Atomic number is essentially a characteristic of an atom and has a value that is unique to each chemical element. Table 948 lists the atomic number of the elements in the periodic table.

Table 948. Atomic number of the elements in the periodic table.

1	2		3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
1																		2
H																		He
3	4												5	6	7	8	9	10
Li	Be												B	C	N	O	F	Ne
11	12												13	14	15	16	17	18
Na	Mg												Al	Si	P	S	Cl	Ar
19	20		21	22	23	24	25	26	27	28	29	30	31	32	33	34	35	36
K	Ca		Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
37	38		39	40	41	42	43	44	45	46	47	48	49	50	51	52	53	54
Rb	Sr		Y	Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe
55	56		71	72	73	74	75	76	77	78	79	80	81	82	83	84	85	86
Cs	Ba	{57-70}	Lu	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
87	88		103	104	105	106	107	108	109	110	111	112		114
Fr	Ra	[89-102]	Lr	Rf	Db	Sg	Bh	Hs	Mt	Ds	Uuu	Uub		Uuq
			57	58	59	60	61	62	63	64	65	66	67	68	69	70
{lanthanides} {57-70}			La	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Th	Yb
			89	90	91	92	93	94	95	96	97	98	99	100	101	102
{actinides} [89-102]			Ac	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No

Many materials are not a single chemical element, but a conglomerate of compounds and mixtures. For a compound, effective atomic number (Z_eff) can be obtained by different methods of calculations. [1]

Case A. EELS measurement

An appropriate model needs to be used for a different purpose, especially for a compound. In EELS analysis, a model based on Lenz model is applied. In this model, the atomic number can be approximated using an effective atomic number Z_eff, [2, 4]
          --------------------------------------- [948a]
where,
          f_i -- the atomic fraction of each element of atomic number Z_i.

Equation 948a can be computed with a DM script. Note that for approximate EELS calculations, an estimate of the 'mean' Z of the region under investigation can often suffice.

Case B. ADF STEM measurement

For ADF STEM, its intensity, I, can be given by,
          --------------------------------------- [948b]
where,
          ε = 1.7, 1.8, 1.9 and 2 (Rutherford)
The effective atomic number Z_eff here is given by the ADF intensity which is proportional to, [6]
          --------------------------------------- [948c]
where,
          f_i -- the atomic fraction of each element of atomic number Z_i.

Case C. Three γ-ray processe

The three γ-ray processes for a single element,, namely photoelectric, Compton and pair production, can be given as a function of photon energy hν and the effective atomic number Z_eff of the elements. [5] The interaction is proportional to Zⁿ where n is different for the three processes. Based on Mayneord formula, this effective atomic number Z_eff can be given by, [3]
         --------------------------------------- [948d]
where,
          a_i -- the fractional contributions of each (i^th) element to the total number of electrons in the mixture.

The exponent, 2.94, in Equation [948d is derived from the relationship between x-ray interactions and atomic number.

Equation 948d can be computed with a DM script.

[1] Z. Kaliman, N. Orlic and I. Jelovica, Calculations of effective atomic number, Nuclear Instruments and Methods in Physics Research A, 580, (2007) 40–42.
[2] Egerton R.F., Electron Energy Loss Spectroscopy in the Electron Microscope (NewYork, Plenum Press, 1986).
[3] F. M. Khan, The Physics of Radiation Therapy (Philadelphia, PA: Lippincott Williams & Wilkins), (2010).
[4] T. Malis, S.C. Cheng, and R.F. Egerton, 'EELS log-ratio technique for specimen thickness measurement in theTEM', J. Electron Microscope Technique, 8 (1988) 193.
[5] R. Murty, Effective Atomic Numbers of Heterogeneous Materials. Nature 207, 398–399 (1965).
[6] T. Walther, Blackwell Publishing Ltd A new experimental procedure to quantify annular dark field images in scanning transmission electron microscopy, Journal of Microscopy, Vol. 221, Pt 2, 137–144 (2006).