106 RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



Perhaps the most important point is to ensure that the instrument is 

 operating properly before use. As a practical procedure, each instrument 

 when first received should be checked at a standard distance from some 

 source, and a record made of the reading. It will then take just a few 

 seconds each day to check it against the same source so that any loss of 

 sensitivity will be noted. After the use of two or three instruments, the 

 order of magnitude of the readings can be anticipated. 



Cutie Pie. This instrument is battery-operated and has an ionization 

 chamber and usually three scale ranges of 25, 250, and 2500 mr/hr. It 

 usually has a 2- to 3-mg/cm- window, so that it is suitable for monitoring 

 the soft-beta emitters such as C^"*, S^^ and Ca^^. It is primarily of value 

 at the higher levels of radiation, as indicated by the scale ranges, and is 

 not suitable for low-level scanning for surface contamination. 



Portable Beta-Gamma Count-rate Meter. This instrument is a battery- 

 operated Geiger-Miiller counter and is useful when the radiation field is 

 less than 20 mr/hr. Thus, in contrast to the Cutie Pie, it is ideal for 

 scanning surfaces and is not suitable at the higher levels of radiation. At 

 high levels it will "jam" and show a zero reading, which must not be 

 interpreted as indicative of zero radiation under such conditions. These 

 instruments can be used with glass counter tubes of about 30-mg/cm- 

 window thickness or thin-mica- window counters up to about 4 mg/cm-. 

 The latter must be used for the soft-beta emitters. 



Line-operated Beta-Gamma Count-rate Meter. This instrument per- 

 forms the same function as the above and is similar except that it is not 

 dependent upon batteries and is therefore not so portable. It is very 

 convenient for scanning desk tops or material that can be brought to it. 

 These instruments usually read in counts per minute. In addition to sur- 

 vey work, they can often be used for special types of quantitative studies. 



Poeket Dosimeter. This instrument is about the size of a fountain pen 

 and is designed to be worn upon the person. It is self-reading, has a 

 scale of 200 mr, and gives the total dose received from the time of charging 

 to the time of reading. An auxiliary charging unit is required which 

 suffices for any number of dosimeters. It is sensitive only to gamma and 

 high-energy beta rays. The advantage of this instrument is that it can 

 be read by the wearer at any time to give the dose received. It can be 

 conveniently placed within the gloved palm of the hand for an estimation 

 of the hand dose during a given operation. 



Ionization pocket meters of a condenser type are similar to the above 

 but must be read on another instrument. These may be more economical 

 when large numbers of personnel are involved, but the dosimeter is more 

 convenient. All these personnel meters have a tendency for spurious 

 readings due to spontaneous discharge, and it is advisable to wear two of 

 them if possible. 



