x units and angstrom star as constants

Like most "measured constants", they're not measured directly, but derived from other measures. However, the list of CODATA values includes these (and their uncertainties and correlations), so it's better to treat them as other constants.
hgrecco · Aug 22, 2024 · 736ee66 · 736ee66
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diff --git a/pint/constants_en.txt b/pint/constants_en.txt
@@ -50,8 +50,6 @@ wien_frequency_displacement_law_constant = wien_u * k / ℎ
 # To some extent, what is measured and what is derived is a bit arbitrary.
 # The choice of measured constants is based on convenience and on available uncertainty.
 # The uncertainty in the last significant digits is given in parentheses as a comment.
-# The K_alpha values are either backtransformed from the corresponding x unit or
-# from the CODATA-2018 publication (doi:10.1103/RevModPhys.93.025010)
 
 newtonian_constant_of_gravitation = 6.67430e-11 m^3/(kg s^2) = _ = gravitational_constant  # (15)
 rydberg_constant = 1.0973731568157e7 * m^-1 = R_∞ = R_inf                                  # (12)
@@ -60,10 +58,9 @@ atomic_mass_constant = 1.66053906892e-27 kg = m_u
 electron_mass = 9.1093837139e-31 kg = m_e = atomic_unit_of_mass = a_u_mass                 # (28)
 proton_mass = 1.67262192595e-27 kg = m_p                                                   # (52)
 neutron_mass = 1.67492750056e-27 kg = m_n                                                  # (85)
-lattice_spacing_of_Si = 1.920155716e-10 m = d_220                                          # (32)
-K_alpha_Cu_d_220 = 0.80232719                                                              # (24)
-K_alpha_Mo_d_220 = 0.36940604                                                              # (19)
-K_alpha_W_d_220 = 0.108852175                                                              # (98)
+x_unit_Cu = 1.00207697e-13 m = Xu_Cu                                                       # (28)
+x_unit_Mo = 1.00209952e-13 m = Xu_Mo                                                       # (53)
+angstrom_star = 1.00001495e-10 = Å_star                                                    # (90)
 
 #### DERIVED CONSTANTS ####
 

diff --git a/pint/default_en.txt b/pint/default_en.txt
@@ -162,9 +162,6 @@ astronomical_unit = 149597870700 * meter = au  # since Aug 2012
 parsec = 1 / tansec * astronomical_unit = pc
 nautical_mile = 1852 * meter = nmi
 bohr = hbar / (alpha * m_e * c) = a_0 = a0 = bohr_radius = atomic_unit_of_length = a_u_length
-x_unit_Cu = K_alpha_Cu_d_220 * d_220 / 1537.4 = Xu_Cu
-x_unit_Mo = K_alpha_Mo_d_220 * d_220 / 707.831 = Xu_Mo
-angstrom_star = K_alpha_W_d_220 * d_220 / 0.20901 = Å_star
 planck_length = (hbar * gravitational_constant / c ** 3) ** 0.5
 
 # Mass

diff --git a/pint/pint_convert.py b/pint/pint_convert.py
@@ -91,28 +91,47 @@ def _set(key: str, value):
     #  m_e: Electron mass
     #  m_p: Proton mass
     #  m_n: Neutron mass
+    #  x_Cu: Copper x unit
+    #  x_Mo: Molybdenum x unit
+    #  A_s: Angstrom star
     R_i = (ureg._units["R_inf"].converter.scale, 0.0000000000012e7)
     g_e = (ureg._units["g_e"].converter.scale, 0.00000000000036)
     m_u = (ureg._units["m_u"].converter.scale, 0.00000000052e-27)
-    m_e = (ureg._units["m_e"].converter.scale, 0.00000000028e-30)
+    m_e = (ureg._units["m_e"].converter.scale, 0.0000000028e-31)
     m_p = (ureg._units["m_p"].converter.scale, 0.00000000052e-27)
     m_n = (ureg._units["m_n"].converter.scale, 0.00000000085e-27)
+    x_Cu = (ureg._units["x_unit_Cu"].converter.scale, 0.00000028e-13)
+    x_Mo = (ureg._units["x_unit_Mo"].converter.scale, 0.00000053e-13)
+    A_s = (ureg._units["angstrom_star"].converter.scale, 0.00000090e-10)
     if args.corr:
         # fmt: off
         # Correlation matrix between measured constants (to be completed below)
-        #         R_i       g_e      m_u      m_e      m_p      m_n
+        #         R_i       g_e      m_u      m_e      m_p      m_n     x_Cu     x_Mo      A_s
         corr = [
-            [ 1.00000, -0.00122, 0.00438, 0.00225, 0.00455, 0.00277],  # R_i
-            [-0.00122,  1.00000, 0.97398, 0.97555, 0.97404, 0.59702],  # g_e
-            [ 0.00438,  0.97398, 1.00000, 0.99839, 0.99965, 0.61279],  # m_u
-            [ 0.00225,  0.97555, 0.99839, 1.00000, 0.99845, 0.61199],  # m_e
-            [ 0.00455,  0.97404, 0.99965, 0.99845, 1.00000, 0.61281],  # m_p
-            [ 0.00277,  0.59702, 0.61279, 0.61199, 0.61281, 1.00000],  # m_n
+            [ 1.00000, -0.00122, 0.00438, 0.00225, 0.00455, 0.00277, 0.00000, 0.00000, 0.00000],  # R_i
+            [-0.00122,  1.00000, 0.97398, 0.97555, 0.97404, 0.59702, 0.00000, 0.00000, 0.00000],  # g_e
+            [ 0.00438,  0.97398, 1.00000, 0.99839, 0.99965, 0.61279, 0.00000, 0.00000, 0.00000],  # m_u
+            [ 0.00225,  0.97555, 0.99839, 1.00000, 0.99845, 0.61199, 0.00000, 0.00000, 0.00000],  # m_e
+            [ 0.00455,  0.97404, 0.99965, 0.99845, 1.00000, 0.61281, 0.00000, 0.00000, 0.00000],  # m_p
+            [ 0.00277,  0.59702, 0.61279, 0.61199, 0.61281, 1.00000,-0.00098,-0.00108,-0.00063],  # m_n
+            [ 0.00000,  0.00000, 0.00000, 0.00000, 0.00000,-0.00098, 1.00000, 0.00067, 0.00039],  # x_Cu
+            [ 0.00000,  0.00000, 0.00000, 0.00000, 0.00000,-0.00108, 0.00067, 1.00000, 0.00100],  # x_Mo
+            [ 0.00000,  0.00000, 0.00000, 0.00000, 0.00000,-0.00063, 0.00039, 0.00100, 1.00000],  # A_s
         ]
         # fmt: on
         try:
-            (R_i, g_e, m_u, m_e, m_p, m_n) = uncertainties.correlated_values_norm(
-                [R_i, g_e, m_u, m_e, m_p, m_n], corr
+            (
+                R_i,
+                g_e,
+                m_u,
+                m_e,
+                m_p,
+                m_n,
+                x_Cu,
+                x_Mo,
+                A_s,
+            ) = uncertainties.correlated_values_norm(
+                [R_i, g_e, m_u, m_e, m_p, m_n, x_Cu, x_Mo, A_s], corr
             )
         except AttributeError:
             raise Exception(
@@ -125,13 +144,19 @@ def _set(key: str, value):
         m_e = uncertainties.ufloat(*m_e)
         m_p = uncertainties.ufloat(*m_p)
         m_n = uncertainties.ufloat(*m_n)
+        x_Cu = uncertainties.ufloat(*x_Cu)
+        x_Mo = uncertainties.ufloat(*x_Mo)
+        A_s = uncertainties.ufloat(*A_s)
 
     _set("R_inf", R_i)
     _set("g_e", g_e)
     _set("m_u", m_u)
     _set("m_e", m_e)
     _set("m_p", m_p)
     _set("m_n", m_n)
+    _set("x_unit_Cu", x_Cu)
+    _set("x_unit_Mo", x_Mo)
+    _set("angstrom_star", A_s)
 
     # Measured constants with zero correlation
     _set(
@@ -141,32 +166,6 @@ def _set(key: str, value):
         ),
     )
 
-    _set(
-        "d_220",
-        uncertainties.ufloat(ureg._units["d_220"].converter.scale, 0.000000032e-10),
-    )
-
-    _set(
-        "K_alpha_Cu_d_220",
-        uncertainties.ufloat(
-            ureg._units["K_alpha_Cu_d_220"].converter.scale, 0.00000024
-        ),
-    )
-
-    _set(
-        "K_alpha_Mo_d_220",
-        uncertainties.ufloat(
-            ureg._units["K_alpha_Mo_d_220"].converter.scale, 0.00000019
-        ),
-    )
-
-    _set(
-        "K_alpha_W_d_220",
-        uncertainties.ufloat(
-            ureg._units["K_alpha_W_d_220"].converter.scale, 0.000000098
-        ),
-    )
-
     ureg._root_units_cache = {}
     ureg._build_cache()