Atoll sources are accreting neutron star ( NS ) low-mass X-ray binaries .
We present a spectral analysis of four persistent atoll sources ( GX 3+1 , 4U 1702 - 429 , 4U 0614+091 , and 4U 1746 - 371 ) observed for \sim 20 ks each with NuSTAR to determine the extent of the inner accretion disk .
These sources range from an apparent luminosity of 0.006 - 0.11 of the Eddington limit ( assuming the empirical limit of 3.8 \times 10 ^ { 38 } ergs s ^ { -1 } ) .
Broad Fe emission features shaped by Doppler and relativistic effects close to the NS were firmly detected in three of these sources .
The position of the disk appears to be close to the innermost stable circular orbit ( ISCO ) in each case .
For GX 3+1 , we determine R _ { in } = 1.8 ^ { +0.2 } _ { -0.6 } R _ { \mathrm { ISCO } } ( 90 % confidence level ) and an inclination of 27 ^ { \circ } -31 ^ { \circ } .
For 4U 1702 - 429 , we find a R _ { in } = 1.5 _ { -0.4 } ^ { +1.6 } R _ { \mathrm { ISCO } } and inclination of 53 ^ { \circ } -64 ^ { \circ } .
For 4U 0614+091 , the disk has a position of R _ { in } = 1.3 _ { -0.2 } ^ { +5.4 } R _ { \mathrm { ISCO } } and inclination of 50 ^ { \circ } -62 ^ { \circ } .
If the disk does not extend to the innermost stable circular orbit , we can place conservative limits on the magnetic field strength in these systems in the event that the disk is truncated at the Alfvén radius .
This provides the limit at the poles of B \leq 6.7 \times 10 ^ { 8 } G , 3.3 \times 10 ^ { 8 } G , and 14.5 \times 10 ^ { 8 } G for GX 3+1 , 4U 1702 - 429 , and 4U 0614+091 , respectively .
For 4U 1746 - 371 , we argue that the most plausible explanation for the lack of reflection features is a combination of source geometry and strong Comptonization .
We place these sources among the larger sample of NSs that have been observed with NuSTAR .