$$B\rho $$-defined isochronous mass spectrometry and mass measurements of $$^{58}$$Ni fragments

<jats:title>Abstract</jats:title><jats:p>A novel isochronous mass spectrometry, termed as <jats:inline-formula><jats:alternatives><jats:tex-math>$$B\rho $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>B</mml:mi> <mml:mi>ρ</mml:mi> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula>-defined IMS, has been established at the experimental cooler-storage ring CSRe in Lanzhou. Its potential has been studied through high precision mass measurements of <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{58}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>58</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>Ni projectile fragments. Two time-of-flight detectors were installed in one of the straight sections of CSRe, thus enabling simultaneous measurements of the velocity and the revolution time of each stored short-lived ion. This allows for calculating the magnetic rigidity <jats:inline-formula><jats:alternatives><jats:tex-math>$$B\rho $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>B</mml:mi> <mml:mi>ρ</mml:mi> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> and the orbit length <jats:italic>C</jats:italic> of each ion. The accurate <jats:inline-formula><jats:alternatives><jats:tex-math>$$B\rho (C)$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>B</mml:mi> <mml:mi>ρ</mml:mi> <mml:mo>(</mml:mo> <mml:mi>C</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> function has been constructed, which is a universal calibration curve used to deduce the masses of the stored nuclides. The sensitivity to single stored ions, fast measurement time, and background-free characteristics of the method are ideally suited to address nuclides with very short lifetimes and smallest production yields. In the limiting case of just a single particle, the achieved mass resolving power allows one to determine its mass-over-charge ratio <jats:italic>m</jats:italic>/<jats:italic>q</jats:italic> with a remarkable precision of merely <jats:inline-formula><jats:alternatives><jats:tex-math>$$\sim 5$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>5</mml:mn> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> keV. Masses of <jats:inline-formula><jats:alternatives><jats:tex-math>$$T_z=-3/2$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>z</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>-</mml:mo> <mml:mn>3</mml:mn> <mml:mo>/</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula><jats:italic>fp</jats:italic>-shell nuclides are re-determined with high accuracy, and the validity of the isospin multiplet mass equation is tested up to the heaviest isospin quartet with <jats:inline-formula><jats:alternatives><jats:tex-math>$$A=55$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>A</mml:mi> <mml:mo>=</mml:mo> <mml:mn>55</mml:mn> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula>. The new masses are also used to investigate the mirror symmetry of empirical residual proton-neutron interactions.</jats:p>