We analyzed archival X-ray spectra of MXB 1728-34 obtained in 1996-99 by the Proportional Counter Array on board of the RXTE satellite .
X-ray spectra were fitted to our extensive grids of model atmosphere spectra to determine the effective temperature T _ { eff } on the neutron star surface , logarithm of surface gravity \log { g } , and the gravitational redshift z simultaneously .
We have chosen fitting by numerical model spectra plus broad Gaussian line , modified by interstellar absorption and the absorption on dust .
We arbitrarily assumed either hydrogen-helium chemical composition of a model atmosphere , or H-He-Fe mixture in solar proportion .
The statistically best values of \log { g } , and z subsequently were used to determine mass and radius of the neutron star .
We obtained the best values of the parameters for the neutron star in X-ray burst source MXB 1728-34 : mass either M = 0.40 or 0.63 M _ { \odot } ( for H-He or H-He-Fe models , respectively ) , radius R = 4.6 or 5.3 km , \log g = 14.6 or 14.6 and the gravitational redshift z = 0.14 or 0.22 .
All the above parameters have very wide 1- \sigma confidence limits .
Their values strongly support the equation of state for strange matter in MXB 1728-34 .

Key words Stars : fundamental parameters – stars : neutron – X-rays : bursts – stars : individual ( MXB 1728-34 )