Path: utzoo!attcan!uunet!bu.edu!att!cbnews!cbnews!military From: rsiatl!jgd@gatech.edu (John G. DeArmond) Newsgroups: sci.military Subject: Re: The Neutron Bomb Message-ID: <1990Nov6.044813.1867@cbnews.att.com> Date: 6 Nov 90 04:48:13 GMT References: <43034@eerie.acsu.Buffalo.EDU> <1990Oct29.031806.9162@cbnews.att.com> <1990Oct30.052109.6742@cbnews.att.com> <1990Nov2.201046.27205@cbnews.att.com> Sender: military@cbnews.att.com (William B. Thacker) Organization: Radiation Systems, Inc. (a thinktank, motorcycle, car and gun works facility) Lines: 101 Approved: military@att.att.com From: rsiatl!jgd@gatech.edu (John G. DeArmond) >From: seeger@thedon.cis.ufl.edu (F. L. Charles Seeger III) >One of my former Nuclear Eng. profs had worked at LANL and had some exposure >(no pun intended) to weapons design. >It is my distinct recollection that >the use of U-238 casing material is almost exclusively a Soviet practice. >That is why Soviet warheads tend to be bigger and dirtier than American. I likewise have had some "exposure" (understatement) to weapons design. I am at an unfortunate disadvantage in that I cannot repeat even publicly available information in some cases, lest it be inadvertently mixed with other data and lest my quoting public information give it credibility. Let me just say that you should consult the literature. Look particularly closely at literature concerning X-ray mirrors. We do indeed use U-238 but much differently than the Russians. >Every explanation that I have heard indicates that the ER is a fisson bomb >that has been purposely tuned to a low yeild. Most of the thermal/blast >effects are generated in last generation or two of fast neutrons. These >are tuned out to give, say, about 1% yield, but there is still a significant >fast neutron flux from this 'dud' explosion. Let me attack this supposition from several angles. First, tactical. The objective in using an ER weapon is to kill enemy soldiers and/or civilians but leave the infrastructure intact. Neutrons are wholly unsuitable for this task. Not only are fast neutrons poorly absorbed by human tissue, they have a nasty propensity to activate materials they impinge on. It specifically is NOT the objective to make the terrain a vast radioactive wasteland. Residual radiation should be as low a possible. This implies a very clean device whose output is primarily gamma rays, a form of energy ideally suited for killing lifeforms but not producing long term damage. Secondly, the mean free path for fast neutrons is relatively short. Most are dissipated via inelastic scattering with the resultant gamma ray emission. The probability of this interaction occuring varies logrithmically with the neutron energy. There is a very good discussion of this phenomena in "Introduction to Health Physics, Cember" on pages 127,8,9. Thirdly, the main conduit of energy from the device is via soft X-rays. These X-rays are emitted as thermal radiation from the recoil particles of the fission process whose equivalent thermal temperature corrisponds to radiation in the X-ray band. Rather than recite a lot of text, I'll refer you to "The Effects of Nuclear Weapons, Glasstone". >Also, the (limited) discussions that I have heard about ER radiation effects >have centered exclusively on neutron exposure. I grant that there will be >a lot of gamma, but I would like see some rough calculations to back up this >assertion that the prompt gamma doses would predominate. Again, the authority on the subject is "The Effects of Nuclear Weapons". Dr. Glasstone devotes scant space to neutrons as a biological hazard. He does supply the equations from which to calculate gamma yield at a given distance for a given device yield and a given slant angle. There is also a convenient circular slide rule "bomb effects calculator" device included in the back slipcover of the book. >I would not expect >fast neutrons to so heavily activate the casing material so as to make this >a more significant biological threat than all those neutrons themselves. >There will also be significant X radiation (the blast does form an energetic >plasma, after all), but the neutrons (being neutral particles) interacting >with the casing shouldn't generate X radiation with lethality comparable to >that of the neutrons themselves. I don't have any references immediately >available to perform any 'back-of-the-envelope' calculations. Again, not true. The fireball which creats the blast wave is itself formed from the effect of soft x-rays being emitted from the weapon with an intensity sufficient to apply several hundred thousand PSI of pressure to the surrounding air. For small weapons, there are actually 2 flashes. The first is caused by the X-rays impacting the air immediately before it becomes optically opaque. And the second is as the fireball "burns through" the ionization-induced opacity. Largers weapons tend to "burn through" immediately with a resultant single long pulse of light. The spectrum of electromagnetic energy at a relatively large (compared to the weapon's size) distance is a complex mix of gammas resulting from prompt fission and fusion and gammas resulting from neutron capture and x-rays emitted by the weapon constituents and the surrounding air. At greater distances, the x-rays are attenuated and the spectrum is almost solely gamma. And since the probability of a neutron suffering an inelastic scatter with the resultant capture gamma emission rises with target Z, it is desirable to make this target from as heavy a material as possable. Thus the use of tungsten and other heavy metals that either do not appreciably activate or have short half lives. I will readily admit that my experience has been with a tiny slice of the weapons that we've used so I won't completely rule out unconventional designs. However, I will rule out theories that are not supported by physics. John -- John De Armond, WD4OQC | "The truly ignorant in our society are those people Radiation Systems, Inc. | who would throw away the parts of the Constitution Atlanta, Ga | they find inconvenient." -me Defend the 2nd {emory,uunet}!rsiatl!jgd| with the same fervor as you do the 1st.