Biomaterial Database

Dose and LET distributions due to neutrons and photons emitted from stopped negative pions. 1977

D J Brenner, and F A Smith

Computer calculations are made of the dose and LET distributions due to neutrons and photons produced when negative pions are stopped in a phantom. When negative pions are stopped in a material they undergo nuclear capture, resulting in the disintegration of the nucleus and the emission of short range charged particles and longer range neutrons and photons. The uncharged radiation constitutes a potentially large source of dose outside the treatment volume. A simple phantom consisting of a 0-25 m cube of either tissue or bone-equivalent material is set up with a 0-05 m cube in the centre to represent the treatment volume. Neutrons and photons are started in this central volume and transported across the phantom using Monte Carlo transport codes. Several different initial energy spectra for the neutrons are used, taken from experimental and theoretical data. These different spectra are found to give significant differences in dose, though the distance to the 80% dose level is always about 0-015 m. Order of magnitude differences in some LET regions are also found. The dose deposited by neutrons in bone is about 24% less than in soft tissue, the photon dose being small compared with the neutron dose.

UI	MeSH Term	Description	Entries
D008961	Models, Structural	A representation, generally small in scale, to show the structure, construction, or appearance of something. (From Random House Unabridged Dictionary, 2d ed)	Model, Structural,Structural Model,Structural Models
D009502	Neutrons	Electrically neutral elementary particles found in all atomic nuclei except light hydrogen; the mass is equal to that of the proton and electron combined and they are unstable when isolated from the nucleus, undergoing beta decay. Slow, thermal, epithermal, and fast neutrons refer to the energy levels with which the neutrons are ejected from heavier nuclei during their decay.	Neutron
D011829	Radiation Dosage	The amount of radiation energy that is deposited in a unit mass of material, such as tissues of plants or animal. In RADIOTHERAPY, radiation dosage is expressed in gray units (Gy). In RADIOLOGIC HEALTH, the dosage is expressed by the product of absorbed dose (Gy) and quality factor (a function of linear energy transfer), and is called radiation dose equivalent in sievert units (Sv).	Sievert Units,Dosage, Radiation,Gray Units,Gy Radiation,Sv Radiation Dose Equivalent,Dosages, Radiation,Radiation Dosages,Units, Gray,Units, Sievert
D004601	Elementary Particles	Individual components of atoms, usually subatomic; subnuclear particles are usually detected only when the atomic nucleus decays and then only transiently, as most of them are unstable, often yielding pure energy without substance, i.e., radiation.	Baryons,Fundamental Particles,Baryon,Elementary Particle,Fundamental Particle,Particle, Elementary,Particle, Fundamental,Particles, Elementary,Particles, Fundamental
D004735	Energy Transfer	The transfer of energy of a given form among different scales of motion. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed). It includes the transfer of kinetic energy and the transfer of chemical energy. The transfer of chemical energy from one molecule to another depends on proximity of molecules so it is often used as in techniques to measure distance such as the use of FORSTER RESONANCE ENERGY TRANSFER.	Transfer, Energy
D012542	Scattering, Radiation	The diversion of RADIATION (thermal, electromagnetic, or nuclear) from its original path as a result of interactions or collisions with atoms, molecules, or larger particles in the atmosphere or other media. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)	Radiation Scattering,Radiation Scatterings,Scatterings, Radiation