Mala Das

Superheated drop as a neutron spectrometer

Abstract Superheated drops are known to vaporise when exposed to energetic nuclear radiation since the discovery of bubble chamber. The application of superheated drops in neutron research especially in neutron dosimetry is a subject of intense research for quite sometime. As the degree of superheat increases in a given liquid, less and less energetic neutrons are required to cause nucleation. This property of superheated liquid makes it possible to use it as a neutron spectrometer. Neutron detection efficiency of superheated drops made of R12 exposed to Am–Be neutron source has been measured over a wide range of temperature −17–60°C and the results have been utilised to construct the energy spectrum of the neutron source. This paper demonstrates that a suitable neutron spectrometer may be constructed by using a single liquid and varying the temperature of the liquid suitably at a closer grid.

How high can the temperature of a liquid be raised without boiling

How high the temperature of a liquid can be raised beyond its boiling point without vaporizing (known as the limit of superheat) is an interesting subject of investigation. A different method of finding the limit of superheat of liquids is presented here. The superheated liquids are taken in the form of drops suspended in a dust free gel. The temperature of the superheated liquid is increased very slowly from room temperature to the temperature at which the liquid nucleates to boiling. The nucleation is detected acoustically by a sensitive piezoelectric transducer, coupled to a multichannel scaler, and the nucleation rate is observed as a function of time. The limit of superheat measured by the present method supersedes other measurements and theoretical predictions in reaching the temperature closest to the critical temperature of the liquids.

Use of basic principle of nucleation in determining temperature-threshold neutron energy relationship in superheated emulsions

Detection of neutrons through use of superheated emulsions has been known for about two decades. The minimum neutron energy (threshold) required to nucleate drops of a given liquid has a dependence on the temperature of the liquid. The basic principle of nucleation has been utilized to find the relationship between the operating temperature and threshold neutron energy for superheated emulsions made of R-114 liquid. The threshold energy thus determined for different temperatures has been compared with accurate experimental results obtained using monoenergetic neutron sources. The agreement is found to be satisfactory and confirms the applicability of the present simple method to other liquids.

Efficiency of neutron detection of superheated drops of Freon-22

Abstract Neutron detection efficiency of superheated drops of Freon-22 for neutrons obtained from a 3 Curie Am-Be neutron source has been reported in this paper. Although Freon-22 having lower boiling point than many other similar liquids (e.g., Freon-12, Freon-114, Isobutane) is expected to be more sensitive to neutrons, it has not been reported so far and therefore this paper constitutes the first report on the subject. Neutron detection efficiency of both Freon-22 and Freon-12 have been determined from the measured nucleation rate using the volumetric method developed in our laboratory. The result shows that the neutron detection efficiency of Freon-22 for the neutron energy spectrum obtained from an Am–Be source, is almost double, while the life time is 58.6% smaller than that of Freon-12, for a particular neutron flux of that source.

A sensitive neutron dosimeter using superheated liquid

The present work relates to a sensitive neutron dosimeter, a device for monitoring neutron dose in some accelerator and reactor sites. This device is capable of measuring a neutron dose as small as 0.1 microSv using superheated liquid as a sensitive liquid. The nucleation was measured by the volumetric method developed in our laboratory. The dose response of superheated drops of four liquids having boiling points of 8.92, -29.79, -40.75 and -45.6 degrees C, irradiated by a 3 Ci Am-Be neutron source has also been presented in this article.

Neutron-gamma discrimination by pulse analysis with superheated drop detector

Abstract Superheated drop detector (SDD) consisting of drops of superheated liquid of halocarbon is irradiated to neutrons and gamma-rays from 252Cf fission neutron source and 137Cs gamma source, respectively, separately. Analysis of pulse height of signals at the neutron and gamma-ray sensitive temperature provides significant information on the identification of neutron and gamma-ray induced events.

Superheated drops of R114—as a neutron spectrometer

Abstract The basic principle that has been used in the application of superheated drops in neutron spectrometry is its dependence of threshold energy of nucleation on temperature. In the present work, superheated drops of R114 suspended in a visco-elastic gel were irradiated at different temperatures by neutrons obtained from an 241 Am–Be source. The temperature of the detector was converted to the energy of the incident neutrons following the method developed by us to unfold the neutron energy spectrum. The threshold energy obtained by us agrees well with other results obtained using monochromatic neutron sources, clearly demonstrating the validity of our principle of spectrometry.

Variation of γ-ray and particle fluxes at the sea level during the Total Solar Eclipse of 24 October, 1995

A Total Solar Eclipse (TSE) was observed from Diamond Harbour (lat. 22.2°N, long 88.2°E) on 24 October 1995. The variation of γ-ray intensity was measured in the energy range of 0.3–3.0 MeV for different time spans throughout the period of the eclipse. A CR-39 detector was used to look at the change in the fluxes of neutral and charged particles. The maximum drop (∼ 25%) in the intensity of γ-ray was observed in the range 2.5–3 MeV during TSE. The CR-39 results showed the appearance of a good number of tracks and a small variation of proton and neutron flux of ≤ 10% which was not significant statistically. Low energy γ-ray fluxes at sea level originate from the secondary electron-photon components of cosmic rays in the atmosphere; its modulation by TSE is interpreted as follows. The cooling of the atmosphere in the path of the umbra induces a reduction of the height of the main production layer of the nuclear component, as a result of which, fewer µ± mesons (from the decay of theπ± mesons) decay to e±. This leads to a small reduction in the flux of electron-photon component at sea level which originates from this branch; the main branch of e - γ component from π0 decay remains nearly unaffected. As the total mass of air remains the same, little or no change in the slow proton or the neutron flux at sea level is expected. These are consistent with the present observations. For a better understanding, further studies of this new phenomenon during future TSE are suggested.

The nucleation parameter for heavy-ion induced bubble nucleation in superheated emulsion detector

The values of the nucleation parameter, k, for bubble nucleation induced by high energy heavy ions 12C (180 MeV/u), 20Ne (400 MeV/u) and 28Si (350 MeV/u) in superheated emulsion detector are determined by comparing the experimentally obtained normalized count rates with those obtained from simulations done using the GEANT3.21 simulation code. The results show that the nucleation parameter depends on the mass number of the incident heavy ions, and decreases with increasing mass number.

An active drop counting device using condenser microphone for superheated emulsion detector

An active device for superheated emulsion detector is described. A capacitive diaphragm sensor or condenser microphone is used to convert the acoustic pulse of drop nucleation to electrical signal. An active peak detector is included in the circuit to avoid multiple triggering of the counter. The counts are finally recorded by a microprocessor based data acquisition system. Genuine triggers, missed by the sensor, were studied using a simulated clock pulse. The neutron energy spectrum of (252)Cf fission neutron source was measured using the device with R114 as the sensitive liquid and compared with the calculated fission neutron energy spectrum of (252)Cf. Frequency analysis of the detected signals was also carried out.