Presented in the following section is a description of some of the earliest portable radiation measuring instruments that emerged in the mid to late 1920's and throughout the 1930's. Although there are various reasons for the their development, there was increasing use of x-ray generating devices and radium in the diagnosis and treatment of medical conditions. The instruments originally were developed to provide dose estimates for monitoring and patient treatment. The Geiger Mueller tube was invented in 1928 and is described in the famous papers   by H. Geiger and W. Mueller (Geiger, H. and Mueller, W., Phys. Ztschr., 1928, 29, 839; 1929, 30, 523). These tubes were known as ionization chambers or spark gaps. When a voltage is applied across the electrodes to the point of near breakdown, only a slight pertubation, such as an incoming gamma ray can cause a discharge and the resulting signal. As such a small amount of radiation can result in a energetic signal which can be measured with electronic circuitry.

In 1925, R. Kegerreis developed a portable apparatus for measuring x-rays. Its design and construction "involves many complicated laws of physics of x-rays and electricity". Different filter for absorption can be added depending on the x-ray tube being measured. It is contained in an aluminum cabinet about the size of any ordinary suitcase. When opened the ionization chamber can be removed via a 15 foot armored cable. The unit weighs 40 lbs. and uses several 22.5 volt batteries which contribute to most of the weight.

Kegerreis Portable Apparatus (closed) 1925

Kegerreis Portable Apparatus (open) 1925

Around this same period, there was also the commercial Solomon’s Ionometer, designed by Iser Solomon, a French radiologist. It was also at this time in 1928, that Geiger and Mueller published an announcement of the developed of a device for measuring radiation.

Victoreen is credited with building several condenser-type ionization chamber instruments in 1927 which were stored in the laboratory due to lack of need. The chamber was 1 cm³ consisting of a carbon wall and aluminum electrode. The charge was applied with a friction wheel. Glasser and Seitz made an experimental condenser-type ionization chamber with a removable chamber that could be separated from the electrometer. Glasser turned to Jack Victoreen in 1928 to market the first commercial instrument know as the Condenser R-Meter. It was an ionization meter connected to an electrometer. These units would later become the precursor to the first commercial U.S. ionization chambers developed by Victoreen in 1930.

Victoreen Condenser R-Meter 1928

In 1929, Lauriston Taylor at the National Bureau of Standards developed the first portable survey meter incorporating interchangeable chambers for various radiation exposure rate ranges. The lead-lined Lauritsen electroscope is a medium-sized, portable survey instrument for x-rays. It was developed to conduct international comparisons of x-ray standards. It has an ion chamber that is charged and then discharges proportional to the amount of radiation measured.  It was 8” x 3” x 14” and weighed 8 lbs.

Lauriston Taylor Meter 1931

In 1933, Dr. Curtiss, also of the National Bureau of Standards, developed a portable ionization chamber detector for locating lost radium. The unit had an external probe with an ionization chamber measuring 2.5” diameter x 8” long. The unit weighed 18 lbs and was battery operated. The unit was referred to as the “Curtiss Radium Detector”. It was easy to use for untrained personnel. The unit had a shoulder strap for carrying and a long extension probe for checking around hospital containers and cracks in floors. The unit was reportedly sensitive to 25 mg of radium at 7.5 feet.

Curtiss Radium Detector 1933

The Curtiss Radium Detector was marketed in 1934 by the American Instrument Company as the Radium Detector under catalog No. 2100-01 and sold for $180.

American Instrument Company Radium Detector 1934

In one case a pig swallowed a radium needle. It took a gold-leaf electroscope to find it.

Early story on locating a radium needle in a pig

Dr. Taft began working with radium in 1933. Radium is used in very small quantities for the treatment of medical diseases. The quantities were typically about the size of a quarter inch of pencil lead. These radium sources could cost as much as $12,000 each in 1938. Dr. Taft employed an early homemade electroscope for his routine exposure measurements when working with the radium. A colleague requested that Dr. Taft assist him in locating a lost 75 mg radium source. He used his electroscope and then after locating the source began improvements to his instrument.  His instrument became known as the “Radium Hound”.

Dr. Taft worked with charging devices for electroscopes and various derivations as early as 1926. He responded to a request for locating a lost radium source in a doctor’s office. He used his electroscope and then after locating the source began improvements to his instrument. Radium is used in very small quantities for the treatment of medical diseases. The quantities were typically about the size of a quarter inch of pencil lead. These radium sources could cost as much as $12,000 each in 1938. His instrument became known as the “Radium Hound”.  In 1944, Dr Taft was Professor of Radiology at the Medical College of Charleston.

Small Electroscope used for early radium searches 1933

The instrument consisted of a simple gold leaf electroscope with a charging device. The electroscope is mounted in a small glass flask about 4 inches high. The gold leaf is 1” x ¼” with a 2” cork fishing float coated with aluminum paint. It was determined that 1/13,000 R will produce a noticeable movement in the gold leaf.

Simple Radium Detector 1934

The first units were friction charged with a battery powered light for the meter. The unit was later know as the Victoreen R-meter.

Victoreen R-Meter 1935

Dr. Locher developed a GM counter for locating radium and for measuring x-ray intensities. The unit consisted of a portable control unit with the GM tube at the end of a 3 foot cable. The operator listening to the clicks using headphones. The unit's amplifier and recording equipment was made by Herbach and Rademan. The unit provides 900 volts from a 90 volt dry battery and a ten-to-one DC "voltage multiplier". This new approach allowed for much lighter weight of the control unit.

Locher GM Counter 1936

A sensitive portable detector was developed by J. E. Morgan in 1936. Although the unit was portable, it was connected to AC power via an extension cord. It had lead shielding on three sides to give it a directional feature for isolating radium needles. It was designed specifically for recovering lost radium needles in the hospital setting. Other uses were found including measuring radioactive chemicals such as thorium dioxide and hydroxide within the body of patients undergoing diagnostic treatment. By placing the instrument next to the patient, it is possible to determine which organs are accumulating the radioactive chemical and the rate of excretion.

Morgan Portable Detector 1936

In 1937, C.B. Braestrup developed a GM to locate the weak signals that may be encountered with lost radium. He used a glass GM tube with low pressure argon gas and operated at 800 volts. The GM tube schematic is shown below.

Schematic of Braestrups GM Counter 1937

Two types of GM tubes were used. One had the GM tube in a separate unit which was tethered by a short cable. The cable had to remain short since all of the power and electronics were in the main control box. In a later version, the GM tube with associated electronics and power were all contained in the smaller unit and as such the cable  could be 25 feet allowing more flexibility. He employed the unit as a "Radium Finder" and employed its directional effect. He did this by placing the GM tube in a 12 cm long lead cylinder which was 2 cm thick. It could easily detect 1 mg radium at 15 feet. He has used the Radium Finder to locate lost radium which was found in a drain pipe and in the ash of incinerators. In additional to being valuable material, these quantities of radium can also cause harm if it was next to the skin. In one particular case, one of the lab technicians lab coat was found to be contaminated from a leaking radon tube.

Braestrup GM Counters (left and right of control unit) 1937

Radium tubes and needles were routinely moved around in hospitals pre-1950 and undoubtedly lost or misplaced. Using the radioactivity, it was possible to locate the radium as long as you could detect the radiation. The loss of material was an emergency both for safety and value. The following is a quote about the Radium Hen - "Radium hen" also known as the "Clucking Hen" a GM detector with audio output developed by Thomas Chalmers at the National Physical Laboratory in England in 1934. The name derived from the audio output which sounded like clucking. Quoting an August 24, 1935 article in the Reno Evening Gazette: "The hen family can well be proud of the "bird." It is sexless and yet clucks excitedly like any barnyard Leghorn. It needs no food, except electricity, looks like an ordinary watering can, and has led perplexed scientists to the location of many radium eggs." The Radium Hen would get my vote as the first true survey meter. The unit has a neon "Osglim" lamp that will arc over due to ionizing radiation at the right electrode potential. The interrupted circuit results in a "cluck cluck" sound in the earphones. The potential is adjusted to give just a few clucks per minute caused by the natural radioactivity. The lamp is located in a tin can at the end of the probe. The probe is attached to an attaché case via a cable. As such the probe can be used to search in tight spots such as incinerators and other places where radium can be lost in discarded medical dressing.

Radium Hen Geiger Muller Counter 1934

In 1938, Curtiss produced a Portable Geiger Counter Unit. It contained a neon lamp flasher as an indicator. This unit had a low voltage Geiger counter operating at 450-650 volts as opposed to earlier units operating at 1200 volts. The Geiger counter was 5 to 6 cm in diameter with a gas mixture of hydrogen and argon at 6 to 7 cm pressure. It also contained a Cenco counter attached at the end of the unit for readout. The Geiger counter is mounted in the lightweight cylinder on on the top of the unit under the handle.

Curtiss Portable Geiger Counter Unit 1938