Neutron capture

Basic Concept

Neutron is absorbed and issued by a gamma ray after colliding with the nucleus. In some cases, the beta decline or fission will also be caused.

When a neutron is squeezed into the nucleus, it is often referred to as neutron capture.

Principle introduction

Neutron enters the nucleus to form a "composite nucleus", it may transmit one or more photons, or may transmit one or more particles Back to the ground state. The former becomes "radiation capture", while the latter corresponds to various neutron nuclear reactions. For example:

¹ h + n → ² h + γ

⁶ li + n → ³ H + α

There are several heavy moments (such as ²³⁵ u), capturing a neutron and divided into two or three Lighter atomic core, simultaneously issuing 2 to 3 neutrons and a large energy (about 200mev), which is the nuclear fission reaction.

Neutron Captive

In the case of low neutron flux, such as nuclear reactor, a single neutron is captured by an atomic nucleation. For example, when the gold (197au) is neutron radiation, it is generated by high-transducer, and then the decay transition is generated, and the gamma rays are emitted. In this process, the mass number increases 1. This nuclear reaction can be expressed in the following simplicity:

• 197au (n, γ) 198au

is used in this nuclear reaction It is generally called thermal capture.

Isotope Gold 198 (198au) It is prone to β-decay attenuating athletes (198HG). In this process, the atomic order increases by 1.

Neutron capture of high neutron flip

If the density of neutron flux is high enough, the atomic core is between neutron traps There is no time to perform β decay, then the R-process takes the inside of the star. In this way, the mass number will increase significantly, and the atomic order is unchanged (the type of nuclear is unchanged). Only after this process, the height unstable atomic nucleus produces β decay, transitions into a atomic nucleus having a higher atomic number, stable or unstable.

Application

This is because different chemical elements will release different characteristics after absorbing neutrons. This feature makes this method very useful in mining exploration and security.

Neutron absorbent

The most effective neutron absorbent is a radioisotope which can produce a stabilized atomic core by absorbing a neutron. For example, xenon 135 (about 9.1 hours of half-life) can absorb a neutron to become a stable xenon 136. The xenon 135 can be fractured by uranium 235, uranium 233 and 239 in the nuclear reactor, accompanying the iodine 135. The iodine 135 rapidly decays, emits a beta particle (high energy electron) and produces xenon 135.

Other main neutron absorbers also include helium 3 isotope, which absorbs neutron (a hetero-homopathy) of (hydrogen); boron 10, which absorbs neutron and can produce lithium and The helium core; 钐 149 is also an effective neutron absorbing agent to absorb neutron after a stable isotope 150.

Other neutron absorbers used in the nuclear reactor include cadmium, hafnium and rare earth metal ruthenium, which contain several isotope, and some are still very efficient neutron absorbers.

The niobium element is one of the stable elements of the final discovery of mankind, showing some interesting situations. Although hafnium is a heavier element, its electronic structure is actually the same as zirconium, and both are always found in the same ore zircon. However, the nature of the two atomic core has a deep difference. Hiurium is easy to absorb neutron, which can be used in the control rod of the atomic reactor, and zirconium is allowed to pass. Thus, zirconium can also be used to make the outer casing of the fuel rod in the atomic reactor. In view of this, zirconium and hafnium separated from natural alloy conditions are very important. This can be achieved with ion exchange technology in modern chemistry and is relatively low. Some new methods such as methyl isobutyl ketone-thiocyanic acid, phosphate tributyl, tritteromethum method, and improved N235-H2SO4 method, solvent extraction separation technology is being studied