Seaton, K. A.Batchelor, M. T.2015-10-202015-10-200022-2488http://hdl.handle.net/1885/15980The exact perturbation approach is used to derive the (seven) elementary correlation lengths and related mass gaps of the two-dimensional dilute A₄ lattice model in regime 2⁻ from the Bethe ansatz solution. This model provides a realisation of the integrable ϕ(1,2) perturbation of the c=7/10 conformal field theory, which is known to describe the off-critical thermal behaviour of the tricritical Ising model. The E₇masses predicted from purely elastic scattering theory follow in the approach to criticality. Universal amplitudes for the tricritical Ising model are calculated.http://www.sherpa.ac.uk/romeo/issn/0022-2488..."Publishers version/PDF may be used on author's personal website, institutional website or institutional repository" from SHERPA/RoMEO site (as at 20/10/15). Copyright 2002 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Mathematical Physics and may be found at https://doi.org/10.1063/1.14655152002-0510.1063/1.14655152015-12-12