docs: def calculate_transmission(thickness_cm: np.float, atoms_per_cm3: np.float, sigma_b: np.array):
      """calculate the transmission signal using the formula
      
      transmission = exp( - thickness_cm * atoms_per_cm3 * 1e-24 * sigma_b)
      
      Parameters:
      ===========
      thickness: float (in cm)
      atoms_per_cm3: float (number of atoms per cm3 of element/isotope)
      sigma_b: np.array of sigma retrieved from database
      
      Returns:
      ========
      transmission array
      """
      miu_per_cm = calculate_linear_attenuation_coefficient(atoms_per_cm3=atoms_per_cm3, sigma_b=sigma_b)
      transmission = calculate_trans(thickness_cm=thickness_cm, miu_per_cm=miu_per_cm)
      return miu_per_cm, transmission