STUDIES OF NUCLEAR RESONANT ABSORPTION OF GAMMA RAYS. Final Report

Abstract

The feasibility of employing the Mossbauer resonant absorption phenomenon for new and useful applications of radioisotopes was studied and evaluated. For these experimental studies radioactive Co/sup 57/ sources were used which allow observations of the Mossbauer resonance in Fe/sup 57/ at room temperatures. However, the results of the investigations can be extrapolated to other Mossbauer isotopes which, unfortunately, usually require low-temperature apparatus to obtain an appreciable fraction of recoilless emissions and absoiptions. The investigations centered aiound the utilization of the Mossbauer effect for practical problems in measui ement and control technology. The use of nuclear resonant techniques in the general areas involving small velocity, acceleration, and displacement measurements appears very promising. For example, velocities in the range from 0.005 to 0.0l5 cm/sec are easily measured using Fe/ sup 57/ nuclear resonance, and this range can be extended several orders of magnitude in both directions if other sources and techniques are endployed. Measurements of gravitational fields in interplanetary space or on the surfaces of celestial bodies, together with altitude measurements of space vehicles, using Mossbauer techniques do not appear practical because the measurement times required to obtain reasonably accurate results is of the order of hours or days under the most favorable circumstances. Experimental measurements of the effects of high pressures on the fractional resonant absorptions showed no observable changes when a Co/sup 57/-stainless steel source was subjected to pressures up to 40,000 psi, although higher pressures or other Mossbauer sources may make pressure measurements practical. Experiments showed that it is possible to determine the direction and strengths of homogeneous magnetic fields in a range from 300 to 1000 gauss by measuring the percentage of nuclear resonance in iron foils. Although the method is not, in general, as accurate as conventional techniques, such a system warrants further study since it might have definite practicality when hostile environments or accessibility problems limit or prohibit the use of conventional techniques. Initial studies also showed that nuclear resonance techniques could be used to measure the amplitudes of acoustical (mechanical) motion in the megacycle frequency region. The results gave every indication that such measurements could be extended to higher frequencies and possibly into the hypersonic, kilo-megacycle ranges where currently there are no suitable methods available to measure acoustical power or acoustical energy densities. (auth)