Technical conditions of the remote NQR signal detection experiment
Those present: J. Henderson, A.Taylor, R.Fisher
Experimentors: prof. V.Anferov, doz. G.Mozjoukhine (Kaliningrad State University)
Equipment used: Nuclear quadrupole resonance spectrometer with the following specifications: frequency range 0.1 – 30 MHz, pulse duration 20 – 250 μs, radio frequency pulses power up to 2.5 kW.
The following procedures were employed: quadrature detection, quality modulation for damping the ringing of the radio frequency transmitting coil, damping the ringing of the receiver path. To detect NQR signals, a sequence of uninterrupted radio pulses with 180
° phase shift after the second pulse was used.The spectrometer consists of: Hewlett-Packard signal generator 8648C, homemade radio frequency gate (based on Mini-Circuit 15542 ZYSWA-2-50DR), power amplifiers (ENI A150, KENWOOD TL-922, ICOM IC-2KL), homemade receiver (based on Mini-Circuit 15542 ZFL-500LN), homemade transmit-receiver head-probe, homemade receiver gate, homemade two channel modulator, Hewlett-Packard digital processing system.
Transmit-receiver head-probe includes: flat receive-transmit coil (with external diameter 36 cm, internal diameter 15 cm, 12 turns of the cable Beldon RG213, quality of the coil Q within 360-400), homemade damping circuit, homemade preamplifier, screen consisting of a copper band with diameter 53 cm 20 cm high and a semi-sphere made of copper mesh 53 cm.
The sample is presented by 150 g RDX inside the model of an anti-personnel mine, having the shape of a cylinder with diameter 12 cm, and height 4.5 cm. The frequency of detection is 5.189 MHz .
The distance between the surface of the coil and the sample is 22 cm. The observation time is 81 s.
Duration
of radio frequency pulses is 200 μs . Peak power of the radio frequency pulses is 1.5 kW (the measurements made on RF POWER ANALYST MODEL 4391A, BIRD ELECTRONIC CORP).Pulse spacing
is 1800μs.Conditions
for the registration: number of averages is 40 000, observation window contains 512 points with spacing 2 μs between the points, delay between the radio frequency pulse and the obsevation window is 800μs.
Results of experiment are given in Figs. 1, 2, 3.
Figure 1.
The signal after averaging in channel 1 of the quadrature detector.
Figure 2.
The signal after averaging in channel 2 of the quadrature detector.
Figure 3.
Modulus squared Fourier Transform of signal
Signitures:
John Henderson – Development Manager
Alan Taylor –Aviation Technical Manager
Ron Fisher – Laboratory Supervisor
Vladimir Anferov – Research Scientist
Gueorgui Mozjoukhine - Research Scientist
29.06.98
E-mail: mgeorge@gazinter.net
HOMEPAGE