diff --git a/numass-main/src/main/java/inr/numass/actions/ShowLossSpectrumAction.java b/numass-main/src/main/java/inr/numass/actions/ShowLossSpectrumAction.java
index 25f69541..9d9c3e57 100644
--- a/numass-main/src/main/java/inr/numass/actions/ShowLossSpectrumAction.java
+++ b/numass-main/src/main/java/inr/numass/actions/ShowLossSpectrumAction.java
@@ -40,9 +40,9 @@ import hep.dataforge.tables.MapPoint;
 import hep.dataforge.tables.Table;
 import hep.dataforge.tables.XYAdapter;
 import hep.dataforge.values.NamedValueSet;
-import inr.numass.NumassIntegrator;
 import inr.numass.models.ExperimentalVariableLossSpectrum;
 import inr.numass.models.LossCalculator;
+import inr.numass.utils.NumassIntegrator;
 import org.apache.commons.math3.analysis.UnivariateFunction;
 import org.apache.commons.math3.analysis.interpolation.LinearInterpolator;
 import org.apache.commons.math3.analysis.interpolation.UnivariateInterpolator;
diff --git a/numass-main/src/main/java/inr/numass/models/CustomNBkgSpectrum.java b/numass-main/src/main/java/inr/numass/models/CustomNBkgSpectrum.java
index 5a09050f..24ea4e92 100644
--- a/numass-main/src/main/java/inr/numass/models/CustomNBkgSpectrum.java
+++ b/numass-main/src/main/java/inr/numass/models/CustomNBkgSpectrum.java
@@ -7,8 +7,7 @@ package inr.numass.models;
 
 import hep.dataforge.stat.parametric.ParametricFunction;
 import hep.dataforge.values.NamedValueSet;
-import inr.numass.NumassIntegrator;
-import inr.numass.Numass;
+import inr.numass.utils.NumassIntegrator;
 import inr.numass.utils.TritiumUtils;
 import org.apache.commons.math3.analysis.UnivariateFunction;
 
diff --git a/numass-main/src/main/java/inr/numass/models/GunSpectrum.java b/numass-main/src/main/java/inr/numass/models/GunSpectrum.java
index d0767af3..0c3aed61 100644
--- a/numass-main/src/main/java/inr/numass/models/GunSpectrum.java
+++ b/numass-main/src/main/java/inr/numass/models/GunSpectrum.java
@@ -16,15 +16,13 @@
 package inr.numass.models;
 
 import hep.dataforge.exceptions.NotDefinedException;
-import hep.dataforge.stat.parametric.AbstractParametricFunction;
 import hep.dataforge.maths.integration.UnivariateIntegrator;
+import hep.dataforge.stat.parametric.AbstractParametricFunction;
 import hep.dataforge.values.NamedValueSet;
-import inr.numass.NumassIntegrator;
-import static java.lang.Math.exp;
-import static java.lang.Math.sqrt;
+import inr.numass.utils.NumassIntegrator;
 import org.apache.commons.math3.analysis.UnivariateFunction;
-import static java.lang.Math.abs;
-import static java.lang.Math.abs;
+
+import static java.lang.Math.*;
 
 /**
  *
diff --git a/numass-main/src/main/java/inr/numass/models/LossResConvolution.java b/numass-main/src/main/java/inr/numass/models/LossResConvolution.java
index 59ce44b0..e5b88f54 100644
--- a/numass-main/src/main/java/inr/numass/models/LossResConvolution.java
+++ b/numass-main/src/main/java/inr/numass/models/LossResConvolution.java
@@ -15,7 +15,7 @@
  */
 package inr.numass.models;
 
-import inr.numass.NumassIntegrator;
+import inr.numass.utils.NumassIntegrator;
 import org.apache.commons.math3.analysis.BivariateFunction;
 import org.apache.commons.math3.analysis.UnivariateFunction;
 
diff --git a/numass-main/src/main/java/inr/numass/models/TransmissionConvolution.java b/numass-main/src/main/java/inr/numass/models/TransmissionConvolution.java
index 00abd9d9..7e9961a0 100644
--- a/numass-main/src/main/java/inr/numass/models/TransmissionConvolution.java
+++ b/numass-main/src/main/java/inr/numass/models/TransmissionConvolution.java
@@ -18,8 +18,7 @@ package inr.numass.models;
 import hep.dataforge.stat.parametric.AbstractParametricFunction;
 import hep.dataforge.stat.parametric.ParametricFunction;
 import hep.dataforge.values.NamedValueSet;
-import inr.numass.NumassIntegrator;
-import inr.numass.Numass;
+import inr.numass.utils.NumassIntegrator;
 import org.apache.commons.math3.analysis.BivariateFunction;
 import org.apache.commons.math3.analysis.UnivariateFunction;
 
diff --git a/numass-main/src/main/java/inr/numass/models/VariableLossSpectrum.java b/numass-main/src/main/java/inr/numass/models/VariableLossSpectrum.java
index 888cb7ac..98fed436 100644
--- a/numass-main/src/main/java/inr/numass/models/VariableLossSpectrum.java
+++ b/numass-main/src/main/java/inr/numass/models/VariableLossSpectrum.java
@@ -16,17 +16,17 @@
 package inr.numass.models;
 
 import hep.dataforge.exceptions.NotDefinedException;
+import hep.dataforge.maths.integration.UnivariateIntegrator;
 import hep.dataforge.stat.parametric.AbstractParametricFunction;
 import hep.dataforge.stat.parametric.ParametricFunction;
-import hep.dataforge.maths.integration.UnivariateIntegrator;
 import hep.dataforge.values.NamedValueSet;
 import hep.dataforge.values.ValueProvider;
-import inr.numass.NumassIntegrator;
-import inr.numass.Numass;
-import java.util.List;
+import inr.numass.utils.NumassIntegrator;
 import org.apache.commons.math3.analysis.BivariateFunction;
 import org.apache.commons.math3.analysis.UnivariateFunction;
 
+import java.util.List;
+
 /**
  *
  * @author Darksnake
diff --git a/numass-main/src/main/java/inr/numass/models/sterile/SterileNeutrinoSpectrum.java b/numass-main/src/main/java/inr/numass/models/sterile/SterileNeutrinoSpectrum.java
index 811316e4..1861c12a 100644
--- a/numass-main/src/main/java/inr/numass/models/sterile/SterileNeutrinoSpectrum.java
+++ b/numass-main/src/main/java/inr/numass/models/sterile/SterileNeutrinoSpectrum.java
@@ -16,8 +16,8 @@ import hep.dataforge.stat.parametric.AbstractParametricBiFunction;
 import hep.dataforge.stat.parametric.AbstractParametricFunction;
 import hep.dataforge.stat.parametric.ParametricBiFunction;
 import hep.dataforge.values.NamedValueSet;
-import inr.numass.NumassIntegrator;
 import inr.numass.models.FSS;
+import inr.numass.utils.NumassIntegrator;
 import org.apache.commons.math3.analysis.UnivariateFunction;
 
 import java.io.FileInputStream;
@@ -148,10 +148,17 @@ public class SterileNeutrinoSpectrum extends AbstractParametricFunction {
         }
 
         UnivariateIntegrator integrator;
-        if (fast && eMax - u < 500) {
-            integrator = NumassIntegrator.getFastInterator();
-        } else {
-            integrator = NumassIntegrator.getDefaultIntegrator();
+        if(fast){
+            if (eMax - u < 300) {
+                integrator = NumassIntegrator.getFastInterator();
+            } else if(eMax - u > 2000){
+                integrator = NumassIntegrator.getHighDensityIntegrator();
+            } else {
+                integrator = NumassIntegrator.getDefaultIntegrator();
+            }
+
+            } else {
+            integrator = NumassIntegrator.getHighDensityIntegrator();
         }
 
         return integrator.integrate(eIn -> fsSource.value(eIn) * transResFunction.value(eIn, u, set), u, eMax);
@@ -196,9 +203,9 @@ public class SterileNeutrinoSpectrum extends AbstractParametricFunction {
             double secondPart;
             if (eIn > border) {
                 if (fast) {
-                    secondPart = NumassIntegrator.getFastInterator().integrate(integrand, border, eIn);
-                } else {
                     secondPart = NumassIntegrator.getDefaultIntegrator().integrate(integrand, border, eIn);
+                } else {
+                    secondPart = NumassIntegrator.getHighDensityIntegrator().integrate(integrand, border, eIn);
                 }
             } else {
                 secondPart = 0;
diff --git a/numass-main/src/main/java/inr/numass/NumassIntegrator.java b/numass-main/src/main/java/inr/numass/utils/NumassIntegrator.java
similarity index 75%
rename from numass-main/src/main/java/inr/numass/NumassIntegrator.java
rename to numass-main/src/main/java/inr/numass/utils/NumassIntegrator.java
index f14f1da0..b4029714 100644
--- a/numass-main/src/main/java/inr/numass/NumassIntegrator.java
+++ b/numass-main/src/main/java/inr/numass/utils/NumassIntegrator.java
@@ -3,7 +3,7 @@
  * To change this template file, choose Tools | Templates
  * and open the template in the editor.
  */
-package inr.numass;
+package inr.numass.utils;
 
 import hep.dataforge.maths.integration.GaussRuleIntegrator;
 import hep.dataforge.maths.integration.UnivariateIntegrator;
@@ -14,27 +14,29 @@ import hep.dataforge.maths.integration.UnivariateIntegrator;
  */
 public class NumassIntegrator {
 
+    private static double mult = 1.0;
+
     private static UnivariateIntegrator fastInterator;
     private static UnivariateIntegrator defaultIntegrator;
     private static UnivariateIntegrator highDensityIntegrator;
 
     public static UnivariateIntegrator getFastInterator() {
         if (fastInterator == null) {
-            fastInterator = new GaussRuleIntegrator(100);
+            fastInterator = new GaussRuleIntegrator((int) (mult*100));
         }
         return fastInterator;
     }
 
     public static UnivariateIntegrator getDefaultIntegrator() {
         if (defaultIntegrator == null) {
-            defaultIntegrator = new GaussRuleIntegrator(300);
+            defaultIntegrator = new GaussRuleIntegrator((int) (mult*300));
         }
         return defaultIntegrator;
     }
 
     public static UnivariateIntegrator getHighDensityIntegrator() {
         if (highDensityIntegrator == null) {
-            highDensityIntegrator = new GaussRuleIntegrator(500);
+            highDensityIntegrator = new GaussRuleIntegrator((int) (mult*500));
         }
         return highDensityIntegrator;
     }