CN102127255A - Neutron-shielding 8%-boron-content polyethylene board and production technique thereof - Google Patents

Abstract

The invention relates to a neutron-shielding 8%-boron-content polyethylene board and a production technique thereof, belonging to the field of application of nuclear technology in ionizing radiation shielding. The invention aims to solve the following technical problems: (1) how to design an 8%-boron-content polyethylene board; and (2) how to enable the hot melt temperatures of boric acid and polyethylene to be identical in the technique so as not to form metaboric acid and pyroboric acid, so that the boric acid and polyethylene can be uniformly mixed, heated, extruded and rolled to form in an easier way. The technical scheme is as follows: calculating that the percentage of boron is 17.48% according to the chemical molecular formula of boric acid H3BO3 and the atomic weight, and calculating that 46% by weight of boric acid is added into every one hundred kilo of boron-containing polyethylene, thereby designing the 8%-boron-content polyethylene board. An agent A, which can increase the processing temperature of boric acid to 120 DEG C while the boric acid is not decomposed, and an agent B, which can simultaneously lower the melting point of high-density polyethylene to 120 DEG C, are developed, thereby solving the problem of coking of boric acid. The invention is used for neutron radiation shielding in nuclear power stations, medium (high) energy accelerators, atomic reactors, nuclear submarines, medical accelerators, neutron therapeutic equipment and the like.

Description

Anti-neutron 8% boracic polyethylene board and production technique

Affiliated technical field:

The present invention relates to a kind of boron-containing quantity and be 8% boracic polyethylene board, thickness is 2cm-30cm.Affiliated technical field is the Application of Nuclear Technology ionization radiation protection.This kind 8% boracic polyethylene board is used for the fast neutron of shielding neutron radiation field, ionization radiation protection field, neutron and γ mixed radiation field, prevents that neutron radiation from producing radiation hazradial bundle and damage to the Job personnel and the public.

Background technology:

At present, when neutron is carried out shielding protection, generally use 5% to contain boron polyethylene both at home and abroad, it is many based on import that China contains boron polyethylene, for raising contains the shield effectiveness of boron polyethylene to fast neutron, solve domestic boracic polyethylene board and be difficult to commercial scale production problem, developed boron-containing quantity and be 8% boracic polyethylene board.With regard to shielding fast neutron principle, because middle proton rest mass is 1.0086649u, and the rest mass of hydrogen atom (being proton) is 1.007825u ^[1], the atomic mass of neutron is close with the atomic mass of hydrogen atom, therefore, when in fast neutron and the shielding during hydrogen nuclei generation elastic collision, gives hydrogen nuclei and expended energy with its transmission ofenergy the easiliest, thereby is thermal neutron and thermal neutron with the fast neutron slowing down.Hydrogen content is many more in the shielding, and then the slowing down effect is strong more, and in the hydrogen content of neutron shielding material relatively more commonly used, the polyethylene hydrogen content is the highest, can reach 7.92 * 10 ²²Atom/cm ^3[2]So polyethylene is the best moderator of shielding fast neutron.After fast neutron is thermal neutron by slowing down, need use thermal neutron absorption cross section is produced high energy gamma radiating shielding material absorption thermal neutron greatly and not, just can reach the purpose that shields fast neutron fully.Because ¹⁰B has higher thermal neutron absorption cross section, is (3840 ± 11) * 10 ^-24Cm ^2[3], and in the natural boron ¹⁰The abundance of B is 18.98% ^[3], be easy to obtain, so containing boron material is the good absorption agent of shielding thermal neutron.

Summary of the invention:

Contain the shielding protection effect of boron polyethylene in order to improve to fast neutron; in conjunction with polyethylene the slowing down mechanism and the boron of fast neutron have been developed 8% boracic polyethylene board to the high absorption characteristic of thermal neutron; and innovation the production and processing technology of this kind boracic polyethylene board, solved the large-scale production problem of domestic boracic polyethylene board.

Description of drawings:

Attached 4 accompanying drawings in the present patent application book, Fig. 1: 8% boracic polyethylene board; Fig. 2: 8% boracic polyethylene board is right ²⁴¹The shielding properties of Am-Be neutron source neutron; Fig. 3: 8% to contain boron polyethylene right ²⁵²The shielding properties of Cf neutron source neutron; Fig. 4: 8% boracic polyethylene board is right ²⁴¹Am-Be and ²⁵²The shielding efficiency of Cf source neutron.

Fig. 1 is in order to show 8% boracic polyethylene board material object, and Fig. 2 and Fig. 3 are in order to explanation ²⁴¹Am-Be and ²⁵²Cf neutron source neutron is with the attenuation law of different boracic polyethylene board thickness; Fig. 4 is in order to illustrate this 8% boracic polyethylene board shielding ²⁴¹Am-Be and ²⁵²The shielding efficiency and the protection effect of Cf neutron source neutron.

Embodiment:

The present invention passes through technical know-how design phase, process study stage and solves key technical problem to implement, and has finally reached design requirements.The present invention solves the technical scheme that its technical problem takes:

The design that the characteristic that absorbs thermal neutron according to polyethylene slowing down fast neutron and boron has proposed to develop 8% boracic polyethylene board is as follows:

Key points in design: planned boron content is 8% boracic polyethylene board, ask should add how much boric acid in this boracic polyethylene board and just can meet design requirement?

Separate: the chemical molecular formula of known boric acid is: H ₃BO ₃, nucleidic mass is: 61.83, calculate the shared ratio of boron (B).

Known: H ₃BO ₃Various composition nucleidic mass sums are:

1.0079(H)×3+10.81(B)+15.9994(O)×3＝61.8

Then trying to achieve the ratio that boron (B) accounts for is: (10.81 ÷ 61.8) * 100=17.48%

What kilogram boric acid if this boracic polyethylene board material by 100 kilograms of calculating, is obtained and should be added and just can be mixed with 8% boracic polyethylene board? need add boric acid weight is calculated as follows:

Be mixed with 8% boracic polyethylene board if should add X kilogram boric acid material in 100 kilograms of boracic polythene materials, then need add boric acid weight and be calculated as follows:

$\frac{0.1748\mathrm{<figure-callout\; id="100"\; label="X"\; filenames="HSA00000337798000012.png,HSA00000337798000021.png"\; state="\{\{state\}\}">X</figure-callout>}}{100}=0.08$

X=0.08 * 100 ÷ 0.1748=45.77 kilograms

The weight percent that calculates materials such as 8% boracic polyethylene board mesoboric acid and polyethylene is:

(45.77÷100)×100＝45.77％

Conclusion: the actual production mesoboric acid is 46% proportioning by weight percentage, promptly produces 8% boracic polyethylene board.

Production technique is described below:

1,8% contains in the boron polyethylene, according to the boric acid weight percent is 46%, the high density polyethylene(HDPE) weight percent is 50%, the carbon black weight percent is 2%, and each 2% is mixed with mixed powder to add A properties-correcting agent and B melting agent, put into the high speed kneader and mix, pump to the twin screw planetary extruder with automatic feeding system;

2, the extruder barrel temperature is controlled at 110-115 ℃, barrel temperature is controlled at 120 ℃, be extruded into the boracic polyethylene micelle of strip in 2 minutes by the planetary extruder plasticizing, micelle is put into the sheet sheet material that five roll calendars are rolled into 0.5-0.8mm thickness, 800mm width, it is standby to be cut into 1500mm length more again;

3, according to the requirement of shelter of actual radiation protected working place shielding neutron, the sheet sheet material that calendering is good overlaps by several layers, puts into pressure and is 2500 tons elevated temperature heat press die cavity and suppress.Sheet material begins preheating after putting into elevated temperature heat press die cavity, warm-up time is 25 minutes, and temperature progressively heats up from 80-120 ℃, and vapor pressure is controlled at 0.35-0.5Mpa; Began to cool down after heating 25 minutes and pressurize, mechanical pressure is controlled at 7-8Mpa; Cooled off 45 minutes, temperature begins release and depanning when reducing to 54-55 ℃, and the sheet material after the depanning is through fully sawing limit and check warehouse-in after the cooling.But this production technique manufacturing specification is 8% a boracic polyethylene board of 1500mm * 800mm specification different thickness.

The technical problem that emphasis solves:

Usually making in the technology of boracic polyethylene board, boric acid can lose a water molecules when heating to 105 ℃ and form metaboric acid, and long-time heating changes pyroboric acid in the time of 104-160 ℃, and higher temperature will form anhydride.Metaboric acid and pyroboric acid that boric acid heating back is decomposed to form all can reduce protection effect greatly.The high density polyethylene(HDPE) melting temperature is 130 ℃.Boric acid and high density polyethylene(HDPE) can fully be merged and do not reduce protection effect.For solving this difficult problem, through research experiment repeatedly, development can make the boric acid processing temperature be increased to 120 ℃ and the A melting agent that do not decompose in short-term, can simultaneously the fusing point of high density polyethylene(HDPE) be reduced to 120 ℃ B melting agent again.Contain in the boron polyethylene add A melting agent and B melting agent after, make the boracic polyethylene board be easy to curing molding in the production process.

The beneficial effect of patent of the present invention is:

By experiment research, checked this 8% boracic polyethylene board to americium-beryllium ( ²⁴¹Am-Be) standard neutron source and californium-252 ( ²⁵²Cf) the protective shielding efficient of two kinds of energy neutrons of standard neutron source.Assay shows that this 8% boracic polyethylene board is 4.5MeV's to average energy ²⁴¹Am-Be source fast neutron and 2.35MeV's ²⁵²Cf source fast neutron shielding efficiency is remarkable, and barrier propterty is good.This 8% boracic polyethylene board is right ²⁴¹Am-Be and ²⁵²The fast neutron shielding efficiency of Cf neutron source is listed in the table 1:

Table 18% boracic polyethylene board is to the shield effectiveness of fast neutron

During sub-in practice shielding protection is used; can be according to the size of neutron radiation amount and the shielding efficiency of plan shielding neutron, by choosing 8% corresponding boracic polyethylene board thickness among Fig. 1; can effectively shield neutron, reach the protection purpose of protection staff's health and safety.

This 8% boracic polyethylene board in kind and to americium-beryllium ( ²⁴¹Am-Be) standard neutron source and californium-252 ( ²⁵²Cf) the protective shielding performance study result of two kinds of energy neutrons of standard neutron source is illustrated in Figure of description.

This 8% boracic polyethylene board is applicable to the neutron shield protection in neutron radiation field and neutron, the gamma-rays mixed radiation field, for example, the neutron shielding that is used for working spaces such as Nuclear power plants, (height) energy accelerator, reactor, nuclear-propelled submarine, medical accelerator, neutron therapy equipment.

Reference

[1] Lu Xiting master. Nuclear Physics. Beijing: Atomic Energy Press's distribution, 2000:295.

[2] Zhang Danfeng, Zhao Lancai. radiation protection technique and management. Nanning: Guangxi Nationalities Press, 2003:85.

[3] draw long pine work. the neutron detector experimental technique. Beijing: Atomic Energy Press, 1998:64.

[4] Chang Wenbao, Li Kean. simple and clear chemical analysis handbook. Beijing: BJ University Press, 1981:15.

Claims (1)

1. According to polythene material to the strong absorption characteristic that the slowing down effect and the boron atom pairs thermal neutron of fast neutron has, developed the anti-neutron boracic polyethylene board of 8% boron content.This 8% boracic polyethylene board is that the weight percent according to boric acid is 46%, all the other for polyethylene and a small amount of hard calcium solidify material through stirring and evenly mixing, gel, prolong processes such as pressures, overlapping hot pressing, cutting and form, this anti-neutron boracic polyethylene board has that intensity height, density are even, the characteristics of acid-alkali-corrosive-resisting, neutron shield superior performance.

   Its technical characteristic is:

   1, boron-containing quantity reaches 8%, is significantly higher than the poly boron-containing quantity of common 5% boracic.

   2, the protection americium-beryllium ( ²⁴¹Am-Be) neutron source (neutron average energy 5MeV) and californium-252 ( ²⁵²Cf) the shielding efficiency height of neutron source (neutron average energy 2.158MeV) fast neutron.In thickness is 2cm～30cm, shielding ²⁴¹The shielding efficiency of Am-Be neutron source fast neutron shields neutron source between 32.6%～99.2% ²⁵²The shielding efficiency of Cf neutron source fast neutron is between 33.8%～99.3%.This 8% boracic polyethylene board is listed in the table 1 with the variation relation of thickness the shielding efficiency of fast neutron.

   The scope of asking for protection:

   1. boron-containing quantity is 8% boracic polyethylene board, and thickness is that 1cm is to 30cm.

   2. production and processing technology.

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