Recently, precision laser spectroscopy on 6 He atoms determined accurately the isotope shift between 4 He and 6 He and, consequently, the charge radius of 6 He. A similar experiment for 8 He is under way. We have performed large-scale ab initio calculations for 4,6,8 He isotopes using highprecision nucleon-nucleon (NN) interactions within the no-core shell model (NCSM) approach. With the CD-Bonn 2000 NN potential we found point-proton root-mean-square (rms) radii of 4 He and 6 He 1.45(1) fm and 1.89(4), respectively, in agreement with experiment and predict the 8 He point proton rms radius to be 1.88(6) fm. At the same time, our calculations show that the recently developed nonlocal INOY NN potential gives binding energies closer to experiment, but underestimates the charge radii.PACS numbers: 21.60. Cs, 21.30.Fe, 24.10.Cn, 27.20.+n Recent advances in the theory of the atomic structure of helium [1] as well as in the techniques of isotopic shift measurement made it possible to determine accurately the charge radius of 6 He [2]. Precision laser spectroscopy on individual 6 He atoms confined and cooled in a magneto-optical trap was performed and measured the isotope shift between 6 He and 4 He. With the help of precise quantum mechanical calculations with relativistic and QED corrections [3] and from the knowledge of the charge radius of 4 He (1.673(1) [4]), it was possible to determine the charge radius of 6 He to be 2.054 ± 0.014 fm [2]. The large difference between the 4 He and 6 He charge radii is due to the extra two loosely bound neutrons in 6 He that form a halo [5]. A similar experiment to determine the charge radius of 8 He is under way [6].It is a challenge for ab initio many-body methods to calculate the nuclear radii with an accuracy comparable to current experimental accuracy and test in this way the nuclear Hamiltonians used as the input of ab initio calculations. At present, there are two ab initio approaches capable of describing simultaneously the 4 He, 6 He and 8 He isotopes starting from realistic inter-nucleon interactions. One is the Green's function Monte Carlo (GFMC) method [7] and the other is the ab initio no-core shell model (NCSM) [8]. In this paper, we calculate the ground-state properties of 4 He, 6 He and 8 He within the NCSM. We test two vastly different accurate nucleonnucleon (NN) potentials, the CD-Bonn [9] and the the INOY (Inside Nonlocal Outside Yukawa) [10,11].In the NCSM, we consider a system of A point-like non-relativistic nucleons that interact by realistic two-or two-plus three-nucleon interactions. The calculations are * etienne.caurier@ires.in2p3.fr † navratil1@llnl.gov performed using a finite harmonic oscillator (HO) basis. As in the present application we aim at describing loosely bound states, it is desirable to include as many terms as possible in the expansion of the total wave function. By restricting our study to two-nucleon (NN) interactions, even though the NCSM allows for the inclusion of threebody forces [12], we are able to maximize the model space and t...