Title: Title
Author: Philippe CHOMAZ
Last saved by: Murphy
Company: GANIL

^44Ti Abundance as a Probe of Nucleosynthesis in Core Collapse Supernovae

Abstract  
Core collapse supernovae are remarkable astrophysical sites, representing one of the most extreme physics laboratories in Nature. There is immense interest in attempting to elucidate the physics that drives them, and perhaps the single most important diagnostic tool at our disposal is the isotope ^44Ti. Unlike any other observable, it combines the specificity of isotopic (not elemental) abundance, can be observed promptly and directly (by γ-ray observing satellites), and its production can be associated with specific aspects of the core collapse mechanism. The quantative interpretation of these observations urgently requires that several key nuclear reaction rates, such as ^44Ti(α,p), and ^45V(p,γ) be measured.

Keywords 
Core collapse supernovae, nuclear abundances, ^44Ti, satellite gamma-ray observation

Physics case

Despite there being general agreement on the mechanism by which a massive evolves and explodes, some fundamental uncertainty remains; even the best models fail to generate a robust explosion. Gamma-ray emission from the decay of newly synthesised ^44Ti, and ^44Ca excesses in presolar grains, provide a powerful tool for testing the dynamics used in a particular model. However, for this method to be useful, several key nuclear reactions that determine the abundance of ^44Ti urgently need to be determined.
  
Observable
Reaction rate near and within Gamow window
Spins, parities, energies and widths of low energy resonances
 
Proposed experiment
Direct measurement of the ^44Ti(α,p)^47V reaction.  
A previously attempted measurement (PRL 84 (2000) 1651) was unable to explore the astrophysically interesting energy regime. Extrapolation of the result to lower energies suggests the ^44Ti(α,p)^47V reaction rate is significantly higher than previously expected (reducing the amount of ^44Ti synthesised), but too much uncertainty remains to be useful. An experiment with sensitivity at energies corresponding to those in the astrophysical environment is needed.
Indirect measurements of the ^45V(p,γ) reaction: ^45V(p,p) and (for example) ^45V(d,p).
Extremely limited previous data exist (PRL 87 2001 1325) and do not cover the relevant energy region
Shell model and isobaric analogue considerations (PRC 66 (2002) 015801) suggest several relevant states should be suitable for this technique

Requirements:
Beam properties
Low energy (~0.5-2 MeV/u) beams of ^45V and ^44Ti. Beam currents in excess of 10^7 pps will be required. 
Detection
Silicon charged particle arrays, similar to the Louvain-Edinburgh Detector Array.
A CH_2 target for the ^45V(p,p) measurement
A deuterated polyethylene target for the ^45V(d,p) measurement
A gas target for the ^44Ti(α,p) measurement, ~10^18 cm^-2, thin window/windowless
Theoretical support
Hydrodynamical and network calculations to allow interpretation of results.
Shell model calculations to help identify states in ^46Cr.