27118
X - ray fluorescence intensities from Ni K alpha core levels recorded at the incidence angles below and above the critical angle of total reflection allow for the determination of the position and lateral density of Ni ( 2 ) ( + ) ions associated with chelator headgroups with a high spatial accuracy ( +/- 5 A ) .
 Chemical: Ni; Chemical: Ni ( 2 ) ( + )
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: Ni; Chemical: Ni ( 2 ) ( + )