Device for measurement of gamma resonance form of long-lived nuclear isomers

FIELD: physics.

SUBSTANCE: invention refers to nuclear technology area, to devices for measurement of the form of gamma radiation microspectrum which are emitted at disintegration of long-lived isomeasured conditions of nuclei, such as an isomeasured 109Ag nucleus condition with 88.03 keV energy and average life time of 57 seconds. In the device for measurement of the form of a gamma resonance of long-lived nuclear isomers, beams of gamma-ray quantums from a source are directed to detectors in parallel to a platform plane. The source is placed in the cryostat, conditioned in a temperature providing Moessbauer conditions and executed in the form of a metal plate from the atoms with the nuclei having an investigated isomeasured condition, with the atoms of a parent nuclide input into it. The cryostat and detectors are installed on a platform. Intensity of gamma lines of basic and auxiliary non-resonant gamma sources is measured depending on a slope of beams concerning horizontal plane. The inclination is carried out by platform turn. In each angular position the measurement can be spent at a natural direction of Earth magnetic field and at the component of a terrestrial magnetic field compensated by an additional magnetic field perpendicular to a direction of registered gamma beams. The pair of Helmholtz rings located coaxially to the cryostat serves for terrestrial field compensation.

EFFECT: invention allows raising resolving power Moessbauer spectrometers.

 

The invention relates to the field of nuclear engineering, more specifically to a device for measuring the shape microspectra gamma radiation emitted during the decay of long-lived isomeric States of nuclei, such as the isomeric state of the kernel,109Ag energy 88,03 Kev and an average lifetime of 57 C.

The known device, based on the application of the Mossbauer effect, by which investigated the form microspectra emitted (and absorbed) without loss of energy to the recoil nuclei components of the gamma-ray line (Hortham. The Mossbauer Effect. Ed. Mir, Moscow, 1966). In these devices, this problem is solved by shifting energy gamma-ray source relative to the position of the absorption line of the resonant absorber. In most cases, this shift is carried out using the Doppler effect, which is manifested in the movement of the source relative to the absorber with a speed ν; this shift is equal to ΔEγ=Eγν/c, where Eγ- energy gamma-quantum, C is the speed of light.

Closest to the claimed device is a technical solution implemented in experiments with gamma rays67Zn (W.Potzel, C.Schäfer, M.Steiner et al., Hyperfine Interactions, v.72, p.197 (1992)). The natural width of the gamma-ray line of this nuclide equal value of 4.76×10-11eV, and the energy of the gamma quanta equal 93,31 Kev. A disadvantage of this device is the restriction of e is about the resolution value of 0.96×10 -10eV.

The objective of the proposed technical solution is the creation of gamma-spectrometric device using as gamma-sources of long-lived nuclear isomers with average lifetimes in the excited state is of the order of minutes or more, and it gives the opportunity to increase by 7-8 orders of magnitude resolution of existing mössbauer spectrometers with nuclide57Fe.

Isomeric state of the nucleus109Ag has a natural width of ~10-17eV. The gravitational field near the Earth's surface shifts the position of the gamma-resonance isomer109Ag at its natural width if the difference between the vertical position of the emitting and absorbing nuclei in a ~10-4see the Earth's Magnetic field splits gamma-line109mAg 14 component, the gaps between which exceeds the natural width of the gamma-ray line in ~106time. In metallic silver at a temperature of liquid helium (4.2 K) is the probability of emission (absorption) of gamma-quantum with energy 88,03 Kev without loss of energy at impact engine is 0,0535 that allows these gamma rays mössbauer experiments, but not by a standard method of creating a Doppler shift of the energy line emission relative to the position of the absorption line, since in this case would require technical is if unavailable the speed of the source relative to the absorber, equal ~10-12cm/sec.

Numerous experiments of recent years, including those made by our group show that the Mossbauer gamma-line isomer109mAg if and broadened, very small - no more than a few dozen times. This allows you to use gravity to measure the shape of the gamma-resonance of this isomer.

This goal is achieved by the fact that in the inventive device, the gamma source, representing a record high purity silver embedded in it by thermal diffusion of atoms of the parent nuclide# l09Cd placed in a cryostat and cooled to the temperature of liquid helium (4.2 K). The cryostat is located on a platform which can be rotated around the horizontal axis in both directions at an angle of 30 degrees relative to the horizontal plane. Beams of gamma rays emitted by the source in opposite directions parallel to the plane of the platform, are registered on the platform two germanium detectors. Resonant absorption of gamma rays occurs directly in the substance of the source, the thickness of which is 0.5-1.0 mm, It is maximized when the recorded gamma beams horizontal. The tilting of the platform beams deviate from the horizontal, and this decreases the probability of resonance absorption of gamma rays as a result of which their gravitational shift of gamma-resonance, because the point of emission and the possible absorption of gamma quanta are at different heights. With increasing angle of inclination increases the attenuation of the resonance absorption of gamma quanta. Calculations done for the gamma source with a thickness of 1 mm, which introduced the109Cd with both parties, and the average depth of penetration of cadmium equal to 0.15 mm on each side, show that the deflection angle of the gamma-ray beam from the horizontal, corresponding to the decrease of resonance absorption half, α1/2is determined by a simple formula:

α1/2=0,197k,

where k is the factor for the broadening of the Mossbauer gamma-ray line, and the angle is expressed in degrees.

Measurement of the dependency of the number of counts of the detectors from the angle of the platform allows to obtain data on the profile of gamma-resonance than achieved this goal. To improve the reliability of the received data unit is supplied with the following additional details.

1. On both sides of the silver plate is installed close to her delicate control of gamma-sources241Am, emitting gamma rays with energies 59,54 Kev. The rotation of the platform should not affect the recorded intensity of these gamma rays.

2. Coaxial to the cryostat is mounted a pair of Helmholtz rings, the inclusion of current through that allows you to compensate in the area of gamma-IP is a regular component of the magnetic field of the Earth, perpendicular detected gamma beams. This leads to an increase in the probability of resonance absorption of gamma-rays in 2.5 times. Periodic switching on and off of Helmholtz rings will cause a simultaneous change in the detected intensity of gamma-rays of silver (but not americium), corresponding to the change of 60% of the cross section of resonant absorption.

Diagram of the device shown in the accompanying drawing, where 1 - cryostat, 2 - germanium γ - detectors, 3 - rotatable platform 4 to the axis of rotation of the platform 5 - ring Helmholtz 6 - gamma sources, 7 - support of the cryostat and of Helmholtz rings.

Device for measuring the shape of the gamma-resonance of long-lived nuclear isomers, characterized in that, to improve the resolution gamma-ray spectrometry, gamma beams from placed in a cryostat and maintained at providing mössbauer conditions the temperature of the source in the form of metal plates of atoms whose nuclei have investigated isomeric state, with the introduction of a atoms of the parent nuclide, directed to the detectors parallel to the plane of the platform, which is equipped with a cryostat and detector, and depending on the angle of the beam relative to the horizontal plane by rotation of the platform, measured the intensity of gamma-lines osnovnoj the and auxiliary resonant gamma-ray sources, moreover, in each angular position measurement can be carried out in the natural direction of the magnetic field of the Earth and when offset by additional magnetic field component of the earth's magnetic field perpendicular to the direction of the detected gamma beams, which is a pair of Helmholtz rings located coaxially to the cryostat.



 

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