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Saga about Neutrons
April 1, 2008 19:47


Russian nuclear physicists confirmed some aspects of current hypothesis of origin and structure of the Universe.

Physicists from Russian Institute of Nuclear Physics (Russian Academy of Sciences) performed very accurate measurements (0.1%) of neutron lifetime, which eliminate existing contradictions and correspond with predictions of the Standard Model. Moreover, received value of neutron lifetime fits better to description of primary nucleosynthesis, which is the process taking place simultaneously with Universe formation.

We should remind our readers that Standard Model of elementary particles is a theory, describing electromagnetic, weak and strong interactions between all elementary particles and formation process of matter, which composes our Universe. New data on neutron lifetime, which now is 878 +/-0.8 s, came from an experiment with ultra-cold neutrons, performed together with researchers from Joint Institute for Nuclear Research (Dubna, Moscow region).

Ultra-cold neutron gas (consisting of neutrons with extremely low energy, about 10-7 eV) is trapped by a very simple technique: by turning the trap around its horizontal axis. As a result, neutrons, having kinetic energy lower than potential energy of Earth gravitational field, stay in this trap. Then the trap is turned upside down, neutrons flow to a detector, and scientists find out how many neutron remain in the trap. The whole process is repeated for various confinement times, thus measuring neutron exponential decay.

Further measurements by means of magnetic trap of ultra-cold neutrons, performed in the same institute, gave same results for neutron lifetime as gravitational experiment did. Ultra-cold neutrons allowed checking several theories, suggesting existence of transition of a neutron to a mirror neutron, which is a hypothetical particle. Such particles are regarded as possible candidates for being dark matter of the Universe. Scientists claim that their experiments abandon such theories.

However, physicists are waiting for another problem to be solved neutrons electric dipole moment is still unknown. Electric dipole moment of a neutron may exist only due to violation of time reversal invariance principle CP-violation (invariance principle says that any physical process goes on the same way, when repeated after some time period). CP-violation is very important for understating how our Universe was born. Well, we still do not know anything about neutrons electric dipole moment, because our measurements of ultra-cold neutron gas are not precise enough. Experimental accuracy can be increased by introduction of a new high-intensity source of said gas. Scientists suggest a project with such a source, which utilizes superfluid helium under 1.2 K.

Ultra-cold neutrons, born in superfluid helium, show high yield due to extremely high transparency of this quantum fluid for low energy neutrons. Calculations show that ultra-cold neutron gas can have density about 3x103 n/cm3, which is 100-500 times more than existing density. Russians can have the best source of ultra-cold neutrons in the world, but the only problem is funding, required for reactor maintenance.

Source:
    Science & Life

Kizilova Anna


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