أكاديميا - كولنز - معاجم الجيب العلمية - الفيزياء - انكليزي - فرنسي - عربي الحرف ٢_ r

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radioactivity
radioactivity f

Radioactivity. The collapse (or decay) of unstable nuclei into more stable forms. The speed at which this happens is related to the half-life period. During radioactive decay, energy is transferred to the products, and they move away, carrying kinetic energy.

Alpha radioactivity is the release of alpha particles during this decay. The alpha particle is a helium nucleus. The “parent” nucleus (X parent) changes to the daughter nucleus (Y daughter). The mass of the latter is four units less than the mass of the mother. The number of protons is less than two.

There are a number of forms of beta-decay. In its most common form, a neutron in the parent nucleus is transformed into a proton, and an electron escapes (the “beta particle” - B particle).

Gamma rays follow a simpler change in the energy structure inside the nucleus. Gamma photon light appears, which takes no charge with it and very little mass. The energy of light (photon) W is equal to its frequency multiplied by Planck's constant... and its mass is equal to its energy divided by the square of the speed of light (see - mass energy).

The fourth form of radioactivity is fission. In this case, the parent nucleus splits into two smaller daughters, releasing a few neutrons. A chain reaction may occur here.

Finally, there are a few radioactive nuclei that become more stable by releasing protons.

Note that in all cases the daughter nuclei may also be radioactive. Therefore, it is not easy to provide a pure source of any single form of radioactivity radiation.


radioisotopes
radioisotopes mpl

Radioactive isotopes. Radioactive isotopes result from irradiating materials with neutrons in a nuclear reactor, or bombarding them with protons, deuterons, etc., using an accelerator. These isotopes can be used in cancer treatment, as well as tracers in medicine, and for a wide variety of tasks in industry.


rainbow
arc en ciel m

rainbow. The effect of refraction and reflection of sunlight in raindrops, where a person can see one or more spectra if it is present between the sun and the rain.

Rainbow: dispersed by raindrops.


rate
taux m

an average. Speed. The rate of a measurement, in physics, is its value per unit time in most cases). Thus, the rate of change of an object's speed (acceleration, in other words) is equal to the change in speed during one second. The rate of decay of a radioactive sample is equal to the number of its nuclei that disintegrates in one second.

The rate is represented by the slope of the graph of the measurement with respect to time.


rate meter
compteur m

Rate scale. When a Geiger-Müller tube detects radioactivity, the pulses can be counted with a rate meter to give a direct “counts per second” reading.