |
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Pulse Sequences included with PS-15 |
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| Name | Description |
| ONE-PULSE | |
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1P_X 1P_Y 1P_-X 1P_-Y |
One-pulse sequences are used to generate Free Induction Decays. RF pulses in 1P_X, 1P-Y, and 1P-X sequences have different phase shifts relative to 1P_Y sequence; 90°, 180°, 270°, respectively. |
| TWO-PULSE | |
| 2P_X_D | Useful to generate spin echo or to sample FID after certain time delay. During data acquisition sequence uses delay from Setup page. |
| 2P_X_VD | Universal sequence to measure T1 or T2*. Requires Variable Time Delay file (VTD) during the acquisition experiment to execute delays between pulses. |
| HAHNECHO | Simplified version of 2P_X_D. Second pulse is twice as long as first one is. For a brief generation of Hahn’s spin-echo. |
| THREE-PULSE | |
| 3P_X_D | General use three-pulse sequence. Delays between pulses are set manually at Setup page. |
| STIM_SE | Stimulated Echo sequence that generates multi-echoes. Frequently used in T1 measurements. During data acquisition Variable Time Delay file is required to execute delays between second and third pulse. |
| MULTI-PULSE | |
| CP_25 | Carr-Purcell sequence to measure T2. Drastically reduces spin diffusion effect compared to simple Hahn’s spin-echo sequence. Generates 25 spin echoes. No VTD required. |
| CPMG_25 | Carr-Purcell-Meiboom-Gill sequence to measure T2. Reduces spin diffusion effect and cumulative effect of pulse length accuracy. Generates 25 spin-echoes. No VTD required. |
| SOLID_SE | So called Solid (state) Echo. Used to generate and acquire spin echo signals in solid like samples. |
| SAT | Saturation method for T1 measurements. The method eliminates need for long delay between consecutive experiments. |
| SPINLOCK | Spin locking method used for “rotating frame” experiments. |
| SL_CAL | Method used for locking B1 field calibration. |