Concepts, Problems, & Opportunities for use of Annihilation Energy:

An Annotated Briefing on Near-Term RDT&E to Assess Feasibility

RAND Note N-2302-AF/RC

B. W. Augenstein

TWO BASIC LETHALITY CASES

Case 1 - Ignore pion absorption within annihilating nucleus
- All produced pions escape annihilating nucleus
- Energy deposition occurs in material thickness of tens of cms
Case 2 - Include pion absorption within annihilating nucleus
- Effect increases with atomic number
- For heavy metals (e.g. U) more than ½ annihilation energy absorbed
- Absorption large local energy deposition, great many secondary particles
- Calculations, some experiments exist (including CERN, 1983-84)
Both cases simultaneously present in actual situation
Importance of case 2 warrants consideration of:
- Extended, improved code runs including secondaries
- Special target mockups in pion and beams
- Greatly expanded range of technical, system options

The immediate product of nucleon-antinucleon annihilations isalmost wholly pions. The details of the subsequent reaction trains andthe ultimate forms of the end products, their spectral attributes, thedecay or capture mechanisms, etc., are discussed in our earlierdocumentation.

During the pion lifetimes one can treat the pions in twoalternative ways. One way focuses on the pions which emerge from thenucleus in which annihilation has occurred. These pions are verypenetrating particles which can go through materials many centimetersthick before capture or decay. Focusing on this way is particularlypertinent when one wishes to emphasize, for example, problems of targetshielding against an upper limit of the flux of annihilation products.

Another way focuses on the subsequent history of the annihilationpions within the nucleus where annihilation takes place. The mechanismshere are believed to be relatively well understood, and are referencedin the appended bibliography. Some of the pions are captured withinthat same nucleus; some, while still escaping, are degraded in energy byscattering within that nucleus. These processes excite the nucleus,which then deexcites by particle emission, etc. Two effects arise: aninitial intense local deposition of energy in the regions whereannihilation occurs, and a shorter penetration length for a portion ofthe emerging pions. The effect is to increase the energy deposited percentimeter of travel within the target by the particles. Focusing onthis way is more pertinent when, e.g., one asks for the maximum of theenergy deposition in a particular region of the target

The importance of intranuclear effects has been known for sometime; estimates of the magnitude of the effects occur in some of theearliest comprehensive annihilation phenomenology papers (e.g., Agnew etal. in l960).