Resonance Scattering

Widths and lifetimes as a nuclear observable

Nuclear states are characterised by a number of properties, the most important for nuclear astrophysics being energy, spin and parity and lifetime (width). A great deal of focus has gone into determining energies, and spins and parities but the lifetimes of many nuclear states are unknown. These lifetimes are sensitive probes of the structure of the underlying states. For many of the states in which I'm interested, the main decay path is by particle emission, and so I study the width of the states which is the inverse of the lifetime.

I'm interested in these widths for two main reasons: astrophysics and nuclear structure (but secretly also for astrophysics). To measure them, we use a technique called resonance scattering

Nuclear Astrophysics

Resonance scattering can give access to information on the partial widths of nuclear states, and to information about spins and parities of nuclear systems. Since direct measurement of nuclear cross sections is often experimentally impossible, indirect calculation of the reaction rates is an important alternative method. These resonance scattering reactions can provide important information on the nuclear states which control the reaction rate which we can use to constrain the rate and identify the states which should be targeted in direct measurements.

Nuclear Structure

Resonance scattering can provide a sensitive insight into the underling structure of nuclear states. I am planning on using resonance scattering to try to answer open questions about peculiar structures seen in various nuclei. For example, looking for states which form part of isospin multiplets that have not yet been observed or for which mixing might confound the usual simple quadratic form of the isobaric mass multiplet equation.

Experimental Methods

Texas A&M already has a profitable programme using resonance scattering with the active target TexAT. However, these active targets have limitations relating to the energy resolution which can hide weak states. To overcome this, complementary measurements with high energy resolution can be used to characterise these states.

The main technique I use is resonance scattering with silicon detectors in inverse kinematics at 0 degrees. In this case, the heavy beam hits a hydrogen-containing target (usually a bit of plastic) and slows down. Sometimes we get beam+proton resonance scattering reactions. By using this technique we can get excellent energy resolution (due to being at 0 degrees) and also we can probe a broad range ofcentre-of-mass energies at once. This technique has been used at a number of different facilities around the world but generally rather sparingly and not systematically. I plan to perform a number of measurements of this type at TAMU, and am looking for students who would be interested in working on these measurements.

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