Compact pyroelectric sealed electron beam
View Patent ↗A non-radioactive source for Atmospheric Pressure Ionization is described. The electron-beam sealed tube uses a pyroelectric crystal(s). One end of the crystal is grounded while the other end has a metallic cap with sharp feature to generate an electron beam of a given energy. The rate of heating and/or cooling of the crystal is used to control the current generated from a tube. A heating and/or cooling element such as a Peltier element is useful for controlling the rate of cooling of the crystal. A thin window that is transparent to electrons but impervious to gases is needed in order to prolong the life of the tube and allow the extraction of the electrons. If needed, multiple crystals with independent heaters can be used to provide continuous operation of the device. Dielectric shielding of the pyroelectric crystal is used to minimize discharge of the crystal.
1. A non-radioactive ionization apparatus for ionizing at least some of the sample molecules, comprising:
a sealed tube which separates at least one pyroelectric crystal from the sample molecules to be ionized:
a heat source which heats the pyroelectric crystal from outside the sealed tube without direct contact to the pyroelectric crystal; and
a thin window that is transparent to the emitted electrons but impervious to gases.
2. The non-radioactive ionization apparatus of claim 1 , wherein the heat source provides induction heating.
3. The non-radioactive ionization apparatus of claim 2 , wherein induction heating is provided by a set of loops located outside of the pyroelectric crystal.
4. The non-radioactive ionization apparatus of claim 1 , wherein the heat source uses dielectric heating.
5. The non-radioactive ionization apparatus of claim 4 , wherein dielectric heating is provided by placing a non-conductive material surrounding the pyroelectric crystal.
6. The non-radioactive ionization apparatus of claim 5 , wherein the non-conductive material is heated by RF generated outside of the sealed tube.
7. A non-radioactive ionization apparatus for ionizing at least some of the sample molecules, comprising:
a sealed tube which separates at least one pyroelectric crystal from the sample molecules to be ionized:
a high thermal conductivity material is shunted to the pyroelectric crystal in order to minimize the thermal gradient along the pyroelectric crystal; and
a thin window that is transparent to the emitted electrons but impervious to gases.
8. The non-radioactive ionization apparatus of claim 7 , wherein the high thermal conductivity material is: sapphire, epitaxial diamond, AlN, polished dielectrics, but not limited these.
9. A non-radioactive ionization apparatus for ionizing at least some of the sample molecules, comprising:
a sealed tube which separates at least one pyroelectric crystal from the sample molecules to be ionized;
a thin window that is transparent to the emitted electrons but impervious to gases; and
a dielectric material is placed around the pyroelectric crystal in order to decrease the rate of temperature change when cooling and to prevent electrons from striking regions of the tube without the thin window.
10. The non-radioactive ionization apparatus of claim 9 , wherein the dielectric material is Teflon.
11. A non-radioactive ionization apparatus for ionizing at least some of the sample molecules, comprising:
a sealed tube which separates at least one pyroelectric crystal from the sample molecules to be ionized; and
a brazed window that is: metallic with an insulating layer, bare metal facing the pyroelectric crystal, transparent to the emitted electrons but impervious to gases, and has a non-conducting coating on the outside.
12. The non-radioactive ionization apparatus of claim 11 , wherein the sealed tube is made from metal.
13. The non-radioactive ionization apparatus of claim 11 , wherein the sealed tube has a dielectric coating towards the outside.